Reasearch On Antenna Design And Optimization Methods Based On Characteristic Mode Theory

Antenna design usually relies on full-wave simulation softwares,so antennas need to be designed by instincts and experiences of the designers.Characteristic mode theory can separate the radiating structure and the feeding structure and provide physical insights for designing,therefore it has received extensive attention from antenna designers.This paper mainly deals with antenna design and optimization methods based on characteristic mode theory,and modern antennas at microwave frequency bands with specific characteristics are designed.The main contents and innovations are as follows:The paper introduces characteristic mode theory and traditional method of characteristic mode analysis and miniaturizes a square patch antenna operating at Ku-band into a triangular antenna.The antenna size is reduced by 50%with an impedance bandwidth of 2.6%.The gain only droped by 0.9dBi and the gain is 6.74dBi.The paper proposes a technique of widebeam pattern combination based on characteristic mode analysis.Based on the proposed technique,a widebeam antenna operating at 10 GHz has been designed.According to the modal weighting coefficients of the fundamental mode and the higherorder mode,a 3-way unequal power divider is designed to excite the fundamental mode and the higher-order mode of the metasurface structure with specific amplitude ratio and phase difference.The unidirectional characteristic of the fundamental mode and the omnidirectional characteristic of the higher-order mode are combined and realized a 3dB half-power beamwidth of over 200 degrees.Based on network characteristic modes,the paper proposes a pattern optimization method of pixel antennas and the technique of frequency and pattern reconfigurability.By introducing the characteristics of modal patterns into the objective functions,the optimization method based on radiation pattern is achieved.The resulting 6×9 pixel antenna operates at 25 GHz,with a peak gain of 5.16dBi and a low cross-polarization level of-34.4dB.The optimization goal of a mainbeam at-45° and 30° are achieved.Therefore the proposed algorithm can realize pattern reconfiguability.