Patent ID: 7881659

Claim:
An antenna system comprising: a plurality of antennas; and a synthesizer configured to synthesize reception signals received by said plurality of antennas, respectively, wherein: a signal obtained from the synthesis carried out by said synthesizer is given to a communication apparatus configured to carry out a first radio communication method in which an instruction to increase transmission power according to a reduction in reception quality is provided, wherein: said antenna system further comprises: a power control part, provided to correspond to one antenna of the plurality of antennas, and configured to carry out gain control on a signal received by said one antenna before the signal is given to the synthesizer; a detecting part configured to detect that a spurious signal is included in the signal received by said one antenna; and a differential amplifier configured to determine whether the detected spurious signal exceeds a predetermined level or not, and generate a control signal to be supplied to the power control part upon determining that the spurious signal exceeds a predetermined level, wherein the power control part attenuates the signal received by said one antenna on the basis of the supplied control signal so as to reduce gain in the power control part and reduce power of the reception signal to be supplied to the synthesizer.