High selectivity and common-mode suppression combline balanced BPF

Abstract

In this study, new balanced microstrip bandpass filter (BPF) based on steppedimpedance combline structure is proposed with high selectivity and high commonmode (CM) suppression performance In the beginning, a single-ended compact stepped-impedance resonator (SIR) combline BPF with enhanced performance including low insertion loss, sharp skirt and wide stopband response is designed by consisting of an array of short quarter-wavelength bi-section SIRs with a new scheme of tapped-transformer coupling at input and output ports. Under CM excitation, no special consideration or design procedure is required to suppress the CM, and the CM suppression is the nature of the parallel-coupled filter. Finally, the second-and third-order SIR combline balanced BPFs for WLAN application, without loss of generality, have been designed and implemented. The simulated and measured results show a good agreement and validate the proposed theory.

High isolation and common-mode suppression balanced-to-balanced microstrip diplexer with mixed coupling

“…The conventional diplexers are constructed by combining two BPFs having distinct frequencies through a three-port impedance-matching network, such as a T-junction. Recently, the balanced circuit has been widely used in modern communication systems due to its good CM rejection capability, which results in higher immunity to the environmental noise [3,4,5,6]. Hence, a great deal of effort has been spent on achieving balanced diplexers through use of innovative circuit topologies [7,8,9].…”