J. Huang, “A Technique for an Array to Generate Circular Polarization with Linearly

7/27/2019 J. Huang, A Technique for an Array to Generate Circular Polarization with Linearly

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. AP-34, NO . 9, SEPTEMBER 1986 1113

A Technique for an Array to Generate CircularPolarization with Linearly Polarized Elements

Ab stru t-A met hod is presented for generating circularly polarizedradiation fro m an array compo sed o f linearly polarized elements havingunique angular and phase arrangements. With this technique thecomplexity, weight, and RF loss of the array feed can be significantlyreduced, especially in a large array. This uniquely formed array has thecapability of generating excellent circular polarization (CP) over arelatively wide frequency bandwidth. In addition, the array is capable ofscanning its main beam in the principal planes to relatively wide anglesfromts broadside direction without serious degradation to its CPquality. An othe r feature of this uniquely arranged array is a redu ction inthe occurrence of mutual coup ling. Th e discussion in this paper placesspecial emphasis on the microstrip type of radiator, although thetechnique presented can be adapted to most types of linearly polarizedantenna elements.

A I. INTRODUCTIONN ARRAY THAT GENERATES circularly polarizedradiation is conventionally constructed by usingcircularly polarized elements. Each element generally requirestwo feed ports with a hybrid to obtain the required twoorthogonal polarizations and a90" phase differential. Forwider bandwidth applications, often four feed ports with 0",go", 180" and 270" phase differentials are necessary. Forexample, in the case of a microstrip radiator, relatively wideimpedance and axial ratio bandwidths ( 2 0 percent) can beachieved by using a thicker substrate with four-probe feeds[l]. These four feeds are needed to suppress the undesiredmodes formed in the thick substrate. For a large array, such amultiple-probe element feedystemwould require manycables, hybrids, power dividers and, consequently, would bemore expensive, heavier, and more prone to RF loss. In thecase of the microstrip radiator, although a printed transmissionline feed system (instead of cables) can be used, a significantamount of radiation leakage is anticipated from the multiple-feed printed lines.A circularly polarized element can also be obtained by usinga single feedwith some perturbation introduced into theradiator. One example is a single-probe feed conical horn withpassive perturbation (tuning) probes orthogonally located inthe circular feed waveguide. Another example is a single feedsquare microstrip patch antenna with a tilted slot [ 2 ] intro-duced at the center of the patch as a perturbation. These

Manuscript received October 7, 1985; revised February 12, 1986. Thiswork was carried out by the Jet Propulsion Laboratory, California Institute ofTechnology, under a contract with the National Aeronautics and SpaceAdministration.The author is with the Jet Propulsion Laboratory, California Institute ofTechnology, Pasadena, CA 91109.IEEE Log Number 8609128.

perturbation techniques for generating circular polarization(CP), however, have veryimited axial ratio bandwidth,generally in the order of one-half percent.This paper presents the theoretical and experimental resultsto demonstrate that an array, which generates circular polar-ization with wide axial ratio bandwidth ( > 10percent), can beconstructed by single feed linearly polarized elements [3]. Thecircular .polarization is achieved by having a basic 2 x 2subarray with unique element angular and phase arrange-ments.Ashown in Fig. 1, both the element angularorientation and feed phaseare arranged in the 0",90", O", 90"or OD , 90", 180", 270" fashion. With such a system, not onlyis the feed complexity reduced, but also the bandwidthperformance is improved. The reason for reduced feedcomplexity is because this technique only requires a singlefeed for each element while four feeds might be needed foreach element in a conventional array withwideaxial ratiobandwidth requirement. Due to the orthogonal orientation ofneighboring elements, the mutual coupling effect is found tobe significantly reduced from that of a conventional array.Finally, this uniquely arranged array can scan its main beam nthe principle planes from its broadside direction to relativelywide angles without serious degradation of its CP quality. Theconcept presented here is good for many different types ofantenna elements, such as microstrip patches, dipoles, open-ended waveguides, horns, etc. The discussion in this paper,however, places special emphasis on the microstrip radiator asa result of a specific project requirement. A brief discussion onthe dipole radiator is also presented.

n. TECHNICAL BACKGROUNDThe reason hat a circularly polarized array canbe con-structed by linearly polarized elements is primarily attributed

to a four-element subarray with unique angular and phasearrangements. This basic subarray has its elements arranged ina 2 X 2 square or rectangular grid configuration with elementangular orientation and feed phase arranged in either a 0 " ,90", O " , 90" or a 0 " , 90", 180", 270" fashion. An examplethatuses microstrip patches is illustrated in Fig. 1. Thepurpose of different angular orientations of the patches is togenerate two orthogonally polarized fields, while differentfeed phases are used to provide the required phase delays forCP generation. It is well known that circular polarization canbe achieved in the broadside direction of an array composed oftwo linearly polarized elements with angle and phase arrangedin a O " , 90" fashion as shown in Fig. 2(a). The CP in thisarrangement, however, becomes very poor at angles greater0018-926X/86/0900-1113$01.00 0 986 IEEE


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114 JEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. AP-34,NO. ,SEPTEMBER 1986

U* = 180I

/ = 00

YI4

* = 90 1 lq/0\ c I = 00

(b)Fig. 1. 2 x 2 microstrip arrays that generate CP with LP elements. (a) O " , go", On, 0" arrangement for narrow-band application,

(b) O" , go", 180", 270" arrangement for wide-band application.

L

AxZ (a) (b)

Fig. 2. (a) Two-element microstrip array with On,90" arrangement. (b) Its spatial phase delay A$ ' = k&x sin 0.

5' ff broadside direction in the x - z plane as llustrated3. This is caused by the spatial phase delay (A$' =d x sin 0, see Fig. 2 ( b ) ) formed between he wo ortho-y polarized elements. This spatial phase delay, which90" phase differential, contributes to theCP quality at angles off broadside. With he 2 x 2

shown in Fig. 1, this spatial phase delay no longerbecause, within he wo principal planes, theone row or column is opposite to that ofA calculated principal plane pattern of the 2 x 2Fig. 4, where drastic polarizationof Fig. 3 can be observed. Due toprincipal plane patterns (4 = 0"d 90") are identical to each other and, therefore, only one is

The phenomenonof the 2 X 2 subarray can also be5, the far-field patterns in THETA ( 8 )two principal planes, the x - z plane or the y - z plane, Fig. 3 . Calculated C P patterns of the two-element array shown in Fig. 2.be obtained by a direct summation of the fields from alltotal far field n the x - z plane beF,, the horizontal field vector frompatch 1 by H I ,

Element spacing is 0.87 wavelength.


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HUANG: IR C ULAR POLAREATIOW 1115

-

-10 -

-90 -6 0 -30 0 30 60 ITHETA ( 8 )

Fig. 4. Calculated principal plane (4 = 0" or 90") CP patterns of the 2 X 2array shown in Fig. 1. Element spacing is 0.87 wavelength.

the vertical field vector from patch 2 by V2, tc. The total farfield can then be written as follows:~ ~ z = H I e - J k o d s i n O e j O a v jkOdsinBej9Oo +H jkOdsinlJejO02 e 3e

+ V4e - j kod sin eej9O0- HI j O o + F/ -jkod sin 0l e

+ ( ~ , ~ j 0 " j900)ejkod sin 02 eSince this is a uniformly excited array, HI = H3and V2 = V4,therefore:

F =(HeJO"+ / e ; 9 0 0 ) ( e - j k o d s i n B + e j k ~ d s i n 0xz 1= ( H e j k o o o +e j k O 9 O " ) 2 cos (kodsin e) . (1)

The two terms in the first bracket together represent a purecircularly polarized wave, and the cosine term isa two-element array factor. This total field F, is thus equivalent tothat generated from two circularly polarized elements. Withinthe x - z plane of the array shown in Fig. 5 , the radiated farfield is essentially equivalent to that generated from twocircularly polarized elements formed by collapsing the top-row two elements with the bottom-row two elements.For a microstrip array with a relatively thick substrate, thereis a distinct advantage if the array has ts 2 X 2 subarraysarranged in the 0", 90", 180", 270" fashion for both tselement orientations and feed phases as shown in Fig. l(b). Inthis fashion, the axial ratio bandwidth of the array can beincreased substantially. This is because most of the radiationimpurity (due to higher order modes of the thick substrate)from the 0" element cancels that from the 180" element, andlikewise for the 90" and 270" elements. This phenomenon isillustrated in Fig. 6. The solid arrows are edge field due tofundamental TMlomode which generates the co-pol radiation.The dashed arrows are edge field due to TMo2mode which isshown here only as an example and is one of the many modesthat contribute to cross-pol. Fig. 6(a) shows that, in the 0",go" , 0", 90" arrangement, both co-pol and cross-pol fieldsfrom the two diagonal elements reinforce each other, while

IL = 90"r!t- X

(b)Fig. 5 . Geometrical layout of the 2 x 2 array for the demonstration of thederivation of (1).

Fig. 6(b) demonstrates that, in the 0", 90", 180", 270"arrangement, only the co-pols are reinforced but the cross-polscancel. It is this cancellation of the cross-pols that permits thewide axial ratio frequency band operation.It is found that he above theory for the principal plane fields

of the 2 x 2 subarray does not hold true in the diagonal plane 4= 45" cut). The calculations have revealed a very high crosspolarized field, as shown in Fig. 7, at theta ( e ) angles not veryfar from the broadside direction. This phenomenon can be bestexplained by referring to Fig. 8. In this figure, the diagonalplane far field can be thought of as the field generated from athree-element linear array, the center element being composedof two horizontally polarized subelements with 90" phasedelay: and each of the two end elements being composed of asingle vertically polarized element with 0" phase delay. Thisthree-element array has a nonuniform amplitude distributionwith the center element (horizontal polarized) amplitude equalto two, and each of the end element (vertically polarized)amplitudes equal to one. This causes polarization and phaseimbalance at angles off the broadside direction in the diagonalplane. The phase imbalance is contributed by the spatial phasedelay, similar to that described in Fig. 2 . This high cross-pollevel in the diagonal plane, however, can be suppressed in alarger array due to its narrower beam and due to an averagingeffect so that the imbalances are averaged out. In other words,in a large array, as shown in Fig. 9 or 10, the diagonal plane'spolarization imbalance is much less than that of Fig. 8 . The


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1116 IEEE TRANSAC TIONSON ANTENNAS AND ROPAGATION, VOL. A P - 3 4 , NO . 9, SEPTEMBER 1986

--*- I;.9 0 0 --311.f=,l:- -- n9900-- -- --+ = 00 + = 00 t(a ) (b)

Fig. 6 . (a ) O", go", 0", 0" arrangement showing cros s-pols reinforce each other . (b)0", o", 180", 270" arrangement showingcross-pols cancel each other. Solid arrows represent co -pol s, dashed arrows represent cro ss-p ols.

'..v

II;IIIII -I c o - P O Lt- - -CROSS-POL-1 1 1~ 30 60 5

Fig. 7. CalculatedCPpatterns in thediagonalplane of the 2 X 2 arrayshown in Fig. 1. Element spacing is 0. 87 wav elength.

reader can see this by performing the same exercise as shownin Fig. 8 for Figs. 9 and 10. To demonstrate this, a 4 X 4array as shown in Fig. 9 , and a 2 X 8 array as shown in Fig.10, haveeen constructed and tested. Both arrays arecomposed of the unique 2 X 2 subarray with linearly polarizedmicrostrip elements. The alculated and measured data of botharrays (to be presented in the next section) have shown verygood CP quality in the diagonal plane, as well as in all otherplanes.It is important to realize that any array with N horizontaland N vertical elements can generateCP at a particular angleby proper adjusting each element's phase. However, withoutproper element location and orientation as presented in thispaper, the calculation has shown that the array will have high

\AMP = 1'\PHASE = @

Fig. 8. 45" diagonalplane confguration.cross-pol radiation (such as 3 dl3 below co-pol peak) in thedirection away from the co-pol peak as shown in Fig. 3 . Thishigh cross-pol is only a result of improper arrangement ofelements and has nothing to do with each element's phase.One important advantage found to be associated with thetype of array discussed here s that the mutual coupling of thearray isignificantly less thanhat f a conventionallyarranged array. This is due to the fact that all the adjacentelements of this uniquely arranged array are orthogonallyoriented and hence causevery little coupling between immedi-ate neighboring elements.The monolithic array with microstrip elements is playing animportant role in the advance of phased array technology. It ismoreeasible to build a linearly, rather than circularly,polarized monolithic array with quarter-wave long microstripelements, as illustrated in Fig. ll(a). This is because, by using


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HUANG: CIRCULAR POLARIZATION 1117

r - F B r . l UFig. 9. 4 X 4 microstrip array composed of the basic 2 X 2 subarray s with LP elements.

Fig. 10. 2 X 8 microstrip array composed of the basic 2 x 2 subarrays with LP elements.

r . P. ELEMENTS7

Fig. 1 1 . Mon olithic array configurations. (a) LP application. @) CP application.

the quarter-wave elements, more area can then be realized [4]between elements for the allocation of a phase shifter, a feedline circuit, etc. For an array to radiate circularly polarizedradiation, this quarter-wave element, with a conventionalarray arrangement, can no longer be used since this elementcan only generate linear polarization. One can certainly resortto a very small circularly polarized element loaded with very

high dielectric constant material. However, such an elementgenerally has a greater amount of electrical loss and can onlybesed for narrow-band operation. With the uniquelyarranged 2 X 2 subarray discussed in this paper, it is possible,by still employing the quarter-wave elements as shown in Fig.1le),o construct a circularly polarized monolithic array withwider bandwidth capability.


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IEEERAh'SACTIONS ONNTENNAS AND PROPAGATION, VOL. A P - 3 4 , NO. 9, SEF'"BER 1986

III. THEORETICALND EXPERIMENTALE~ULTSTo verify the theoretical prediction, a 2 X 2 microstrip

been constructed for the800 to 900 MHz. The array, as

in Fig. 12, has an element spacing of0.87 wavelengthubstrate thickness of one inch and is fed with the O",180", 270" arrangement. The relativelywideelementaimed for a particular program requirement andno special significance here. Both calculated and

in Figs. 13 andwith the calculation based on the multimode cavity theoryIt can be seen in Fig. 13 thathe array isndeed

in the woprincipalplanes (Q = 0" or"). and the agreement between calculation and measurement14 shows that the diagonal cut (4 = 45 " )has a very high cross-pol level at angles immediatelyhe broadside direction as iscussednhe previousagreement between calculation and measurementgood within the angular region of - 0" It- 60". The poor agreement outside of that egion isfact that the calculation is performed on anwhile the measurement is carried out onain x 30 in finite ground plane. Fig. 15 shows twousingof 821 MHz and 876 MHz. It

dB is essentially unchanged within a 6.5 percent band-12 percent bandwidth from 800 to 900the worst axial ratio was measured to be 0.6 dl3 at thebeam peak. One interesting observation of the measuredthat the array patterns are very symmetrical while thesingle linearly polarized element, measured in thes shownFig. 16. The asymmetry of the single element is caused bymodes present in the relatively thick substratefeed andalso caused by mutual coupling effect.

mostly canceled in the array environment with the, 90", 180", 270" arrangement. The same 2 x 2 array has

0", go", 0", 0" arrangement where ittively poor axial ratio bandwidth of about1 percent.0 " , 90", 0 ", 90"ement should be used only with relatively wide-banduch as dipoles. It can be used with thin microstripis required.To demonstrate that the CP performance in the diagonalarray can be substantially improved over thatx 2 subarray, a 4 x 4 microstrip array composed ofof the 2 X 2 subarrays has been fabricated and tested.as illustrated in Fig. 9 and pictured in Fig. 17, has

0.55x 2 subarray has the O" , 90, 180",element angular and phase arrangements. This micros-for operation at 2.27 GHz, as a substrateinch and a relative dielectric constant of

for the substrate material. Both calculated and measured18 and 19. Fig. 18

Fig. 12. U H F 2 X 2 microstrip arraywith I-in hickhoneycombsubstrateand 0.87 wavelength element spacing. Each element is linearly polarizedwith single probe feed.

1u I I I I IMEASURED CALCULATEDc o - P O L 0 " 0 a co-POLx - P O L x x x x x - P O L

----

-90 -60" -30" 0" 30" 60" 90"THETA ( 8

Fig. 13. CP patterns in the principal plane of the 2 x 2 array shown in Fig.1L.

shows a principal plane cut, while Fig. 19 shows the diagonalplane cut. Both figures indicate very good agreement betweencalculated and measured results. The diagonal plane patterndoes show substantial improvement of the cross-pol level overthat of the 2 x 2 subarray illustrated in Fig. 14. In all the otherplanes (between the diagonal and the principal planes), bothmeasured and calculated data have shown that the CP qualityfalls between thatof the diagonal and the principal planes. It isimportant topoint out that he comparison between Fig. 14 andFig. 19 for the diagonal planes may be somewhat misleadingbecause the 2 X 2 array of Fig. 14 has element spacing of 0.87


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HUANG: CIRCULAR POLARIZATION 111910I I I I I I I

MEASURED CALCULATED- o - P O L Q Q Q O CO-POLx - P O L x x x x x - P o t--

THETA I eFig. 14. CP patterns in the diagonal plane of th e 2 X 2 array shown in Fig. 12 .

-72O -36'6' 72O

0

-10

dB

-20

-30

4 0 -720 -36O

wavelengthwhile he 4 x 4 array of Fig. 19 has elementspacing of 0.55 wavelength. However, additional calculationfor a 2 X 2 array with 0.55 wavelength element spacing hasalso showna high cross-pol radiation with a similar peak level.The only difference in this case is that the cross-pol peak ismoved further away from the broadside direction than the caseof 0.87 wavelength spacing. Therefore, one can conclude thatthe larger array will ndeed mprove cross-pol level n hediagonal plane regardless of its element spacing.To demonstrate that the concept presented in thispaper willwork for a variety of array configurations, in addition to theabove 4 X 4 array, a 2 X 8 microstrip array has also beenfabricated and tested. This array also allows an easy demon-stration oftsmainbeam can capability. Thearray,as

sketched in Fig. 10and pictured in Fig. 20, is composed of theexact same element and element spacing as that of the 4 x 4array. Both calculated and measured patterns of the none-scancase are illustrated in Figs. 21, 22, and 23 for pattern cut in theQ = O", 45' and 90" plane, respectively. All three figures notonly have demonstrated good agreement between calculationand measurement, but also show excellent C P quality withinthe main beam region especially in the broadside direction.Since the 4 x 4 and the 2 x 8 arrays are built on relativelythin substrates, both arrays show relatively narrow impedancebandwidths of approximately 3 percent. However, due to thecancellation of higher order modes, as discussed previously,much wider axial ratio bandwidths have been obtained. Themeasured 1 dB axial ratio bandwidth for either array is


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IEEE TRANSACTIONS ON ANTENNAS AN D PROPAGATION, VOL. AP-M, NO. 9, SEPTEMBER 1986

0

-10

d B -20

-30

-40

d B

-9 0 -60 -30 0 30 60 90 -90 -60 -30 0 30 60 90THETA ( 8 ) THETA ( 8

Fig. 16. Measured LP patterns of a single element in th e 2 x 2 array shown in Fig. 12 .

10 I I I I IMEASUREDALCULATED - o - P O L 0 0 0 0 c o - P O L

THETA [ 8 )4 x 4 microstrip rray with uniformly xcited LP elements.Frequency = 2.27 GHz, substrate thickness = 0.125 n, relative dielectric Fig. 18. Principal Plane c p Patterns of th e 4 x 4 rray shown n Fig. 17constant = 2.17, and element spacing = 0.55 wavelen,&.


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10 I I I I IMEA S URED CALCULATED- O - PO L 0 0 0 0 CO-POL

d B

THETA IeFig. 19. Diagonal plane C P patterns of the 4 x 4 rray shown in Fig. 17.

Fig. 0. 2 X 8 microstrip rray with uniformly excited LP lemen ts.Frequency = 2.27 GHz, substrate thickness = 0.125 in, relative dielectricconstant = 2.17, and element spacing = 0.55 wavelength.

10

0

-10d B

-20

I I I I I

MEAS URED- o - P O Lx -POL- -

-30

-40 -90 -60 -30

0$L8

CALCULATED0 0 0 0 c o - P O Lx x x x x - P O L

0 30 60 'THETA ( e )

Fig. 21. Principal plane (6 = O " , see Fig. 10) CP patterns of the 2 X 8array shown in'Fig. 20.

10

0

-10d B

-20

-30

-4c

I I I I I

MEASU R ED CALCULATEDCO-POL 0 0 0 0 c o - P O Lx -POL x x x x x - P O L-- -

)O -60 -30 0 30 60 J90THETA ( e )

Fig. 22 . Diagonal plane (4 = 45', see Fig. 10) CP patterns of the 2 x 8array shown in Fig. 20.


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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. AP-34, NO. 9: SEPTEMBER 198610

0

-10d B

-2 0

-30

-40

I I I I I

MEASURED CALCULATED- o - P O L 0 0 0 0 c o - P O Lx -POL x x x x x - P O L- -

THETA ( e )23 . Principal plane (4 = 90", ee Fig. 10) CP patterns of the 2 X 8

array shown in Fig. 20.7 percent. This further substantiates the theoryan array built on the basis of the technique presented herehave a relatively very wide axial atio bandwidth. The 2 xarray also has adjustable phase shifters so that its main beamscanned off the broadside direction in the x - z plane4 = 0" plane). To avoid the formation of grating lobes, the

shifting for beam scanning is performed at each elementand not at the subarray level. The scanned patterns arein Figs. 24-26 with scan angles 19 equal to 25', 40",SO", espectively. The reader can refer to Fig. 21 for thescan case. As can be seen, the CP quality does degrade as

le increases. However, the degradation is not seriousvery similar to that of a conventional array withbetween calcu-measurement are generally quite good in Figs. 24-

This disagreement is primarily attributed to the fact thatis carried out on a finite ground plane [6].

of the finite ground plane is 28-in by 22-in with thelength oriented in the scan plane. The measured resultsreduces as it scans off the broadside direction. For the' 40', and 50" beam scans, the peak gain reductions are 1dB, and 4.4 dB, respectively.Since it has been pointed out inhe previous sections that hepresented in this paper should work for different typesantenna radiators in addition to the microstrip patches, a

s performed on a 2 X 2 array of half-waveas depicted in Fig. 27, is arrangedthe 0" , 90 " , 0", 90" fashion with element spacing of 0.5O", 90 " , 0", 90" arrangement is

I I I I IMEASURED CALCULATED- o - P O L 0 0 0 0 c o - P O Lx -POL x x x x x - P O L- -

0 -60 -30 0 30 60THETA Ie )

Fig. 24. Principal plane (4 = O " , see Fig. 10) CPpatterns of the 2 x 8array shown in Fig. 20 with main beam scanned to 25 " off broadsidedirection.10

0

1mV

(L- -10W

aWz3 -2cPw(L

-3 (

-4(

I I I I IM E A S URE D CALCULATEDc o - P O L 0 0 0 0 c o - P O Lx -POL x x x x x - P O L-- -

I

I -90 -60 -30 0 30 60 90THETA ( e

Fig. 25 . Principal plane (6= 0", see Fig. 10) CPpatterns of th e 2 x 8array shown in Fig. 20 with main beam scanned to 40" off broadsidedirection.

is a relatively wider band element and no cross-pol needso becancelled by the 0", 90", 180", 270" arrangement as requiredfor the thick microstrip element. The patterns of the array arecalculated by using the moment method technique [7]with theprincipal plane pattern shown in Fig. 28(a) and the diagonalplane pattern shown in Fig. 28(b). Both patterns demonstraterather thanO" , 90, 180",270" is simply because thedipole similar CP characteristics as that shown in Figs. 13 and 14 for


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M E A 5 URED CALCULATEDc o - P O L 0 0 0 0 c o - P O Lx -POL x x x x x - P O L- -

THETA 1.8Fig. 26. Principal plane (4 = 0" , see Fig. 10) CP patterns of the 2 X 8array shown in Fig. 20 with main beam scanned to SO " off broadsidedirection. i o o t

O0

O0-I 9ooI

Fig. 27. 2 X 2 array of linearly polarized dipole elements with 0", 90",O",90" arrangement. Element spacing = 0.5 wavelength.

the 2 X 2 microstrip array. The sharp difference in the patternshapes is primarily a result of different element spacings. Thesimilarity in CP characteristics between the microstrip arrayand the dipole array indicates that linearly polarized dipoles canalso be used in a larger array to generate circularly polarizedradiation. By utilizing the momentmethod [8], the mutualcoupling between the immediate neighboring elements hasbeen calculated and found to be significantly less than that ofaconventional array composed of circularly polarized crossed-dipole elements.

IV.CONCLUSIONBoth theoretical and experimental results have indicated thatan array consisting of linearly polarized elements can indeed

0

-10dB

-30

THETA 1 e(b )Fig. 28. Calculated C P patterns of the 2 X 2 dipolearray . (a) Principalplane. (b) Diagonal plane.

generate circularly polarized radiation. The requirement is thatthe array be composed of the basic 2 X 2 subarray with uniqueelement angular and phase arrangement. Basedn thisconcept, a 2 X 2 UHF array, a 4 X 4 S-band array, and a 2 x8 S-band array have been constructed with linearly polarizedmicrostrip elements. Their measured results have shown- notonly hat the array can generate circular polarization withwider axial ratio bandwidth ndvery symmetrical beampattern but also that the mutual coupling effect can besignificantly reduced. In addition, the 2 X 8 array hasdemonstrated thattsmainbeam anbe cannedn theprincipal plane to relatively wide angles without seriousdegradation to its CP quality. Certainly, since linearlypolarized elements are being used, the feed complexity,weight, cost, and RF feed circuit loss can all be reduced,especially in a very large array. Although the discussion


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1124 IEEE TRANSACTIONS ON ANTE NNAS AND PROPAGATION, VOL. AP-34 , NO . 9, SEPTEMBER 1986presented in this paper has concentrated on the microstrip typeof radiator, with some discussion of the dipole radiator, it isbelieved that the concept can be applied toessentially any typeof antenna element.

ACKNOWLEDGMENTThe uthorwishes to express appreciation to the JetPropulsion Laboratory Directors Discretionary Fund which

made this research effort possible. The author also would liketo thank Dr. Ken Woo for his support and to Mr. WilliamFolwell and Mr. Alex Miyadi for their assistance in perform-ing the experiment.

REFERENCES[ l ] T. Chiba, Y. Suzuki, and N. Miyano, Suppression of higher modesand cross polarized component for microstrip antennas, in IEEEAntennas Propagat. SOC.Int. Symp. Dig,, May 1982, pp. 285-288.[2] J . Kerr, Micr ostrip polarization techniques, in Proc.AntennaAppl . Symp. , Urbana, IL , 1978.[3] J . Huang, C.P. microstrip array with wide axial ratio bandwidth andsingle feed L.P. elements, in IEEE Antennas Propagat. Soc. Int .Symp. Dig., June 1985, pp. 705-708.[4] R. Stockton and M. B alint, 15 GH z micro strip array development.Ball Aerospace Syst. Div. Final Rep. RA DC- TR-8 0403. Feb. 1981.[SI W . Richards, Y . Lo, an d D. Harrison, An improved theory for

microstrip antennas and applications,IEEE Tram. AntennasP ~ O P Q -gat . , vol. AP-29, pp. 38-46, Jan. 1981.[ 6 ] S . Rengarajan, Finite round plane effects on lanar rrays ofmicrostrip patch elements, in IEEE Antennas Propagar. SOC.Symp. Dig., June 1984 , pp. 741-744.[7] J. Richmond, Computeranalysis of threedimensional wire anten-nas, ElectroSci. Lab., Ohio State Univ., Rep. 27084, Dec. 1969.[SI --, Mutual impedance between coplanar-skew dipoles, IEEETrans. Antennas Propagat., pp. 414416 , May 1970.

J. Huang, “A Technique for an Array to Generate Circular Polarization with Linearly

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Transcript of J. Huang, “A Technique for an Array to Generate Circular Polarization with Linearly