CIRCULARLY POLARIZED APERTURE COUPLED MICROSTRIP SHORT BACKFIRE ANTENNA WITH TWO RINGS · 2017. 3....

http://www.iaeme.com/IJECET/index.asp 13 [email protected]

International Journal of Electronics and Communication Engineering and Technology

(IJECET)

Volume 8, Issue 2, March - April 2017, pp. 13–25, Article ID: IJECET_08_02_003

Available online at

http://www.iaeme.com/IJECET/issues.asp?JType=IJECET&VType=8&IType=2

ISSN Print: 0976-6464 and ISSN Online: 0976-6472

© IAEME Publication

CIRCULARLY POLARIZED APERTURE

COUPLED MICROSTRIP SHORT BACKFIRE

ANTENNA WITH TWO RINGS

Kawa ABDOULA

Dept. of Communication Engineering,

Technical University of Varna,

Student SKA Str. 1, 9010 Varna, Bulgaria

ABSTRACT

A circularly polarized microstrip short back fire antenna (CPMSBA) with two ring

corrugated rim using aperture coupling feed method is proposed in this paper. The

antenna is designed to operate in KU-band. The simulation results verify the circular

polarization. The axial ratio bandwidth bwAR is 3.74%, gain is 10.43 dBi and

radiation efficiency is 89.7%. The antenna has a compact structure and high electrical

and mechanical characteristics.

Key words: Aperture Coupled Microstrip Antenna, Back Radiation, Circularly

Polarized Microstrip Antenna with Two Rings, Microstrip Short Backfire Antenna

(MSBA)

Cite this Article: Kawa ABDOULA, Circularly Polarized Aperture Coupled

Microstrip Short Backfire Antenna with Two Rings, International Journal of

Electronics and Communication Engineering and Technology, 8(2), 2017, pp. 13–25.

http://www.iaeme.com/IJECET/issues.asp?JType=IJECET&VType=8&IType=2

1. INTRODUCTION

The microstrip patch antennas have been used in many commercial and military applications

including radar, mobile communications, satellite communications and Wireless Local Area

networks (WLANs). The origin of microstrip antennas apparently dates back to 1953, when

Deschamps proposed the use of microstrip feed lines to feed an array of printed antenna

elements [1] - [ 2].

The microstrip patch antenna was first introduced by Munson in a symposium paper in

1972 [3]. Microstrip antennas are fed by one of four methods (a) microstrip line (b) coaxial

probe (c) aperture coupling and (d) proximity coupling. Microstrip patch antennas have

several well-known advantages over other antenna structures, including their low profile and

hence conformal nature, lightweight, low cost of production, robust nature, and compatibility

with microwave monolithic integrated circuits and optoelectronic integrated circuits

technologies [4]. Microstrip patch antennas suffer from several inherent disadvantage of this

technology in its pure form, namely, they have small bandwidth and relatively poor radiations

Kawa ABDOULA


efficiency resulting from surface wave excitations and conductor and dielectric losses. Many

specialized techniques have been developed to increase the bandwidth of a microstrip

antenna. These include either using thick foam substrates along with aperture coupled feeds to

avoid the probe reactance limitation, or using capacitive elements to compensate for the probe

inductance. Even further increases may be achieved by using configurations that exhibit dual

or multiple resonances, including stacked resonators or antennas surrounded by parasitically

coupled elements. [5]

The microstrip antennas (MSAs) may be designed for circular polarizations by adjusting

their physical dimensions so as to produce two degenerate orthogonal modes with in the

cavity region. This in turn results in the radiation of two orthogonally polarized waves near

the broadside direction. Thus circularly polarized radiation is obtained when two orthogonal

modes are excited with equal amplitude and in-phase quadrature [6].

2. RADIATION MECHANISM

The basic microstrip antenna is consisting of a radiating patch on one side of a dielectric

substrate, which has a ground plane of the other side. The microstrip patch and the ground

plane together form a resonant cavity (filled with the substrate material). The cavity is lossy,

due not only to the material (conductor and dielectric) loss, but also to the (desirable)

radiation into space [7].

In Figure 1. The electromagnetic energy provides by the feed microstrip line passes

though rectangular slot into the first resonator formed by patch element and the ground plane.

After multiple reflections between the inner walls of the first resonator, a part of this energy

radiated directly into the space and other part of this

Figure 1 Geometry of the antenna Cross section (b) Front view

Circularly Polarized Aperture Coupled Microstrip Short Backfire Antenna with Two Rings


Electromagnetic energy penetrates via the short sides of the patch element to the second

resonator, formed by the small reflector and ground plane. After multiple reflections between

the inner walls of the second resonator, the electromagnetic energy radiated between the short

sides of the small reflector and the rim in the broadside of the antenna. The rims reduce the

back and side radiations of the proposed antenna.

3. DESCRIPTION OF THE ANTENNA

Figure 1. shows the geometry of the aperture coupled microstrip short backfire antenna

(ACMSSBFA) The antenna consists of the following elements:

1. Screen 2. Screen Substrate 3. Feed line 4. Feed substrate 5. Ground (D2) 6. Rim 7.

Rectangle Cross-Slot 8. Patch 9. Patch substrate 10. Small Reflector (D1) 11. Additional

substrate. 12.Small reflector Substrate 13. Additional ring and five substrates as follows:

additional substrate AS (Taconic TLX-7: "εrt = 2.6, tan _t = 0.0019); small reflector substrate

SRS (Arlon AD 410: "εrq = 4.1, tan _q = 0.0030, the small reflector substrate is realized by

two layers with standard thickness of 3.175 mm); patch substrate PS (Arlon AD 600: "εrp =

6.15, tan _P =0.0030); feed substrate FS (Arlon AD 600: "εrf = 6.15, tan _f = 0.0030) and

screen substrate SS (Taconic TLX-7: "εrs=2.6, tan_S=0.0019).

4. EFFECT OF THE DIMENSION OF THE ANTENNA ON ITS

ELECTRICAL CHARACTERISTICS

The simulation of the CP antenna model is done by the software package CST Microwave

Studio 2010. The final results are verified with several others software packages.

Seven antenna electrical characteristics such as module of reflections coefficient |S11|

(return loss), axial ratio AR, gain G, back radiations level BRL, radiations efficiency ηeff and

radiations pattern are investigated in this paper.

Nine CP antenna dimension and constructive parameters such as length of patch LP, patch

size coefficient KP= LP/WP, average length of the cross slot La. Cross size coefficient

KS=La1/La2, length of the small reflector Lsr, small reflector size coefficient K1=Lsr/Wsr, width

of the first ring W1, width of the second ring W2 and length of the matching stub LS are chosen

as independent variables in the optimization.

Their influence of the return loss, axial ratio and gain behavior are shown in figures 2-10.

figures 2-10 shows strong influences of the all 9 dimensions and constructive parameters on

the return loss and axial ratio, while the same parameters and dimensions have low influence

on the antenna gain behavior. Co- and cross polar radiation patterns in φ = 45º-plane at three

frequencies (fmin=11.175 GHz, f0 = 0.5(fmin +fmax) =11.388 GHz and fmax = 11.602 GHz) are

shown in figure 11.

Figure 11 shows small changes of the radiations characteristics over the whole operating

frequency range. Figure 12 shows the return loss, axial ratio and gain of the proposed CP

antenna calculated by two different software packages- CST Microwave Studio 2010 and

HFSS version 11.1.

The both curves in the figure 12. (a) have similar behavior and their values close to each

other. CST Microwave gives the following results: central frequency f0=11.709 GHz and

impedance bandwidth bwS11 = 10.83%, while the HFSS Product is f0=11.560 GHz and bwS11 =

9.69% respectively, i.e. the above results differ only by 1.3% with respect to central frequency

and by 10,5% regarding the impedance bandwidth, which indicate a good agreement of the

obtained simulated results.

Figure 12. (b) shows the axial ratio. CST MWS gives the following results: central

frequency f0=11.388 GHz and axial ratio bandwidth bwAR =3.74%, while the HFSS Product is

Kawa ABDOULA


f0=11.42 GHz axial ratio bandwidth bwAR= 3.39% the results differ by 0.3% with respect to

central frequencies and by 9,35% regarding the axial ratio bandwidths bwAR.

Figure 12. (c) shows the antenna gain. CST MWS gives the Gmax=10.43 dBic while the

HFSS gives the Gmax=10.904 dBic, the results differ by 4.54%.

The dimensions of the proposed CP antenna are listed in Table 1, the optimized

parameters of the antenna structure are listed in Table 2, and the e electrical parameters of the

antenna are shown in the Table 3.

Table 1 Dimension of the antenna

Dimensions [ mm] Description

D 2 24 Big Reflectors inner diameter

tg 0.0175 Big reflector& ground thickness

L 13.155 Antenna length

Wsr 3.30 Small reflector width

W 7.6825 Rim width

tt 0.035 Small reflector thickness

tw 0.5 Rim thickness

Wp 2.38 Patch width

tp 0.035 Patch thinness

Wa1 0.45 Slot1 width= 0.1La1

Wa2 0.40 Slot2 width = 0.1 La2

l 11.9 Microstrip feed line length

Ls 1.0 Stub length

Wf 0.98 Microstrip feed line width

tf 0.0175 Microstrip feed line thickness

Ds 24 Screen diameter

ts 0.035 Screen thickness

ht 1.58 Additional substrate thickness

hq 6.35 Small reflector substrate thickness

hp 1.27 Patch substrate thickness

hf 0.635 Feed substrate thickness

hs 3.175 Screen substrate thickness

t1 0.5 Ring thickness

h1, h2 0.4 Distance between the upper edge of the peripheral

screen and the upper edge of the first and second ring



Table 2 Optimized parameters of the antenna

Name Value [ mm] Description

LP 2.7 Patch length

K1 1.12 Small reflector ratio Lsw/Wsr

KP 1.13 Patch Ratio LP/WP

KS 1.10 Slot Ratio La1/La2

La 4.3 Slot Length

La1 (2*La*Ks)/(Ks+1) Aperture 1 Length

La2 2*La/(Ks+1) Aperture 2 Length

Ls 1.0 Stub Length

Lsr 3.7 small reflector Length

Wa1 La1/10 Aperture 1 Width

Wa2 La2/10 Aperture 2 Width

WP LP/KP Patch Width

Wsr Lsr/K1 (W1) Small Reflector Width

W1 3.0 First ring Width

W2 3.0 Second ring Width

Table 3 Electrical parameters of the antenna

Impedance Bandwidth

Minimum frequency fmin , GHz 11.075

Maximum frequency fmax , GHz 12.343

Central frequency f0 , GHz 11.709

Relative bandwidth bw,% 10.83%

Frequency bandwidth BW, GHz 1.27

Axial Ratio bandwidth, Back Radiation, Gain and

efficiency

Minimum frequency fmin AR , GHz 11.175

Maximum frequency fmax AR , GHz 11.602

Central frequency f0 AR , GHz 11.388

Frequency bandwidth BWAR, GHz 0.427

Relative bandwidth bwAR, % 3.74

Gmin, dBi 10.17

Gmax, dBi 10.43

BRmin, dB -17.84

BRmax, dB -16.091

Efficiency ηmax, % 89.74%

Kawa ABDOULA


(a) (b)

(b) (b)

(c) (c)

Fig 2. Effect of the patch length LP (LP = 2.4 Fig. 3. Effect of the coefficient KP = LP/WP

mm –blue dashed line, LP = 2.7 mm – red solid line (KP = 1.03 – blue dashed line, KP = 1.13 – red

and LP = 3.0 mm – green dotted line) on the solid line and KP = 1.23 –green dotted line) on

electrical characteristics of the antenna: (a) the electrical characteristics of the antenna: (a)

return loss, (b) axial ratio, (c) gain return loss, (b) axial ratio, (c) gain.



(a) (a)

(b) (b)

(c) (c)

Fig 4. Effect of the average length of the cross Fig 5. Effect of the coefficient KS = La1/La2

slot La (La = 4.0 mm – Blue dashed line, La = 4.3 (KS = 1.05 –blue dashed line, KS = 1.10 – red

mm – red solid line and La = 4.6 mm –green dotted solid line and KS = 1.15 – green dotted line) on

line) on the electrical ratio, characteristics of the the electrical characteristics of the antenna: (a)

antenna: (a) return loss, (b) axial ratio, (c) gain return loss, (b) axial ratio, (c) gain

Kawa ABDOULA


(a) (a)

(b) (b)

(c) (c)

Fig 6. Effect of the small reflector length Lsr Fig 7. Effect of the coefficient K1 = Lsr/Wsr

(Lsr = 3.1 mm –blue dashed line, Lsr = 3.7 mm – (K1 = 1.02 –blue dashed line, K1 = 1.12 –red

red solid line and Lsr = 4.3 mm –green dotted solid line and K1 = 1.22 – green dotted line) on

line) on the electrical characteristics of the the electrical characteristics of the antenna: (a)

antenna: (a) return loss, (b) axial ratio, (c) gain. return loss, (b) axial ratio, (c) gain.



(a) (a)

(b) (b)

(c) (c)

Fig 8. Effect of the first ring width W1 (W 1= 2.0 Fig 9. Effect of the second ring width W2 (W 2=1.0

mm –blue dashed line, W1 = 3.0 mm – red solid mm –blue dashed line, W2 = 3.0 mm – red solid

line and W1 = 4.0 mm – green dotted line) on the line and W2 = 5.0 mm – green dotted line) on the

electrical characteristics of the antenna: electrical characteristics of the antenna:

(a) return loss, (b) axial ratio, (c) gain. (a) return loss, (b) axial ratio, (c) gain.

Kawa ABDOULA


(a) (a)

(b) (b)

(c) (c)

Fig 10. Effect of the stub length LS (LS = Fig 11. Radiation patterns of the antenna (co-

0.5mm –blue dashed line, LS = 1.0 mm – red polar, RHCP –red solid line and cross-polar,

solid line and LS = 1.5 mm –green dotted line) LHCP –green dashed line), plane φ = 45º: (a) f

on the electrical characteristics of the antenna: = fmin = 11.175 GHz, (b) f = f0 = 11.388 GHz,

(a) return loss, (b) axial ratio, (c) gain. (c) f = fmax = 11.602 GHz



(a) (b)

(c)

Fig 12. (a) Return loss, (b) AR and (c) Gain of the antenna calculated by means of two different

software’s: CST MWS 2010 –red solid line, HFSS v.11.1 –blue dashed line.

5. DISCUSSION AND NUMERICAL RESULTS

In this study an aperture coupled microstrip short backfire antenna was designed and

investigated. The following features of the proposed antenna design need discussion.

Advantages of the antenna

The impedance bandwidth bwS11 of the CP antenna is 10.83% while its polarization

bandwidth bwAR is equal to 3.74% this is good bandwidth compared with the conventional

microstrip antenna. The bandwidth enhancement in this case is due basically to the type of

chosen feed, suitable choice of the values of substrate dielectric constants and thicknesses,

optimization of antenna dimensions and insertion of two resonances in the antenna impedance

characteristic. The first of these resonances (the patch resonance) is at lower frequency while

the second resonance (the backfire resonance) is at higher frequency.

The CP antenna gain ranges from 10.17 dBic to 10.43 dBic within the antenna bandwidth,

at the central frequency f0 = 11.388 GHz the antenna has gain G0 =10.40 dBic, radiation

efficiency ηeff0 = 89.74%. The presence of corrugated rim improves the antenna gain by

approximately 0.5 dBic compared to the antenna with conventional rim.

The back radiation level of the CP antenna varies between -16 dB and -17.84 dB across

the antenna bandwidth. The basic contribution to this good result is due to the presence of the

screen and rim.

Kawa ABDOULA


The antenna construction is compact, robust and with a low volume. The volume and the

aperture area of the antenna, for example are 3.4 times less than the corresponding dimensions

of the CP SBFA with an air cavity.

Disadvantages of the antenna

The antenna gain is lower compared to the conventional CP SBFA with an air cavity due to

the reduced dimension.

6. CONCLUSION

A broadband circularly polarized aperture coupled microstrip short backfire antenna with two

ring corrugated rim has been designed and numerically examined.

The bandwidth widening of the antenna is achieved by use of two resonances: a patch

resonance and a backfire resonance, it has maximum gain 10.43 dBi, maximum back radiation

-16.091 dB, efficiency 89,74% and axial ratio bandwidth 3.74%, this is good bandwidth

compared with conventional microstrip antenna. The antenna is designed to operate within

KU-band. The antenna has a compact construction and high electrical and mechanical

characteristics. It can be used as a single antenna or as an element of microstrip antenna arrays

with various applications in the various communication systems including Radar, Mobile

communications, satellite communications and wireless local area network.

7. ACKNOWLEDGEMENTS

The authors wish to acknowledge associate professor Georgi Kirov and associate professor

Georgi Chervenkov at the Technical University of Varna, Bulgaria to their support during my

study and investigation of the microstrip short backfire antenna (MSBA).

REFERENCES

[1] G. Deschamps, W. Sichak, Microstrip microwave antennas, Proc. of Third Symp. on

USAF Antenna Research and Development Program. October 1953, 18–22,

[2] J. T. Bernhard, E. Mayes, D. Schaubert, and R.J. Mailloux, A Commemoration of

Deschamps ’and Sichak’ s ‘Microstrip Microwave Antennas’ 50 Years of Development,

Divergence, and New Directions, Proc. of the 2003 Antenna Applications Symp.

(September 2003) 189–230.

[3] R. E Munson, Microstrip phased array Antennas, Proc. of Twenty-Second Symp. on

USAF Antenna Research and Development Program. October 1972.

[4] K. F. Lee, Ed. Advances in Microstrip and Printed Antennas. John Wiley, 1997.

[5] J. L. Volakis, Antenna Engineering Handbook, 4. Edition 2007 chapters 7.1.

[6] D. M. Pozar, D., H. Schaubert, The Analysis and Design of Microstrip Antennas and

Arrays, University of Massachusetts at Amherst, a selected Reprint Volume, IEEE

Antennas and propagation Society, Sponsor The Institute of Electrical and Electronics

Engineers. Inc., New York, page 17.

[7] S.D. Tragonski, D. M. Pozar, Design of wideband circularly polarized aperture-coupled

microstrip antennas. IEEE Transactions antennas and propagation. 1993, Vol 41, no 2.



ABOUT AUTHOR

Kawa ABDOULA was born in Sulaimaniyah, Iraq in 1962; he received his MSc degree in

radio and television engineering from the Technical University of Varna, Bulgaria in 1988.

He worked between 1988 and 1990 as engineer at the Technical University of Varna. Since

1990 he lives in Sweden. He worked at Ericsson Energy System 3 years, Emerson Energy

System 2 years, Ericsson Mobile Communications 2 years, and 14 years as system engineer at

Itron AB in Stockholm, Sweden, (current job). He is Ph.D. student by distance at Technical

University of Varna.

CIRCULARLY POLARIZED APERTURE COUPLED MICROSTRIP SHORT BACKFIRE ANTENNA WITH TWO RINGS · 2017. 3....

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