Design of a Triple-Passband Microstrip Bandpass Filter with Compact Size

Abstract

This paper presents the triplepassband microstrip bandpass filter (BPF) with compact size. Two sets of the coupled asymmetric stepped impedance resonators (SIRs) and uniform impedance resonators (UIRs) are arranged for generating the triple-passband properties. It is convenient to control the triple-passband properties by tuning the impedance ratio (K) and length ratio (γ) of the asymmetric SIRs. The UIRs are also employed to enhance the coupling between the coupled resonators at 3rd passband. The filter is designed at 2.4/5.2/8.2 GHz and achieves nearly 50% circuit size reduction compared with the previous works. This study provides a simple method to design a triple-passband filter with compact circuit size. Experimental verification is provided, and good agreement has been found between simulation and measurement.