A low-loss four-channel microstrip diplexer for wideband multi-service wireless applications

Abstract

In this work, a new quad-band microstrip diplexer is designed and fabricated. It consists of two bandpass filters (BPFs) coupled to a U-shape junction. The proposed resonator is a novel stub-loaded U-shape structure. The design process is based on proposing and analysing an approximated LC model of the presented resonator so that the design method gives general information about resonator performance. Based on this information, our diplexer is optimized to have a good performance. Our diplexer resonance frequencies are tuned at 1.8 GHz, 2.45 GHz, 3.5 GHz and 5.2 GHz. The proposed diplexer has four wide fractional bandwidths (FBWs) of 13%, 17.3%, 18.9% and 17.7%, which are the widest FBWs compared to the previously reported four-channel diplexers. Therefore, it is suitable for multi-service wideband applications. Moreover, it has high selectivity, low losses and reasonable isolation. The fabricated diplexer is measured and a good agreement between the simulation and measurement results is obtained.