Radiometric Active Indoor Imaging in the W-Band

Millimeter wave passive imaging systems constitute a good compromise between resolution and penetration depth for a variety of imaging applications. In an outdoor scenario, the cold sky radiation, interacting with the reflectivity characteristics of the targets, constitutes the main source of contrast in the acquired images. In indoor applications such a source is not available, and higher thermal sensitivity is required. Alternatively, one has to provide an artificial illumination to the scene in order to increase its dynamic range. The implementation of an active source for a passive radiometer can, under certain conditions, increase the contrast of the images acquired and add extra information to the measurement. With such a setup, outdoor systems can be used for indoor observations (the absence of cold sky radiation is compensated with active illumination). The subject of our study is to better understand which kind of source and which setup can provide a diffuse illumination over the targets. This topic was investigated by conducting observations of various indoor scenes with two radiometers in the W-Band, using noise and continuous wave (CW) sources as illumination. In this paper we present the results achieved and our conclusions in order to provide an efficient illumination for indoor environment.     

单星条件下基于被动测距的弹道参数估计性能分析

在天基光学监视系统中,根据有限的导弹助推段观测信息估算目标的弹道参数是衡量系统性能的重要指标,对支持目标识别分类、判定威胁程度都有重要意义。本文针对单星观测条件下提高弹道参数估计精度的迫切需求,提出了天基条件下利用氧气A吸收带被动测距提高估计精度的方法。利用MODTRAN对不同大气模型、不同气象、不同信噪比条件下的天基被动测距能力进行了仿真分析,在此基础上深入分析被动测距技术对弹道参数估计精度的提升能力,并与传统经验方法进行对比。仿真表明本文方法能够有效提高单星观测下的弹道参数估计精度。     

一种单站瞬时无源定距技术研究

在无源探测中,对距离的获取是一个关键问题。本文利用线性天线阵,提出了一种基于相位差的差的单站瞬时无源定距技术,并就这种定距技术的精度、解相位模糊、长基线测量精度、长基线情况下相位差的测量、通道校正等一系列关键问题进行了分析。研究表明,本文提出的定距技术在现有工程技术条件下是可行的。     

PRF-ambiguity resolving by wavelength diversity

For high-precision synthetic aperture radar (SAR) processing, the determination of the Doppler centroid is indispensable. The Doppler frequency estimated from azimuth spectra, however, suffers from the fact that the data are sampled with the pulse repetition frequency (PRF) and an ambiguity about the correct PRF band remains. A novel algorithm to resolve this ambiguity is proposed. It uses the fact that the Doppler centroid depends linearly on the transmitted radar frequency for a given antenna squint angle. This dependence is not subject to PRF ambiguities. It can be measured by Fourier-transforming the SAR data in the range direction and estimating the Doppler centroid at each range frequency. The achievable accuracy is derived theoretically and verified with Seasat data of different scene content. The algorithm works best with low contrast scenes, where the conventional look correlation technique fails. It needs no iterative processing of the SAR data and causes only low computational load     

Airborne imaging radiometer scan simulation

An imaging radiometer scan simulation program is developed for comparing the performance of different scan patterns and process behavior under varying circumstances. The program gives the radiometer's antenna beam the desired scan motion over an artificial target scene, computes the antenna radiometric temperature as the convolution of the antenna pattern with the scene brightness temperature deviation, computes a moving average of the antenna output, and records the data values as well as the corresponding coordinates at the sampling moments. The simulation indicated that a helicopter-borne imager needs at least passive attitude stabilization. In addition, the state-of-the-art sampling rate was found to be too slow, if the sampling period is set equal to the integration time. A detailed study revealed the achievable spatial resolution (line pairs/length unit-definition) to be 1.0-1.2×footprint dimensions, but the integration and sampling periods should be as short as 0.2-0.4×footprint dimensions     

采用天线组阵辅助的连线干涉测量载波相位解模糊

针对航天器初始轨道精度无法满足连线干涉测量（CEI）载波相位解模糊需求的问题,提出了一种采用短基线天线阵辅助的解模糊方法。从理论上分析了载波相位模糊产生的原因以及不同方向角、不同基线长度条件下解模糊对轨道预报精度的最低要求,对具有代表性的1 km短基线天线阵在主站测距加两基线方向角（Rlm）体制下的定位精度进行了仿真,结果表明,方向角越大,该方法的无模糊基线长度扩展能力越强。最后给出了达到最优测角精度的基线长度设置和解模糊流程。     

基于红外被动测距的基线拟合算法研究

为了实现红外光谱被动测距技术的准确测距以及透过率的精确计算,采用插值法进行了基线拟合算法研究。以氧气A带为例,利用逐线积分计算出A吸收带两边的带外数据,采用多种插值拟合方法来拟合,进行了详细的理论分析和仿真验证。通过几种拟合结果的对比,多项式插值拟合取得了比较好的结果,拟合精度最高。结果表明,多项式插值拟合基线算法为建立透过率和距离等条件的数据库提供了方法,为被动测距的实时测量提供了坚实的基础。     

基于MEMS的红外动态图像生成技术

提出了一种基于MEMS技术的红外动态图像生成技术。利用热传导方程,建立了可见光/红外图像转换膜的理论模型;介绍了可见光/红外图像转换膜制作的工艺流程,制作了一张像元数为512512、像元尺寸为35m的可见光/红外图像转换膜。并利用转换膜构造了红外动态图像生成装置,通过实验对红外动态图像生成装置的性能进行了研究。利用MEMS技术制作的可见光/红外图像转换膜可以工作在红外3~5m和8~12m两个波段。根据实验测得红外图像生成装置的空间分辨率为14 lp/mm,在3~5m波段,所生成红外图像的温度范围为250~440 K,在8~12m波段,所生成红外图像的温度范围为250~400 K。     

ASTER DEM performance

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument onboard the National Aeronautics and Space Administration's Terra spacecraft has an along-track stereoscopic capability using its a near-infrared spectral band to acquire the stereo data. ASTER has two telescopes, one for nadir-viewing and another for backward-viewing, with a base-to-height ratio of 0.6. The spatial resolution is 15 m in the horizontal plane. Parameters such as the line-of-sight vectors and the pointing axis were adjusted during the initial operation period to generate Level-1 data products with a high-quality stereo system performance. The evaluation of the digital elevation model (DEM) data was carried out both by Japanese and U.S. science teams separately using different DEM generation software and reference databases. The vertical accuracy of the DEM data generated from the Level-1A data is 20 m with 95% confidence without ground control point (GCP) correction for individual scenes. Geolocation accuracy that is important for the DEM datasets is better than 50 m. This appears to be limited by the spacecraft position accuracy. In addition, a slight increase in accuracy is observed by using GCPs to generate the stereo data.     

An optimal linear and elliptical antenna array design using black widow optimisation for 5G communication

This research illustrates a precise linear and elliptical antenna array design for synthesising the optimal far-field radiation pattern in the fifth-generation (5G) communication spectrum using a meta-heuristic optimisation technique known as black widow optimisation (BWO). 5G communication is an emerging technology with revolutionary changes in the wireless communication system with ultra-high data rate, enhanced capacity, low latency and good quality of service. An accurate antenna array design for an ideal far-field radiation pattern synthesis with a suppressed side lobe level (SLL) value and half power beam width (HPBW) is the most crucial aspect of 5G communications. A suppressed SLL is necessary to reduce interference in the entire side lobe region, whereas a low HPBW is required for long-distance communication. Here, the BWO is employed to find the optimal feeding current to each array element to lower the SLL and the HPBW value. The BWO algorithm sustains impeccable equity between the exploration and exploitation stages to impact different potential regions of the search space and generate new solutions to attain the global optima by evading the trap of local optima. The design examples of the linear antenna array (LAA) and elliptical antenna array (EAA) are illustrated in this article by applying the optimal feeding currents to each array element. Compared to the uniform antenna array and methodologies described in the recently published literature, the results obtained utilising the BWO algorithm for designing the LAAs and EAAs demonstrate a substantial development in the reduction of SLL and HPBW.     

Antenna factor of compact antenna range for EMC measurements above1 GHz

A formula is proposed for measuring the antenna factor of an offset-fed parabolic reflector operated as a compact antenna range (CAR) by considering the plane-wave approximation and field-distribution in the collimated region. The antenna factor is determined from the half power beamwidth (HPBW) of the feed, the physical geometry of the reflector and a field-distribution correction factor. The proposed formula is in good agreement with the measured results using a standard double-ridged horn antenna as the feed. The formula can be used to design CARs for EMC applications     

结合空间域与变换域特征提取的盲立体图像质量评价

针对立体图像质量预测准确性不足的问题,该文提出了一种结合空间域和变换域提取质量感知特征的无参考立体图像质量评价模型。在空间域和变换域分别提取输入的左、右视图的自然场景统计特征,并在变换域提取合成独眼图的自然场景统计特征,然后将其输入到支持向量回归(SVR)中,训练从特征域到质量分数域的预测模型,并以此建立SIQA客观质量评价模型。在4个公开的立体图像数据库上与一些主流的立体图像质量评价算法进行对比,以在LIVE 3D Phase I图像库中的性能测试为例,Spearman秩相关系数、皮尔逊线性相关系数和均方根误差分别达到0.967,0.946和5.603,验证了所提算法的有效性。     

CO2相干激光多普勒测速的研究

叙述运用ＣＷＣＯ２相干激光雷达测量运动目标速度的原理和实验装置，并给出了实验结果，测速精度为０．０１ｍ／ｓ速度分辨率为０．０５ｍ／ｓ，外场实验表明，对于漫射目标，作用距离２００ｍ。     

基于矩量法的螺旋天线设计

螺旋天线具有宽波束、圆极化等特性。以往的轴向螺旋天线多为端射式,辐射方向单一。为弥补这一不足,提出了一种新型的中馈轴向螺旋天线。基于RWG(Rao-Wihon-Glisson)边元的矩量法,采用MATLAB仿真计算出中馈螺旋天线的方向图、反射系数、增益等重要参数。又利用高频结构仿真软件(HFSS)对所设计的中馈螺旋天线进行了仿真。通过两种方法仿真得到的结果吻合较好,仿真结果的正确性得到了验证。实验结果表明:中馈轴向螺旋天线不仅具有以往轴向螺旋天线所具备的定向性好和高增益等优点,还具有两个反向且强度相同的辐射方向,同时天线增益可以达到8dB以上,半功率波束宽度可达33°。这种天线可以应用到多边通信及中继通信等领域。     

基于零折射超材料的双频高增益微带天线*

基于双面对称单环开口谐振器对结构奇异的电磁特性,设计了一种频率可控的各向异性零折射超材料。将这种零折射超材料应用于普通双频微带天线,制备了中心频率为5. 15GHz 和6. 8GHz 的零折射双频微带天线。仿真和测试结果显示,由于零折射超材料的引入,天线的侧向辐射减弱,方向性增强。在低频工作时,零折射微带天线E 面和H 面半功率波束宽度分别减小了29°和10°,增益提高了2. 2 dB。在高频工作时,零折射微带天线E面和H 面半功率波束宽度均减小了16毅,增益提高了2. 4 dB。将零折射超材料应用于微带天线的介质基板,为高性能双频微带天线设计提供了有效途径。     

A half-moon antenna

This work presents a half-moon antenna (HMA), which is composed of two semi-circular top and bottom conducting plates joined by a rectangular conducting plate. The HMA has a wide radiation beam. Radiation in the y-z plane (in the E plane) is hemispherical with a half-power beam width (HPBW) of more than 200/spl deg/. Radiation in the x-y plane (in the H plane) forms a sector beam with an HPBW of more than 100/spl deg/. To reduce the backward radiation and improve the gain, chokes are added to the HMA. An increase in the gain of approximately 1 dB is obtained. In order to obtain a tilted beam, the radius of the bottom plate is reduced. The maximum beam direction of the tilted beam /spl theta//sub max/ is not sensitive to frequency. Within a frequency range of 11 to 14 GHz (24%), /spl theta//sub max/=167/spl deg//spl plusmn/2/spl deg/. The gain is found to be G=9.5/spl plusmn/0.5 dBi within this same frequency range.     

Ground plane impact on quadrifilar helix antenna performance with respect to deployment heights

Quadrifilar helix antenna (QHA) has its applications in satellite communications. This paper presents the performance optimisation of input and radiation characteristics of QHA in the presence of infinite and finite metallic ground planes. For the infinite ground plane, it has been observed that input parameters such as impedance and voltage standing wave ratio (VSWR) are stable, and the antenna has broader half power beamwidth (HPBW). Smaller metallic platforms that act as finite ground planes produce better 3‐dB axial ratio beamwidth and boresight axial ratio. Deployment of QHA on smaller metallic platforms such as nanosatellites and CubeSats enhances the circularly polarised beamwidth of the antenna with improved boresight axial ratio. However, on large low earth orbit (LEO) satellites, stable input characteristics and broader HPBW have been achieved at the cost of narrow circularly polarised beamwidth and degraded boresight axial ratio.     

Beamsteering for Non-uniform Weighted Array-Fed Reflector Antenna

In this paper, a beamsteering scheme for an array-fed paraboloid reflector antenna is proposed. In this method, a non-uniform amplitude weighting strategy is used in order to demonstrate an offset fed for the reflector antenna. Steered beam is kept in shape in terms of half power beam width (HPBW) and relative side lobe level (RSLL). To do so, an analytical derivation of beam pattern is performed for the array-fed reflector antenna. Two standard non-uniform weighting techniques, Binomial and Dolf-Tschebyscheff, are employed for this reason. Finally, a multi-object optimization method is proposed to provide the best weighting. The computer simulations are performed for different multi-object optimization scenarios. The results reveal an improvement beam shape in terms of HPBW and RSLL traditional non-uniform weighing methods.

     

基于FPGA的宽带线性调频信号的产生与实现北大核心CSCD

随着激光雷达技术的迅速发展,激光雷达的作用距离、分辨力和测量精度等性能指标不断提高。为了提升测量精度和距离分辨力,要求发射信号具有大的带宽。宽带线性调频信号有助于提高激光雷达的距离分辨力。针对远程测距中激光雷达测距精度低的问题,本文首先分析和比较了几种产生宽带线性调频信号的方法,针对远程测距的应用场景,提出并设计了一种宽带线性调频信号的实现方法。通过Matlab仿真实验,证明实验实现的可行性。最后在FPGA上进行实现,产生了带宽为150 MHz,距离分辨力为1 m的宽带线性调频信号。     

基于子孔径Keystone变换的曲线轨迹大斜视SAR回波模拟

大机动条件下的曲线轨迹大斜视SAR系统传递函数具有复杂的多维空变性,现有的高效频域回波模拟算法均难以实现扩展场景的高精度回波模拟。为此,该文提出一种基于子孔径Keystone变换的机动SAR回波模拟方法。该方法根据距离徙动校正后的距离压缩函数对场景的距离压缩回波进行快速模拟,然后通过高精度的距离向逆处理实现扩展场景的回波模拟。为减少残余距离徙动对回波模拟精度的影响,距离向处理过程中采用子孔径Keystone变换的方法实现空变距离徙动的精确校正。理论分析和仿真结果表明,所提方法能够快速高精度地模拟扩展场景的机动平台大斜视SAR原始回波数据。