This paper presents an ease of dual-mode diplexer with high signal isolation based on amplitude and phase cancellation technique. The dual-mode structure enables a compact and easy asymmetrical frequency response which also requires considerable attenuation between the proximity in frequency of the transmitter and that of the receiver. Two back-to back dual-mode three-port diplexers and a 180˚ phase shifter are easily employed to construct the proposed device, which are combined to form a four-port dual-mode diplexer. A 180˚ phase shift in one branch can be achieved by delayed transmission line. The simulated and measured four-port dual-mode diplexers are designed at the operational frequency of Tx/Rx at 1.95 GHz and 2.14 GHz, respectively. The measured results of Tx/Rx dual-mode diplexer devices are presented of 48.5 dB Tx/Rx isolation. This four-port dual-mode diplexer achieves the isolation (S32) more than 21.5 dB compared with a conventional three-port dual-mode diplexer.
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