Design Of X-Band Radar Antenna Array Based On Substrate Integrated Waveguide

X-band radar has strong azimuth discrimination ability,flexible installation,good maneuverability,and wide application.Substrate integrated waveguide（SIW）is a new type of transmission line with a planar structure,which has the advantages of small size,lightweight,low profile,easy processing.The traveling-wave waveguide slot antenna array has the advantages of wide impedance bandwidth and easy control of current distribution.The design of a traveling-wave slot antenna array based on the SIW can combine the advantages of the SIW and waveguide slot antenna,and it has become a popular direction of researches on slot antenna arrays.However,the gain of the existing SIW slot antenna array is low,and the method for achieving circular polarization is complicated.Therefore,this thesis focuses on how to improve the gain of the SIW slot antenna array and realize circular polarization,and the design of the SIW slot antenna array for X-band radar applications.The specific work completed includes the following aspects:（1）A SIW transverse-slot linearly-polarized radar antenna array loaded with rectangular patches is designed.The antenna array is divided into upper and lower layers.The gain of the antenna array is increased by loading twelve rectangular patches above the traveling-wave SIW transverse-slot structure of the lower layer.The upper layer is closely attached to the lower layer,so the antenna array has a low profile and compact structure.Based on the related theory of the waveguide transverse-slot array,the antenna array is designed and analyzed,and a prototype is fabricated and measured.The measurement results show that:near the center frequency of 9.41 GHz,the impedance bandwidth for|S₁₁|<-15 d B is 290 MHz（9.185-9.475GHz）,and the impedance matching is good.The measured gain of the antenna array is 17.67d Bi,and a flat gain near the center frequency is obtained.At the center frequency,the horizontal-plane half-power lobe width is 6.5°,the side-lobe level is-18.7 d B,and the cross-polarization discrimination rate is 57.7 d B.The designed antenna array not only improves the gain but also improves the cross-polarization discrimination rate.（2）A circularly-polarized radar antenna array based on SIW longitudinal slots and deformed rectangular patches is designed.Ten deformed rectangular patches loaded on the upper layer are rotated by 45°to realize circularly-polarized radiation,and the traveling-wave SIW longitudinal slots are used as the feeding of the patches.In addition,there is an air gap between the upper and lower substrates to broaden the bandwidth.The measured results show that the frequency range for|S₁₁|<-10 d B is 9.0～12.8GHz.The bandwidth for axial ratio（AR）less than 3 d B is 460 MHz（9.19-9.65 GHz）,which has a wide circular polarization bandwidth.The measured gain of the antenna array is 14.49 d Bic,and the gain is relatively flat in the range from 9.2 to 9.6 GHz.At the center frequency of 9.41 GHz,the horizontal-plane half-power lobe width is 10.8°,and the side-lobe level is-24.41 d B.The designed antenna array not only achieves good circular polarization characteristics but also achieves a lower side-lobe level.（3）A circularly-polarized radar antenna array based on modified SIW structure and dual-ring patch unit is designed.The dual-ring circularly-polarized patch unit is used as the radiating part of the antenna array,and ten longitudinal slots are etched on the modified SIW structure as the feeding part of the antenna array.By offsetting the via holes of the SIW,all the longitudinal slots are located on the same straight line,and the double-ring patch units are also on a straight line to improve the radiation characteristics of the antenna array.The measured results show that the impedance bandwidth for|S₁₁|<-15 d B is 540 MHz（9.26-9.80 GHz）.The bandwidth for AR less than 3 d B is 204 MHz（9.318-9.522 GHz）.At the center frequency of 9.41 GHz,the horizontal-plane half-power lobe width is 10.6°,the side-lobe level is-19.61 d B,and the gain is 15.34 d Bic.The designed antenna array not only achieves good circular polarization characteristics but also further improves the gain.