A radar transmitting circuit uses an injection-locked oscillator, for example, a magnetron, as its output stage. Keeping the injection-locked bandwidth centred on the transmission frequency of the radar source poses problems. The invention maintains this alignment by allowing the astable frequency of the magnetron (38) to drift with the injection-locked bandwidth, and then making the frequency of the radar source (30) follow the magnetron frequency. A measurement (44) of the phase difference between the injection signal (35) and the output signal (37) from the magnetron enables a feedback loop (60) to be controlled, and this makes it possible to adjust a tunable voltage-controlled oscillator (48) or to select from a set of fixed-frequency oscillators (78). IMAGE
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