Transmitter/receiver for radio communication, RFID system and receiving method for transmitter/receiver for radio communication

A transmitter/receiver for radio communication, comprising:

• a transmission circuit for generating a transmission signal;
• a demodulation circuit for demodulating a receive signal;
• an antenna circuit for transmitting said transmission signal from said transmission circuit, and receiving said receive signal and guiding said receive signal to said demodulation circuit;
• a phase shift circuit which is disposed between said transmission circuit and said antenna circuit;
• a switching circuit which switches between connecting said transmission circuit and said demodulation circuit to said antenna circuit not via said phase shift circuit, and connecting said transmission circuit and said demodulation circuit to said antenna circuit via said phase shill circuit;
• and
• a control circuit which causes said switching circuit to perform switching repeatedly and causes said switching circuit to stop switching when a demodulation signal from said demodulation circuit can be obtained,
• wherein a phase shift amount of said phase shill circuit is (2N−1) times of 45 degrees of a carrier wave in said transmission signal±15 degrees, N being an integer equal to or greater than two.