Imaging Simulation for MMW Synthetic Aperture Radiometer

A synthetic aperture radiometer is a new type of passive remote sensing instrument that can reach high spatial resolution. Restricted by antenna element size and operating wavelength, however, the system design is difficult at MMW band. In this paper, main technical parameters optimization of a synthetic aperture radiometer is discussed. Based on low-redundancy linear arrays, a millimeter wave synthetic aperture radiometric imaging scheme is presented. The simulation experimental results show that the system imaging effect depends on the synthetic aperture antenna pattern.     

一种新的机载单站无源定位方法

根据合成孔径技术原理,提出一种基于合成孔径雷达成像原理的机载单站无源定位方法。提出电子战系统中的合成孔径构造方法,分析这种无源定位方法的定位误差分布。通过仿真确定了合成孔径的建立时间与定位精度的关系。     

用于被动式毫米波成像的小型化Ka波段接收机

研制了一种工作于Ka波段用于被动式毫米波成像的基于单片微波集成电路(MMIC)的小型化接收机.该接收机主要由毫米波宽带低噪声放大器模块、毫米波小信号二极管检波器和视频放大电路组成.设计、制作、测试了接收机各个组成模块,对接收机的整体特性进行了测试.测试结果表明,该接收机的有效带宽约为7.4GHz、噪声小于3.8dB、增益约为30dB.应用喇叭天线和该接收机获得的一些毫米波图像表明,该接收机可以应用于被动毫米波成像.     

综合孔径微波辐射计二阶量化数字相关器研究

微波辐射计作为一种无源遥感器,在遥感技术领域有着巨大的应用前景.传统的微波辐射计的空间分辨率受到天线孔径的限制.综合孔径微波辐射计利用了干涉测量原理和复相关技术,是一种可以有效地提高空间分辨率的新型辐射计.本文针对综合孔径微波辐射计的数字相关器进行了深入研究,分析论证了二阶量化数字相关器的工作机理,并对采用该种相关器的系统的信噪比进行了分析.初步的试验验证结果证明了该方案的有效性.     

一种多体制兼容的微波成像新技术

虚拟透镜成像技术是一种可以兼顾远、中、近不同距离的成像新技术,但该技术是在被动成像的基础上发展起来的,适用于被动成像、半主动成像以及常规相控阵成像。在主动全息成像以及合成孔径成像系统中,由于天线单元依次工作并收发信号,目标回波信号具有不同的传播路径和相位延迟特性,因而不能直接采用虚拟透镜成像技术。文中对虚拟透镜成像技术进行扩展,针对主动全息成像和合成孔径成像的特点,引入了阵列属性参数,将其与信号传播路径和相位延迟特性进行关联,建立了一种多体制兼容的成像快速算法统一架构,并对相位加权算法进行了优化。所提出的新算法适用范围更广泛,且相位加权算法简洁易实现。最后进行了成像验证,实验及仿真结果证实了新算法的有效性。     

ANALYSIS OF WAVEFORM ERRORS IN MILLIMETER-WAVE LFMCW SYNTHETIC APERTURE RADAR

In remote sensing applications, there is a special interest in the lightweight, cost effective, and high resolution imaging sensors. The combination of linearly frequency modulated continuous wave (LFMCW) technology and synthetic aperture radar (SAR) technique can lead to such a sensor. This paper concentrates on the analysis of waveform errors in millimeter-wave (MMW) LFMCW SAR. The generating scheme of millimeter-wave LFMCW waveforms with phase locked loop (PLL) and direct digital synthesizer (DDS) combined frequency synthesizer is investigated. The impacts of quantization errors, spurs, and frequency nonlinearities are analyzed. Simulation results show that the quality of LFMCW waveforms has a direct influence on the SAR images. Hence a scheme of frequency synthesizer to achieve high performance MMW LFMCW waveform is proposed. This synthesizer driven by a DDS array can adaptive suppress the spurious level without degradation of excellent frequency linearity and fast switching speed.     

一种毫米波全息成像系统方案及其仿真

提出了一种双频毫米波全息成像系统方案。该方案不仅可以准确地测定目标与成像雷达天线口径的距离,而且可以对一定距离但事先未知的目标进行全息成像。相比于需要放置在预知位置的美国太平洋西北国家实验室研究的单频和宽带毫米波全息成像系统,该方案具有更为广泛应用的潜力,不仅可以用于个人携带的藏匿武器或者违禁物品的检查,还可以作为毫米波成像雷达用于军事目的。文中根据该成像系统确定了毫米波全息成像方法,建立了相应算法,给出了成像仿真结果。该方案可对实际系统设计提供一定参考。     

Development of a Multiband Passive Scanning Imager

A passive scanning imaging system that can operate at multiband spectra covering infrared, THz, and MMW regions has been developed. A high-quality optical system, which consists of a scanning swing planar mirror and a concave mirror, is used to be compatible in different frequency ranges. An elliptical aperture is opened at the center of the swing mirror to allow the focused light to pass through. Four types of detectors that contain two homemade bolometric detectors are used to distinguish images that range from infrared to millimeter waves. Our results demonstrate that the reflection-type imaging system performs well and exhibits compatibility to operate at different frequencies.     

FM—CW SAR系统及其发展概况

FM-CW SAR是一种新近被提出来的成像雷达体制，它结合连续波与合成孔径成像技术，具有体积小、重量轻、成本低、分辨率高等一系列优点。文章概述了FM-CW SAR系统及其信号处理特点，讨论了FM-CW SAR系统实现的难题所在；归纳了目前FM-CW SAR的几种应用背景及其主要参数；根据FM-CW SAR发展概况，讨论了FM-CW SAR进一步的发展趋势。     

一种基于回波相关的无源合成孔径雷达成像方法

利用机会照射源的无源雷达因为可以解决频带拥挤和具有良好的电子对抗性能,是雷达领域的一个研究热点。鉴于大多数机会照射源发射窄带或超窄带的连续波信号,该文研究采用窄带连续波信号的无源合成孔径雷达(SAR)成像。通过不同接收机回波之间进行相关,建立成像的数据模型,并给出一种滤波反投影(FBP)成像算法,详细分析了影响该成像方法分辨率的因素。通过仿真实验,验证了基于回波相关和FBP的无源SAR成像方法。该方法无需发射机位置信息,适用于任意载机飞行轨迹。     

干涉合成孔径辐射计的相位误差分析

干涉合成孔径辐射计是一种被动成像手段,可以根据目标和背景的亮温差别,实现目标探测功能,在揭露伪装、发现隐蔽目标方面有应用价值。介绍了干涉综合孔径辐射计成像基本原理,给出了一种毫米波干涉综合孔径成像系统的系统结构,分析了通道间相位误差对其性能的影响,设计了消除相位误差的校准方案,并对校准方案进行了仿真分析。     

合成孔径激光雷达下视三维成像构型及算法

传统激光三维成像均采用实孔径成像技术,其分辨率会随着作用距离的变远而降低。相比于实孔径成像,合成孔径成像的一个显著优势是沿航向的分辨率不随作用距离的变化而变化。基于合成孔径技术提出一种合成孔径激光三维成像雷达的工作模型。该系统采用激光泛光发射模式和多波束相干接收,首先,在高度向,采用大时宽带宽的线性调频信号,并利用解线频调技术实现高分辨率;其次,沿航向利用合成孔径技术频域压缩算法实现高分辨率,其中考虑到激光调频信号的长扫频周期,对于平台连续运动引入的多普勒平移项进行了补偿;在跨航向通过实孔径阵列实现高分辨率。最后,通过仿真实验验证了该系统的有效性。     

Synthetic aperture radiometry evaluated by a two-channeldemonstration model

The Technical University of Denmark (TUD) Synthetic Aperture Radiometer (SARad) is a two-channel demonstration model that can simulate a two-dimensional (2D) thinned array radiometer having an unfilled aperture populated with several small antenna elements. Aperture synthesis obtained by interferometric measurements using the antenna elements in pairs, followed by an image reconstruction based on an inverse Fourier transform, results in an imaging instrument without the need of mechanical scan. The thinned aperture and the nonscanning feature make the technique attractive for spaceborne radiometer systems, especially at low frequencies. The TUD SARad demonstration model consists of a two-channel K_u-band correlation radiometer with two horn antennas and an antenna mounting structure enabling the horns to be mounted in relevant positions within a certain aperture. A total aperture synthesis is obtained by sequentially placing the two antenna elements in all required pairs of positions and measuring the corresponding samples of the visibility function. The system has been used to demonstrate 2D synthetic aperture imaging of complex targets in outdoor ground experiments, a special feature of the system is that it uses a focused antenna system, thus enabling a short distance to the target. Set still utilizing image reconstruction algorithms identical to those used in a normal far-field situation. The aperture synthesis theory is discussed, with special emphasis on focused systems; the radiometer system is described; and images suitable for demonstration of resolution and other imaging properties are presented and discussed     

一种220GHz 波段太赫兹合成孔径成像雷达

微波频段的机载合成孔径成像雷达在对地观测方面具有广泛应用,但其合成孔径成像积累时间长,成像帧率低,提高雷达工作频率能够减小合成孔径所需转角,提高成像帧率。设计了一种工作在220GHz 波段的太赫兹合成孔径成像雷达系统,采用收发天线分置、发射宽带线性调频连续波的体制,最大信号带宽4. 8GHz,输出信号功率约20mW。宽带回波信号幅度相位经外标校补偿,通过成像试验,验证了太赫兹ISAR 与SAR 成像分辨率约3.2cm,可实现5Hz 的成像帧率,证明太赫兹波段能够大幅提升成像帧率,满足快速成像的要求。     

CGLS 算法在综合孔径微波辐射计中的应用

高效的反演成像算法是综合孔径微波辐射计的关键技术之一。由于综合孔径微波辐射计反演成像在数学上是病态的反问题,所以需要进行正则化处理以克服其病态特性而获得稳定的解。与直接正则化方法相比,共轭梯度最小二乘(Conjugate Gradients Least Squares, CGLS)迭代法具有无须明确正则化参数、无须对传递矩阵求逆等优点。提出将共轭梯度最小二乘法应用于综合孔径辐射计成像中,并基于全极化干涉式微波辐射计(Full Polarization Interferometric Radiometer, FPIR)系统,比较了其与经典的最小范数正则化的性能。仿真结果表明:与最小范数正则化相比,CGLS 正则化算法能有效降低FPIR 系统图像反演误差,以获取高精确度的观测场景的亮温分布满足FPIR 系统探测海面风场、海表面盐度和土壤湿度等应用需求。     

Analysis of ground target stealth based on Passive Millimeter-Wave detection

Passive Millimeter-Wave（MMW）detection has become a threat to ground targets.To enhance the survivability of the ground target in the future battlefield,passive MMW stealth technology is analyzed in this paper.Based on the passive MMW detection principle,computation and analysis are made for the MMW apparent temperature of tank in different actual combat conditions.The necessity of the passive MMW stealth is analyzed and the passive MMW stealth methods are also studied.     

基于光子学处理技术的被动毫米波成像

提出了一种采用电光调制和光子学处理技术的被动毫米波扫描成像方法.该成像方法中辐射计通过电光调制将毫米波信号转换到光波频率,采用光子学滤波器和光电探测器进行信息获取和处理.阐述了毫米波辐射信号光子学处理的工作原理,研究了器件参数对信号转换的影响,分析了该处理方法中系统的噪声特性.依据上述原理设计了一个基于光子学技术的机械...     

Cassini RADAR Sequence Planning and Instrument Performance

The Cassini RADAR is a multimode instrument used to map the surface of Titan, the atmosphere of Saturn, the Saturn ring system, and to explore the properties of the icy satellites. Four different active mode bandwidths and a passive radiometer mode provide a wide range of flexibility in taking measurements. The scatterometer mode is used for real aperture imaging of Titan, high-altitude (around 20 000 km) synthetic aperture imaging of Titan and Iapetus, and long range (up to 700 000 km) detection of disk integrated albedos for satellites in the Saturn system. Two SAR modes are used for high- and medium-resolution (300–1000 m) imaging of Titan's surface during close flybys. A high-bandwidth altimeter mode is used for topographic profiling in selected areas with a range resolution of about 35 m. The passive radiometer mode is used to map emission from Titan, from Saturn's atmosphere, from the rings, and from the icy satellites. Repeated scans with differing polarizations using both active and passive data provide data that can usefully constrain models of surface composition and structure. The radar and radiometer receivers show very good stability, and calibration observations have provided an absolute calibration good to about 1.3 dB. Relative uncertainties within a pass and between passes can be even smaller. Data are currently being processed and delivered to the planetary data system at quarterly intervals one year after being acquired.      

镜面反射综合孔径成像方法研究

常规的综合孔径成像方法需要进行相干探测,阵列单元为结构复杂的超外差结构,随着成像频率的增加,其研制难度和性能要求将限制综合孔径成像技术在高频段的发展。文章提出的镜面反射综合孔径成像方法采用非相干探测方法,通过探测器阵列或单元扫描对目标场景进行幅度(功率)探测即可获得可视度函数,然后通过成像反演方法获得场景的亮温图像。镜面反射综合孔径成像方法使用的非相干探测单元结构简单,实现难度低,可避免在高频段实现综合孔径成像的难点。镜面反射综合孔径成像方法相比常规综合孔径成像方法实现相同的成像结果可节约一半的天线阵列孔径,并且最少只需一个阵列单元即可实现综合孔径成像。通过理论分析、仿真计算和点目标源成像实验对镜面反射综合孔径成像技术进行了研究。镜面反射综合孔径成像技术为实现综合孔径成像技术提供了一种新途径。     

Compressed Sensing for Millimeter-wave Ground Based SAR/ISAR Imaging

Millimeter-wave (MMW) ground based (GB) synthetic aperture radar (SAR) and inverse SAR (ISAR) imaging are the powerful tools for the detection of foreign object debris (FOD) and concealed objects that requires wide bandwidths and highly frequent samplings in both slow-time and fast-time domains according to Shannon/Nyquist sampling theorem. However, thanks to the compressive sensing (CS) theory GB-SAR/ISAR data can be reconstructed by much fewer random samples than the Nyquist rate. In this paper, the impact of both random frequency sampling and random spatial domain data collection of a SAR/ISAR sensor on reconstruction quality of a scene of interest was studied. To investigate the feasibility of using proposed CS framework, different experiments for various FOD-like and concealed object-like targets were carried out at the Ka and W band frequencies of the MMW. The robustness and effectiveness of the recommend CS-based reconstruction configurations were verified through a comparison among each other by using integrated side lobe ratios (ISLR) of the images.