Patent ID: 7929934

Claim:
An identification information reader comprising: an antenna commonly used for transmission of a radio wave to a radio frequency identification tag and reception of a radio wave that has been modulated with at least identification information and transmitted from a radio frequency identification tag; a transmitter which outputs a radio wave to be transmitted from the antenna; a receiver which demodulates a radio wave received by the antenna to acquire at least the identification information; a directional coupler which is connected between the transmitter and the receiver, guides the radio wave output from the transmitter to the antenna and guides the radio wave received by the antenna to the receiver; and attenuating means, connected between the antenna and the directional coupler, for attenuating the radio wave guided to the receiver to the extent that the receiver is prevented from saturating if a voltage standing wave ratio of the antenna increases, wherein the attenuation ATT (dB) of the attenuating means satisfies: ATT ≧( IS−IL 1 −IL 2−RL)/2 where IS (dB) represents an isolation between transmitter and receiver ends of the directional coupler, IL 1 (dB) represents an insertion loss that occurs in the directional coupler with respect to the radio wave guided from the transmitter to the antenna, IL 2 (dB) represents an insertion loss that occurs in the directional coupler with respect to the radio wave guided from the antenna to the receiver, and RL (dB) represents a return loss of the antenna.