Due to the problem that the large aperture of sparse array antennas leads to most interested targets lying in the near-field, we propose a novel near-field beam synthesis method for sparse array antennas. By utilizing the propagation model of near-field electromagnetic waves, we analyze the original propagation delay expression. When the number of antenna elements and the interval bounds are fixed, this method achieves a lower peak side-lobe level of the linear sparse array via differential evolution, with the steps of the algorithm given. Computer simulation shows the effectiveness and feasibility of the algorithm by realizing near-field beam focusing and PSLL controlling under high sparseness. It is proved that the proposed method reduces the high peak side-lobe level brought by the large array aperture, and has better performance than traditional methods.

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Considering the broadband interference caused by the broadcast signal to the parasitic signal in the Parasitic Transmission System, this paper provides an interference suppression technology based on Amplitude Domain Processing(ADP). With the simplified method of Continuous Polynomial Approximation for expressing mathematically the Probability Density Function(PDF), the nonlinear function derived from this PDF can be applied to nonlinear processing in the amplitude domain of the received signal to suppress interference. This technique reduces the error from inaccuracy of PDF estimation and does not need any training sequence. Simulation results indicate that the Parasitic Transmission System with this technique can effectively suppress broadband interference of the QPSK modulated signal, and that the bit error rate(BER) of the system is about 10^{-3}, even when the interference-to-signal ratio is 20dB.

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