Broadband Five-Port Direct Receiver Based on Low-Pass and High-Pass Phase Shifters

A simple five-port direct receiver achieving broadband performance and high local oscillator to RF isolation is presented. The new circuit comprises three power detectors exhibiting high series impedance, four resistors, and two low-pass and two high-pass phase shifters. It is shown that the phase-shift networks can be designed to optimize receiver operation over a theoretical decade bandwidth. A 300-MHz-2.7-GHz prototype is built and measured to prove feasibility of this proposal.