Design methodology of a class of triple-mode bandpass filters using a patch-loaded cross resonator

A class of microstrip triple-mode bandpass filters (BPFs) using a patch-loaded cross resonator are modeled, designed and tested in this paper. First, a symmetrical equivalent LC network is developed for a symmetrical patch structure. The values of all the inductors and the capacitors are extracted by applying the even-odd mode analysis. Then, three 1-port networks are developed to analyze the resonant conditions of the corresponding modes. Finally, these first three resonant modes are used to form a passband with three transmission poles. To verify the proposed design methodology, two sets of filter prototypes with different loaded patches are designed, fabricated and measured in the end. The predicted results are well confirmed with the experimental ones.