Design of wideband bandpass filter using short-circuited circular patch resonator loaded with slots

This paper presents a wideband bandpass filter design based on a short-circuited circular patch resonator with inductively loaded slots. The cavity model method is used to analyze the excited resonances of the resonator. According to the illustration of the cavity model, the TM010 mode is excited as the fundamental mode, the resonant frequency of which is much lower than that of the TM110 mode and can be further lowered by the loaded arc-oriented slots. Therefore, the proposed resonator can be used to design a filter with compact size. In addition, one of the two orthogonal degenerate TM110 modes can be independently tuned by the slot along the symmetric plane without affecting the TM010 mode. Since the resonant frequency of each mode can be tuned independently by the parameters of the slots, and the coupling between resonant modes of the resonator and source/load can be adjusted by the feeding angle and the capacitive loaded stubs on the feeding lines, the center frequencies and bandwidths of the designed bandpass filters can be tuned easily. The analysis is theoretically and experimentally verified by two examples with good agreement between the simulated and measured results.