New design techniques for coupled-line filters with transmission zeros

New design techniques for multicoupled line, bandpass, MIC filters, with general transfer functions are presented. Approximate equations are derived relating coupled line electrical models to filter coupling matrices, allowing the introduction of real and imaginary frequency transmission zeros to the transfer function, leading to a greater flexibility in the optimization of selectivity and/or group delay responses. The general concept is applicable to any type of coupled transmission line geometry, such as stripline, microstripline, coplanar waveguide, suspended stripline etc. Numerical and experimental results are presented for elliptic and pseudo-elliptic response 4 and 6-pole filters.