| Synthetic Aperture Radar(SAR)is a high-resolution active imaging radar.Besides high resolution,SAR also has other advantages including long detecting range and strong penetrating power not affected by light and the weather situations.To a great extent,the performance of SAR is determined by the performance of the antenna.Key parameters such as resolution,sensitivity,signal-noise ratio and detection range of SAR are directly related to the bandwidth,pattern and gain of the antenna.To improve the performance of the radar system,improving the performance of the antenna system is an important work.Microstrip array antenna is an important realization form of SAR antenna.Enhancement of the bandwidth and optimization of the pattern are important research directions of SAR antenna research.Impedance bandwidth has always been the bottleneck of the microstrip antenna.Lamination and patch transformation can expand antenna bandwidth,but pattern performance turn to be worse with zero lobe and minor lobe.Many scholars and researchers tried to improve this phenomenon,but the effect was unsatisfactory.Meanwhile,the antenna performance is often destroyed to miniaturization antenna size.Therefore it is a technology problem to be solved that how to satisfy demands of the bandwidth,pattern and miniaturization.Combining with lamination and aperture technology,the U-slot stacked microstrip antenna is designed,which has three resonance frequencies and impedance bandwidth up to 24.5%.Based on U-slot stacked microstrip antenna,half U-slot stacked microstrip antennas is designed to miniaturization,which the 2D size is reduced by 29.1%and impedance bandwidth is 19.5%.The designed antenna pattern is not ideal,because broadband and miniaturization technique cause some problems including big side lobe and back lobe of the pattern,asymmetry of the E-plane and the H-plane and zero offset of maximum gain.In order to solve this problem,an asymmetric slot image compensation method is proposed to optimize the pattern of laminate aperture antenna.The inverted C-slot and inverted half U-slot stacked microstrip antenna are designed using above optimization method.The experiment results indicate that,the zero offset is improved;the gain is increased;the back lobe is reduced;the front-to-back ratio is also increased.Combined with the EBG reflector technique,the front-to-back ratio of inverted half U-slot stacked microstrip antenna is increased by 4.15 dB compared to the antenna without reflector,1.07 dB compared to antenna with common reflector.Max side lobe level of E-plane is-10.05 dB,which is 7.75 dB lower than that of antenna without reflector,3.58 dB lower than that of antenna with common reflector.No obvious side lobe can be found in H-plane.These results show that the directivity pattern of the antenna is remarkably improved.The microstrip array antennas with high gain,strong directivity and low or lower side lobe are need for radar imaging,BS communication,satellite communication and other fields.The technology of manufacture wideband lamination microstrip array antennas is complex.The array forms of array antenna are flexible and diverse based on different scenes.The comprehensive method of traditional array antenna is restricted by algorithm and cannot to be suitable for all array forms.The culture algorithm of array comprehensive method is brought in this paper,which has advantages of global multivariable optimization and fast rate of convergence,and suitable for solving the problem of lower side lobe pattern.By verifying multi-aspect,the culture algorithm is effective,universal and superior to solve super lower side lobe patter problem.Based on above research,an 8-element array of SAR antenna is designed which achieves excellent performance including the gain of 16.12 dB,the main lobe width of 14 Deg,and the side sobe suppression ratio of 20.12 dB. |
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