Two Back-to-back Three-port Microstrip Open-loop Diplexers

A four-port diplexer consisting of two back-to-back three-port microstrip-open loop diplexers combined with a 180° phase shifter in one branch is presented. The technique achieves high Tx/Rx isolation with relatively low degree filters. Two back-to-back three-port microstrip-open loop diplexers with tapped-feeds are simulated which enabling miniaturization and cost reduction. Simulated results of Tx/Rx diplexer devices at 1.95/2.14 GHz are presented and 52.05dB Tx/Rx isolation is achieved with only second-order filters.