A new switching structure using branch-line hybrid couplers for time division duplex system

This paper describes a new switching structure for time division duplex systems. Existing circuits use a circulator to provide isolation among the antenna (ANT), transmitter (Tx), and receiver (Rx) ports. This circuit presents some problems which are high cost, non-linearity and conditional power damage due to using the circulator. In this paper, we describe a new switching structure that uses branch-line hybrid couplers. This new circuit provides isolation among the three ports without an expensive circulator. To study the improved performance of this circuit, we built and tested a physical model tailored for the 2.3 GHz wireless portable Internet service. The measured Tx-to-Rx isolation, the most important parameter of the circuit, was -59.91 dB.