Transmitt/Receive Switch (T/R Switch) Circuit is appeared in the diagram
below. Transmit / Receive Antenna Switches are commonly used to connect
the transceiver’s antenna to either the Transmitter port or the
Receiver port. This is one of the most important control circuit applications for specific wireless system applications using PIN diodes.
This quarter wave antenna switch is a narrow band SPST switch configured to switch the Antenna Port. When both pin diode
D1 & D2 are forward biased, the transmitter is connect to the
Antenna, and the Receiver is protected by the isolation network of D2
terminating the quarter wavelength line.
D1 & D2 are reversed biased, the Transmitter Port is isolated by
D1, and the quarter wavelength line and the Receiver Port are connected to the Antenna. The biasing scheme is requiring only one RF Choke Coil and a few d-c blocking capacitors.