Highly-Selective RF Duplexers Using Multi-Resonant Junctions

摘要

This paper reports on a simple RF design methodology for the realization of RF duplexers with quasi-elliptic-type filtering channels. It is based on Nth-order in-line bandpass filters (BPF) that are connected to the duplexer input through a multi-resonant junction that introduces three additional transmission zeros (TZs) and two in-band poles. Whereas the TZs are present in both channels, the poles are shared between them. As such, a quasi-elliptic-type BPF response is obtained in each channel that is shaped by N+1 poles and three TZs. As an important advantage to be highlighted, the aforementioned response is obtained without the use of cross couplings. For practical validation, a third-order (N=2) microstrip prototype with channels set at 2.14 and 2.84 GHz was designed, manufactured, and measured.