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Algorithmic method of «compression» of radar antenna pattern


V.P. Kortnev

The article covers the so-called algorithmic method of mathematically simulated radar pattern “compression”, based on the multichannel signal processing, when antenna pattern is digitally generated. The method ensures enhancement of measuring accuracy of target angular co-ordinates in a cluster of targets, identification of a target type and improvement of radar ECCM parameters. The term “compression” of radar antenna pattern implies a method of signal processing, by which the initial antenna pattern can be tapered (become more directional), excluding the procedure of its deduction from the main pattern, which, as is well known, results in loss of signal power. Methods of synthesized aperture and Doppler beam sharpening are widely used to enhance radar angular resolution. These methods can ensure considerable improvement of angular resolution, but can be applied only for relative movement of antenna and resolution objects. In addition, to synthesize aperture the resolution objects must be within sectors close to 90 degrees with respect to the aircraft velocity vector and close to 0 degree for Doppler beam sharpening. Method of angular strobing does not reduce an angular sighting error. The so called functional method does not improve angular accuracy either, and requires great time resource for calculating operations, because in this case it is necessary to solve a system of equations, whose number is defined by the unknown ёpredetermined number of reflected objects. Method of antenna pattern sharpening by differential beam forming and adaptive methods of using antenna pattern nulls are also described in literature. But they result in time waste and cause non stable noise, complexity of processing and insufficient sharpening of antenna pattern. Algorithmic method of angular resolution enhancement ensuring angular co-ordinates measurement accuracy is based on the use of artificial increase of interelement spacing by method of multiplication of signal phase of each AESA radiating element by the value equal to the coefficient of antenna pattern “compression”. As a result of mathematical simulation it was revealed: the real antenna pattern is “compressed” by multiplication of signal phase of each radiating element by a constant coefficient (“compression” coefficient of antenna pattern); signal/noise ratio at the output of compression algorithm under the influence of additive white noise does not change practically; amplitude-phase non identity and number of AESA channels influence the characteristics of “compressed” antenna pattern; under the random (rms) deviation of the phase στ = 4º, number of channels N=20 and compression coefficient 10, losses do not exceed 3,5dB; when N=20, στ = 3 º and c=10, losses equal 1 dB. Such parameters of antenna pattern can be considered acceptable, while 3 degrees can be ensured by the equalization of amplitude phase characteristics. The antenna pattern compression algorithm gives rise to diffraction sidelobes, caused by the artificial increase of interelement spacing while the wave length remains constant. These sidelobes are suppressed, when signals of compressed and real diagrams are multiplied.

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