A Dualband Coupling Matrix Method for Designing Quad-channel Diplexer

In this paper, an efficient EM-based design method for designing quad-channel diplexer is presented. An analytical method for dualband filter design is presented. In the proposed method, a dualband coupling matrix is directly obtained by adding diagonal rejection resonances and branch coupling elements to a conventional bandpass coupling matrix to produce arbitrary asymmetric bandwidth and arbitrary placed transmission zeros. It also presents a very efficient approach to reconfiguring a simple bandpass filter into a dual-band filter design by adding number of rejection resonators. The design theory is briefly discussed. A quad-channel diplexer including two dual-band filters connected using a T-connection is designed in Sonnet em simulator to validate the proposed method.