Design of a high band-isolation diplexer based on asymmetric stepped-impedance resonators with side-coupling structure

Abstract

In this paper, a high band-isolation diplexer based on two bandpass filters (BPFs) formed using asymmetric stepped-impedance resonators is presented. The passbands of the diplexer are operated at 1.8 GHz for global system for mobile communications (GSM) and 2.4 GHz for wireless local area network (WLAN). Side-coupling structure is adopted in BPFs to create two additional transmission zeros, thus enhancing the band isolation and stopband region. The measured results of the proposed diplexer show the passband at 1.8 GHz with a low insertion loss of 1.09 dB, a 3 dB fractional bandwidth (FBW) of 9.4% in the first channel and a passband at 2.4 GHz with an insertion loss of 2.6 dB, a 3 dB FBW of 6.2% in the second channel. The measured results of the fabricated diplexer also show a good agreement with the simulated ones.