随着新型作战武器和样式的出现，雷达面临越来越复杂的“四大威胁”，单个雷达节点的能力逐渐接近物理“极限”，雷达必须从“点”向“网”演进，在这种背景下，产生了一种全新雷达体制——网络化雷达。网络化雷达包含许多广域空间零散分布的雷达节点，多个子处理系统以及多个中心处理系统，具有稀疏大孔径的特点。目标往往处于近场范围，远场阵列接收模型已不适用。网络化雷达与稀疏孔径综合、雷达通信一体化等其他领域相结合时，仍有很多问题需要解决。本文基于近场信号传播模型，研究网络化雷达稀疏孔径综合以及基于正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)线性调频(Linear Frequency Modulated, LFM)雷达通信一体化信号的设计与处理问题。本文的主要内容概括如下：

(1) 研究网络化雷达的基础理论与探测模型。简单介绍近场和远场的划分、近场信号传播模型、波束形成原理和OFDM-LFM雷达通信一体化信号模型，为后续工作提供理论基础。基于近场信号传播模型，构建网络化雷达的三维近场收发信号模型。从目标散射系数、多普勒单元一致性和距离单元一致性方面对网络化雷达的回波相参性进行分析，得出网络化雷达探测处理实际是空域角度和距离的三维匹配过程的结论。

(2) 研究网络化雷达稀疏孔径综合问题。首先，推导网络化雷达在稀疏大孔径下的近场收发联合方向图，引入阵列孔径、节点数量、节点间距等约束条件，通过优化方向图的最大旁瓣电平，提出节点位置优化模型。然后，针对均匀稀疏布阵带来的密集栅瓣和高旁瓣问题，提出两种布阵思路：随机稀疏布阵和随机稀布布阵，并对方向图性能进行分析。随机稀疏布阵将阵列孔径划分成若干栅格点，选择其中一部分栅格点作为节点位置。随机稀布布阵在实际可分配空间内生成若干随机点后逆映射回阵列孔径作为节点位置。仿真结果表明，降低稀疏率或提高稀布率能够有效抑制栅瓣问题，降低旁瓣。最后，引入量子粒子群算法，设计优化操作步骤，实现在这两种布阵方式下的节点位置的优化，进一步降低方向图的最大旁瓣电平。

(3) 研究OFDM-LFM雷达通信一体化信号在网络化雷达体制下的设计与处理。首先，对基于OFDM-LFM雷达通信一体化波形的发射信号进行仿真分析，验证发射信号具有良好的自相关性和互相关性，能够实现发射信号分离。然后，提出雷达回波信号相参处理方法以及通信信号解调方法。最后，通过一系列仿真实验进行验证。在单目标场景下，通过分析角度-距离匹配结果在时延和相位补偿、距离分辨率、近场波束形成、信噪比等方面的性能验证所提雷达回波相参处理方法的有效性；通过分析栅格失配情况，得到搜索间隔取值上限，并在多目标场景下进行验证。通过分析通信误码率，验证所提通信信号解调方法的有效性。仿真结果证明，所提方法在不影响网络化雷达探测性能的同时，完成数据传输，实现网络化雷达通信一体化。

With the emergence of new combat weapons and styles, the "four major threats" is severer to radar. The ability of single radar node is gradually approaching its physical "limit", radar must evolve from "point" to "network", and the networked radar is a new system radar produced under this background. Networked radar is composed of many wide-area scattered nodes, multiple sub-processing systems and multiple central processing systems. Because of the characteristics of sparse and large aperture, the targets are usually within the near-field range, therefore the far-field array receiving model is no longer applicable. There are still many problems to be solved when networked radar is combined with other fields, such as sparse aperture synthesis and radar communication integration. Based on the near-field signal propagation model, this thesis studies the sparse aperture synthesis and the design and processing of Orthogonal Frequency Division Multiplexing(OFDM) Linear Frequency Modulated(LFM) radar communication integrated signal of networked radar. The main content of this thesis can be summarized as follows.

 

(1) The basic theory and detection model of networked radar are studied. We simply introduce the division of near field and far field, the propagation model of near field signal, the principle of beamforming and the radar communication integrated signal model of OFDM-LFM, which provides theoretical basis for the follow-up work. Based on the near-field signal propagate-on model, a three-dimensional near-field transmitting and receiving signal model of networked radar is constructed. The coherence of networked radar echoes is analyzed from the aspects of target scattering coefficient, doppler unit consistency and range unit consistency. It is concluded that networked radar detection processing is actually a three-dimensional matching process of spatial angle and range.

 

(2) The sparse aperture synthesis of networked radar is studied. Firstly, the near-field joint pattern of transceiver and receiver of networked radar under the sparse and large aperture is derived. Constraints such as array aperture, number of nodes and node spacing are introduced. By optimizing the maximum sidelobe level of the pattern, the node position optimization model is proposed. Then, two kinds of layout ideas: random sparse array and random thinned array are proposed in order to solve the problem of dense gate lobes and high sidelobe caused by uniform sparse array, and the performance of the pattern is analyzed. The random sparse array divide aperture array into several grid points and select some grid points as the nodes position. The random thinned array generates several random points in the actual distributable space and then inverse map to array aperture as the node position. The simulation results show that reducing the sparse rate or increasing the thinning rate can suppress the gate lobe problem and reduce the sidelobe. The quantum particle swarm optimization simulates the process of quantum particles moving to the direction of the lowest potential energy in the potential field and has good global convergence. At last, we introduce the quantum particle swarm optimization to design the optimization operation steps to realize the optimization of the node position under the two layout modes, and further reduce the maximum sidelobe level of the pattern.

 

(3) The design and processing of radar communication integrated signal of OFDM-LFM under networked radar system are studied. Firstly, the transmitted signals based on the radar communication integrated waveform of OFDM-LFM are simulated and analyzed to verify that the transmitted signals have good autocorrelation and mutual correlation, and can realize the separation of transmitted signals. Then the radar echo signal coherent processing method and communication signal demodulation method are proposed. Finally, a series of simulate on experiments are carried out to verify those methods. In a single target scenario, the effectiveness of the proposed radar echo coherent processing method is verified by analyzing the performance of angle-range matching results in time delay and phase compensation, range resolution, near-field beamforming, signal-to-noise ratio and other aspects. By analyzing the grid mismatch, the upper limit of the search interval is obtained and verified in the multi-object scenario. The effectiveness of the proposed demodulation method is verified by analyzing the error rate of communication signals. Simulation results show that the proposed method does not affect the detection performance of networked radar and can carry out data transmission, realizing the integration of networked radar communication.

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