Transmitting and receiving apparatus

摘要

A transmitting and receiving apparatus (1) including a transmitting system and a receiving system which prevents fluctuations in insertion losses caused by changes in transmission power, while obviating the need for the provision of a battery and a current control circuit for providing a switching current, and suppresses losses in the transmission system so as to improve the power efficiency, and also decreases the cost of parts. The transmitting and receiving apparatus (1) having a transmitter (3) and a receiver (4) sharing a single antenna (2) is configured as follows. A circulator (9) is provided at a feed point (A) of the antenna between the transmitting system and the receiving system. Also, a changeover switch (10) is disposed between a terminating resistor (11) connected to ground and a point where the circulator (9) and the receiver (4) are connected so that the changeover switch (10) can be automatically switched to the terminating resistor (11) in response to input power supplied from the transmitter (3) during transmission.