Dual-band bandpass filter using stub loaded resonators with multiple transmission zeros

Abstract

A dual-band bandpass filter using both an open stub-loaded resonator (OSLR) and a short stub-loaded resonator (SSLR) is presented. The use of SSLR has the advantage that a transmission zero can be flexibly controlled by tuning the length of the short stub, which can be employed as a new but convenient way to create transmission zeros in front of passbands in filter design. By further introducing a two-order planar transversal filter structure using the OSLR as well as the source-load coupling, a dual-band filter is implemented with four transmission zeros and exhibits high skirt selectivity based on the simulated result. Two passbands with center frequencies of 2.45 GHz and 3.5 GHz are achieved with compact size of about 0.18λ × 0.12λ at 2.45 GHz.