Characteristic-Mode-Analysis-Aided Design of Filtering Patch Antennas

A characteristic-mode-analysis (CMA)-aided design method for filtering patch antennas is proposed in this article. The method mainly includes three parts: first, use the theory of characteristic mode (TCM) to analyze the filtering antenna without feed structure (i.e., the radiator) to find the resonant modes in the passband and predict the positions of the inherent radiation nulls, which are then utilized to obtain the suitable size of the radiator and filtering elements; second, use modal analysis to find the best feed position to excite the resonant modes and simultaneously generate the inherent radiation nulls; and third, optimize the filtering antenna to obtain the optimal overall performance. For demonstration, two different types of filtering patch antennas are investigated using the proposed method. It has been shown that the method can truly realize the independent analysis and design of the radiator structure and the feed with the help of characteristic modal analysis, making the design process of both filtering antennas clearer and more efficient. In addition, the proposed method can find out and fully utilize the inherent radiation nulls, including the modal nulls and the nonmodal nulls of the radiator itself.