Novel microstrip lowpass-bandpass diplexer with low loss and compact size for wireless applications

Abstract

Abstract This paper presents a lowpass-bandpass diplexer based on a novel microstrip structure. The lowpass channel is appropriate for wireless applications with a cut-off frequency at 2.4\u202fGHz while the bandpass channel is located at 4.2\u202fGHz for WiMAX applications. The lowpass channel is created by a novel structure, which is proposed for the first time in this work. A novel combination of thin transmission lines, rectangular and triangular patches is used to make the bandpass channel. The lowpass and bandpass filters are integrated by a compact simple transmission line. The diplexer structure is well miniaturized with an overall size of 0.036\u202fλg2. The proposed diplexer has the most compact size in comparison with the previous lowpass-bandpass diplexers. Moreover, the insertion losses at both channels are better than 0.18\u202fdB, while the return losses at the lower and upper channels are 18.2\u202fdB and 41.4\u202fdB respectively. In comparison with the previous works, the designed diplexer has the lowest insertion and return losses. To confirm the simulation results, the introduced diplexer is fabricated and measured.