M.S.E.E. degree from Yon-Sei University,. Korea, in 1965, and the Ph.D. degree from the. University of California, Los Angeles, in 1979. He was employed at ...
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structures,” Proc. IEEE (Letters), vol. 57, pp.2170-2171,Dec. 1969. [7]H. C. Bakerand A . H.LaGrone,“Digitalcomputationofthe IEEE Trans. Anrennas mutualimpedancebetweenthindipoles,” Propagar., vol.AP-IO,pp.172-178,Mar.1962. [8] S . W. Leeand S . Safavi-Naini, “Approximate asymptotic solution of surfacefieldduetoamagneticdipole on acylinder.” ZEEE Trans. Antennas Propagat., vol. AP-26. pp. 593-598, July 1978.
IC. Park wasbornin Seoul,Korea,on August 3, 1941. He received the B.S.E.E. degree from In-Ha University, Korea, in 1962, the M.S.E.E. degree from Yon-Sei University, Korea,in1965, andthePh.D.degreefromthe University of California, Los Angeles, in 1979. Hewasemployedat TRW during1973-1976 and at Ford Aeonutronics during 1976-1979. He recently joined the Hughes Missile Systems DivisioninCanogaPark,CA.Hiscurrentinterest is in phased slot arrays. Pyong
1, JANUARY 1981
Robert S. Elliott (S’46-A’52SM’54-F’61) re-
ceived the A.B. degree in English literature and theB.S.degreeinelectricalengineeringfrom ColumbiaUniversity, NewYork, NY, in1942 and 1943,respectively,the M.S. andPh.D. degrees in electricalengineeringfromtheUniversity of Illinois, Urbana, in 1947 and 1952, and theM.A.degreeineconomicsfromtheUniversity of California, Santa Barbara, in 1971. He has been Professor of Electrical Sciences at the University of California, L o s Angeles, since 1957. Hispriorexperienceincludesperiods at theAppliedPhysics LaboratoryofJohnHopkinsUniversityand at theHughesResearch Laboratories, where he headed the antenna research activities. He has also been on the faculty of the University of Illinois and was a founder of RantecCorporation,serving as its firstVicePresidentandTechnical Director. He has recently completed a two-year stint as a Distinguished Lecturer for the IEEE and is Chairman of the Coordinating Committee for the 1981 AP/URSI Symposium to be held in Los Angeles. He currently serves as a consultant to Hughes, Canoga Park, CA. Dr. Elliott is a member of Sigma Xi, Tau Beta Pi, and the New York Academy of Sciences.
Communications Broadband Microstrip Antenna Element and Array ANDERS G. DERNERYD, MEMBER, IEEE AND INGMAR KARLSSON Absiroct-Foam-supported highly efficient microstrip antennas are described. Theoretical and experimentalresults show that bandwidths up to 15 percent can he obtained at the expense of an increase in the antennaheight(toabout 0.1 wavelength).Theperformance of an array of broadbandelementsfed by amicrostripcorporate feed network is also described.
ELEMENT DESIGN The microstrip element chosen in this study was the rectangularmicrostripelement.Thecavitymodelwithanopencircuitededgeconditionwasusedinthetheoretical design [4].Fig. 1 shows the theoretical bandwidth of the rectangular microstrip patch with air as a dielectric and with the width-tolengthratioastheparameter.Thelengthofthepatchwas always assumed to be a half wavelength. The bandwidth is very nearly proportional to the thickness of the element. The slight upturn at very small substrate thicknesses is due to the increased copper losses in the patch and ground plane. To achieve a t least a 15 percent bandwidth with a square element, the thickness should be greater than 0.10 Anarrowermicrostripelementsimplifiesmatchingbutrequiresaslightlylargerspacingbetweenthepatchandthe ground plane for the same bandwidth.
x.
INTRODUCTION Microstrip antenna elements are inexpensive radiators suitable to conformal arraying. Their bandwidth is usually restrict e d t o 2-4 percent. Other microstrip antennas such as radiating meander lines [ 11 , curved lines [ 11, and series-fed microstrip is low, arrays [2] canbeverybroadband.Theirefficiency however, due t o loss in the terminating load. Theoreticallyithasbeenshownthatthefractionalbandof the width is approximately proportional to the thickness microstrip element [3]. It was also shown that the conductor and dielectric losses are usually very small, only some tenth of a decibel. This method t o increase the bandwidth was selected in a study of printed-circuit antennas. The goal was t o find a broadband microstrip radiating element that could be used in flat-plate antennas and electronically scanned arrays. Manuscript received February 29, 1980;revised July 20, 1980. The authors are with Telefon AB L M Ericsson, MI Division, 431 26 Moelndal, Sweden.
EXPERIMENTAL ELEMENT The microstrip patch was etched on a very thin glass fiberreinforced plastic (GFRP) substrate and supported by a lowdensity foam above a ground plate. Foam was chosen to give a rigid supporttotheelementand alsobecausethedielectric constant is very close t o t h a t of air. 3 GHz. For 15percentbandThe designfrequencywas widthaIO-mmspacingbetweenthemicrostripelementand thegroundplane is required.Aslightlylargerspacing was chosen in order to make possible a narrowing of the element and still reach the 15 percentgoal. The microstrip patch was narrowed until a good match to the 50 L?input line connected at the edge of the element was achieved. A single 43-mm long and 8-mm wide element spaced
0018-926X/81/0100-0140$00.75 0 1981 IEEE
TRANSACTIONS IEEE
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_.Ep 1 ._ d = Id vs*n d
IS/*)
2
10 ..
0. . 0. 00
0. 05
1s
0. 8. 10
h/X,
Fig. 1. Fractionalbandwidthof k / 2 rectangular microstripantenna. L is length, W is width of radiating element.
Fig. 2.
(b) Broadband microstrip array. (a) Front view. (b) Back view.
14mmfromthegroundplanehadavoltagestanding-wave ratio (VSWR) better than 2: 1 over a 15 percent band. The gain a t resonance was better than 7 dB indicating negligible losses as estimated by comparison with the directivity [4]. EXPERIMENTAL ARRAY A four-element linear array shown in Fig. 2(a) was designed using the broadband microstrip element spaced 0.75 along t h e H-plane. The elements were probe-fed by a separate microstrip network placed on the rear side of the ground plane, Fig. 2(b). A feed network in the same plane as the microstrip radiators was n o t feasible because of unacceptably wide lines, (e.g., 68 mm-width, if 50 Alsononconnectingcouplingtechniquesmightbeused,butthiswasnotpossibleduetothe large spacing. Recorded co- and cross-polarized radiation patterns in the H-plane are shown in Fig. 3. The sidelobe level is 14 dB and the cross-polarized field is 1 9 dB below the main beam peak. The increased cross-polarized level that can be seen at higher frequencies and large angles is probably due to radiation from the feed probe. The measured gain was 12.5 dB at the center frequency and the VSWRwas better than 2: 1 over a 13 percent band. The estimated loss in the feed networkis 0.9 dB.
(b)
Fig. 3. Recorded H-plane pattern of four-element linear microstrip array. (a) 2.8 GHz. (b) 3.2 GHz.
x
a).
CONCLUSION It has been demonstrated that microstrip antenna elements can be designed with a 15 percent bandwidth by increasing the
thickness of the antenna element. This was accomplished while maintaining the losses at a very low level. Also the cost and the weight were kept to a minimum since the microstrip element was supported by an inexpensive low-density filler. Excellent performance was demonstrated for a small broadband microstrip array. REFERENCES J . R . James et al.. “Microstrip antenna research at the Royal Militav College of Science.” i n Proc. PrintedCircuitAntenna Tech. Workshop. New Mexico State U n i v . . Las Cruces. Oct. 1979. pp. 1.1-1.10. [2] T. Metzler. “Microstrip series array.” in Proc.PrintedCircuit AntennaTech.Workshop. New Mexico State Univ.. Las Cruces. Oct. 1979. pp. 20.1-20.16. [3] A. G. Derneryd and A . G . Lind. “Cavity model of the rectangular microstrip antenna.” in Proc.PrintedCircuitAntennaTech. Workshop. NewMexico State Univ., Las Cruces, Oct. 1979. pp. [I]
12.1-12.11. [ 4 ] A . G. Derneryd and A. G . Lind. “Extended analysis of rectangular microstrip resonator antennas,” IEEE Trans. Antennas Propagat.. VOI.AP-27. pp. 846-849. NOV.1979.
