Compact low-pass filter using a slow-wave structure

In this paper a compact low-pass filter that makes use of coupled microstrip lines is investigated. A slow-wave structure is used to equalize the even and odd mode phase velocities of a pair of coupled microstrip lines and thereby improve the directivity of the coupled lines. Two low-pass filters were fabricated: one using the slow-wave structure and one using conventional coupled lines. The results reveal that the rejection of the low-pass filter is significantly improved by using the slow-wave structure.