【摘要】：天基監(jiān)視雷達是陸-海-空-天一體化戰(zhàn)略預警監(jiān)視系統(tǒng)的重要組成部分,基于合成孔徑雷達(SAR)成像、逆合成孔徑雷達(ISAR)成像以及動目標顯示等多種技術(shù)手段和工作模式,同時具備監(jiān)視地面、海面目標以及空間目標的能力。天基監(jiān)視雷達搭載的觀測平臺運行于外部空間軌道,可以通過觀測高度的提升突破地球曲率的影響,同時憑借其較強的抗摧毀能力自由進出敵方控制區(qū)域,實現(xiàn)對全球任何熱點地區(qū)的連續(xù)監(jiān)視并提供充足的戰(zhàn)略防御監(jiān)視時間,因而具備全天時、全天候和全球覆蓋等優(yōu)點,可有效彌補地基、�；蜋C載監(jiān)視雷達的局限性和不足,在軍事和民用領(lǐng)域均得到了廣泛應用。天基監(jiān)視雷達系統(tǒng)可分為對地監(jiān)視模式和空間監(jiān)視模式。對地監(jiān)視模式中,天基監(jiān)視雷達指向區(qū)域的電磁環(huán)境相對較為復雜,包含非蓄意干擾和電子對抗中人為施放的各種窄帶干擾和寬帶干擾,由于天基監(jiān)視雷達發(fā)射信號的寬帶特性,使得對地監(jiān)視模式極易受到各類干擾源輻射信號的影響;空間監(jiān)視模式中,由于星載雷達發(fā)射功率孔徑積受限,且觀測空間目標的作用距離往往較遠(幾百公里~幾千公里),使得星載ISAR成像系統(tǒng)的回波信噪比降低,導致包絡(luò)對齊結(jié)果中出現(xiàn)明顯的突跳誤差和積累誤差,并最終影響ISAR成像質(zhì)量,為后續(xù)的圖像判讀及目標識別帶來障礙。本論文緊密圍繞天基監(jiān)視雷達系統(tǒng)對地監(jiān)視模式和空間監(jiān)視模式對各類目標實施監(jiān)視過程中的實際問題,針對復雜電磁環(huán)境下的SAR干擾抑制及低信噪比條件下的ISAR包絡(luò)對齊方法等關(guān)鍵技術(shù)進行深入研究。主要工作和貢獻為:1、對天基監(jiān)視雷達涉及的工作模式進行了介紹,分析了各類工作模式的特點;以條帶模式正側(cè)視情況為例,分析了對地監(jiān)視模式的回波信號基本模型;研究了天基監(jiān)視雷達系統(tǒng)對地監(jiān)視模式可能面臨的干擾類型及其信號形式和基本特點;結(jié)合天基監(jiān)視雷達的特點和任務要求,給出空間監(jiān)視模式工作模式總體方案設(shè)想;以直線運動模型為例,給出空間監(jiān)視模式的回波信號基本模型,并結(jié)合散射點斜距方程展開式詳細分析了天基ISAR面臨的主要問題及其產(chǎn)生原因。2、基于時變窄帶干擾信號模型,在充分考慮窄帶干擾信號時變特性的基礎(chǔ)上對時變窄帶干擾抑制問題展開深入研究,針對時變窄帶干擾條件下傳統(tǒng)窄帶干擾抑制方法性能下降問題,提出一種基于迭代自適應方法的時變窄帶干擾抑制方法。該方法無需進行參數(shù)搜索和模型定階,可以利用少量訓練樣本自適應迭代估計窄帶干擾信號頻譜,并采用子空間投影方法對干擾信號進行濾除。仿真結(jié)果表明所提方法能夠有效抑制窄帶干擾,并復原被遮蓋有用信號、重現(xiàn)SAR圖像細節(jié)信息,從而大幅改善時變窄帶干擾影響下的SAR成像質(zhì)量,具有良好的干擾抑制性能。3、基于天基監(jiān)視雷達寬帶非蓄意干擾的時頻聚集性,針對傳統(tǒng)時頻濾波方法頻率分辨率受限所導致的寬帶干擾抑制性能下降問題,提出一種SAR寬帶非蓄意干擾抑制方法。該方法無需進行參數(shù)搜索和模型定階,可以在短時傅里葉變換分析窗函數(shù)對應的小時寬范圍內(nèi),利用少量觀測數(shù)據(jù)自適應迭代估計寬帶干擾信號瞬時頻率,并采用子空間投影方法對干擾信號進行濾除,同時,還可獲得高分辨率且無交叉項的線性時頻分析結(jié)果。仿真分析表明所提方法能夠有效抑制寬帶干擾且有用信號損失較小,可以大幅改善寬帶干擾影響下的SAR成像質(zhì)量,具有良好的干擾抑制性能。4、針對低信噪比條件下傳統(tǒng)包絡(luò)對齊算法性能下降問題,提出基于迭代加權(quán)最小二乘擬合的ISAR包絡(luò)對齊方法(Iterative Cleaning and Weighted Least Squares,ICWLS)。該方法利用目標的平穩(wěn)運動特性,對目標走動量和加權(quán)矩陣采用迭代交替更新方式,在估計出目標運動參數(shù)的基礎(chǔ)上實現(xiàn)包絡(luò)對齊。上述方法基于數(shù)據(jù)懲罰構(gòu)造加權(quán)矩陣且采用對角形式,可顯著提高包絡(luò)對齊精度,但加權(quán)矩陣的估計尚未達到統(tǒng)計最優(yōu)。因此考慮根據(jù)包絡(luò)對齊誤差統(tǒng)計參數(shù)構(gòu)造最優(yōu)加權(quán)矩陣并進行迭代更新,提出一種迭代的最優(yōu)加權(quán)擬合包絡(luò)對齊方法(Iterative Optimized Weighted Fitting,IOWF),以期進一步優(yōu)化ICWLS方法包絡(luò)對齊性能。仿真結(jié)果表明所提方法能有效抑制突跳誤差的傳播和緩解積累誤差所導致的參數(shù)估計精度下降問題,具有良好的包絡(luò)對齊性能。
[Abstract]:The space-based surveillance radar is an important part of the land-sea-air-day integrated strategy early-warning monitoring system, and is based on various technical means and working modes such as synthetic aperture radar (SAR) imaging, inverse synthetic aperture radar (ISAR) imaging and moving target display, The capabilities of the sea and space targets. the observation platform mounted by the space-based monitoring radar is operated on an external space track, can break through the influence of the curvature of the earth by observing the elevation of the height, the continuous monitoring of any hot spot area in the world is realized and sufficient strategic defense monitoring time is provided, so that the invention has the advantages of all-day, all-weather and global coverage and the like, and can effectively make up the limitation and the defect of the foundation, the sea base and the on-board monitoring radar, It has been widely used in the military and civil fields. The space-based surveillance radar system can be divided into a local monitoring mode and a space monitoring mode. in the ground monitoring mode, the electromagnetic environment of the space-based monitoring radar pointing area is relatively complex, so that the ground monitoring mode is very easy to be influenced by various interference source radiation signals; in the space monitoring mode, because the star-borne radar transmission power aperture area is limited, and the action distance of the observation space target is often far from (several hundred kilometers to several thousand kilometers), so that the echo signal-to-noise ratio of the star-borne ISAR imaging system is reduced, the obvious process-jump error and the accumulation error in the envelope alignment result are caused, and finally the ISAR imaging quality is influenced, and the obstacle is brought for subsequent image interpretation and target recognition. In this paper, the real problems of the space-based surveillance radar system in the monitoring process of various targets are closely studied, and the key technologies such as the SAR interference suppression and the ISAR envelope alignment method under the condition of low signal-to-noise ratio are deeply studied. The main work and contribution are: 1. The work mode involved in space-based surveillance radar is introduced, the characteristics of various working modes are analyzed, and the basic model of the echo signals of the ground monitoring mode is analyzed in the case of the positive side view of the strip mode. This paper studies the type of interference that the space-based surveillance radar system may face in the ground monitoring mode and its signal form and basic characteristics. In combination with the characteristics and task requirements of the space-based surveillance radar, the general scheme of the working mode of the space monitoring mode is given. The linear motion model is an example. in this paper, the basic model of the echo signal of the space monitoring mode is given, and the main problems and the causes of the space-based ISAR are analyzed in detail with the expansion of the oblique distance equation of the scattering point. On the basis of fully considering the time-varying characteristics of the narrow-band interference signal, the problem of the interference suppression of the narrow-band interference in the time-span is studied. In the light of the problem of the performance degradation of the conventional narrow-band interference suppression method under the condition of the narrow-band interference, a method for suppressing the interference of the narrow-band interference in the time of the iterative adaptive method is proposed. in that method, a parameter search and a model order are not needed, a small amount of training sample can be used to adaptively and iteratively estimate the narrow-band interference signal spectrum, and a subspace projection method is adopted to filter the interference signal. The simulation results show that the proposed method can effectively suppress the narrow-band interference and recover the masked useful signal to reproduce the SAR image detail information, thereby greatly improving the SAR imaging quality under the influence of the narrow-band interference when the narrow-band interference is greatly improved, and has good interference rejection performance. Based on the time-frequency aggregation of the wideband non-intentional interference of the space-based surveillance radar, the problem of the performance of the wideband interference suppression caused by the limited frequency resolution of the conventional time-frequency filtering method is a problem, and a method for suppressing the SAR wideband non-intentional interference is proposed. the method does not need to perform parameter search and model order, can estimate the instantaneous frequency of the broadband interference signal by using a small amount of observation data in an hour wide range corresponding to the short-time Fourier transform analysis window function, and filter the interference signal by adopting a subspace projection method, At the same time, a linear time-frequency analysis result of high resolution and no cross term can be obtained. The simulation analysis shows that the proposed method can effectively suppress the broadband interference and the signal loss is small, can greatly improve the SAR imaging quality under the influence of the broadband interference, and has good interference rejection performance. An ISAR envelope alignment method based on iterative weighted least squares fitting (ICWLS) is proposed. The method utilizes the stationary motion characteristics of the target, adopts an iterative and alternating updating method to the target walking momentum and the weighting matrix, and realizes the envelope alignment on the basis of estimating the target motion parameters. in that method, the weight matrix is construct based on the data penalty, and the diagonal form is adopted, so that the envelope alignment precision can be obviously improved, but the estimation of the weight matrix has not reached the statistical optimal. Considering that the optimal weighting matrix is constructed according to the statistical parameters of the envelope alignment error and the iterative updating is carried out, an iterative optimal weighted fitting envelope alignment method (IWF) is proposed, with a view to further optimizing the envelope alignment performance of the ICWLS method. The simulation results show that the proposed method can effectively suppress the propagation of the process-jump error and reduce the estimation precision of the parameter estimation caused by the accumulation error, and has good envelope alignment performance.
【學位授予單位】：西安電子科技大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TN957.52

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本文編號：2364501