Study On Near Field Beamforming Technology Of Sparse Node Array Radar

The sparse node array radar is composed of three levels of antenna elements,nodes and clusters.A small number of antenna elements form a node,several nodes form a cluster,and multiple clusters form a large sparse array.Compared with the traditional dense array radar,the sparse node array radar has a higher spatial resolution due to the larger array aperture under the same system complexity.Compared with traditional radars,sparse node array radars have greater three-anti-one resistance(anti-radiation,anti-reconnaissance,anti-stealth,anti-jamming)enhancement potential and stronger battlefield survivability.However,because the electrical wavelength between nodes(distance between nodes divided by wavelength)is large,that is,spatial sparse sampling,and spatial sparseness brings high side lobes or grating lobes,how to optimize node positions and reduce side lobes is a problem worthy of study.While the large aperture of the sparse node array brings good resolution,it also causes the target position to usually be in the near field of the array,that is,the assumption of the far-field plane wave is no longer valid,and the target scattered echo received by the large-aperture array radar is a near-field spherical surface.wave.In view of the fact that the sparse node array echo model is rarely reported in the literature,the study of echo model description and echo generation has been carried out.Using the frequency division stepping multi-transmission waveform between nodes,the echo formula of the sparse node array detection target is derived,and the echo model describing the near-field target is established.According to this model,the time-frequency relationship of the frequency-divided LFM signal is explained.Then,the ambiguity function of the frequency-divided LFM signal was studied,and the autocorrelation function and the cross-correlation function were given,and the orthogonality of the signal was verified by simulation.Generated the echo data of multi-node transmission and multi-node reception where the target is in the near field.In the simulation,the effectiveness of the target signal generation is verified by the result of a single transmitted signal matched filter detection.Aiming at the problem of sparse node array airspace reduction of sidelobes and near-field spherical wave model,the research on near-field beamforming technology of sparse node array is carried out.The geometric configuration of the sparse node array is designed,and a near-field three-dimensional beamforming scheme of transmission signal separation and transmission and reception delay compensation is proposed,and the sparse node array near-field detection beamforming formula is derived.Through simulation,the peak sidelobe ratio in the case of uniform linear array matching is 8.05 d B,and the peak sidelobe ratio drops quickly at the distance of other mismatches.When the exponential distribution coefficient in the symmetric exponential distribution linear array is 6,the peak sidelobe ratio under matching conditions is 13.81 d B.The beamforming performance of symmetric exponentially distributed array and uniform array is compared.Compared with a uniform linear array,the simulation results show that the near-field beamforming peak sidelobe ratio of the designed sparse symmetrical exponentially distributed array is improved by 5.7d B.By changing the exponential distribution coefficient,the peak sidelobe ratios under different exponential distribution coefficients are obtained.It can be concluded that the symmetric exponential distribution under the same system complexity reduces the airspace sidelobes and reduces the false alarm rate of the system.And the symmetry index distribution coefficient around 3 can have better results.