Transmitting/receiving antenna, isolator, high-frequency oscillator, and high-frequency transmitter-receiver using the same

A high-frequency transmitter-receiver comprising:

• first and second circulators each having a first terminal, a second terminal and a third terminal around a magnetic element, for outputting a high-frequency signal inputted from one of the terminals, from the first terminal to the second terminal, and from the second terminal to the third terminal, and from the third terminal to the first terminal;
• a high-frequency oscillator connected to the first terminal of the first circulator, for generating a high-frequency signal;
• a modulator arranged in a signal transmission line connecting between the second terminal of the first circulator and the first terminal of the second circulator, for transmitting the high-frequency signal to the second circulator in a case where the modulator is in an ON state and for reflecting the high-frequency signal to the first circulator in a case where the modulator is in an OFF state;
• a transmitting/receiving antenna connected to the second terminal of the second circulator;
• and
• a mixer connected between the third terminal of the first circulator and the third terminal of the second circulator, for mixing the high-frequency signal reflected on the modulator and inputted from the third terminal of the first circulator and the high-frequency signal received by the transmitting/receiving antenna and inputted from the third terminal of the second circulator, and outputting an intermediate-frequency signal,
• wherein when the high-frequency signal is transmitted through the modulator, the high-frequency signal is outputted to the second circulator, and when the high-frequency signal is reflected on the modulator, the high-frequency signal is outputted from the third terminal of the first circulator to the mixer, and
• wherein the transmitter-receiver is configured such that δ=±π in which δ is a phase difference at a center frequency between a signal Wa, which is a high-frequency signal which passes through and leaks from the modulator in the OFF state, and a signal Wb, which is a high-frequency signal which is reflected on the modulator in the OFF state and passes through the third terminal of the first circulator to the mixer and is reflected on the mixer and passes through the second circulator to an output terminal of the modulator and is reflected on the output terminal of the modulator.