Clutter elimination radar

A radar receiver having a clutter-elimination filter in the receiver's intermediate frequency stage. The filter is centered on the intermediate frequency fi and has a transfer function in which a band-pass characteristic is superimposed on a band-rejection characteristic. The band-pass response has a principal lobe substantially conforming to the function (sin x)/x with x=(w-wi) pi T. The band-rejection response presents an attenuation zone centered about fi; this zone is wide enough to suppress much of the response from clutter but narrow enough to avoid suppressing much of the energy in the echo from the target. For example, the width of the attenuation zone may be from about fi-0.2/T to about fi+0.2/T. The filter provides a maximum response on each side of the attenuation zone, spaced from fi by about 0.4/T Hz in each direction. Outside the maxima, the response is dominated by the band-pass characteristic and achieves transmission minima at about 1/T Hz above and below fi. Examples are given of filters providing such transfer functions.