A miniaturized bandpass filter with two transmission zeros using a novel square patch resonator

This paper presents a miniaturized square patch resonator with two different pairs of etched slots for bandpass filter applications. The slots split the fundamental degenerate modes of the resonator and allow the control of both central frequency and bandwidth, providing filter design flexibility. A two- and a four-pole filter centered at 2.4 GHz were designed using the same resonator and fabricated. Experimental results of the two-pole filter showed a bandwidth of 14%, return loss better than 18 dB, and minimum insertion loss of 0.6 dB. This filter exhibited a size reduction of 49% compared to an unperturbed square patch resonator at the same frequency. The four-pole filter results showed a bandwidth of 9.8%, and 33 dB rejection at the second harmonic band.