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° 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 miniaturisation and cost reduction. Measured results of Tx/Rx diplexer devices at 2.13/1.73 GHz are presented and 40 dB Tx/Rx isolation is achieved with only second-order filters.

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