A transmitting and receiving apparatus for transmitting transmission signals and receiving reception signals, the transmission signals and the reception signals having different respective frequencies, by switching one antenna, comprising:
- a transmitter/receiver having a microphone and a speaker;
- a first signal processing part for converting an output signal output from the microphone of said transmitter/receiver into a transmission base band signal;
- a modulation part for performing predetermined modulation processing upon the transmission base band signal output from said first signal processing part;
- a transmission part for converting a modulated signal output from said modulation part into a transmission signal having a first frequency in a first frequency band;
- an antenna duplexer unit including
- a high-frequency switching circuit for receiving the transmission signal output from said modulation part and supplying the transmission signal to the antenna,
- a delay circuit having a characteristic impedance and first and second ends for delaying a signal passing between said first and second ends for a predetermined delay period, said first end of said delay circuit being coupled to the one antenna, and
- a band-pass filter having an input end coupled to said second end of said delay circuit and having a reception impedance at a second frequency in a second frequency band nonoverlapping with the first frequency band such that a received signal received by the antenna which has the second frequency in the second frequency band nonoverlapping with the first frequency band is passed, and having an increased impedance in the first frequency band such that the transmission signal in the first frequency band is suppressed and a reflected signal having a phase characteristic advanced by a predetermined phase advance period is supplied, the reflected signal being delayed by the predetermined delay period while passing through said delay circuit such that a sum of the predetermined delay of the transmission signal passing through said delay circuit and the predetermined delay of the reflected signal passing through said delay circuit is complementary to the predetermined phase advance period and the reflected signal exiting said delay circuit has a substantially zero phase shift from the transmission signal in the first frequency band;
- a reception part for receiving the received signal output from said antenna duplexer unit and received by the antenna, and converting the received signal into a reception signal;
- a demodulation part for performing upon the reception signal output by said reception part demodulation processing corresponding to the modulation processing performed in said modulation part and supplying a base band signal generated therefrom;
- and
- a second signal processing part for converting the base band signal output from said demodulation part into an audio signal and supplying the audio signal to the speaker of said transmitter/receiver.