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Abstract

The invention relates to a coherent radar comprising a magnetron (MAG), a modulator (MOD) for pulsing the magnetron, a stable local oscillator (STALO) and a mixer (B.sub.1) for producing an intermediate frequency signal of incoming echoes and an intermediate frequency oscillator (MFO) and a phase sensitive detector (D) for detecting the echo pulses and producing a so called bipolar video signal. The modulator (MOD) and the intermediate frequency oscillator (MFO) are mutually time controlled in such manner that the front flank of the modulator pulse and thereby the magnetron pulse always appears in a predetermined phase position of the output signal of the intermediate frequency oscillator. According to the invention the oscillations of the magnetron are phase locked to an external signal in two steps. This is effected by applying a signal derived from the stable local oscillator to the tuning cavities of the magnetron before triggering. After triggering of the magnetron the supply of the signal is interrupted at a moment when the oscillations in the magnetron have started but not reached their final amplitude. Before the oscillations in the magnetron have reached their final amplitude, a signal of the transmission frequency of the magnetron is applied to the tuning cavities. The oscillations in the magnetron (MAG) are then phase locked to this signal, which is derived from a stable oscillator device (STALO, MFO, B.sub.2).

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First Claim