A system for protecting sensitive zones includes detection bases disposed in such a way that each base performs the monitoring of a part of the limit of the protected zone. To each base n is allocated a frequency channel of width B′ centered on a frequency Fn. Each base comprises a plurality of UHF radars emitting pulses of spectral width B, with a high repetition frequency Fr. Each radar processes a fraction b0 of the global Doppler band b1 concerned. The emission frequencies of the various radars constituting one and the same base are defined in such a way that the gap between the emission frequency Fi of a radar of the base and the frequency Fn is less than the repetition frequency Fr and that the gap between the emission frequencies Fi and Fj of two radars of one and the same base is greater than (b1+b0)/2. The channel allocated to a base n as well as the emission frequencies allocated to the radars of this base are defined in such a way that, having regard to the position of the base, none of the radars constituting the base concerned is liable to be disturbed from a radioelectric point of view by the radars of the other bases.