Compact Quad-Mode BPF Based on Half-Mode Short-Circuited Semicircular Patch Resonator

Abstract

Wideband bandpass filter (BPF) design using a half-mode patch resonator with multiple resonant modes is proposed in this paper. The resonator is formed from a short-circuited circular patch loaded with radial slots. The metallized vias are positioned in a circle. Its radius is used to tune the resonant frequencies of the resonator. According to the surface current distributions of the eigenmodes, different numbers of the radial slots can be distributed on the patch to prolong the current paths of the relevant eigenmodes, the resonant frequencies of which can be shifted down to that of the dominant mode, the TM010 mode. As a result, a semicircular patch resonator loaded with three slots is used to design a compact quad-mode wideband BPF, which employs TM010, TM110, TM210, and TM310 modes. Furthermore, the coupling between input and output feeding lines is introduced to realize two transmission zeros at both sides of the passband. Therefore, the selectivity is improved. The experiment has verified the theoretical analysis and the design approach.