A switch used in a radar system that has a common antenna for both transmission and reception. The TR switch automatically decouples the receiver from the antenna during the transmitting period. It is commonly used in conjunction with an anti-transmit-receive switch (ATR switch) that automatically decouples the transmitter from the antenna during the receiving period; extra protection is thus provided for the transmitter from return echoes received by the antenna.

A common type of transmit-receive switch is a combination of a gas-discharge tube and a cavity resonator. The cavity resonator is used to connect the antenna to the transmitter (or receiver). When a discharge is established in the gas-discharge tube, i.e. when the tube is fired, the electrical conditions of the cavity resonator become such that resonance is not possible and the transmitter (or receiver) is therefore disconnected. A keep-alive circuit is frequently incorporated in the switch to maintain the discharge in the tube during periods when it is not operative.