Design of a wideband isolated out-of-phase filtering power divider/combiner with sharp selectivity

Abstract

A new isolated out-of-phase filtering power divider/combiner with high selectivity is presented. Based on a single-layer microstrip, required coupling strength and phase difference are achieved by two pairs of three-line coupled feeding structures. To realize desired bandpass responses, a specific resonator is located between the input and output coupled structures. By connecting a half-wavelength transmission line which is centrally loaded with a grounded resistor between two output ports, high port-to-port isolation is attained. Based on the impedance matrix of coupled three-line structure, theoretical filtering responses are predicted with the specified bandwidth and return loss. For demonstration, a prototype is designed, fabricated, and tested. Both simulated and measured results are displayed to verify the design mechanism.