Design and Implementation of Aperture Coupled Microstrip IFF Antenna

Transcription

1 PIERS ONLINE, VOL. 4, NO. 1, Design and Implementation of Aperture Coupled Microstrip IFF Antenna M. N. Jazi 1, Z. H. Firouze 2, H. Mirmoammad-Sadegi, and G. Askari 1 Institut National de la Recerce Scientifique, Université de Québec, Canada 2 Department of Electrical Engineering, Amirkabir University of Tecnology, Iran Information and Communication Tecnology Institute, Isfaan University of Tecnology, Iran Abstract Design and implementation procedure of a wideband aperture coupled microstrip antenna in L-band frequency is introduced. To improve radiation performance of te microstrip antenna four structures are proposed. Te structure wit air substrate as te maximum frequency bandwidt. Experimental results of frequency bandwidt and radiation patterns of te optimum structure agree wit te simulation results. Te antenna as te gain of 8.5 db, te frequency bandwidt of greater tan 25%, and F/B better tan 15 db. Tis aperture coupled microstrip antenna can be used as an element of microstrip array antennas in IFF systems. 1. INTRODUCTION Microstrip antennas (MA) are simple planar structures tat ave advantages suc as low profile, conformal availability, simple fabrication using printed circuit tecnology, low cost and compatibility wit integrated circuits. In spite of limitations suc as small bandwidt, low gain and low power andling capability [1], MA offers over tan oter type of antennas due to teir advantages and increasingly used in a variety applications suc as military, industry and wireless communication [2]. Different tecniques ave been used to increase bandwidt suc as using tick substrate []. Tis tecnique improves bandwidt less tan 5 percent. Aperture coupled stacked patc microstrip antenna can improve bandwidt more tan 50 percent at te expense of increasing in back lobe radiation level. To reduce back radiation, metallic rods or resonance planes are used in te back of te antenna or appropriate cavities are put next to te coupling aperture [5 8]. Aperture coupled microstrip antenna as been used for IFF (or Secondary Surveillance Radar) systems wit 6 percent bandwidt for VSWR < 1.5. However, Front to Back (F/B) ratio as been reported 10 db wic is not enoug for IFF application [9]. In tis paper, bot tecniques ave been used to increase te bandwidt and decrease te back radiation. Te design process of te proposed structure is organized as followed. First of all, an aperture coupled microstrip antenna will be designed according to te requirements. Ten, four structures will be introduced and compared to eac oter. After simulation, te best structure will be selected and optimized to fabricate. Finally, te measurements and conclusion will be reported. 2. DESIGN AND SIMULATION Te structure of te aperture coupled microstrip antenna as been depicted in Figure 1. Tis antenna as been designed to use as an element in te microstrip array antenna for IFF (or SSR) systems. Te central frequency is 1060 MHz and te bandwidt is at least 250 MHz. Te tickness of patc substrate, is cosen 20 mm due to te desired bandwidt. Te feed substrate is RT/Duroid 5880 wit tickness of 2 = mm and relative dielectric constant of 2.2. FR4 is used as cover wit tickness of 4 = 1 mm and ε r4 = 4.. According to [1], te preliminary antenna dimensions are designed and calculated at te central frequency of 1060 MHz. [4] recommends tat aperture widt W s is te alf of its lengt L sl and T s is te one-tent of L sl. Te lengt of te stub, L st is 0.22λ g, in wic λ g is te wavelengt in te feed substrate. Te antenna parameters suc as patc dimensions, aperture lengt, te lengt of stub, and te distance between feed line and back plane are optimized by use of full wave simulator IED until frequency bandwidt greater tan 25% and F/B greater tan 20 db will be obtained at te central frequency of 1060 MHz. Four different structures as sown in Figure 2 are designed, simulated and compared to recognize te structure wit best performance. Aperture as been designed to resonate near te resonance frequency of te patc. Aperture sape is very important to control te maximum coupling between te feed line and te patc and

2 PIERS ONLINE, VOL. 4, NO. 1, also te minimum back radiation. A metallic plane is placed beind of te antenna to reduce back radiation power to 20 db. Actually, tis plane functions as a resonator and generates appropriate current distribution to eliminate undesired radiation fields in te rear of te antenna. Te distance between te back plane and te feed line influences on te amplitude of te current distribution but te pase of te current distribution is controlled by te size of te back plane. Te four structures ave been simulated and optimized by IED software. Te grap of teir return losses as been depicted in Figure. According to Figure 2, structure (a) as te maximum bandwidt. Te simulation results indicate tat te smallest bandwidt will be acieved wen Teflon dielectric is directly beneat te patc. In addition, te frequency center of structure (d) is lower tan oter structures. Te simulation results ave been indicated in Table 1 in wic f u and f l are te low and ig frequency corresponding to 10 db return loss. Cover 4, ε r4 Slot L p L sl W p T s W s, ε r Air (a) Air substrate (b) substrate Feed Line L st 2, ε r2 1, ε r1 (c) -Teflon substrate Back Plane (d) Teflon- substrate Figure 1: structure. Aperture coupled microstrip antenna Figure 2: Four different structures of aperture coupled microstrip antenna. Structure Central Frequency (MHz) (f u + f l ) /2 Bandwidt (MHz) f u f l (a) (b) (c) (d) Table 1: Simulation results of four different structures as sown in Figure 2. Figure : Return losses of four structures simulated by IED. E- and H-plane radiation patterns at 100 MHz and 1090 MHz ave been represented for structure (a) in Figures 4 and 5, respectively. Te Front to Back ratio is greater tan 20 db. E- and H-plane Half Power Beam Widt (HPBW) at 100 MHz are 65 and 75, respectively. At 1090 MHz, E-plane HPBW is 6 and H-plane HPBW is 74. Figure 6 sows simulated results for gain of four structures. Te gain difference between 100 MHz and 1090 MHz is less tan 0.5 db for four structures. For example, te gain of structure (a) at 100 MHz is 8.5 db but at 1090 MHz is 8.8 db.

3 PIERS ONLINE, VOL. 4, NO. 1, 2008 After consideration and comparison of te simulation results of four structures sow tat structure (a) i.e., te antenna wit air substrate as te performance to realize te desired antenna. Consequently, tis structure is selected to be fabricated and measured its radiation parameters. Figure 4: E- and H-plane radiation patterns at 100 MHz simulated by IED. Figure 5: E- and H-plane radiation patterns at 1090 MHz simulated by IED. Figure 6: Comparison te gain of four different structures simulated by IED. Figure 7: Te poto of te fabricated aperture coupled microstrip antenna wit air substrate. Figure 8: Simulation and measurement results of return loss of te antenna.

4 PIERS ONLINE, VOL. 4, NO. 1, Figure 9: Measurement of co- and cross-polarization radiation patterns at 100 MHz. Figure 10: Measurement of co- and crosspolarization radiation patterns at 1090 MHz.. MEASUREMENT Figure 7 sows poto of te fabricated aperture coupled microstrip antenna. Return loss of te antenna as been measured and compared wit simulation result in Figure 8. A little frequency difference between two curves is observed because of simulation accuracy, simulation settings, measurement accuracy and fabrication tolerance. Te return loss of te antenna is less tan 10 db in te frequency range of 875 MHz 1150 MHz, i.e., te frequency bandwidt is greater tan 25%. Figures 9 and 10 sow respectively co- and cross-polarization radiation patterns at 100 MHz and 1090 MHz. F/B of E- and H-plane radiation patterns are greater tan 15 db and 1 db at 100 MHz, respectively. Figure 10 indicates F/B of E-plane radiation pattern is greater tan 20 db but tat of H-plane radiation pattern is greater tan 15 db. Tis difference is due to low accurate measurement of anecoic camber for tis frequency bandwidt. Te gain difference of bot planes is less tan 0.5 db. Tis antenna as better performance suc as bandwidt and F/B tan te antenna reported in [9]. 4. CONCLUSIONS In tis paper, four different structures of aperture coupled microstrip antenna ave been considered to acieve te maximum bandwidt wit good radiation performance in tis bandwidt. Te air substrate antenna was selected and optimized by IED simulator. Te simulation and measurement results ave te good agreement wit eac oter. Te antenna as te gain of 8.5 db, te bandwidt of greater tan 25%, and F/B better tan 15 db. Tis aperture coupled microstrip antenna can be used as an element of microstrip array antennas in IFF (or SSR) systems. ACKNOWLEDGMENT Te autors would like to tank te staff of Information and Communication Tecnology Institute (ICTI), Isfaan University of Tecnology (IUT), Isfaan, Iran for teir co-operator and supporting tis work. REFERENCES 1. Garg, R., P. Bartia, I. Bal, and A. Ittipioon, Microstrip Antenna Design Handbook, Artec House, Pozar, D. M. and D. H. Scaubert, Microstrip Antenna, te Analysis, and Design of Microstrip Antenna and Arrays, IEEE Press, New York, Pozar, D. M., Review of Aperture Coupled Microstrip Antenna: History, Operation, Development, and Application, Microwave Online System Company world wide web site, July Targonski, H. S., R. B. Waterous, and D. M. Pozer, Design of wideband aperture stacked patc microstrip antennas, IEEE Trans. on Antennas and Propagation, Vol. 46, No. 9, , Sept Targonski, S. D., R. B. Waterouse, and D. M. Pozar, Reflector elements for aperture coupled microstrip antennas, Antennas Propag. Symp. Dig., 1997.

5 PIERS ONLINE, VOL. 4, NO. 1, Blefko, M. J. and W. N. Klimczak, A secondary surveillance radar (SSR) antenna wit integrated difference and sidelobe suppression (SLS) cannel, APS International Symposium, USA, July Sin, H. S. and N. Kim, Wideband and ig gain-one patc microstrip antenna coupled wit H-saped aperture, Electronic Letters, Vol. 8, No. 19, Sept Amed, Z., M. B. Isan, N. Caudry, and J. Kiani, Design of a low sidelobe aperture coupled microstrip antenna array, IEEE, Kreczkowski, A., T. Rutkowski, A. Buda, and S. Kostka, Te microstrip IFF antenna for te airborne radar, International Conference on Microwaves, Radar and Wireless Communications, MIKON, 2002.