【摘要】：作為一種高分辨成像雷達技術,合成孔徑雷達(Synthetic Aperture Radar,SAR)在軍事偵察、遙感觀測等領域發(fā)揮了重要的作用。然而,單個發(fā)射和接收天線的常規(guī)SAR系統(tǒng)不能滿足對空間分辨率和測繪帶寬度日益增長的需求。多天線技術(Multiple-Input Multiple-Output,MIMO)與SAR技術相結合,利用波形分集和天線分集,可以獲得遠多于單個天線的空間自由度,從而實現(xiàn)高分辨率寬測繪帶成像,漸漸成為了人們的研究熱點。鑒于此,本文以SAR成像處理方法為基礎,研究MIMO-SAR雷達的正交發(fā)射波形以及MIMO-SAR成像的基本處理方法。本文具體研究內容如下:(1)MIMO-SAR雷達正交發(fā)射波形設計。依據(jù)雷達發(fā)射信號正交性原理,本文研究了采用OFDM(Orthogonal Frequency Division Multiplexing)調制技術的正交波形集。首先,研究了子載波采用線性調頻(Linear Frequency Modulation,LFM)信號的正交信號,對其自相關、互相關和模糊函數(shù)特性進行了仿真分析。其次,研究了相位編碼(Phase Coded,PC)OFDM信號的正交性。采用混沌映射序列來產生新型的相位編碼信號,該類信號具有保密性強、低截獲的優(yōu)點。針對混沌PC-OFDM信號的自相關性、互相關性、模糊函數(shù)以及多普勒容忍性展開仿真分析,并且討論了該類信號的優(yōu)缺點。(2)傳統(tǒng)單天線SAR成像方法研究。首先,分析SAR成像原理以及建立SAR信號回波模型。其次,采用距離-多普勒(Range-Doppler,R-D)算法進行成像仿真研究,并利用RADARSAT-1雷達數(shù)據(jù)驗證R-D算法的有效性。最后,針對稀疏場景的SAR成像,采用壓縮感知理論對SAR點目標回波信號聚焦成像,實驗表明壓縮感知在SAR成像旁瓣抑制方面有很大優(yōu)勢。(3)多天線SAR成像處理方法的研究。首先,分析常規(guī)SAR最小天線面積限制,建立三發(fā)三收基于OFDM-LFM正交信號的MIMO-SAR成像模型。其次,結合距離向高分辨的要求,對回波信號采用子帶拼接的方法在距離向合成大帶寬信號。最后,針對SAR方位向高分辨與寬測繪帶的要求,采用低脈沖重復頻率發(fā)射雷達信號,在方位向利用多通道重建法,消除頻譜混疊。實驗仿真驗證該方法的有效性,與常規(guī)SAR成像算法的聚焦圖像進行對比,表明MIMOSAR能夠實現(xiàn)高分辨寬測繪帶成像。
[Abstract]:As a high resolution imaging radar technology, synthetic Aperture Radar (Synthetic Aperture Radar,SAR) plays an important role in military reconnaissance, remote sensing observation and other fields. However, conventional SAR systems with single transmitting and receiving antennas cannot meet the increasing demand for spatial resolution and the width of mapping bands. Combining multi-antenna technology (Multiple-Input Multiple-Output,MIMO) with SAR technology, using waveform diversity and antenna diversity, the spatial degree of freedom can be obtained much more than a single antenna, thus the high resolution and wide mapping band imaging has gradually become a hot research topic. In view of this, based on the SAR imaging processing method, the orthogonal transmitting waveform of MIMO-SAR radar and the basic processing method of MIMO-SAR imaging are studied in this paper. The main contents of this paper are as follows: (1) MIMO-SAR radar orthogonal waveform design. Based on the principle of orthogonality of radar transmitted signals, the orthogonal waveform set using OFDM (Orthogonal Frequency Division Multiplexing) modulation technique is studied in this paper. Firstly, the orthogonal signals with linear frequency modulated (Linear Frequency Modulation,LFM) subcarriers are studied, and the characteristics of autocorrelation, cross-correlation and ambiguity function are simulated and analyzed. Secondly, the orthogonality of phase coded (Phase Coded,PC) OFDM signal is studied. Chaotic mapping sequences are used to generate new phase coded signals, which have the advantages of high security and low interception. The self-correlation, cross-correlation, ambiguity function and Doppler tolerance of chaotic PC-OFDM signals are simulated, and the advantages and disadvantages of these signals are discussed. (2) the traditional single-antenna SAR imaging method is studied. Firstly, the principle of SAR imaging and the echo model of SAR signal are analyzed. Secondly, the range Doppler (Range-Doppler,R-D) algorithm is used for imaging simulation, and RADARSAT-1 radar data are used to verify the validity of R-D algorithm. Finally, for sparse SAR imaging, compression sensing theory is used to focus SAR point target echo signal. Experiments show that compression sensing has a great advantage in sidelobe suppression of SAR imaging. (3) Multi-antenna SAR imaging processing method is studied. Firstly, the limit of minimum antenna area of conventional SAR is analyzed, and a MIMO-SAR imaging model based on OFDM-LFM orthogonal signal is established. Secondly, according to the requirement of high resolution in range direction, the echo signal is synthesized with large bandwidth signal in range direction by subband splicing. Finally, according to the requirement of SAR azimuth high resolution and wide mapping band, low pulse repetition frequency is used to transmit radar signal, and multi-channel reconstruction method is used in azimuth direction to eliminate spectrum aliasing. The experimental results show that the proposed method is effective and compared with the focus image of conventional SAR imaging algorithm. It shows that MIMOSAR can achieve high resolution and wide mapping band imaging.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN958

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