HIGH ISOLATION MICROSTRIP DIPLEXER WITH ENHANCED STOPBAND CHARACTERISTICS FOR GSM AND WLAN APPLICATION

In this article, a high-isolation microstrip diplexer with enhanced stopband characteristics is presented for GSM and Wireless Local Area Network (WLAN) application. The proposed diplexer consists of two compact bandpass filters (BPFs) using short-circuit centered stepped impedance resonators (SCSIRs), operated at 1.8 and 2.45 GHz, respectively. Due to the intrinsic characteristics of the SCSIRs, multiple transmission zeros can be generated for high selectivity and wide upper-stopband. By locating the transmission zero of one channel at the passband of the other channel, and utilizing good impedance matching between two BPFs, high output isolation can be achieved. A microstrip diplexer prototype is designed and fabricated. The upper-stopband of two channels in experiment is extended up to 10.2 GHz with an insertion loss larger than 28 dB. Meanwhile, the measured isolation greater than 48 dB in GSM passband and more than 52 dB in WLAN passband is achieved between two channels. A satisfactory agreement between the simulated and measured results validates the proposed configuration. The size without the 50- feed lines is only 0.250x0.112 in which is the guided wavelength at 1.8 GHz. (c) 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2990-2993, 2013