Compact designs of a band-pass filter with novel open-loop resonators

In this article, several square open-loop resonators with transmission lines are proposed to design the optimized bandpass filters A compact microstrip filter using an open-loop resonator was designed, fabricated and measured. At the center frequency f(o) 1.80 GHz, a 3-dB bandwidth of 5% can be varied from 1.76 to 1.85 GHz. The filter shows a maximum insertion loss in passband of 0.1 dB. A transmission zero is realized at about 3.1 GHz, and the attenuation at this frequency exceeds 70 dB. When compared with the conventional filters using cou-pled square open-loop resonators, the proposed filter has a size reduction of 30%. Good agreement between measurements and simulations are obtained. (C) 2007 Wiley Periodicals, Inc.