Abstract: A process for protecting radars against jamming, in which a pseudo signal is transmitted simultaneously with the useful signal and is formed from pulses synchronous with those of the useful signal. The amplitude of the pseudo signal is higher than that of the useful signal in order that a countermeasure device hooks onto this pseudo signal and ignores the useful signal. The frequency of the pseudo signal differs sufficiently from that of the useful signal to ensure that the jamming signals, retransmitted by the countermeasure device on the pseudo frequency, are rejected in the intermediate frequency amplifier of the radar receiver.

Abstract: A coherent radar including separate transmitting and receiving chains. The transmitting chain includes a master oscillator providing a signal at frequency F0. A multiplier multiplies F0 by a predetermined amount to produce a signal at a frequency F1. A second multiplier multiplies the signal at frequency F1 to produce a signal at frequency F2, F1 and F2 being coherent with F0. A first mixer mixes F1 with F0 and a second mixer mixes F2 with the product of the first mixer to produce a transmission signal. In the receiving chain, a received signal is amplified and filtered and then mixed in a third mixer with the second signal at frequency F2 from the transmitting chain. The mixing product of the third mixer is amplified and filtered and mixed in a fourth mixer with the first signal. The fourth mixer product is then coupled to a processor for producing a radar display.