Novel Diplexer with Improved Isolation Using Asymmetric Transmission Zeros Technique

High isolation and compact size diplexer with two cascaded triplet sections is presented in this paper. By using the quarter-wavelength resonators and stepped impedance resonator to form cascaded triplets, size reduction is achieved. By exploiting different coupling between the resonators, multiple transmission zeros can be obtained to improved the isolation between the two channels. An experimental diplexer with lower and upper channels centered at 1.8GHz and 2.2GHz is designed to verify the proposed theory. Without extra matching network, the proposed diplexer shows high isolation of greater than 41dB.