Coupler and method for converting signals

A coupler comprises difference ports, an antenna port, a receiver port, a local port and a transmission path. The difference ports are adapted to receive a differential signal. The antenna port is designed to output a transmitted signal and a received signal input. The transmitted signal is derived from the difference signal. The receiver port is configured to output a portion or version of the received signal. The local port outputs a local signal, which is also derived from the difference signal. The transmission path is coupled to the differential port, the antenna port, the receiver port and the local port.