PURPOSE: To process correctly a laser signal with a single oscillator by using a radio-frequency oscillator manufactured from a gallium element in combination with a varactor diode.

CONSTITUTION: The output of a radio-frequency oscillator 11 operated in association with a varactor diode operated by a modulation pulse 13 comes to the transmitter-receiver circulator 19 via an electric power amplifier 17, and reaches a dual-purpose antenna 21. Echo received by the antenna 21 returns to the circulator 19. The circulator 19 operates to send these signals to a low noise radio-frequency amplifier 23, and then to a balance mixer 24. Signals transmitted by the oscillator 11 is also rent to the mixer 24. A demodulation intermediate frequency is sent from the mixer 24 to an intermediate frequency amplifier 28 and amplified to produce a video output that is led to a signal process system. By manufacturing the oscillator 11 from gallium arusenic, the frequency is made significantly so stable and deviated extremely quickly that a short laser pulse can be transmitted.