INTERROGATOR FOR COMMUNICATION SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide an interrogator of simple structure for a communication system in which an S/N of a reflected wave from a transponder is increased by improving an amplification gain of a low noise amplifier or a conversion gain of a mixer.

SOLUTION: A signal from a local oscillator 41 is amplified by a power amplifier 43 and transmitted from an antenna 47 via a circulator 44. Received signals from transponders 20-22 are amplified by an LNA 45 via the circulator 44 and inputted to mixers 70 and 71 as reflected wave signals and subjected to homodyne detection. A main carrier signal from the local oscillator 41 to be inputted to the mixer 71 is controlled by a variable phase shifter 49 to be a phase which becomes π/4 radian with respect to the reflected wave signal. The output of the variable phase shifter 49 is inputted to the mixer 70 after its phase is further changed by π/2 radian by a fixed phase shifter 48. The outputs of the mixers 71 and 70 are inputted to a differential amplifier 73, and a differential signal is outputted.

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