Compact Diplexer with High Isolation and Wide Stopband Based on SIRs

Abstract

AbstractA compact microstrip diplexer with a high isolation and improved out-of-band performance is proposed in this paper. The proposed diplexer is based on cascaded-quadruplet (CQ) bandpass filters (BPFs), which is composed of λ/4 stepped-impedance resonators (SIRs). By employing the edge and quasi-lumped coupling topology, a compact diplexer with improved passband selectivity can be achieved. Meanwhile, by appropriately adjusting the impedance and electric length ratios of SIRs, the stopband can be extended to 20 GHz with a rejection level of 10 dB, which is 12.7 times of the fundamental frequency. The predicted results on S parameters are compared with the measured ones and good agreement is achieved.