Hindawi Publishing CorporationJournal of Electrical and Computer EngineeringVolume 2013 Article ID 325746 7 pageshttpdxdoiorg1011552013325746

Research ArticleTunable Reflectarray Cell for Wide AngleBeam-Steering Radar Applications

F Venneri S Costanzo and G Di Massa

Dipartimento di Ingegneria Informatica Modellistica Elettronica e Sistemistica Universita della Calabria 87036 Rende (CS) Italy

Correspondence should be addressed to S Costanzo costanzodeisunicalit

Received 10 May 2013 Accepted 1 July 2013

Academic Editor Alvaro Rocha

Copyright copy 2013 F Venneri et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

An electronically tunable reflectarray element is proposed in this work to design beam-steering antennas useful for radarapplications A reduced size reflectarray unit cell is properly synthesized in order to extend the antenna beam scanning capabilitieswithin a wider angular region The radiating structure is accurately optimized to provide a full phase tuning range by adoptinga single varactor load as phase shifter element A 046120582-reflectarray cell is designed at the frequency of 115 GHz obtaining aphase agility of about 330∘ The cell is successfully adopted for the design of a 21 times 21 reconfigurable reflectarray The antennais numerically tested for different configurations of the varactors capacitance values and good beam-steering performances aredemonstrated within a wide angular range

1 Introduction

Modern radar systems usually adopt phased array antennas astransmissionreception modules Phased arrays integrate theactual radiating structures consisting of an array of elemen-tary antennas with phase shifter components tunable poweramplifiers and switches [1] These additional devices allowto control the input signal of each radiating element thusoffering the capabilities to electronically steer the radiatedmain beam Phased arrays offermany advantageswith respectto mechanically scanned antennas such as low profile agilebeams and scalability Furthermore electronically scannedantennas offer increased data rates instantaneous positioningof the radar beam avoiding also mechanical vibrations anderrors associated with mechanically scanned systems

An attractive alternative to traditional phased arrayantennas is offered by the reflectarray antenna concept [2]As a matter of fact reflectarrays may be specifically designedalso for applications requiring pattern reconfigurability orbeam-scanning capabilities Reconfigurable reflectarraysmayoffer many advantages over conventional phased arrays suchas reduced costs and volume a simpler architecture dueto the absence of complicated beam-forming networks andincreased efficiencies due to the adoption of spatial feeding

They consist of an array of microstrip elements illuminatedby a feed antenna (Figure 1(a)) Each radiator is properlydesigned to compensate for the phase delay in the pathcoming from the feed and to introduce a phase contributionable to create a total reradiated field with some desiredfeatures such as prescribed beam directions andor shapes

Many different reflectarray configurations have beenproposed in the literature [2] also for mm waves applications[3] and recentlymany efforts have been spent in the design ofreconfigurable reflectarray elements which are usually basedon the use of tunable components andor materials such asMEMs varactor diodes and liquid crystal substrates [4ndash6]

Recently the authors have proposed a novel tunablereflectarray element based on the use of an aperture-coupledpatch electronically driven by a single varactor diode [7ndash10] The radiating patch is coupled to a microstrip lineprinted onto a different substrate and loaded by a varactor(Figure 1(b)) By changing the bias voltage across the diodethe phase response of each element can be dynamicallymodified A detailed description of the proposed phasecontrol mechanism is reported in [10]

The phase tuning capabilities of the proposed reflectarrayconfiguration have been already demonstrated in [7] while in[8ndash10] a reflectarray prototype composed by 3 times 15 elements

2 Journal of Electrical and Computer Engineering

Feed

yx

z

Δy

Δx

Reflectarr

ay

(a)

Varactor

Δy

Δx

Biasingline

L Ls

La

W

L

Patch

Slot

Phase tuning line

120576r2

120576r1

Air

z

y

t

d

h

(b)

Figure 1 (a) Reflectarray antenna and (b) aperture-coupled reconfigurable reflectarray cell

with a unit cell with equal to Δ119909 times Δ119910 = 071205820times 07120582

0

has been successful designed at the frequency of 115 GHzThe synthesis approach described in [11 12] has been adoptedin order to compute the desired voltages distributions acrossthe diodes The antenna has been tested into the MicrowaveLaboratory at the University of Calabria equipped with bothnear-field [13 14] and far-field facilities Various measure-ments of its radiation pattern for different configurationsof the varactors biasing voltages have been performed thusdemonstrating in [10] the reconfiguration capabilities ofthe fabricated reflectarray prototype In particular goodbeam-steering performances have been obtained within anangular region going from minus25∘ up to 25∘ In this work thereflectarray cell proposed in [7ndash10] is properly redesignedin order to enlarge the allowable beam scanning area so togive the opportunity for designing wide-angle beam-steeringantennas suitable for radar applications Pointing out that alarge scan angle requires a close element spacing less thanor equal to half wavelength at the operating frequency [15]a reflectarray unit cell with a reduced size equal to 046120582

0times

0461205820(1198910= 115GHz) is proposed In order to accommo-

date the phasing circuitries inside the reduced available areaembedded in the unit cell the antenna stratification layersare properly modified by choosing a higher permittivity forthe phasing line substrate According to the considerationsreported in [10] the varactor loaded line is accurately resizedin order to maximize the antenna phase agility A phase

tuning range of about 330∘ is numerically demonstrated byvarying the capacitance of the varactor diode within thevalues ranging from 02 pF up to 2 pF

The designed cell is adopted to synthesize a 21 times 21reflectarray antenna able to steer the main beam up to 65∘as assessed numerically

2 Design of a Reconfigurable ReflectarrayElement Embedded into a Unit Cell withReduced Size

21 Performance Limitations of Beam-Steering Arrays Theangular displacement of an electronically scanned radarbeam is practically limited by two main factors namely theelement pattern and the array elements spacing As a matterof fact the radiation pattern of an array of identical radiatorsis given by the product of the array factor and the elementpattern If the single array radiator is isotropic that is thearray elements radiate an electric field quite uniform alongthose directions belonging to the scanning plane only thearray factor will affect the total radiation pattern

However practical array element patterns are not omni-directional showing an amplitude that decays when movingaway from the broadside direction In these cases the singleelementwill significantly reduce the amplitude of the scannedbeam except in the zone where it is nearly isotropic [15]

Journal of Electrical and Computer Engineering 3

The second limitation namely the array elements spac-ing is more relevant As a matter of fact it is well known thata large scan angle requires a close element spacing in orderto avoid grating lobes appearance The maximum scan anglethat a linear phased array can achieve may be derived fromthe well-known relation [15]

120579119904 max = sin

minus1

(120582

119889minus 1) (1)

where 120579119904 max is the maximum scan angle from broadside

direction 119889 is the spacing between two adjacent elementsand 120582 is the operating wavelength Equation (1) is derivedfrom the array factor expression of a linear array placed alongthe 119909-axis or 119910-axis and its validity can be extended to theprincipal cuts of a planar array placed in the 119909-119910 plane [15] Ifthe array scan angle exceeds the value imposed by (1) gratinglobes will appear along other directions This last behavioris clearly illustrated in Figure 2 which shows the scanninglimitations of a 07120582-spaced array In this case if the scanangle 120579

119904is greater than 120579

119904 max = 25∘ as given by (1) the array

factor will show a grating lobe having the same amplitude ofthe scanned main beam (Figure 2(c))

Equation (1) also states that half wavelength spaced arrayswill have a complete theoretical scan range of plusmn90∘ asillustrated in Figure 3

The maximum scan angle achievable by a phased array isalso a function of the array length and the desired half-powerbeam width [15] however the condition imposed by (1) isnecessary for the design of an array with prescribed beam-steering capabilities

22 Reflectarray Element Design In order to improve thescanning capabilities of the reconfigurable reflectarray con-figuration proposed in [7ndash10] the single reflectarray elementis properly redesigned by reducing the unit cell size In fact asdiscussed in the previous paragraph a closer array elementsspacing assures a larger scanning region

The unit cell dimension is fixed to a value less than halfwavelength at the operating frequency 119891

0= 115GHz In

particular the array grid size Δ119909 times Δ119910 is set to 0461205820times

0461205820 Furthermore as demonstrated in [16ndash18] a reduced

unit cell size allows to improve the bandwidth performancesof reflectarray antennas This last aspect is not considered inthe present paper but the relative analysis will be performedin a future work

In order to allow the accommodation of the tuningcircuitries in the smaller area embedded into the unit cell thephasing line substrate adopted in [7] is properly substitutedwith a dielectric layerwith 120576

119903= 6 and thickness ℎ = 0762mm

(see Table 1) As a matter of fact the use of a substrate witha higher permittivity allows to reduce the wavelength insidethe printed lines thus providing the possibility to design ashorter phase tuning line As reported in Table 1 the otherlayers composing the antenna stratification are equal to thoseadopted in [7]

The reflectarray unit cell is synthesized through a full-wave simulation code (AnsoftDesigner) based on themethodof moments The infinite array approach is adopted in order

Theoretical scanning minus25∘ 25∘

middot middot middotmiddot middot middot1 2

Z

NNminus 1

region

07120582 07120582

(a)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(b)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(c)

Figure 2 Scanning performances of an N-elements linear arraywith spacing equal to 07120582 (a) allowable scanning area given byrelation (1) (b) array factor for a scan angle 120579

119904

= 15∘ and119873 = 21 (c)

array factor for a scan angle 120579119904

= 30∘ and119873 = 21

to take into account the mutual coupling effects relevant forthe assigned reduced interelement spacing

The radiating structure design is performed by a propertuning of patch and slot sizes with the aim to satisfy theresonance condition as well as the matching between thepatch and the phasing line at the operating frequency of115 GHz

A varactor diode with a tunable capacitance 119862V rangingfrom 02 pF to 2 pF is integrated to the microstrip line inorder to obtain the required reconfiguration capabilitiesThe varactor diode is modeled with the equivalent circuit

4 Journal of Electrical and Computer Engineering

Z

minus90∘ 90∘

Theoretical scanning region

middot middot middotmiddot middot middot1 2 NNminus 1

05120582 05120582

(a)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(b)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(c)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(d)

Figure 3 Scanning performances of an N-elements linear array with spacing equal to 05120582 (a) allowable scanning area given by relation (1)(b) array factor for a scan angle 120579

119904

= 15∘ and119873 = 21 (c) array factor for a scan angle 120579

119904

= 30∘ and119873 = 21 (d) array factor for a scan angle

120579119904

= 50∘ and119873 = 21

C

Cp

sim Lp

Rs

A

A998400

A

A998400

Zvar

Figure 4 Equivalent circuit model of a varactor diode

illustrated in Figure 4 which takes into account the packageparasitic effects (119871

119901 119862119901) and the diode losses (119877

119904) The

varactor lumped parameters are fixed to the following valuesderived by the Microsemi MV31011-89 diode datasheet 119871

119901=

02 nH 119862119901= 015 pF and 119877

119904= 136Ω

As described in [10] the two line sections 119871V and119871119904(see Figure 1(b)) are optimized in order to maximize

the phase agility of the element for the assigned varactorcapacitance range At this purpose a parametric analysis ofthe reflectarray element is performed with respect to the

lengths 119871V and 119871119904 by assuming a normally incident plane

wave Figure 5 shows the reflection phase curves versus thevaractor capacitance computed for different values of the linelength

It can be observed that by increasing 119871119904 for a fixed value

of 119871V (Figure 5(a)) a higher phase tuning range is obtainedAs accurately demonstrated in [10] this last result is due tothe introduction of a proper inductive effect which is directlyrelated to the stub length As a proof of this concept theinput impedance 119885

1199051015840 of the designed aperture coupled patch

evaluated at the slot center is reported under Figure 6 fordifferent values of the stub length 119871

119904ranging from 105mm

(the matched case) up to 52mm It can be observed that foran increased input reactance a wider phase tuning range isachieved (Figure 5(a)) In particular a phase tuning of about330∘ is obtained for 119871

119904= 52mm On the other hand the

length 119871V is tuned in order to match the maximum phasevariation with the available varactor capacitance range [10]As a matter of fact Figure 5(b) shows that for any fixed valueof 119871119904 the section 119871V can be chosen to shift the phase curve

within the capacitance range with the aim to increase theallowable phase tuning range so obtaining a phasing lineacting as a 360∘ phase shifter

Journal of Electrical and Computer Engineering 5

1 2

minus180

0

90

180

minus90

02 04 06 08 12 14 16 18Diode capacitance (pF)

Refle

ctio

n ph

ase (

deg)

2 552544

35

45

Ls (mm)

(a)

1 202 04 06 08 12 14 16 18Diode capacitance (pF)

Ls = 52mm

Ls = 45mm

L = 42mmL = 425mm

L = 43mmL = 44mm

Refle

ctio

n ph

ase (

deg)

minus200

minus150

minus100

minus50

0

50

100

150

200

(b)

Figure 5 Phase curves versus diode capacitance for different line lengths (a) 119871V = 42mm and 119871119904

ranging from 2mm up to 54mm (b) 119871Vranging from 42mm up to 44mm for some fixed values of 119871

119904

Table 1 Element stratification

LayerElement designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Material Thickness Material ThicknessPatch Copper 35 120583m Copper 35 120583m

Antenna substrate 1205761199031

= 233 119905 = 0762mm 1205761199031

= 233 119905 = 0762mmAir 119889 = 0762mm Air 119889 = 0762mm

Ground plane with slot Copper 35 120583m Copper 35 120583mPhasing line substrate 120576

1199032

= 233 ℎ = 0762mm 1205761199032

= 6 ℎ = 0762mmPhasing line Copper 35120583m Copper 35 120583m

The dimensions of the optimized reflectarray element arereported in Table 2

Furthermore the same table shows that the designedtuning line is shorter than the line controlling the reflectarrayelement described in [7] In particular a 35 length reduc-tion is obtained thus allowing the allocation of the tuningcircuitries inside the smaller 046120582

0times 046120582

0cell (12mm times

12mm at 115 GHz)The simulated element pattern of the designed unit cell

is reported in Figure 7 The depicted diagrams refer to thereflectarray element with a phasing line having dimensions119871V = 42mm and 119871

119904= 52mm The radiation patterns

computed in the two principal planes show a nearly isotropicbehavior within the range from minus45∘ up to 45∘ as in the caseof a typical cos(120579) source

In conclusion the proposed unit cell could be suitablefor the design of reflectarray antennas with improved beam-steering capabilities as the main beam could be scannedwithin a quite large angular region ranging from minus45∘ up

to 45∘ without occurring in the grating lobes phenomenaFurthermore within this scanning range the main lobe willhave at most a 3 dB amplitude reduction as demonstrated bythe simulated element pattern (Figure 7)

3 Design of a Beam-Steering Reflectarray

In order to prove the effectiveness of the proposed cell a21 times 21 reflectarray is designed at the frequency of 115 GHzThe array is illuminated by a broadside feed placed at adistance of 34 cm A synthesis algorithm [11] is adopted inorder to compute the varactor capacitance values which allowto steer the radiated main beam from 0∘ up to 65∘ in the H-plane The computed radiation patterns depicted in Figure 8show the validity of the proposed approach as the mainbeam is successfully moved along the desired directionsAs expected by the array theory Figure 8 shows that themain beam amplitude decreases when moving away fromthe broadside direction In particular it can be observed that

6 Journal of Electrical and Computer Engineering

Table 2 Element dimension

Element designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Patch size 119882times 119871 = 82mm times 93mm 119882times 119871 = 775mm times 775mmSlot size 119871

119886

times119882119886

= 58mm times 06mm 119871119886

times119882119886

= 57mm times 05mmPhase tuningline

119871V = 65mm + 119871119904

= 78mm119882119904

= 307mm119871V = 42mm + 119871

119904

= 52mm119882119904

= 16mm

105 11 115 12 125

0

50

100

150

(GHz)

Matched case

(Ω)

Re (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 35mm

Im (Zt998400 ) minus Ls = 45mmIm (Zt998400 ) minus Ls = 52mm

Figure 6 Input impedance 1198851199051015840 for different stub lengths

minus90

minus60

minus30

0

30

60

90

minus10000

minus20000

minus30000

minus40000

x-z planey-z plane

Figure 7 Element pattern of designed reflectarray element

the scan loss increases away from broadside by following thecosine behavior of the element pattern Thus an acceptable3 dB scan loss is obtained when the main lobe is pointedalong the direction 120579

119904= 45

∘ while for 120579119904= 65

∘ agreater scan loss of about 7 dB is observed FurthermoreFigure 8 shows a broader main lobe for greater scan anglesDespite limitations imposed by the array theory (ie scanlosses and main lobe broadening) the obtained numericalresults demonstrate wide angle beam-steering capabilities ofthe designed antenna without occurring in grating lobesappearance

minus90 minus60 minus30 0 30 60 90minus40

minus30

minus20

minus10

0

(dB)

120579 (deg)

120579s = 0∘

120579s = 25∘

120579s = 45∘

120579s = 65∘

Element pattern

Figure 8 Computed radiation patterns for different configurationsof the varactors capacitance values

4 Conclusion

The reflectarray concept has been applied in this work todesign beam-steering antennas suitable for radar applica-tions A reflectarray unit cell based on the use of a singlevaractor diode has been proposed and optimized to providewide angle steering capabilities At this purpose the antennahas been properly designed by reducing the unit cell sizein order to achieve a large angular scanning As a specificnumerical example a varactor loaded reflectarray elementembedded into a 046120582

0times 046120582

0cell at 119891

0= 115GHz

has been synthesized obtaining a full phase tuning rangeof about 330∘ The designed unit cell has been adopted todesign a 21 times 21 reconfigurable reflectarray The antennahas been numerically tested showing good beam-steeringperformances within a wide angular range from minus45∘ up to45∘

Acknowledgment

This work has been carried out under the framework of PON01 01503 National Italian Project ldquoLandslides EarlyWarningrdquofinanced by the Italian Ministry of University and Research

References

[1] A J Fenn D H Temme W P Delaney and W E CourtneyldquoThe development of phased-array radar technologyrdquo LincolnLaboratory Journal vol 12 pp 321ndash340 2000

Journal of Electrical and Computer Engineering 7

[2] J Huang and J Encinar Reflectarray Antennas Wiley-IEEEPress 2008

[3] S Costanzo F Venneri A Borgia I Venneri and G DiMassa ldquo60 GHz microstrip reflectarray on a benzocyclobutenedielectric substraterdquo IET Science Measurement and Technologyvol 5 no 4 pp 134ndash139 2011

[4] R Sorrentino R V Gatti L Marcaccioli and B MencaglildquoElectronic steerable mems antennasrdquo in Proceedings of the 1stEuropean Conference on Antennas and Propagation (EuCAPrsquo06) pp 1ndash8 Nice France November 2006

[5] S V Hum M Okoniewski and R J Davies ldquoRealizing anelectronically tunable reflectarray using varactor diode-tunedelementsrdquo IEEE Microwave and Wireless Components Lettersvol 15 no 6 pp 422ndash424 2005

[6] M Riel and J J Laurin ldquoDesign of an electronically beamscanning reflectarray using aperture-coupled elementsrdquo IEEETransactions on Antennas and Propagation vol 55 no 5 pp1260ndash1266 2007

[7] F Venneri S Costanzo and G Di Massa ldquoReconfigurableaperture-coupled reflectarray element tuned by single varactordioderdquo Electronics Letters vol 48 no 2 pp 68ndash69 2012

[8] F Venneri S Costanzo G Di Massa A Borgia P Corsonelloand M Salzano ldquoDesign of a reconfigurable reflectarray basedon a varactor tuned elementrdquo in Proceedings of the 6th EuropeanConference on Antennas and Propagation (EUCAP rsquo12) pp2628ndash2631 Prague Czech Republic March 2012

[9] F Venneri S Costanzo G Di Massa et al ldquoBeam-scanningreflectarray based on a single varactor-tuned elementrdquo Interna-tional Journal of Antennas and Propagation vol 2012 Article ID290285 5 pages 2012

[10] F Venneri S Costanzo and G Di Massa ldquoDesign and valida-tion of a reconfigurable single varactor-tuned reflectarrayrdquo IEEETransactions on Antennas and Propagation vol 61 no 2 pp635ndash645 2013

[11] F Venneri S Costanzo G Di Massa and G Angiulli ldquoAnimproved synthesis algorithm for reflectarrays designrdquo IEEEAntennas andWireless Propagation Letters vol 4 no 1 pp 258ndash261 2005

[12] S Costanzo F Venneri GDiMassa andGAngiulli ldquoSynthesisof microstrip reflectarrays as planar scatterers for SAR interfer-ometryrdquo Electronics Letters vol 39 no 3 pp 266ndash267 2003

[13] S Costanzo and G Di Massa ldquoDirect far-field computationfrom bi-polar near-field samplesrdquo Journal of ElectromagneticWaves and Applications vol 20 no 9 pp 1137ndash1148 2006

[14] S Costanzo and G Di Massa ldquoNear-field to far-field transfor-mation with planar spiral scanningrdquo Progress in Electromagnet-ics Research vol 73 pp 49ndash59 2007

[15] C A Balanis AntennaTheory Analysis and Design JohnWileyamp Sons New York NY USA 2nd edition 1997

[16] S Costanzo F Venneri and G DiMassa ldquoBandwidth enhance-ment of aperture-coupled reflectarraysrdquo Electronics Letters vol42 no 23 pp 1320ndash1321 2006

[17] F Venneri S Costanzo G Di Massa and G AmendolaldquoAperture-coupled reflectarrays with enhanced bandwidth fea-turesrdquo Journal of Electromagnetic Waves and Applications vol22 no 11-12 pp 1527ndash1537 2008

[18] F Venneri S Costanzo and G Di Massa ldquoBandwidth behaviorof closely spaced aperture-coupled reflectarraysrdquo InternationalJournal of Antennas and Propagation vol 2012 Article ID846017 11 pages 2012

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2 Journal of Electrical and Computer Engineering

Feed

yx

z

Δy

Δx

Reflectarr

ay

(a)

Varactor

Δy

Δx

Biasingline

L Ls

La

W

L

Patch

Slot

Phase tuning line

120576r2

120576r1

Air

z

y

t

d

h

(b)

Figure 1 (a) Reflectarray antenna and (b) aperture-coupled reconfigurable reflectarray cell

with a unit cell with equal to Δ119909 times Δ119910 = 071205820times 07120582

0

has been successful designed at the frequency of 115 GHzThe synthesis approach described in [11 12] has been adoptedin order to compute the desired voltages distributions acrossthe diodes The antenna has been tested into the MicrowaveLaboratory at the University of Calabria equipped with bothnear-field [13 14] and far-field facilities Various measure-ments of its radiation pattern for different configurationsof the varactors biasing voltages have been performed thusdemonstrating in [10] the reconfiguration capabilities ofthe fabricated reflectarray prototype In particular goodbeam-steering performances have been obtained within anangular region going from minus25∘ up to 25∘ In this work thereflectarray cell proposed in [7ndash10] is properly redesignedin order to enlarge the allowable beam scanning area so togive the opportunity for designing wide-angle beam-steeringantennas suitable for radar applications Pointing out that alarge scan angle requires a close element spacing less thanor equal to half wavelength at the operating frequency [15]a reflectarray unit cell with a reduced size equal to 046120582

0times

0461205820(1198910= 115GHz) is proposed In order to accommo-

date the phasing circuitries inside the reduced available areaembedded in the unit cell the antenna stratification layersare properly modified by choosing a higher permittivity forthe phasing line substrate According to the considerationsreported in [10] the varactor loaded line is accurately resizedin order to maximize the antenna phase agility A phase

tuning range of about 330∘ is numerically demonstrated byvarying the capacitance of the varactor diode within thevalues ranging from 02 pF up to 2 pF

The designed cell is adopted to synthesize a 21 times 21reflectarray antenna able to steer the main beam up to 65∘as assessed numerically

2 Design of a Reconfigurable ReflectarrayElement Embedded into a Unit Cell withReduced Size

21 Performance Limitations of Beam-Steering Arrays Theangular displacement of an electronically scanned radarbeam is practically limited by two main factors namely theelement pattern and the array elements spacing As a matterof fact the radiation pattern of an array of identical radiatorsis given by the product of the array factor and the elementpattern If the single array radiator is isotropic that is thearray elements radiate an electric field quite uniform alongthose directions belonging to the scanning plane only thearray factor will affect the total radiation pattern

However practical array element patterns are not omni-directional showing an amplitude that decays when movingaway from the broadside direction In these cases the singleelementwill significantly reduce the amplitude of the scannedbeam except in the zone where it is nearly isotropic [15]

Journal of Electrical and Computer Engineering 3

The second limitation namely the array elements spac-ing is more relevant As a matter of fact it is well known thata large scan angle requires a close element spacing in orderto avoid grating lobes appearance The maximum scan anglethat a linear phased array can achieve may be derived fromthe well-known relation [15]

120579119904 max = sin

minus1

(120582

119889minus 1) (1)

where 120579119904 max is the maximum scan angle from broadside

direction 119889 is the spacing between two adjacent elementsand 120582 is the operating wavelength Equation (1) is derivedfrom the array factor expression of a linear array placed alongthe 119909-axis or 119910-axis and its validity can be extended to theprincipal cuts of a planar array placed in the 119909-119910 plane [15] Ifthe array scan angle exceeds the value imposed by (1) gratinglobes will appear along other directions This last behavioris clearly illustrated in Figure 2 which shows the scanninglimitations of a 07120582-spaced array In this case if the scanangle 120579

119904is greater than 120579

119904 max = 25∘ as given by (1) the array

factor will show a grating lobe having the same amplitude ofthe scanned main beam (Figure 2(c))

Equation (1) also states that half wavelength spaced arrayswill have a complete theoretical scan range of plusmn90∘ asillustrated in Figure 3

The maximum scan angle achievable by a phased array isalso a function of the array length and the desired half-powerbeam width [15] however the condition imposed by (1) isnecessary for the design of an array with prescribed beam-steering capabilities

22 Reflectarray Element Design In order to improve thescanning capabilities of the reconfigurable reflectarray con-figuration proposed in [7ndash10] the single reflectarray elementis properly redesigned by reducing the unit cell size In fact asdiscussed in the previous paragraph a closer array elementsspacing assures a larger scanning region

The unit cell dimension is fixed to a value less than halfwavelength at the operating frequency 119891

0= 115GHz In

particular the array grid size Δ119909 times Δ119910 is set to 0461205820times

0461205820 Furthermore as demonstrated in [16ndash18] a reduced

unit cell size allows to improve the bandwidth performancesof reflectarray antennas This last aspect is not considered inthe present paper but the relative analysis will be performedin a future work

In order to allow the accommodation of the tuningcircuitries in the smaller area embedded into the unit cell thephasing line substrate adopted in [7] is properly substitutedwith a dielectric layerwith 120576

119903= 6 and thickness ℎ = 0762mm

(see Table 1) As a matter of fact the use of a substrate witha higher permittivity allows to reduce the wavelength insidethe printed lines thus providing the possibility to design ashorter phase tuning line As reported in Table 1 the otherlayers composing the antenna stratification are equal to thoseadopted in [7]

The reflectarray unit cell is synthesized through a full-wave simulation code (AnsoftDesigner) based on themethodof moments The infinite array approach is adopted in order

Theoretical scanning minus25∘ 25∘

middot middot middotmiddot middot middot1 2

Z

NNminus 1

region

07120582 07120582

(a)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(b)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(c)

Figure 2 Scanning performances of an N-elements linear arraywith spacing equal to 07120582 (a) allowable scanning area given byrelation (1) (b) array factor for a scan angle 120579

119904

= 15∘ and119873 = 21 (c)

array factor for a scan angle 120579119904

= 30∘ and119873 = 21

to take into account the mutual coupling effects relevant forthe assigned reduced interelement spacing

The radiating structure design is performed by a propertuning of patch and slot sizes with the aim to satisfy theresonance condition as well as the matching between thepatch and the phasing line at the operating frequency of115 GHz

A varactor diode with a tunable capacitance 119862V rangingfrom 02 pF to 2 pF is integrated to the microstrip line inorder to obtain the required reconfiguration capabilitiesThe varactor diode is modeled with the equivalent circuit

4 Journal of Electrical and Computer Engineering

Z

minus90∘ 90∘

Theoretical scanning region

middot middot middotmiddot middot middot1 2 NNminus 1

05120582 05120582

(a)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(b)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(c)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(d)

Figure 3 Scanning performances of an N-elements linear array with spacing equal to 05120582 (a) allowable scanning area given by relation (1)(b) array factor for a scan angle 120579

119904

= 15∘ and119873 = 21 (c) array factor for a scan angle 120579

119904

= 30∘ and119873 = 21 (d) array factor for a scan angle

120579119904

= 50∘ and119873 = 21

C

Cp

sim Lp

Rs

A

A998400

A

A998400

Zvar

Figure 4 Equivalent circuit model of a varactor diode

illustrated in Figure 4 which takes into account the packageparasitic effects (119871

119901 119862119901) and the diode losses (119877

119904) The

varactor lumped parameters are fixed to the following valuesderived by the Microsemi MV31011-89 diode datasheet 119871

119901=

02 nH 119862119901= 015 pF and 119877

119904= 136Ω

As described in [10] the two line sections 119871V and119871119904(see Figure 1(b)) are optimized in order to maximize

the phase agility of the element for the assigned varactorcapacitance range At this purpose a parametric analysis ofthe reflectarray element is performed with respect to the

lengths 119871V and 119871119904 by assuming a normally incident plane

wave Figure 5 shows the reflection phase curves versus thevaractor capacitance computed for different values of the linelength

It can be observed that by increasing 119871119904 for a fixed value

of 119871V (Figure 5(a)) a higher phase tuning range is obtainedAs accurately demonstrated in [10] this last result is due tothe introduction of a proper inductive effect which is directlyrelated to the stub length As a proof of this concept theinput impedance 119885

1199051015840 of the designed aperture coupled patch

evaluated at the slot center is reported under Figure 6 fordifferent values of the stub length 119871

119904ranging from 105mm

(the matched case) up to 52mm It can be observed that foran increased input reactance a wider phase tuning range isachieved (Figure 5(a)) In particular a phase tuning of about330∘ is obtained for 119871

119904= 52mm On the other hand the

length 119871V is tuned in order to match the maximum phasevariation with the available varactor capacitance range [10]As a matter of fact Figure 5(b) shows that for any fixed valueof 119871119904 the section 119871V can be chosen to shift the phase curve

within the capacitance range with the aim to increase theallowable phase tuning range so obtaining a phasing lineacting as a 360∘ phase shifter

Journal of Electrical and Computer Engineering 5

1 2

minus180

0

90

180

minus90

02 04 06 08 12 14 16 18Diode capacitance (pF)

Refle

ctio

n ph

ase (

deg)

2 552544

35

45

Ls (mm)

(a)

1 202 04 06 08 12 14 16 18Diode capacitance (pF)

Ls = 52mm

Ls = 45mm

L = 42mmL = 425mm

L = 43mmL = 44mm

Refle

ctio

n ph

ase (

deg)

minus200

minus150

minus100

minus50

0

50

100

150

200

(b)

Figure 5 Phase curves versus diode capacitance for different line lengths (a) 119871V = 42mm and 119871119904

ranging from 2mm up to 54mm (b) 119871Vranging from 42mm up to 44mm for some fixed values of 119871

119904

Table 1 Element stratification

LayerElement designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Material Thickness Material ThicknessPatch Copper 35 120583m Copper 35 120583m

Antenna substrate 1205761199031

= 233 119905 = 0762mm 1205761199031

= 233 119905 = 0762mmAir 119889 = 0762mm Air 119889 = 0762mm

Ground plane with slot Copper 35 120583m Copper 35 120583mPhasing line substrate 120576

1199032

= 233 ℎ = 0762mm 1205761199032

= 6 ℎ = 0762mmPhasing line Copper 35120583m Copper 35 120583m

The dimensions of the optimized reflectarray element arereported in Table 2

Furthermore the same table shows that the designedtuning line is shorter than the line controlling the reflectarrayelement described in [7] In particular a 35 length reduc-tion is obtained thus allowing the allocation of the tuningcircuitries inside the smaller 046120582

0times 046120582

0cell (12mm times

12mm at 115 GHz)The simulated element pattern of the designed unit cell

is reported in Figure 7 The depicted diagrams refer to thereflectarray element with a phasing line having dimensions119871V = 42mm and 119871

119904= 52mm The radiation patterns

computed in the two principal planes show a nearly isotropicbehavior within the range from minus45∘ up to 45∘ as in the caseof a typical cos(120579) source

In conclusion the proposed unit cell could be suitablefor the design of reflectarray antennas with improved beam-steering capabilities as the main beam could be scannedwithin a quite large angular region ranging from minus45∘ up

to 45∘ without occurring in the grating lobes phenomenaFurthermore within this scanning range the main lobe willhave at most a 3 dB amplitude reduction as demonstrated bythe simulated element pattern (Figure 7)

3 Design of a Beam-Steering Reflectarray

In order to prove the effectiveness of the proposed cell a21 times 21 reflectarray is designed at the frequency of 115 GHzThe array is illuminated by a broadside feed placed at adistance of 34 cm A synthesis algorithm [11] is adopted inorder to compute the varactor capacitance values which allowto steer the radiated main beam from 0∘ up to 65∘ in the H-plane The computed radiation patterns depicted in Figure 8show the validity of the proposed approach as the mainbeam is successfully moved along the desired directionsAs expected by the array theory Figure 8 shows that themain beam amplitude decreases when moving away fromthe broadside direction In particular it can be observed that

6 Journal of Electrical and Computer Engineering

Table 2 Element dimension

Element designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Patch size 119882times 119871 = 82mm times 93mm 119882times 119871 = 775mm times 775mmSlot size 119871

119886

times119882119886

= 58mm times 06mm 119871119886

times119882119886

= 57mm times 05mmPhase tuningline

119871V = 65mm + 119871119904

= 78mm119882119904

= 307mm119871V = 42mm + 119871

119904

= 52mm119882119904

= 16mm

105 11 115 12 125

0

50

100

150

(GHz)

Matched case

(Ω)

Re (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 35mm

Im (Zt998400 ) minus Ls = 45mmIm (Zt998400 ) minus Ls = 52mm

Figure 6 Input impedance 1198851199051015840 for different stub lengths

minus90

minus60

minus30

0

30

60

90

minus10000

minus20000

minus30000

minus40000

x-z planey-z plane

Figure 7 Element pattern of designed reflectarray element

the scan loss increases away from broadside by following thecosine behavior of the element pattern Thus an acceptable3 dB scan loss is obtained when the main lobe is pointedalong the direction 120579

119904= 45

∘ while for 120579119904= 65

∘ agreater scan loss of about 7 dB is observed FurthermoreFigure 8 shows a broader main lobe for greater scan anglesDespite limitations imposed by the array theory (ie scanlosses and main lobe broadening) the obtained numericalresults demonstrate wide angle beam-steering capabilities ofthe designed antenna without occurring in grating lobesappearance

minus90 minus60 minus30 0 30 60 90minus40

minus30

minus20

minus10

0

(dB)

120579 (deg)

120579s = 0∘

120579s = 25∘

120579s = 45∘

120579s = 65∘

Element pattern

Figure 8 Computed radiation patterns for different configurationsof the varactors capacitance values

4 Conclusion

The reflectarray concept has been applied in this work todesign beam-steering antennas suitable for radar applica-tions A reflectarray unit cell based on the use of a singlevaractor diode has been proposed and optimized to providewide angle steering capabilities At this purpose the antennahas been properly designed by reducing the unit cell sizein order to achieve a large angular scanning As a specificnumerical example a varactor loaded reflectarray elementembedded into a 046120582

0times 046120582

0cell at 119891

0= 115GHz

has been synthesized obtaining a full phase tuning rangeof about 330∘ The designed unit cell has been adopted todesign a 21 times 21 reconfigurable reflectarray The antennahas been numerically tested showing good beam-steeringperformances within a wide angular range from minus45∘ up to45∘

Acknowledgment

This work has been carried out under the framework of PON01 01503 National Italian Project ldquoLandslides EarlyWarningrdquofinanced by the Italian Ministry of University and Research

References

[1] A J Fenn D H Temme W P Delaney and W E CourtneyldquoThe development of phased-array radar technologyrdquo LincolnLaboratory Journal vol 12 pp 321ndash340 2000

Journal of Electrical and Computer Engineering 7

[2] J Huang and J Encinar Reflectarray Antennas Wiley-IEEEPress 2008

[3] S Costanzo F Venneri A Borgia I Venneri and G DiMassa ldquo60 GHz microstrip reflectarray on a benzocyclobutenedielectric substraterdquo IET Science Measurement and Technologyvol 5 no 4 pp 134ndash139 2011

[4] R Sorrentino R V Gatti L Marcaccioli and B MencaglildquoElectronic steerable mems antennasrdquo in Proceedings of the 1stEuropean Conference on Antennas and Propagation (EuCAPrsquo06) pp 1ndash8 Nice France November 2006

[5] S V Hum M Okoniewski and R J Davies ldquoRealizing anelectronically tunable reflectarray using varactor diode-tunedelementsrdquo IEEE Microwave and Wireless Components Lettersvol 15 no 6 pp 422ndash424 2005

[6] M Riel and J J Laurin ldquoDesign of an electronically beamscanning reflectarray using aperture-coupled elementsrdquo IEEETransactions on Antennas and Propagation vol 55 no 5 pp1260ndash1266 2007

[7] F Venneri S Costanzo and G Di Massa ldquoReconfigurableaperture-coupled reflectarray element tuned by single varactordioderdquo Electronics Letters vol 48 no 2 pp 68ndash69 2012

[8] F Venneri S Costanzo G Di Massa A Borgia P Corsonelloand M Salzano ldquoDesign of a reconfigurable reflectarray basedon a varactor tuned elementrdquo in Proceedings of the 6th EuropeanConference on Antennas and Propagation (EUCAP rsquo12) pp2628ndash2631 Prague Czech Republic March 2012

[9] F Venneri S Costanzo G Di Massa et al ldquoBeam-scanningreflectarray based on a single varactor-tuned elementrdquo Interna-tional Journal of Antennas and Propagation vol 2012 Article ID290285 5 pages 2012

[10] F Venneri S Costanzo and G Di Massa ldquoDesign and valida-tion of a reconfigurable single varactor-tuned reflectarrayrdquo IEEETransactions on Antennas and Propagation vol 61 no 2 pp635ndash645 2013

[11] F Venneri S Costanzo G Di Massa and G Angiulli ldquoAnimproved synthesis algorithm for reflectarrays designrdquo IEEEAntennas andWireless Propagation Letters vol 4 no 1 pp 258ndash261 2005

[12] S Costanzo F Venneri GDiMassa andGAngiulli ldquoSynthesisof microstrip reflectarrays as planar scatterers for SAR interfer-ometryrdquo Electronics Letters vol 39 no 3 pp 266ndash267 2003

[13] S Costanzo and G Di Massa ldquoDirect far-field computationfrom bi-polar near-field samplesrdquo Journal of ElectromagneticWaves and Applications vol 20 no 9 pp 1137ndash1148 2006

[14] S Costanzo and G Di Massa ldquoNear-field to far-field transfor-mation with planar spiral scanningrdquo Progress in Electromagnet-ics Research vol 73 pp 49ndash59 2007

[15] C A Balanis AntennaTheory Analysis and Design JohnWileyamp Sons New York NY USA 2nd edition 1997

[16] S Costanzo F Venneri and G DiMassa ldquoBandwidth enhance-ment of aperture-coupled reflectarraysrdquo Electronics Letters vol42 no 23 pp 1320ndash1321 2006

[17] F Venneri S Costanzo G Di Massa and G AmendolaldquoAperture-coupled reflectarrays with enhanced bandwidth fea-turesrdquo Journal of Electromagnetic Waves and Applications vol22 no 11-12 pp 1527ndash1537 2008

[18] F Venneri S Costanzo and G Di Massa ldquoBandwidth behaviorof closely spaced aperture-coupled reflectarraysrdquo InternationalJournal of Antennas and Propagation vol 2012 Article ID846017 11 pages 2012

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International Journal of

Journal of Electrical and Computer Engineering 3

The second limitation namely the array elements spac-ing is more relevant As a matter of fact it is well known thata large scan angle requires a close element spacing in orderto avoid grating lobes appearance The maximum scan anglethat a linear phased array can achieve may be derived fromthe well-known relation [15]

120579119904 max = sin

minus1

(120582

119889minus 1) (1)

where 120579119904 max is the maximum scan angle from broadside

direction 119889 is the spacing between two adjacent elementsand 120582 is the operating wavelength Equation (1) is derivedfrom the array factor expression of a linear array placed alongthe 119909-axis or 119910-axis and its validity can be extended to theprincipal cuts of a planar array placed in the 119909-119910 plane [15] Ifthe array scan angle exceeds the value imposed by (1) gratinglobes will appear along other directions This last behavioris clearly illustrated in Figure 2 which shows the scanninglimitations of a 07120582-spaced array In this case if the scanangle 120579

119904is greater than 120579

119904 max = 25∘ as given by (1) the array

factor will show a grating lobe having the same amplitude ofthe scanned main beam (Figure 2(c))

Equation (1) also states that half wavelength spaced arrayswill have a complete theoretical scan range of plusmn90∘ asillustrated in Figure 3

The maximum scan angle achievable by a phased array isalso a function of the array length and the desired half-powerbeam width [15] however the condition imposed by (1) isnecessary for the design of an array with prescribed beam-steering capabilities

22 Reflectarray Element Design In order to improve thescanning capabilities of the reconfigurable reflectarray con-figuration proposed in [7ndash10] the single reflectarray elementis properly redesigned by reducing the unit cell size In fact asdiscussed in the previous paragraph a closer array elementsspacing assures a larger scanning region

The unit cell dimension is fixed to a value less than halfwavelength at the operating frequency 119891

0= 115GHz In

particular the array grid size Δ119909 times Δ119910 is set to 0461205820times

0461205820 Furthermore as demonstrated in [16ndash18] a reduced

unit cell size allows to improve the bandwidth performancesof reflectarray antennas This last aspect is not considered inthe present paper but the relative analysis will be performedin a future work

In order to allow the accommodation of the tuningcircuitries in the smaller area embedded into the unit cell thephasing line substrate adopted in [7] is properly substitutedwith a dielectric layerwith 120576

119903= 6 and thickness ℎ = 0762mm

(see Table 1) As a matter of fact the use of a substrate witha higher permittivity allows to reduce the wavelength insidethe printed lines thus providing the possibility to design ashorter phase tuning line As reported in Table 1 the otherlayers composing the antenna stratification are equal to thoseadopted in [7]

The reflectarray unit cell is synthesized through a full-wave simulation code (AnsoftDesigner) based on themethodof moments The infinite array approach is adopted in order

Theoretical scanning minus25∘ 25∘

middot middot middotmiddot middot middot1 2

Z

NNminus 1

region

07120582 07120582

(a)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(b)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(c)

Figure 2 Scanning performances of an N-elements linear arraywith spacing equal to 07120582 (a) allowable scanning area given byrelation (1) (b) array factor for a scan angle 120579

119904

= 15∘ and119873 = 21 (c)

array factor for a scan angle 120579119904

= 30∘ and119873 = 21

to take into account the mutual coupling effects relevant forthe assigned reduced interelement spacing

The radiating structure design is performed by a propertuning of patch and slot sizes with the aim to satisfy theresonance condition as well as the matching between thepatch and the phasing line at the operating frequency of115 GHz

A varactor diode with a tunable capacitance 119862V rangingfrom 02 pF to 2 pF is integrated to the microstrip line inorder to obtain the required reconfiguration capabilitiesThe varactor diode is modeled with the equivalent circuit

4 Journal of Electrical and Computer Engineering

Z

minus90∘ 90∘

Theoretical scanning region

middot middot middotmiddot middot middot1 2 NNminus 1

05120582 05120582

(a)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(b)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(c)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(d)

Figure 3 Scanning performances of an N-elements linear array with spacing equal to 05120582 (a) allowable scanning area given by relation (1)(b) array factor for a scan angle 120579

119904

= 15∘ and119873 = 21 (c) array factor for a scan angle 120579

119904

= 30∘ and119873 = 21 (d) array factor for a scan angle

120579119904

= 50∘ and119873 = 21

C

Cp

sim Lp

Rs

A

A998400

A

A998400

Zvar

Figure 4 Equivalent circuit model of a varactor diode

illustrated in Figure 4 which takes into account the packageparasitic effects (119871

119901 119862119901) and the diode losses (119877

119904) The

varactor lumped parameters are fixed to the following valuesderived by the Microsemi MV31011-89 diode datasheet 119871

119901=

02 nH 119862119901= 015 pF and 119877

119904= 136Ω

As described in [10] the two line sections 119871V and119871119904(see Figure 1(b)) are optimized in order to maximize

the phase agility of the element for the assigned varactorcapacitance range At this purpose a parametric analysis ofthe reflectarray element is performed with respect to the

lengths 119871V and 119871119904 by assuming a normally incident plane

wave Figure 5 shows the reflection phase curves versus thevaractor capacitance computed for different values of the linelength

It can be observed that by increasing 119871119904 for a fixed value

of 119871V (Figure 5(a)) a higher phase tuning range is obtainedAs accurately demonstrated in [10] this last result is due tothe introduction of a proper inductive effect which is directlyrelated to the stub length As a proof of this concept theinput impedance 119885

1199051015840 of the designed aperture coupled patch

evaluated at the slot center is reported under Figure 6 fordifferent values of the stub length 119871

119904ranging from 105mm

(the matched case) up to 52mm It can be observed that foran increased input reactance a wider phase tuning range isachieved (Figure 5(a)) In particular a phase tuning of about330∘ is obtained for 119871

119904= 52mm On the other hand the

length 119871V is tuned in order to match the maximum phasevariation with the available varactor capacitance range [10]As a matter of fact Figure 5(b) shows that for any fixed valueof 119871119904 the section 119871V can be chosen to shift the phase curve

within the capacitance range with the aim to increase theallowable phase tuning range so obtaining a phasing lineacting as a 360∘ phase shifter

Journal of Electrical and Computer Engineering 5

1 2

minus180

0

90

180

minus90

02 04 06 08 12 14 16 18Diode capacitance (pF)

Refle

ctio

n ph

ase (

deg)

2 552544

35

45

Ls (mm)

(a)

1 202 04 06 08 12 14 16 18Diode capacitance (pF)

Ls = 52mm

Ls = 45mm

L = 42mmL = 425mm

L = 43mmL = 44mm

Refle

ctio

n ph

ase (

deg)

minus200

minus150

minus100

minus50

0

50

100

150

200

(b)

Figure 5 Phase curves versus diode capacitance for different line lengths (a) 119871V = 42mm and 119871119904

ranging from 2mm up to 54mm (b) 119871Vranging from 42mm up to 44mm for some fixed values of 119871

119904

Table 1 Element stratification

LayerElement designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Material Thickness Material ThicknessPatch Copper 35 120583m Copper 35 120583m

Antenna substrate 1205761199031

= 233 119905 = 0762mm 1205761199031

= 233 119905 = 0762mmAir 119889 = 0762mm Air 119889 = 0762mm

Ground plane with slot Copper 35 120583m Copper 35 120583mPhasing line substrate 120576

1199032

= 233 ℎ = 0762mm 1205761199032

= 6 ℎ = 0762mmPhasing line Copper 35120583m Copper 35 120583m

The dimensions of the optimized reflectarray element arereported in Table 2

Furthermore the same table shows that the designedtuning line is shorter than the line controlling the reflectarrayelement described in [7] In particular a 35 length reduc-tion is obtained thus allowing the allocation of the tuningcircuitries inside the smaller 046120582

0times 046120582

0cell (12mm times

12mm at 115 GHz)The simulated element pattern of the designed unit cell

is reported in Figure 7 The depicted diagrams refer to thereflectarray element with a phasing line having dimensions119871V = 42mm and 119871

119904= 52mm The radiation patterns

computed in the two principal planes show a nearly isotropicbehavior within the range from minus45∘ up to 45∘ as in the caseof a typical cos(120579) source

In conclusion the proposed unit cell could be suitablefor the design of reflectarray antennas with improved beam-steering capabilities as the main beam could be scannedwithin a quite large angular region ranging from minus45∘ up

to 45∘ without occurring in the grating lobes phenomenaFurthermore within this scanning range the main lobe willhave at most a 3 dB amplitude reduction as demonstrated bythe simulated element pattern (Figure 7)

3 Design of a Beam-Steering Reflectarray

In order to prove the effectiveness of the proposed cell a21 times 21 reflectarray is designed at the frequency of 115 GHzThe array is illuminated by a broadside feed placed at adistance of 34 cm A synthesis algorithm [11] is adopted inorder to compute the varactor capacitance values which allowto steer the radiated main beam from 0∘ up to 65∘ in the H-plane The computed radiation patterns depicted in Figure 8show the validity of the proposed approach as the mainbeam is successfully moved along the desired directionsAs expected by the array theory Figure 8 shows that themain beam amplitude decreases when moving away fromthe broadside direction In particular it can be observed that

6 Journal of Electrical and Computer Engineering

Table 2 Element dimension

Element designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Patch size 119882times 119871 = 82mm times 93mm 119882times 119871 = 775mm times 775mmSlot size 119871

119886

times119882119886

= 58mm times 06mm 119871119886

times119882119886

= 57mm times 05mmPhase tuningline

119871V = 65mm + 119871119904

= 78mm119882119904

= 307mm119871V = 42mm + 119871

119904

= 52mm119882119904

= 16mm

105 11 115 12 125

0

50

100

150

(GHz)

Matched case

(Ω)

Re (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 35mm

Im (Zt998400 ) minus Ls = 45mmIm (Zt998400 ) minus Ls = 52mm

Figure 6 Input impedance 1198851199051015840 for different stub lengths

minus90

minus60

minus30

0

30

60

90

minus10000

minus20000

minus30000

minus40000

x-z planey-z plane

Figure 7 Element pattern of designed reflectarray element

the scan loss increases away from broadside by following thecosine behavior of the element pattern Thus an acceptable3 dB scan loss is obtained when the main lobe is pointedalong the direction 120579

119904= 45

∘ while for 120579119904= 65

∘ agreater scan loss of about 7 dB is observed FurthermoreFigure 8 shows a broader main lobe for greater scan anglesDespite limitations imposed by the array theory (ie scanlosses and main lobe broadening) the obtained numericalresults demonstrate wide angle beam-steering capabilities ofthe designed antenna without occurring in grating lobesappearance

minus90 minus60 minus30 0 30 60 90minus40

minus30

minus20

minus10

0

(dB)

120579 (deg)

120579s = 0∘

120579s = 25∘

120579s = 45∘

120579s = 65∘

Element pattern

Figure 8 Computed radiation patterns for different configurationsof the varactors capacitance values

4 Conclusion

The reflectarray concept has been applied in this work todesign beam-steering antennas suitable for radar applica-tions A reflectarray unit cell based on the use of a singlevaractor diode has been proposed and optimized to providewide angle steering capabilities At this purpose the antennahas been properly designed by reducing the unit cell sizein order to achieve a large angular scanning As a specificnumerical example a varactor loaded reflectarray elementembedded into a 046120582

0times 046120582

0cell at 119891

0= 115GHz

has been synthesized obtaining a full phase tuning rangeof about 330∘ The designed unit cell has been adopted todesign a 21 times 21 reconfigurable reflectarray The antennahas been numerically tested showing good beam-steeringperformances within a wide angular range from minus45∘ up to45∘

Acknowledgment

This work has been carried out under the framework of PON01 01503 National Italian Project ldquoLandslides EarlyWarningrdquofinanced by the Italian Ministry of University and Research

References

[1] A J Fenn D H Temme W P Delaney and W E CourtneyldquoThe development of phased-array radar technologyrdquo LincolnLaboratory Journal vol 12 pp 321ndash340 2000

Journal of Electrical and Computer Engineering 7

[2] J Huang and J Encinar Reflectarray Antennas Wiley-IEEEPress 2008

[3] S Costanzo F Venneri A Borgia I Venneri and G DiMassa ldquo60 GHz microstrip reflectarray on a benzocyclobutenedielectric substraterdquo IET Science Measurement and Technologyvol 5 no 4 pp 134ndash139 2011

[4] R Sorrentino R V Gatti L Marcaccioli and B MencaglildquoElectronic steerable mems antennasrdquo in Proceedings of the 1stEuropean Conference on Antennas and Propagation (EuCAPrsquo06) pp 1ndash8 Nice France November 2006

[5] S V Hum M Okoniewski and R J Davies ldquoRealizing anelectronically tunable reflectarray using varactor diode-tunedelementsrdquo IEEE Microwave and Wireless Components Lettersvol 15 no 6 pp 422ndash424 2005

[6] M Riel and J J Laurin ldquoDesign of an electronically beamscanning reflectarray using aperture-coupled elementsrdquo IEEETransactions on Antennas and Propagation vol 55 no 5 pp1260ndash1266 2007

[7] F Venneri S Costanzo and G Di Massa ldquoReconfigurableaperture-coupled reflectarray element tuned by single varactordioderdquo Electronics Letters vol 48 no 2 pp 68ndash69 2012

[8] F Venneri S Costanzo G Di Massa A Borgia P Corsonelloand M Salzano ldquoDesign of a reconfigurable reflectarray basedon a varactor tuned elementrdquo in Proceedings of the 6th EuropeanConference on Antennas and Propagation (EUCAP rsquo12) pp2628ndash2631 Prague Czech Republic March 2012

[9] F Venneri S Costanzo G Di Massa et al ldquoBeam-scanningreflectarray based on a single varactor-tuned elementrdquo Interna-tional Journal of Antennas and Propagation vol 2012 Article ID290285 5 pages 2012

[10] F Venneri S Costanzo and G Di Massa ldquoDesign and valida-tion of a reconfigurable single varactor-tuned reflectarrayrdquo IEEETransactions on Antennas and Propagation vol 61 no 2 pp635ndash645 2013

[11] F Venneri S Costanzo G Di Massa and G Angiulli ldquoAnimproved synthesis algorithm for reflectarrays designrdquo IEEEAntennas andWireless Propagation Letters vol 4 no 1 pp 258ndash261 2005

[12] S Costanzo F Venneri GDiMassa andGAngiulli ldquoSynthesisof microstrip reflectarrays as planar scatterers for SAR interfer-ometryrdquo Electronics Letters vol 39 no 3 pp 266ndash267 2003

[13] S Costanzo and G Di Massa ldquoDirect far-field computationfrom bi-polar near-field samplesrdquo Journal of ElectromagneticWaves and Applications vol 20 no 9 pp 1137ndash1148 2006

[14] S Costanzo and G Di Massa ldquoNear-field to far-field transfor-mation with planar spiral scanningrdquo Progress in Electromagnet-ics Research vol 73 pp 49ndash59 2007

[15] C A Balanis AntennaTheory Analysis and Design JohnWileyamp Sons New York NY USA 2nd edition 1997

[16] S Costanzo F Venneri and G DiMassa ldquoBandwidth enhance-ment of aperture-coupled reflectarraysrdquo Electronics Letters vol42 no 23 pp 1320ndash1321 2006

[17] F Venneri S Costanzo G Di Massa and G AmendolaldquoAperture-coupled reflectarrays with enhanced bandwidth fea-turesrdquo Journal of Electromagnetic Waves and Applications vol22 no 11-12 pp 1527ndash1537 2008

[18] F Venneri S Costanzo and G Di Massa ldquoBandwidth behaviorof closely spaced aperture-coupled reflectarraysrdquo InternationalJournal of Antennas and Propagation vol 2012 Article ID846017 11 pages 2012

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

4 Journal of Electrical and Computer Engineering

Z

minus90∘ 90∘

Theoretical scanning region

middot middot middotmiddot middot middot1 2 NNminus 1

05120582 05120582

(a)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(b)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(c)

minus90minus40

minus60 minus30 30 60 90

minus30

minus20

minus10

0

0

(dB)

120579 (deg)

(d)

Figure 3 Scanning performances of an N-elements linear array with spacing equal to 05120582 (a) allowable scanning area given by relation (1)(b) array factor for a scan angle 120579

119904

= 15∘ and119873 = 21 (c) array factor for a scan angle 120579

119904

= 30∘ and119873 = 21 (d) array factor for a scan angle

120579119904

= 50∘ and119873 = 21

C

Cp

sim Lp

Rs

A

A998400

A

A998400

Zvar

Figure 4 Equivalent circuit model of a varactor diode

illustrated in Figure 4 which takes into account the packageparasitic effects (119871

119901 119862119901) and the diode losses (119877

119904) The

varactor lumped parameters are fixed to the following valuesderived by the Microsemi MV31011-89 diode datasheet 119871

119901=

02 nH 119862119901= 015 pF and 119877

119904= 136Ω

As described in [10] the two line sections 119871V and119871119904(see Figure 1(b)) are optimized in order to maximize

the phase agility of the element for the assigned varactorcapacitance range At this purpose a parametric analysis ofthe reflectarray element is performed with respect to the

lengths 119871V and 119871119904 by assuming a normally incident plane

wave Figure 5 shows the reflection phase curves versus thevaractor capacitance computed for different values of the linelength

It can be observed that by increasing 119871119904 for a fixed value

of 119871V (Figure 5(a)) a higher phase tuning range is obtainedAs accurately demonstrated in [10] this last result is due tothe introduction of a proper inductive effect which is directlyrelated to the stub length As a proof of this concept theinput impedance 119885

1199051015840 of the designed aperture coupled patch

evaluated at the slot center is reported under Figure 6 fordifferent values of the stub length 119871

119904ranging from 105mm

(the matched case) up to 52mm It can be observed that foran increased input reactance a wider phase tuning range isachieved (Figure 5(a)) In particular a phase tuning of about330∘ is obtained for 119871

119904= 52mm On the other hand the

length 119871V is tuned in order to match the maximum phasevariation with the available varactor capacitance range [10]As a matter of fact Figure 5(b) shows that for any fixed valueof 119871119904 the section 119871V can be chosen to shift the phase curve

within the capacitance range with the aim to increase theallowable phase tuning range so obtaining a phasing lineacting as a 360∘ phase shifter

Journal of Electrical and Computer Engineering 5

1 2

minus180

0

90

180

minus90

02 04 06 08 12 14 16 18Diode capacitance (pF)

Refle

ctio

n ph

ase (

deg)

2 552544

35

45

Ls (mm)

(a)

1 202 04 06 08 12 14 16 18Diode capacitance (pF)

Ls = 52mm

Ls = 45mm

L = 42mmL = 425mm

L = 43mmL = 44mm

Refle

ctio

n ph

ase (

deg)

minus200

minus150

minus100

minus50

0

50

100

150

200

(b)

Figure 5 Phase curves versus diode capacitance for different line lengths (a) 119871V = 42mm and 119871119904

ranging from 2mm up to 54mm (b) 119871Vranging from 42mm up to 44mm for some fixed values of 119871

119904

Table 1 Element stratification

LayerElement designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Material Thickness Material ThicknessPatch Copper 35 120583m Copper 35 120583m

Antenna substrate 1205761199031

= 233 119905 = 0762mm 1205761199031

= 233 119905 = 0762mmAir 119889 = 0762mm Air 119889 = 0762mm

Ground plane with slot Copper 35 120583m Copper 35 120583mPhasing line substrate 120576

1199032

= 233 ℎ = 0762mm 1205761199032

= 6 ℎ = 0762mmPhasing line Copper 35120583m Copper 35 120583m

The dimensions of the optimized reflectarray element arereported in Table 2

Furthermore the same table shows that the designedtuning line is shorter than the line controlling the reflectarrayelement described in [7] In particular a 35 length reduc-tion is obtained thus allowing the allocation of the tuningcircuitries inside the smaller 046120582

0times 046120582

0cell (12mm times

12mm at 115 GHz)The simulated element pattern of the designed unit cell

is reported in Figure 7 The depicted diagrams refer to thereflectarray element with a phasing line having dimensions119871V = 42mm and 119871

119904= 52mm The radiation patterns

computed in the two principal planes show a nearly isotropicbehavior within the range from minus45∘ up to 45∘ as in the caseof a typical cos(120579) source

In conclusion the proposed unit cell could be suitablefor the design of reflectarray antennas with improved beam-steering capabilities as the main beam could be scannedwithin a quite large angular region ranging from minus45∘ up

to 45∘ without occurring in the grating lobes phenomenaFurthermore within this scanning range the main lobe willhave at most a 3 dB amplitude reduction as demonstrated bythe simulated element pattern (Figure 7)

3 Design of a Beam-Steering Reflectarray

In order to prove the effectiveness of the proposed cell a21 times 21 reflectarray is designed at the frequency of 115 GHzThe array is illuminated by a broadside feed placed at adistance of 34 cm A synthesis algorithm [11] is adopted inorder to compute the varactor capacitance values which allowto steer the radiated main beam from 0∘ up to 65∘ in the H-plane The computed radiation patterns depicted in Figure 8show the validity of the proposed approach as the mainbeam is successfully moved along the desired directionsAs expected by the array theory Figure 8 shows that themain beam amplitude decreases when moving away fromthe broadside direction In particular it can be observed that

6 Journal of Electrical and Computer Engineering

Table 2 Element dimension

Element designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Patch size 119882times 119871 = 82mm times 93mm 119882times 119871 = 775mm times 775mmSlot size 119871

119886

times119882119886

= 58mm times 06mm 119871119886

times119882119886

= 57mm times 05mmPhase tuningline

119871V = 65mm + 119871119904

= 78mm119882119904

= 307mm119871V = 42mm + 119871

119904

= 52mm119882119904

= 16mm

105 11 115 12 125

0

50

100

150

(GHz)

Matched case

(Ω)

Re (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 35mm

Im (Zt998400 ) minus Ls = 45mmIm (Zt998400 ) minus Ls = 52mm

Figure 6 Input impedance 1198851199051015840 for different stub lengths

minus90

minus60

minus30

0

30

60

90

minus10000

minus20000

minus30000

minus40000

x-z planey-z plane

Figure 7 Element pattern of designed reflectarray element

the scan loss increases away from broadside by following thecosine behavior of the element pattern Thus an acceptable3 dB scan loss is obtained when the main lobe is pointedalong the direction 120579

119904= 45

∘ while for 120579119904= 65

∘ agreater scan loss of about 7 dB is observed FurthermoreFigure 8 shows a broader main lobe for greater scan anglesDespite limitations imposed by the array theory (ie scanlosses and main lobe broadening) the obtained numericalresults demonstrate wide angle beam-steering capabilities ofthe designed antenna without occurring in grating lobesappearance

minus90 minus60 minus30 0 30 60 90minus40

minus30

minus20

minus10

0

(dB)

120579 (deg)

120579s = 0∘

120579s = 25∘

120579s = 45∘

120579s = 65∘

Element pattern

Figure 8 Computed radiation patterns for different configurationsof the varactors capacitance values

4 Conclusion

The reflectarray concept has been applied in this work todesign beam-steering antennas suitable for radar applica-tions A reflectarray unit cell based on the use of a singlevaractor diode has been proposed and optimized to providewide angle steering capabilities At this purpose the antennahas been properly designed by reducing the unit cell sizein order to achieve a large angular scanning As a specificnumerical example a varactor loaded reflectarray elementembedded into a 046120582

0times 046120582

0cell at 119891

0= 115GHz

has been synthesized obtaining a full phase tuning rangeof about 330∘ The designed unit cell has been adopted todesign a 21 times 21 reconfigurable reflectarray The antennahas been numerically tested showing good beam-steeringperformances within a wide angular range from minus45∘ up to45∘

Acknowledgment

This work has been carried out under the framework of PON01 01503 National Italian Project ldquoLandslides EarlyWarningrdquofinanced by the Italian Ministry of University and Research

References

[1] A J Fenn D H Temme W P Delaney and W E CourtneyldquoThe development of phased-array radar technologyrdquo LincolnLaboratory Journal vol 12 pp 321ndash340 2000

Journal of Electrical and Computer Engineering 7

[2] J Huang and J Encinar Reflectarray Antennas Wiley-IEEEPress 2008

[3] S Costanzo F Venneri A Borgia I Venneri and G DiMassa ldquo60 GHz microstrip reflectarray on a benzocyclobutenedielectric substraterdquo IET Science Measurement and Technologyvol 5 no 4 pp 134ndash139 2011

[4] R Sorrentino R V Gatti L Marcaccioli and B MencaglildquoElectronic steerable mems antennasrdquo in Proceedings of the 1stEuropean Conference on Antennas and Propagation (EuCAPrsquo06) pp 1ndash8 Nice France November 2006

[5] S V Hum M Okoniewski and R J Davies ldquoRealizing anelectronically tunable reflectarray using varactor diode-tunedelementsrdquo IEEE Microwave and Wireless Components Lettersvol 15 no 6 pp 422ndash424 2005

[6] M Riel and J J Laurin ldquoDesign of an electronically beamscanning reflectarray using aperture-coupled elementsrdquo IEEETransactions on Antennas and Propagation vol 55 no 5 pp1260ndash1266 2007

[7] F Venneri S Costanzo and G Di Massa ldquoReconfigurableaperture-coupled reflectarray element tuned by single varactordioderdquo Electronics Letters vol 48 no 2 pp 68ndash69 2012

[8] F Venneri S Costanzo G Di Massa A Borgia P Corsonelloand M Salzano ldquoDesign of a reconfigurable reflectarray basedon a varactor tuned elementrdquo in Proceedings of the 6th EuropeanConference on Antennas and Propagation (EUCAP rsquo12) pp2628ndash2631 Prague Czech Republic March 2012

[9] F Venneri S Costanzo G Di Massa et al ldquoBeam-scanningreflectarray based on a single varactor-tuned elementrdquo Interna-tional Journal of Antennas and Propagation vol 2012 Article ID290285 5 pages 2012

[10] F Venneri S Costanzo and G Di Massa ldquoDesign and valida-tion of a reconfigurable single varactor-tuned reflectarrayrdquo IEEETransactions on Antennas and Propagation vol 61 no 2 pp635ndash645 2013

[11] F Venneri S Costanzo G Di Massa and G Angiulli ldquoAnimproved synthesis algorithm for reflectarrays designrdquo IEEEAntennas andWireless Propagation Letters vol 4 no 1 pp 258ndash261 2005

[12] S Costanzo F Venneri GDiMassa andGAngiulli ldquoSynthesisof microstrip reflectarrays as planar scatterers for SAR interfer-ometryrdquo Electronics Letters vol 39 no 3 pp 266ndash267 2003

[13] S Costanzo and G Di Massa ldquoDirect far-field computationfrom bi-polar near-field samplesrdquo Journal of ElectromagneticWaves and Applications vol 20 no 9 pp 1137ndash1148 2006

[14] S Costanzo and G Di Massa ldquoNear-field to far-field transfor-mation with planar spiral scanningrdquo Progress in Electromagnet-ics Research vol 73 pp 49ndash59 2007

[15] C A Balanis AntennaTheory Analysis and Design JohnWileyamp Sons New York NY USA 2nd edition 1997

[16] S Costanzo F Venneri and G DiMassa ldquoBandwidth enhance-ment of aperture-coupled reflectarraysrdquo Electronics Letters vol42 no 23 pp 1320ndash1321 2006

[17] F Venneri S Costanzo G Di Massa and G AmendolaldquoAperture-coupled reflectarrays with enhanced bandwidth fea-turesrdquo Journal of Electromagnetic Waves and Applications vol22 no 11-12 pp 1527ndash1537 2008

[18] F Venneri S Costanzo and G Di Massa ldquoBandwidth behaviorof closely spaced aperture-coupled reflectarraysrdquo InternationalJournal of Antennas and Propagation vol 2012 Article ID846017 11 pages 2012

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Journal of Electrical and Computer Engineering 5

1 2

minus180

0

90

180

minus90

02 04 06 08 12 14 16 18Diode capacitance (pF)

Refle

ctio

n ph

ase (

deg)

2 552544

35

45

Ls (mm)

(a)

1 202 04 06 08 12 14 16 18Diode capacitance (pF)

Ls = 52mm

Ls = 45mm

L = 42mmL = 425mm

L = 43mmL = 44mm

Refle

ctio

n ph

ase (

deg)

minus200

minus150

minus100

minus50

0

50

100

150

200

(b)

Figure 5 Phase curves versus diode capacitance for different line lengths (a) 119871V = 42mm and 119871119904

ranging from 2mm up to 54mm (b) 119871Vranging from 42mm up to 44mm for some fixed values of 119871

119904

Table 1 Element stratification

LayerElement designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Material Thickness Material ThicknessPatch Copper 35 120583m Copper 35 120583m

Antenna substrate 1205761199031

= 233 119905 = 0762mm 1205761199031

= 233 119905 = 0762mmAir 119889 = 0762mm Air 119889 = 0762mm

Ground plane with slot Copper 35 120583m Copper 35 120583mPhasing line substrate 120576

1199032

= 233 ℎ = 0762mm 1205761199032

= 6 ℎ = 0762mmPhasing line Copper 35120583m Copper 35 120583m

The dimensions of the optimized reflectarray element arereported in Table 2

Furthermore the same table shows that the designedtuning line is shorter than the line controlling the reflectarrayelement described in [7] In particular a 35 length reduc-tion is obtained thus allowing the allocation of the tuningcircuitries inside the smaller 046120582

0times 046120582

0cell (12mm times

12mm at 115 GHz)The simulated element pattern of the designed unit cell

is reported in Figure 7 The depicted diagrams refer to thereflectarray element with a phasing line having dimensions119871V = 42mm and 119871

119904= 52mm The radiation patterns

computed in the two principal planes show a nearly isotropicbehavior within the range from minus45∘ up to 45∘ as in the caseof a typical cos(120579) source

In conclusion the proposed unit cell could be suitablefor the design of reflectarray antennas with improved beam-steering capabilities as the main beam could be scannedwithin a quite large angular region ranging from minus45∘ up

to 45∘ without occurring in the grating lobes phenomenaFurthermore within this scanning range the main lobe willhave at most a 3 dB amplitude reduction as demonstrated bythe simulated element pattern (Figure 7)

3 Design of a Beam-Steering Reflectarray

In order to prove the effectiveness of the proposed cell a21 times 21 reflectarray is designed at the frequency of 115 GHzThe array is illuminated by a broadside feed placed at adistance of 34 cm A synthesis algorithm [11] is adopted inorder to compute the varactor capacitance values which allowto steer the radiated main beam from 0∘ up to 65∘ in the H-plane The computed radiation patterns depicted in Figure 8show the validity of the proposed approach as the mainbeam is successfully moved along the desired directionsAs expected by the array theory Figure 8 shows that themain beam amplitude decreases when moving away fromthe broadside direction In particular it can be observed that

6 Journal of Electrical and Computer Engineering

Table 2 Element dimension

Element designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Patch size 119882times 119871 = 82mm times 93mm 119882times 119871 = 775mm times 775mmSlot size 119871

119886

times119882119886

= 58mm times 06mm 119871119886

times119882119886

= 57mm times 05mmPhase tuningline

119871V = 65mm + 119871119904

= 78mm119882119904

= 307mm119871V = 42mm + 119871

119904

= 52mm119882119904

= 16mm

105 11 115 12 125

0

50

100

150

(GHz)

Matched case

(Ω)

Re (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 35mm

Im (Zt998400 ) minus Ls = 45mmIm (Zt998400 ) minus Ls = 52mm

Figure 6 Input impedance 1198851199051015840 for different stub lengths

minus90

minus60

minus30

0

30

60

90

minus10000

minus20000

minus30000

minus40000

x-z planey-z plane

Figure 7 Element pattern of designed reflectarray element

the scan loss increases away from broadside by following thecosine behavior of the element pattern Thus an acceptable3 dB scan loss is obtained when the main lobe is pointedalong the direction 120579

119904= 45

∘ while for 120579119904= 65

∘ agreater scan loss of about 7 dB is observed FurthermoreFigure 8 shows a broader main lobe for greater scan anglesDespite limitations imposed by the array theory (ie scanlosses and main lobe broadening) the obtained numericalresults demonstrate wide angle beam-steering capabilities ofthe designed antenna without occurring in grating lobesappearance

minus90 minus60 minus30 0 30 60 90minus40

minus30

minus20

minus10

0

(dB)

120579 (deg)

120579s = 0∘

120579s = 25∘

120579s = 45∘

120579s = 65∘

Element pattern

Figure 8 Computed radiation patterns for different configurationsof the varactors capacitance values

4 Conclusion

The reflectarray concept has been applied in this work todesign beam-steering antennas suitable for radar applica-tions A reflectarray unit cell based on the use of a singlevaractor diode has been proposed and optimized to providewide angle steering capabilities At this purpose the antennahas been properly designed by reducing the unit cell sizein order to achieve a large angular scanning As a specificnumerical example a varactor loaded reflectarray elementembedded into a 046120582

0times 046120582

0cell at 119891

0= 115GHz

has been synthesized obtaining a full phase tuning rangeof about 330∘ The designed unit cell has been adopted todesign a 21 times 21 reconfigurable reflectarray The antennahas been numerically tested showing good beam-steeringperformances within a wide angular range from minus45∘ up to45∘

Acknowledgment

This work has been carried out under the framework of PON01 01503 National Italian Project ldquoLandslides EarlyWarningrdquofinanced by the Italian Ministry of University and Research

References

[1] A J Fenn D H Temme W P Delaney and W E CourtneyldquoThe development of phased-array radar technologyrdquo LincolnLaboratory Journal vol 12 pp 321ndash340 2000

Journal of Electrical and Computer Engineering 7

[2] J Huang and J Encinar Reflectarray Antennas Wiley-IEEEPress 2008

[3] S Costanzo F Venneri A Borgia I Venneri and G DiMassa ldquo60 GHz microstrip reflectarray on a benzocyclobutenedielectric substraterdquo IET Science Measurement and Technologyvol 5 no 4 pp 134ndash139 2011

[4] R Sorrentino R V Gatti L Marcaccioli and B MencaglildquoElectronic steerable mems antennasrdquo in Proceedings of the 1stEuropean Conference on Antennas and Propagation (EuCAPrsquo06) pp 1ndash8 Nice France November 2006

[5] S V Hum M Okoniewski and R J Davies ldquoRealizing anelectronically tunable reflectarray using varactor diode-tunedelementsrdquo IEEE Microwave and Wireless Components Lettersvol 15 no 6 pp 422ndash424 2005

[6] M Riel and J J Laurin ldquoDesign of an electronically beamscanning reflectarray using aperture-coupled elementsrdquo IEEETransactions on Antennas and Propagation vol 55 no 5 pp1260ndash1266 2007

[7] F Venneri S Costanzo and G Di Massa ldquoReconfigurableaperture-coupled reflectarray element tuned by single varactordioderdquo Electronics Letters vol 48 no 2 pp 68ndash69 2012

[8] F Venneri S Costanzo G Di Massa A Borgia P Corsonelloand M Salzano ldquoDesign of a reconfigurable reflectarray basedon a varactor tuned elementrdquo in Proceedings of the 6th EuropeanConference on Antennas and Propagation (EUCAP rsquo12) pp2628ndash2631 Prague Czech Republic March 2012

[9] F Venneri S Costanzo G Di Massa et al ldquoBeam-scanningreflectarray based on a single varactor-tuned elementrdquo Interna-tional Journal of Antennas and Propagation vol 2012 Article ID290285 5 pages 2012

[10] F Venneri S Costanzo and G Di Massa ldquoDesign and valida-tion of a reconfigurable single varactor-tuned reflectarrayrdquo IEEETransactions on Antennas and Propagation vol 61 no 2 pp635ndash645 2013

[11] F Venneri S Costanzo G Di Massa and G Angiulli ldquoAnimproved synthesis algorithm for reflectarrays designrdquo IEEEAntennas andWireless Propagation Letters vol 4 no 1 pp 258ndash261 2005

[12] S Costanzo F Venneri GDiMassa andGAngiulli ldquoSynthesisof microstrip reflectarrays as planar scatterers for SAR interfer-ometryrdquo Electronics Letters vol 39 no 3 pp 266ndash267 2003

[13] S Costanzo and G Di Massa ldquoDirect far-field computationfrom bi-polar near-field samplesrdquo Journal of ElectromagneticWaves and Applications vol 20 no 9 pp 1137ndash1148 2006

[14] S Costanzo and G Di Massa ldquoNear-field to far-field transfor-mation with planar spiral scanningrdquo Progress in Electromagnet-ics Research vol 73 pp 49ndash59 2007

[15] C A Balanis AntennaTheory Analysis and Design JohnWileyamp Sons New York NY USA 2nd edition 1997

[16] S Costanzo F Venneri and G DiMassa ldquoBandwidth enhance-ment of aperture-coupled reflectarraysrdquo Electronics Letters vol42 no 23 pp 1320ndash1321 2006

[17] F Venneri S Costanzo G Di Massa and G AmendolaldquoAperture-coupled reflectarrays with enhanced bandwidth fea-turesrdquo Journal of Electromagnetic Waves and Applications vol22 no 11-12 pp 1527ndash1537 2008

[18] F Venneri S Costanzo and G Di Massa ldquoBandwidth behaviorof closely spaced aperture-coupled reflectarraysrdquo InternationalJournal of Antennas and Propagation vol 2012 Article ID846017 11 pages 2012

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

6 Journal of Electrical and Computer Engineering

Table 2 Element dimension

Element designed in [7]Δ119909 times Δ119910 = 07120582

0

times 071205820

Element designed in this workΔ119909 times Δ119910 = 046120582

0

times 0461205820

Patch size 119882times 119871 = 82mm times 93mm 119882times 119871 = 775mm times 775mmSlot size 119871

119886

times119882119886

= 58mm times 06mm 119871119886

times119882119886

= 57mm times 05mmPhase tuningline

119871V = 65mm + 119871119904

= 78mm119882119904

= 307mm119871V = 42mm + 119871

119904

= 52mm119882119904

= 16mm

105 11 115 12 125

0

50

100

150

(GHz)

Matched case

(Ω)

Re (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 105mmIm (Zt998400 ) minus Ls = 35mm

Im (Zt998400 ) minus Ls = 45mmIm (Zt998400 ) minus Ls = 52mm

Figure 6 Input impedance 1198851199051015840 for different stub lengths

minus90

minus60

minus30

0

30

60

90

minus10000

minus20000

minus30000

minus40000

x-z planey-z plane

Figure 7 Element pattern of designed reflectarray element

the scan loss increases away from broadside by following thecosine behavior of the element pattern Thus an acceptable3 dB scan loss is obtained when the main lobe is pointedalong the direction 120579

119904= 45

∘ while for 120579119904= 65

∘ agreater scan loss of about 7 dB is observed FurthermoreFigure 8 shows a broader main lobe for greater scan anglesDespite limitations imposed by the array theory (ie scanlosses and main lobe broadening) the obtained numericalresults demonstrate wide angle beam-steering capabilities ofthe designed antenna without occurring in grating lobesappearance

minus90 minus60 minus30 0 30 60 90minus40

minus30

minus20

minus10

0

(dB)

120579 (deg)

120579s = 0∘

120579s = 25∘

120579s = 45∘

120579s = 65∘

Element pattern

Figure 8 Computed radiation patterns for different configurationsof the varactors capacitance values

4 Conclusion

The reflectarray concept has been applied in this work todesign beam-steering antennas suitable for radar applica-tions A reflectarray unit cell based on the use of a singlevaractor diode has been proposed and optimized to providewide angle steering capabilities At this purpose the antennahas been properly designed by reducing the unit cell sizein order to achieve a large angular scanning As a specificnumerical example a varactor loaded reflectarray elementembedded into a 046120582

0times 046120582

0cell at 119891

0= 115GHz

has been synthesized obtaining a full phase tuning rangeof about 330∘ The designed unit cell has been adopted todesign a 21 times 21 reconfigurable reflectarray The antennahas been numerically tested showing good beam-steeringperformances within a wide angular range from minus45∘ up to45∘

Acknowledgment

This work has been carried out under the framework of PON01 01503 National Italian Project ldquoLandslides EarlyWarningrdquofinanced by the Italian Ministry of University and Research

References

[1] A J Fenn D H Temme W P Delaney and W E CourtneyldquoThe development of phased-array radar technologyrdquo LincolnLaboratory Journal vol 12 pp 321ndash340 2000

Journal of Electrical and Computer Engineering 7

[2] J Huang and J Encinar Reflectarray Antennas Wiley-IEEEPress 2008

[3] S Costanzo F Venneri A Borgia I Venneri and G DiMassa ldquo60 GHz microstrip reflectarray on a benzocyclobutenedielectric substraterdquo IET Science Measurement and Technologyvol 5 no 4 pp 134ndash139 2011

[4] R Sorrentino R V Gatti L Marcaccioli and B MencaglildquoElectronic steerable mems antennasrdquo in Proceedings of the 1stEuropean Conference on Antennas and Propagation (EuCAPrsquo06) pp 1ndash8 Nice France November 2006

[5] S V Hum M Okoniewski and R J Davies ldquoRealizing anelectronically tunable reflectarray using varactor diode-tunedelementsrdquo IEEE Microwave and Wireless Components Lettersvol 15 no 6 pp 422ndash424 2005

[6] M Riel and J J Laurin ldquoDesign of an electronically beamscanning reflectarray using aperture-coupled elementsrdquo IEEETransactions on Antennas and Propagation vol 55 no 5 pp1260ndash1266 2007

[7] F Venneri S Costanzo and G Di Massa ldquoReconfigurableaperture-coupled reflectarray element tuned by single varactordioderdquo Electronics Letters vol 48 no 2 pp 68ndash69 2012

[8] F Venneri S Costanzo G Di Massa A Borgia P Corsonelloand M Salzano ldquoDesign of a reconfigurable reflectarray basedon a varactor tuned elementrdquo in Proceedings of the 6th EuropeanConference on Antennas and Propagation (EUCAP rsquo12) pp2628ndash2631 Prague Czech Republic March 2012

[9] F Venneri S Costanzo G Di Massa et al ldquoBeam-scanningreflectarray based on a single varactor-tuned elementrdquo Interna-tional Journal of Antennas and Propagation vol 2012 Article ID290285 5 pages 2012

[10] F Venneri S Costanzo and G Di Massa ldquoDesign and valida-tion of a reconfigurable single varactor-tuned reflectarrayrdquo IEEETransactions on Antennas and Propagation vol 61 no 2 pp635ndash645 2013

[11] F Venneri S Costanzo G Di Massa and G Angiulli ldquoAnimproved synthesis algorithm for reflectarrays designrdquo IEEEAntennas andWireless Propagation Letters vol 4 no 1 pp 258ndash261 2005

[12] S Costanzo F Venneri GDiMassa andGAngiulli ldquoSynthesisof microstrip reflectarrays as planar scatterers for SAR interfer-ometryrdquo Electronics Letters vol 39 no 3 pp 266ndash267 2003

[13] S Costanzo and G Di Massa ldquoDirect far-field computationfrom bi-polar near-field samplesrdquo Journal of ElectromagneticWaves and Applications vol 20 no 9 pp 1137ndash1148 2006

[14] S Costanzo and G Di Massa ldquoNear-field to far-field transfor-mation with planar spiral scanningrdquo Progress in Electromagnet-ics Research vol 73 pp 49ndash59 2007

[15] C A Balanis AntennaTheory Analysis and Design JohnWileyamp Sons New York NY USA 2nd edition 1997

[16] S Costanzo F Venneri and G DiMassa ldquoBandwidth enhance-ment of aperture-coupled reflectarraysrdquo Electronics Letters vol42 no 23 pp 1320ndash1321 2006

[17] F Venneri S Costanzo G Di Massa and G AmendolaldquoAperture-coupled reflectarrays with enhanced bandwidth fea-turesrdquo Journal of Electromagnetic Waves and Applications vol22 no 11-12 pp 1527ndash1537 2008

[18] F Venneri S Costanzo and G Di Massa ldquoBandwidth behaviorof closely spaced aperture-coupled reflectarraysrdquo InternationalJournal of Antennas and Propagation vol 2012 Article ID846017 11 pages 2012

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Journal of Electrical and Computer Engineering 7

[2] J Huang and J Encinar Reflectarray Antennas Wiley-IEEEPress 2008

[3] S Costanzo F Venneri A Borgia I Venneri and G DiMassa ldquo60 GHz microstrip reflectarray on a benzocyclobutenedielectric substraterdquo IET Science Measurement and Technologyvol 5 no 4 pp 134ndash139 2011

[4] R Sorrentino R V Gatti L Marcaccioli and B MencaglildquoElectronic steerable mems antennasrdquo in Proceedings of the 1stEuropean Conference on Antennas and Propagation (EuCAPrsquo06) pp 1ndash8 Nice France November 2006

[5] S V Hum M Okoniewski and R J Davies ldquoRealizing anelectronically tunable reflectarray using varactor diode-tunedelementsrdquo IEEE Microwave and Wireless Components Lettersvol 15 no 6 pp 422ndash424 2005

[6] M Riel and J J Laurin ldquoDesign of an electronically beamscanning reflectarray using aperture-coupled elementsrdquo IEEETransactions on Antennas and Propagation vol 55 no 5 pp1260ndash1266 2007

[7] F Venneri S Costanzo and G Di Massa ldquoReconfigurableaperture-coupled reflectarray element tuned by single varactordioderdquo Electronics Letters vol 48 no 2 pp 68ndash69 2012

[8] F Venneri S Costanzo G Di Massa A Borgia P Corsonelloand M Salzano ldquoDesign of a reconfigurable reflectarray basedon a varactor tuned elementrdquo in Proceedings of the 6th EuropeanConference on Antennas and Propagation (EUCAP rsquo12) pp2628ndash2631 Prague Czech Republic March 2012

[9] F Venneri S Costanzo G Di Massa et al ldquoBeam-scanningreflectarray based on a single varactor-tuned elementrdquo Interna-tional Journal of Antennas and Propagation vol 2012 Article ID290285 5 pages 2012

[10] F Venneri S Costanzo and G Di Massa ldquoDesign and valida-tion of a reconfigurable single varactor-tuned reflectarrayrdquo IEEETransactions on Antennas and Propagation vol 61 no 2 pp635ndash645 2013

[11] F Venneri S Costanzo G Di Massa and G Angiulli ldquoAnimproved synthesis algorithm for reflectarrays designrdquo IEEEAntennas andWireless Propagation Letters vol 4 no 1 pp 258ndash261 2005

[12] S Costanzo F Venneri GDiMassa andGAngiulli ldquoSynthesisof microstrip reflectarrays as planar scatterers for SAR interfer-ometryrdquo Electronics Letters vol 39 no 3 pp 266ndash267 2003

[13] S Costanzo and G Di Massa ldquoDirect far-field computationfrom bi-polar near-field samplesrdquo Journal of ElectromagneticWaves and Applications vol 20 no 9 pp 1137ndash1148 2006

[14] S Costanzo and G Di Massa ldquoNear-field to far-field transfor-mation with planar spiral scanningrdquo Progress in Electromagnet-ics Research vol 73 pp 49ndash59 2007

[15] C A Balanis AntennaTheory Analysis and Design JohnWileyamp Sons New York NY USA 2nd edition 1997

[16] S Costanzo F Venneri and G DiMassa ldquoBandwidth enhance-ment of aperture-coupled reflectarraysrdquo Electronics Letters vol42 no 23 pp 1320ndash1321 2006

[17] F Venneri S Costanzo G Di Massa and G AmendolaldquoAperture-coupled reflectarrays with enhanced bandwidth fea-turesrdquo Journal of Electromagnetic Waves and Applications vol22 no 11-12 pp 1527ndash1537 2008

[18] F Venneri S Costanzo and G Di Massa ldquoBandwidth behaviorof closely spaced aperture-coupled reflectarraysrdquo InternationalJournal of Antennas and Propagation vol 2012 Article ID846017 11 pages 2012

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of