Four-port diplexer for high Tx/Rx isolation for integrated transceivers

A four-port diplexer consisting of two back-to-back three-port diplexers combined with a 180 degree phase shifter in one branch is presented. The technique achieves high Tx/Rx isolation with relatively low degree filters. Two experimental diplexers are demonstrated, one with equal Q resonators in all filters and the other with dissimilar Q factors, enabling miniaturization and cost reduction. Measured results of Tx/Rx diplexer devices at 2.13/1.73GHz are presented and 40dB Tx/Rx isolation is achieved with only second-order filters.