A triple‐mode bandpass filter using a modified circular patch resonator

This article presents a triple‐mode bandpass filter using a modified circular patch resonator. Etched slots in the resonator split the TM degenerate fundamental modes and also perturb the TM mode, approximating their resonant frequencies to form a third‐order bandpass filter. A 2.42 GHz centered filter was designed and fabricated. Experimental results showed a fractional bandwidth of 29%, return loss better than 16 dB, insertion loss of 0.5 dB, and good second harmonic band rejection. The filter exhibited a size reduction of 51% compared with a filter using an unperturbed circular patch resonator at the same frequency.