Abstract: In the field of the radar monitoring of airspace zones, and more particularly to the low altitude air surveillance of zones that are more or less densely populated with fixed objects comprising moving parts, such as wind turbines for example, two processing modules are applied to the raw signal Sb(t) received by the radar. The first module carries out the recognition in the signal Sb(t) of a signal reflected by a wind turbine, the recognition being performed by detecting an evolution in the course of time of the amplitude of the signal received Sb(t), characteristic of this type of signal. The first module also formulates a spurious-signal model either directly on the basis of the signal Sb(t) or on the basis of external real-time information relating to the operating state of the wind turbine whose signal has been detected. The second module executes the filtering proper of the signal Sb(t), this filtering consisting in subtracting the spurious-signal model s(t) from the signal Sb(t).

Abstract: Coaxial filter having at least one of the internal and external conductors which is divided into sections (S.sub.1 to S.sub.4) separated by breaks having to form of annular slits whose thickness is very slight in relation to the wavelength.Each section comprises at least one reactive tuning element such as an open or short-circuited coaxial line portion and at least one switch element located in the vicinity of the corresponding break in order selectivity to short-circuit the said break or bring about the insertion of the corresponding reactive tuning element in response to electronic control devices.Application to telecommuncations.