Patent ID: 8164455

Claim:
A communication system of a backscatter type, the communication system comprising: a reflector that transmits data by a reflected wave formed by subjecting a non-modulated wave to a modulation process; and a reflected wave reader that reads the data from the modulated reflected wave from the reflector, wherein, the reflector includes: an antenna that receives a radio wave coming from a transfer destination; a phase controller that controls a phase of the reflected wave with respect to the radio wave received by the antenna according to transmission data; an amplitude controller that controls the reflected wave controlled in phase by the phase controller in an amplitude direction according to the transmission data; a signal line formed by connecting an antenna switch formed by one of a diode and a gallium arsenide field-effect transistor and a λ/4 (where λ is a wavelength being used) phase shifter, the antenna switch and the λ/4 phase shifter being connected between the antenna and a ground, and connecting a variable high-frequency attenuator between the antenna and the antenna switch, the reflector performs data transmission by a multilevel phase-modulated reflected wave signal, and the reflected wave reader transmits the non-modulated wave, and subjects the multilevel phase-modulated reflected wave signal from the reflector to a demodulation process.