Stepped-Impedance Hairpin Resonators with Asymmetric Capacitively Loaded Coupled Lines for Improved Stopband Characteristics

Abstract

New microstrip bandpass filters with extended stopband bandwidths are proposed by using new asymmetric stepped-impedance hairpin resonators (ASIHRs). The size of the proposed resonators has been reduced around 16%, comparing with the conventional stepped-impedance hairpin resonators (SIHRs) structure. The first bandpass filter is a combination of differ resonators with the same fundamental frequency but differ in harmonic frequencies, resulting in improved suppression spurious responses in stopbands. Furthermore, another bandpass filter uses the ASIHRs periodically loaded on a microstrip line to improve stopband characteristics. The proposed filters not only have compact size of resonators, but also provide improved upper stopband characteristics. The proposed filters provide 20 dB rejection levels in the stopband up to 6f 0 . The measured filters responses agree very well with the simulated expectations.