Triple-Band Bandpass Filter and Triplexer Using Quad-Ridge Cavity Resonators

Abstract

This article presents a novel quad-ridge cavity resonator to realize a trimode response based on the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> , and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">111</sub> modes. The basic structure of the quad-ridge resonator (QRR) contains four ridges located at the center around the cavities. With an appropriate combination of the main parameters (length and width of the resonator and heights of the ridges), the first three TE resonant modes can be flexibly controlled, and each mode can carry the signal of a channel. Compared with a traditional rectangular cavity, the QRR provides more design freedoms for controlling the first three TE resonant modes and features a wider spurious-free window. The electric field distributions of the QRR are thoroughly analyzed to guide the realization of a filtering response. Intracavity coupling is achieved by an all-iris structure, including horizontal and vertical coupling slots with offsets to the cavity center, capable of easy fabrication and assembly. A nine-pole triple-band filter and a 12-pole triplexer are designed and manufactured to validate the concept. A comparison with other reported multiplexers indicates that the proposed triplexer exhibits the advantages of size reduction and high isolation.