A millimeter wave, two-pole, circular-electric mode, channel-dropping filter structure

Interest in circular-electric mode channel-dropping filters has been stimulated by recent advances in the repeater art. This paper presents the theory and establishes design procedures for filters having two-pole maximally flat response functions. The basic structure uses mode-conversion resonators, i.e., the resonating mode is the TE 02 circular electric mode, for three of the resonators. The rejection filter portion of the structure is conventional in that two resonators separated by an odd multiple of π/2 radians realize the desired characteristic. The branching filter is novel in that a rectangular waveguide is wrapped around a mode-conversion resonator and coupled to the TE 02 resonating mode via a multiplicity of apertures. The rectangular guide is then resonated to permit realization of the two-pole branching filter. The theory developed is an extension of Marcatili's original work on mode-conversion resonators. The mode-conversion resonator parameters are related to the elements of a lumped constant prototype network thus extending the utility of mode-conversion resonators. Experimental results are presented on several filter models. The agreement between theory and experiment is generally good. Four filters were developed for use in an all solid-state repeater experiment with successful results.