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The algorithm of selection of radar objects in a dense group on the basis of the doppler beam sharpening


V.P. Fedosov – Dr.Sc.(Eng.), Professor, Department of radio engineering theory, Radio Engineering Systems and Management Institute of SFU (Taganrog)
D.G. Kovtun – Post-graduate Student, Department of radio engineering theory, Radio Engineering Systems and Management Institute of SFU (Taganrog)

A modified algorithm for constructing a range-Doppler portrait of a group target is proposed, and its simulation is performed. The al-gorithm for recognizing an additive mixture of modulated and narrowband signals based on a nonparametric iterative adaptive algorithm (IAA) is investigated.
For mobile targets the acceleration has a significant effect on the reflected signal, while the Doppler frequency shift changes during the formation of the reflected signal. As the time of accumulation of the echo signal stack increases, both the range and the radial velocity resolution of the echoes of the group object deteriorate. If there is a constant acceleration of the target in the group, then a linear frequency modulation of the reflected signal appears. In the presence of uniformly accelerating targets in the group and targets with constant speed, the problem arises of separating the echoes from the group object in order to store information about the carrier Doppler shift and amplitudes. In the article it is proposed to apply the modification of the radar algorithm in the Doppler beam sharpening (DBS) mode due to the dependence of the Doppler frequency increment on the direction relative to the movement of the radar carrier. For this, both the harmonic and the chirp oscillations are used as basis functions. The modification of the nonparametric iterative adaptive algorithm (IAA) allows to obtain estimates of the power of the coefficients |s(k)|2 of the considered signal basis, where k determines the line number in the system matrix of basis oscillations.
To evaluate the efficiency of the modified algorithm, an echo signal was used based on the simulation, which is an additive mixture of harmonic oscillations with Doppler increments: Fc = [0,1; 0.105; 0.24; 0.25; 0.26; 0.4; 0.41; 0.49] fs, where fs is the carrier frequency of the signal, and the chirp signal with an initial frequency of 0.49fs, whose rate of change is 495 Hz / s. The pulse repetition frequency is 1 kHz, the accumulation time is 100 ms. Based on the simulation results, the standard deviation (RMS) of the Doppler signal bias estimate was 0.4 Hz with a signal-to-noise ratio of 0 dB, with a uniformly accelerating target within the group.
The reduced IAA with a modified basis allows both to increase the resolving power and to separate echoes from maneuvering and non-maneuvering objects in a group having different frequency modulation laws. The proposed modified algorithm makes it possible to isolate an echo signal with a complex modulation from the target within the group, and also to obtain a sufficiently low value of the RMS estimating the Doppler echo frequency increment from individual targets in the presence of a uniform accelerating target.

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