Design of high‐performance microstrip diplexers with stub‐loaded parallel‐coupled lines

Abstract

A compact and high‐performance microstrip diplexer is designed by using stub‐loaded parallel‐coupled lines and half‐wavelength resonators. First, the traditional equivalent circuit of the parallel‐coupled line is extended to consider the length effect of the loaded stub. Second, by choosing the length of the stub, the multiple transmission zeros can be introduced and allocated to reduce the coupling between two signal channels and improve the isolation between two out‐put ports. Finally, a prototype of the proposed microstrip diplexer is designed and fabricated. The simulated insertion losses are 1.34 dB at 1.8 GHz (first band) and 1.28 dB at 2.4 GHz (second band), while the measured ones achieve 1.54 and 1.47 dB, respectively. More than 40‐dB isolation level is obtained over the whole concerned frequency range.