Contiguous triplexer based on combining method of two filtering circuits using CRLH and RH isolation circuits

Designing contiguous channel multiplexer has always been a challenge due to the strong interaction between the channels. In this paper, we present a contiguous triplexer based on combining method of two filtering circuits (CMTC) using isolation circuits. A triplexer based on CMTC consists of two isolation circuits. One is composed of a conventional transmission line (TL) for a diplexer, and another comprises a composite right/left handed (CRLH) TL connected to a filter. There are two significant advantages of using CMTC. One is that a designer does not need to modify the design of a stand-alone filter and diplexer and there is no limitation in the choice of filtering circuits. Also, 3-D full-wave optimization is not necessary, because of a simple and straightforward design concept. For verifying the concept, a triplexer prototype having 1 GHz, 1.125 GHz, and 1.25 GHz center frequencies, is designed and fabricated. The measured results show good agreement with the simulation results.