Repeater

A relay device, in which a radio wave of a parent station is received and amplified and a transmission radio wave having the same frequency as that of the radio wave of the parent station is transmitted, comprising:

• a main reception antenna for receiving both the radio wave of the parent station and a go-around radio wave of a relay station;
• a subsidiary reception antenna for receiving the go-around radio wave of the relay station;
• a changeable attenuator for changing an amplitude of a signal of the go-around radio wave received by the subsidiary reception antenna;
• a phase shifter for changing a phase of the signal of the go-around radio wave received by the subsidiary reception antenna;
• a composite signal producer for producing a composite signal from a signal of the radio wave of the parent station received by the main reception antenna, the signal of the go-around radio wave of the relay station and the signal of which the amplitude is changed by the changeable attenuator and the phase is changed by the phase shifter;
• a directivity coupler for extracting a composite voltage of the composite signal output from the composite signal producer;
• an electric power detector for obtaining a composite electric power from the composite voltage extracted by the directivity coupler;
• and
• a microcomputer for controlling both a change of the amplitude performed by the changeable attenuator and a change of the phase performed by the phase shifter so as to minimize an average value of the composite electric power obtained by the electric power detector.