A circuit comprises a transmitter to provide a transmit signal. The circuit also comprises a coupler element to receive the transmit signal at an input port, to provide a first representation of the transmit signal at an antenna port and a second representation of the transmit signal at a testing port. The circuit further comprises a monitoring receiver unit. The monitoring receiver unit is coupled to the testing port. Furthermore, the monitoring receiver unit is configured to determine a characteristic of the second representation of the transmit signal.