【摘要】：發(fā)射低頻段的對墻壁等非金屬障礙物有很好穿透能力的電磁波,超寬帶穿墻成像雷達(dá)有著廣闊的發(fā)展前景,在反恐、救援、安檢等軍事與民用領(lǐng)域具有重要的應(yīng)用價值�；诙噍斎攵噍敵�(Multiple-Input Multiple Output,MIMO)陣列的超寬帶雷達(dá)系統(tǒng)能夠提供高分辨率的雷達(dá)圖像,有利于后續(xù)的檢測、跟蹤等工作,并且具有高實時性、低成本等優(yōu)點�？紤]穿墻雷達(dá)系統(tǒng)的便攜性,并為了節(jié)約成本,MIMO陣列通常采用稀疏陣,天線數(shù)量不多,間距大于波長。因此柵瓣將不可避免地出現(xiàn),引起虛假像,降低成像質(zhì)量。因此本文主要研究稀疏陣列所引起的柵瓣抑制問題。研究了單程陣列的方向圖,從波形上分析了柵瓣的成因,指出均勻且等幅加權(quán)單程陣列的方位向分辨率較高且柵瓣水平較低。由于雷達(dá)用雙程陣列成像,接著研究了雙程陣列,引出等效陣列的概念,它是將雙程陣列轉(zhuǎn)化為單程陣列的重要工具。不同的雙程陣列具有不同的單程等效陣列,柵瓣水平也不同。因此通過陣列配置,設(shè)計陣元的權(quán)重及位置,可以降低柵瓣水平,抑制柵瓣。而在成像角度,介紹了步進(jìn)頻信號的BP成像算法,指出各通道所成的像在主瓣與柵瓣處有不同的特點,為成像中的柵瓣抑制奠定基礎(chǔ)。研究了三種陣列的配置方法,達(dá)到了較低的柵瓣水平。首先研究了收發(fā)分置MIMO陣列的配置問題,可以根據(jù)需要的柵瓣水平及分辨率設(shè)計陣列。然后研究了收發(fā)共置MIMO陣列,對天線數(shù)為4和大于4的情況分別提出一種性能優(yōu)越的配置方法,并對后面一種方法做了改進(jìn),提高了陣列的效率。最后研究了二維陣列,分別提出了單程和雙程陣列配置方法,比已有方法的柵瓣更低。接著在成像域研究抑制柵瓣的方法。介紹了相干因子(Coherence Factor,CF)與相位相干因子(Phase Coherence Factor,PCF),說明它們能夠抑制方位向柵瓣而非距離向旁瓣。因而提出CF與PCF結(jié)合雙切趾(Dual Apodization,DA)的方法,可以同時抑制方位向柵瓣與距離向旁瓣。為進(jìn)一步抑制柵瓣,提出利用步進(jìn)頻信號子頻段的CF與PCF的改進(jìn)方法,比CF與PCF抑制柵瓣的能力更強(qiáng),且能抑制距離向旁瓣。最后研究利用子孔徑的柵瓣抑制方法,介紹了孔徑差分方法和互相關(guān)方法,分析了這兩種方法抑制柵瓣的優(yōu)缺點,并提出了互相關(guān)加權(quán)孔徑差分的方法,能夠大幅抑制柵瓣。這些方法已成功應(yīng)用于穿墻雷達(dá)成像,切實能夠抑制柵瓣,提高成像質(zhì)量。
[Abstract]:The electromagnetic wave which can penetrate the wall and other non-metallic obstacles in low frequency band has a broad prospect of development. It has important application value in the military and civilian fields such as anti-terrorism rescue and security inspection. The UWB radar system based on multiple input multiple output (Multiple-Input Multiple Output,MIMO) arrays can provide high resolution radar images, which is conducive to subsequent detection, tracking and other work, and has the advantages of high real-time, low cost and so on. Considering the portability of wall-penetrating radar systems and in order to save the cost MIMO arrays usually use sparse arrays with a small number of antennas and spacing larger than wavelength. Therefore, the gate lobe will inevitably appear, causing false images and reducing the imaging quality. Therefore, the problem of gate lobe suppression caused by sparse array is studied in this paper. The pattern of single pass array is studied and the origin of gate lobe is analyzed from the waveform. It is pointed out that the uniform and equal amplitude weighted single pass array has higher azimuth resolution and lower level of gate lobe. Because of the imaging of dual-pass array in radar, the concept of equivalent array is introduced, which is an important tool to transform two-pass array into single-pass array. Different dual-pass arrays have different single-pass equivalent arrays and different levels of gate lobes. Therefore, the weight and position of array elements are designed by array configuration, which can reduce the level of grid lobe and restrain gate lobe. From the point of view of imaging, the BP imaging algorithm of stepping frequency signal is introduced, and it is pointed out that the image generated by each channel has different characteristics at the main lobe and the gate lobe, which lays a foundation for the suppression of the gate lobe in the imaging process. Three kinds of array configuration methods are studied, and the lower gate lobe level is achieved. Firstly, the configuration of transceiver split MIMO array is studied. The array can be designed according to the level and resolution of grid lobe. Then we study the transceiver co-set MIMO array, and propose a superior performance configuration method for the antenna number of 4 and greater than 4, and improve the latter method to improve the efficiency of the array. Finally, the two-dimensional array is studied, and the single-pass and two-way array configurations are proposed, which are lower than the existing gate lobes. Then the method of suppressing the grating lobe is studied in the imaging domain. Coherence factor (Coherence Factor,CF) and phase coherence factor (Phase Coherence Factor,PCF) are introduced. It is shown that they can suppress azimuth gate lobe rather than range sidelobe. Therefore, a double toe cutting (Dual Apodization,DA) method combined with CF and PCF is proposed, which can suppress both azimuth gate lobe and distance sidelobe. In order to further suppress the gate lobe, an improved method using step frequency signal subband CF and PCF is proposed, which is more powerful than CF and PCF in suppressing the gate lobe and can suppress the distance sidelobe. Finally, using the subaperture gate lobe suppression method, the aperture difference method and the cross-correlation method are introduced. The advantages and disadvantages of these two methods are analyzed, and the cross-correlation weighted aperture difference method is proposed, which can suppress the gate lobe greatly. These methods have been successfully applied to wall penetrating radar imaging, which can effectively suppress the grating lobe and improve the imaging quality.
【學(xué)位授予單位】：國防科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TN957.52

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