Yu.A. Skobelev – Engineer, JSC «Oktava» (Novosibirsk)
The radar image of the point target is calculated. The image is created by SAR when random multiplicative hindrance distorts a phase of the reflected pulses with sweep frequency modulation and frequency manipulation. It is accepted that the phase of a trajectory signal changes only at the moments of reception of the reflected impulses and the method of calculation of the image of the point target on an azimuth and range is offered.
At calculation of the image on an azimuth the trajectory signal is presented by subsignals on number of the periods of repetition on a synthesizing interval. In a phase of each subsignal, except coherent, it is included a casual component, evenly distributed within some range. The image of the point target formed by summation of any two trajectory subsignals is calculated and the size and intensity of such image are determined.
It is shown that in the presence of a multiplicative hindrance each reflected radar pulse with sweep frequency modulation creates the image of the point target on range in the form of uncertainty function (sinx/x)2. It is known that on resolution capability and uncertainty function the group of narrowband pulses with the frequency manipulation is equivalent to one pulse with sweep frequency modulation. Therefore when using of the frequency manipulated impulses the calculation of the image of the point target on range is replaced with calculation of the image of the point target on range when using pulse with sweep frequency modulation. This impulse is divided on equal in size and not crossed subimpulses. It is established that in this case the image of the point target on range is described by the expressions similar to formulas of calculation of the image of the point target on an azimuth.
It is established that the three-dimensional image of the point target formed by one of trajectory subsignals and one of subimpulses at equal quantity of subsignals and subimpulses and equal resolution capability on an azimuth and range has a bell appearance. The image of the point target as the sum of all images of a bell look also has a bell appearance. Sections of this image on an azimuth and range represent typical function of uncertainty with the intensity determined by the range of change of a phase. It is established that at a large number of the reflected impulses within the period of repetition and on a synthesizing interval the impact of the casual evenly distributed fluctuations of a phase doesn't lead to the essential shift and extension of the image of the point target on an azimuth and range. Dependence of rated intensity of the image of the target purpose on the size of range of casual change of a phase (η) is well approximated by expression (sinη/η)2. According to this expression, in the field of values 0,8π ≤ η ≤ 2π rated intensity of the image doesn't exceed 0.06 and can be commensurable with the level of side lobes.
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