A New Class of Waveguide Dual-Mode Filters Using TM and Nonresonating Modes

An innovative class of very compact and selective waveguide dual-mode filters is presented in this paper. The basic structure is the TM dual-mode cavity. Such a cavity employs both resonant and nonresonating modes so as to provide two reflection and two transmission zeros. The high design flexibility in terms of transmission zero positioning and response bandwidth has been demonstrated by means of several single cavity designs. The design of Nth-order multiple cavity filters with N transmission zeros is presented and discussed. Different filter topologies are obtained depending on the waveguide structure used to connect adjacent cavities. An efficient mode-matching analysis method is proposed and verified for fast filter optimization. An eighth-order filter with eight transmission zeros has been designed, manufactured, and tested to demonstrate the potentialities of the filter class proposed.