Sharp-Rejection In-Line Groove-Gap-Waveguide Bandpass Filter With Multiple Transmission Zeros for Ku-Band Application

A class of high-selectivity groove-gap-waveguide (GGW) bandpass filter (BPF) with multiple out-of-band transmission zeros (TZs) for Ku-band application is reported. It consists of an in-line third-order BPF unit with a reactive load connected at its input port, which results in the generation of several out-of-band TZs. The number of TZs and their locations can be flexibly controlled by adjusting the physical dimensions of the reactive load. This is done while preserving the characteristics of the filter passband in the overall response unaltered, as defined by its third-order BPF unit. Thus, a sharp-rejection GGW BPF in an in-line topology—i.e., without cross coupling—is realized. The RF operational foundations of the devised quasi-elliptic-type GGW BPF architecture are theoretically expounded using the transmission-matrix formalism. Furthermore, for experimental-demonstration purposes, a third-order BPF prototype with multiple out-of-band TZs centered at 15.12 GHz is manufactured and characterized.