Balanced switchable bandpass filter with differential-mode reflectionless characteristics

This paper presents a balanced switchable bandpass filter (SBPF) with differential-mode (DM) reflectionless characteristics in the on-state. The proposed SBPF consists primarily of dual-mode resonators loaded with p-type-intrinsic-n-type diodes, absorptive stubs, and common-mode suppression (CMS) networks. The resonance conditions of the diode-loaded dual-mode resonator in both on/off states, as well as the design principles of the balanced SBPF's, are analyzed and derived. To verify the design concept, a balanced SBPF prototype with a center frequency of 2.6 GHz was designed and manufactured. The measured results show that the proposed SBPF exhibits low DM insertion loss and a wide DM reflectionless bandwidth in the on-state, high DM isolation in the off-state, and effective CMS.