EVALUATION OF THE SIDELOBE SUPPRESSION FILTER EFFECTIVENESS IN THE CONDITION OF THE BARKER SIGNALS MATCHED FILTERING
Abstract
The aim of the study is the synthesis of an additional filter for suppressing side lobes, providing the best compromise between the SNR decreasing and reduction of the sidelobe level at the filter output, consistent with the signals based on the Barker codes. To achieve this goal, it is necessary to find the coefficients of the filter for sidelobe suppression and evaluate its effec-tiveness. The digital sidelobe suppression filter is synthesized on the basis of solving the optimi-zation problem of searching the relative value conditional maximum in the main lobe of the output signal in a non-optimal filter under the condition of limiting the value of its sidelobes. Sidelobe suppression filters are investigated for matched filtering of signals formed on the basis of Barker sequences of different lengths. In all cases, the minimum possible length of the side lobes suppression filter pulse characteristic has been chosen, which is equal to the number of reports in the matched filter output. Quantitative estimates of the side lobes suppression and the accompanying SNR decreasing at the output of the synthesized filter for signals based on differ-ent Barker codes are obtained. It is established that the maximum suppression of sidelobe is achieved in the case of 5-element (11.65 dB) and 13-element (11.7 dB) Barker codes. The value of the side lobes in the output signal are minus 25,63 dB and minus 33,98 dB respectively. The minimum loss in SNR is obtained for signals based on 11-element (1.56 dB) and 13-element (0.73 dB) Barker codes. For a signal with a 5-element Barker code, this value is 1.75 dB. Thus, for 13-element Barker code signals the optimal ratio between the degree of sidelobe suppression and SNR decreasing in the processing of the matched filter output by an additional non matched filter is achieved. In cases where significant restrictions are imposed on the duration of the output sig-nal, the use of a 5-element Barker code is preferred.
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