Abstract: In this paper, several square open-loop resonators with transmission lines are proposed to design optimized bandpass filters. In comparison with conventional open-loop resonator bandpass filters, the proposed filter can achieve size reduction. A compact microstrip filter using one of these open-loop resonators is fabricated and measured. Simulation and measurement on the fabricated filter show highfrequency selectivity and good stop-band characteristic with small dimensions. Compared with conventional filters using coupled square openloop resonators, the proposed filter has a size reduction of 30%.

Key words: bandpass filter, microstrip
, open-loop resonator, miniaturization