Transmission zero generation for wideband high frequency evanescent mode filters

A new technique to generate transmission zeros in wideband high frequency evanescent mode filters is presented in this paper. The proposed technique is based on the inverted strongly coupled resonator pair (ISCRP), which is used to provide both a resonant node and a by-pass coupling. Large sequential coupling coefficients are obtained by inverting one or both resonators of the pair. Moreover, in order to realize a sufficiently strong intra-coupling, the two resonators are embedded within a section of dielectric-loaded waveguide or alternatively connected one to each other. The ISCRP allows for the realization of a sharp transmission zero that can be located extremely close to the passband edges of a wideband filter. The experimental results of a Ku-band filter with passband ranging from 11.60 to 19.40 GHz and having a transmission zero located 120 MHz away from the lower edge of the passband validate the proposed technique.