Interdigital coupled-line bandpass filters: effects of a cross coupling and an inhomogeneous medium

Presented are frequency-dependent characteristics of three-, four- and five-strip interdigital band-pass filters designed in various structures of coupled lines, demonstrating effects of a cross coupling between nonadjacent lines and an inhomogeneous medium. A new class of wide-band band-pass filters with a pair of attenuation poles near cut-off frequencies of the pass-band, composed of homogeneous TEM lines with a tight cross coupling, is originally proposed. Simulated and measured responses of two interdigital 5/sup th/ order band-pass filters are also shown. The theoretical results are in a good agreement with the experimental ones.