Compact Band-Pass Filters Based on Parallel-Coupled Lines with Open Stubs

Abstract

In this paper, two parallel coupled line band-pass filters are proposed. The proposed parallel coupled line band-pass filters are composed of the parallel coupled lines and open stubs. The equivalent circuit of the proposed parallel coupled line band-pass filter is proposed and analyzed. By using odd–even mode analytical method, the design equations are derived. The relation between the center resonant frequency of the proposed band-pass filters and the electrical length is analyzed. The relation between the fractional bandwidth and the impedances is discussed. Two proposed parallel coupled line band-pass filters are designed, fabricated and measured based on the calculated results. The spurious frequencies of the proposed filters are suppressed and the transmission zeros improve the filters’ selectivity. The measured results and the simulated results show good agreement with each other, which verifies the design theory.