Design of Balanced Filter with Wide Stopband by Using Discriminating Coupling

摘要

This paper presents a novel balanced filter with enhanced stopband by using discriminating coupling. The proposed design utilizes third-order quarter-wavelength coupled resonators to obtain the filtering responses. Discriminating coupling is applied between feedline and resonator. The circuit is theoretically analyzed and implemented for demonstration. The operating frequency is located at 2.4GHz and the common-mode rejection is larger than 20 dB up to 9GHz (3.75f(0)). Due to discriminating coupling, the differential mode out-of-band rejection is larger than 20 dB up to 18GHz (7.5f(0)), which shows wide stopband.