对地观测的微波散射成像方法

以微波为探测手段进行对地成像观测,能够全天候、全天时工作,在许多技术领域得到了重要应用,对微波成像的新思想、新体制、新技术的探索,也是一个非常活跃的研究领域。该文提出了一种新的微波成像方法,称为微波散射成像方法,该方法可采用收发分置工作方式,工作时只需要以单色波照射待成像地域。原理性成像模拟结果表明,使用这种方法可以获得被观测地域高几何分辨率和高辐射分辨率的微波图像。     

On the sensitivity and the resolution of microwave imaging using ART

The feasibility of using the presently available linear reconstruction techniques in microwave (MW) imaging was suggested and numerically demonstrated in a recent communication [1]. It was shown that although such techniques neglect reflection and refraction effects, they still can be used to obtain suitable MW images. This letter presents some calculated microwave images of phantoms simulating biological objects. These images were obtained using the algebraic reconstruction technique (ART) that was originally used in X-ray and ultrasound computerized tomographic imaging. The resolution and sensitivity of the microwave images are examined and suggestions for improvements are discussed.     

微波综合脉冲孔径雷达技术

低截获概率雷达是现代雷达的一个重要方向发展，但要实现低截获概率雷达的广泛应用尚需较长的时间。综合脉冲孔径雷达在低截获、抗反辐射导弹和抗干扰等性能上具有明显的优势，其基本原理和技术体制已经在米波频段得到了充分的验证，文中将综合脉冲孔径技术应用于微波频段，对微波综合脉冲孔径雷达的主要技术难点和主要性能进行了分析，研究表明其总体性能优于目前正在大力发展中的二维有源相控阵雷达，微波综合脉冲孔径雷达应该得到更广泛的关注和应用。     

微波光子认知雷达技术

针对宽带微波光子雷达易被外界电磁信号干扰,难以在复杂电磁环境下对多样化目标进行高速探测与识别的关键难题,本文提出一种能融合多个机会频带以实现高分辨率探测的微波光子认知雷达系统架构.探讨了与微波光子认知雷达系统相关的微波光子宽带实时频谱侦测、可重构波形产生和稀疏频带成像处理等关键技术,论证了方案的可行性.该方案充分发挥了...     

微波光子成像雷达技术发展综述

随着隐身化、无人化以及微型集群化目标的快速发展,精确获取目标形状和形态的情报需求,对微波成像雷达提出了大带宽和多频段的现实要求。得益于微波光子技术的低相噪、大带宽、宽调谐等显著优势,微波光子成像雷达技术已得到快速发展。本文对微波光子成像雷达研究现状进行了总结,对其典型系统架构和主要工作原理进行了研究分析,进一步结合系统能力优势给出了主要应用方向和相关成像实验结果,最后提出了进一步发展仍需解决的问题。     

Microwave density imaging of perfectly conducting objects in thenear-field region

Analytical and numerical studies of microwave diversity imaging of continuous and discrete conducting objects in the near-field region are presented. Analytical results show that the image of the scattering object can be reconstructed by Fourier inversion of the data acquired from the recorded scattered field using angular and frequency diversity techniques. Different feature information of the scattering object can be obtained using a polarization diversity technique. Various scattering arrangements are studied and compared on the basis of the reconstructed image quality and practical considerations. Numerical results show that the described frequency, angular, and polarization diversity techniques in the backward scattering arrangement can result in a cost-effective approach in near-field microwave imaging systems     

合成孔径雷达三维成像——从层析、阵列到微波视觉

合成孔径雷达3维成像技术可以消除目标和地形在2维图像上产生的严重混叠,显著提升目标识别和3维建模能力,已经成为当前SAR发展的重要趋势。合成孔径雷达3维成像技术经过了数十年的发展,已提出多种技术体制。该文系统性回顾了SAR 3维成像技术领域的发展过程,深入分析了现有SAR 3维成像技术的特点;指出了SAR回波及图像中蕴含的未被现有技术利用的3维信息,提出“合成孔径雷达微波视觉3维成像”的新概念和新思路,将SAR成像方法与微波散射机制和图像视觉语义有机融合,形成SAR微波视觉3维成像理论与方法,实现高效能、低成本的SAR 3维成像。该文重点阐述了SAR微波视觉3维成像的概念、目标和关键科学问题,并给出了初步的技术途径,为SAR 3维成像提供了新的技术思路。      

Terahertz Spectroscopy and Imaging for Defense and Security Applications

Terahertz (THz) radiation, which occupies a relatively unexplored portion of the electromagnetic spectrum between the mid-infrared and microwave bands, offers innovative sensing and imaging technologies that can provide information unavailable through conventional methods such as microwave and X-ray techniques. With the advancement of THz technologies, THz sensing and imaging will impact a broad range of interdisciplinary fields, including chemical and biological detections and identifications. In particular, THz radiation offers the opportunity for transformational advances in defense and security. Recent work shows that THz technologies are promising for the standoff detection and identification of explosive targets.     

Electromagnetic techniques for medical diagnosis: A review

In this paper, potential electromagnetic (EM) methods for medical diagnosis are reviewed. These include impedance plethysmography, microwave methods for lung water measurements, EM flowmeters, and microwave radiometry diagnostic techniques. Other techniques that are in preliminary research stages, such as EM imaging and use of microwave Doppler radar to monitor arterial wall movements, are briefly discussed. The principles underlying the operation of each method are described, along with comments about adequacy for medical diagnosis. The important experimental results that identify the advantages and the limitations of each method are presented. In most cases, it is clear that while the electromagnetic diagnostic techniques are attractive and promising, much more research is still needed before these methods are ready for full clinical use. Suggestions for future development and/or possible extensions are discussed.     

Three-dimensional millimeter-wave imaging for concealed weapondetection

Millimeter-wave imaging techniques and systems have been developed at the Pacific Northwest National Laboratory (PNNL), Richland, WA, for the detection of concealed weapons and contraband at airports and other secure locations. These techniques were derived from microwave holography techniques that utilize phase and amplitude information recorded over a two-dimensional aperture to reconstruct a focused image of the target. Millimeter-wave imaging is well suited for the detection of concealed weapons or other contraband carried on personnel since millimeter-waves are nonionizing, readily penetrate common clothing material, and are reflected from the human body and any concealed items. In this paper, a wide-bandwidth three-dimensional holographic microwave imaging technique is described. Practical weapon detection systems for airport or other high-throughput applications require high-speed scanning on the order of 3 to 10 s. To achieve this goal, a prototype imaging system utilizing a 27-33 GHz linear sequentially switched array and a high-speed linear scanner has been developed and tested. This system is described in detail along with numerous imaging results     

稀疏微波成像研究进展(科普类)

稀疏微波成像是将稀疏信号处理理论系统性地引入微波成像并有机结合形成的微波成像新理论、新体制和新方法。该文阐述了稀疏微波成像中稀疏表征与变换域映射、稀疏观测约束、以及非模糊重建等关键科学问题;在此基础上介绍了稀疏微波成像的主要研究进展以及原理样机的机载飞行实验,实验结果表明了稀疏微波成像原理和方法的可行性和有效性;另外,该文还讨论了稀疏微波成像在3 维雷达成像、逆合成孔径雷达、探地雷达等领域的应用。      

频率分集与极化分集网络

本文介绍了一种可以实现极化分集和双频频率分集的微波网络，具有变极化功能，它可以用于雷达系统中抗雨杂波和海杂波干扰，也可为雷达成象提供更多的信息量。     

Noninvasive imaging for the new century

Noninvasive imaging technologies are expected to play a significant role in the area of medical diagnosis and industrial imaging. The engineers of the 21st century will need the appropriate skill to master the power of new technologies. To face the challenges of the new century, a strong impulse toward a multidisciplinary and diversified engineering knowledge will be essential. Some examples of noninvasive imaging (spiral CT, microwave imaging, hybrid modalities) and image enhancement techniques are presented     

Space For Microwaves

The forty-eight technical papers of the 1965 MTT Symposium provide a great fund of detailed information of the state of the microwave art. In a more general sense, the content of the program also shows unmistakable trends which we must not ignore. Before devoting our attention to the specialized presentations to follow, let us pause to consider where we are headed in microwave theory and techniques. This is our eleventh symposium, and the microwave art is now about twenty-five years old. The record of those years is something to be proud of in scientific applications, in engineering, and in business enterprise---except perhaps for some recent microprofits.     

星载SAR技术的发展趋势及应用浅析

星载合成孔径雷达(Synthetic Aperture Radar, SAR)作为一种主动式微波成像传感器,能够不受天气、气候以及光线的影响,可以全天时、全天候地成像,因此,星载合成孔径雷达已发展成为一种不可或缺的对地观测工具。随着技术的进步,未来星载SAR将实现高分辨率宽测绘带、低成本、小型化、多基多模式微波成像,并具有地面运动目标指示的能力,在最小的成本下获得最丰富的地物信息。这迫切需要星载SAR系统在新模式、新体制、新技术方面取得重大突破。该文将围绕星载合成孔径雷达技术发展现状及未来趋势展开论述。      

A conductive plastic for simulating biological tissue at microwavefrequencies

A conductive plastic composite that exhibits complex dielectric properties similar to biological tissues over the electromagnetic spectrum of 300-900 MHz has been synthesized from compressed carbon black mixed with a castable thermoplastic (polyethyl methacrylate). This paper presents the techniques used to control the electrical properties of the conductive plastic and describes the challenges encountered in fabricating a material containing a high proportion of carbon black. While developed to serve as a housing material for a microwave antenna array for imaging biological bodies, the composite should be useful in any setting requiring a stable, solid, high loss material that simulates biological tissues over the microwave spectrum     

Prospects of microwave-induced thermoacoustic imaging

Microwave-induced thermoacoustic imaging (MTAI) has advantages including the large imaging depth, high imaging resolution, high imaging contrast, and fast imaging speed. The thermoacoustic (TA) group of South China Normal University has dedicated to developing TA imaging for more than a decade and has made many breakthroughs. This review introduces these breakthroughs from two aspects including the improvement in techniques and the exploration of applications. On the technological level, there are ultrashort microwave pulse (USMP)-induced TA imaging that can improve the imaging resolution, nonlinear thermoacoustic imaging (NTAI) that can improve the imaging contrast, polarized microwave-induced thermoacoustic imaging (P-MTAI) that can obtain cellular-level alignment information, and more convenient and accurate handheld and multimodal probes. On the application side, the optimization and expansion have been carried out, mainly concentrating on breast and myocardial imaging. Finally, several current research directions are introduced, including the application of P-MTAI on joint imaging and research on whole-body imaging of small animals.     

Polarization effects on microwave imaging of dielectric cylinder

Theoretical and experimental studies are presented of frequency-swept microwave imaging of an infinitely long lossless homogeneous dielectric cylinder not satisfying the Born approximation and illuminated by a right-hand circularly polarized plane wave. The reconstructed polarization-dependent microwave image is seen as embodying contributions from specular, axial, glory, and stationary ray components of the scattered field of the selected receiving polarization state. An automated microwave imaging system using frequency and polarization diversity techniques is used to verify the theoretical and numerical results     

The theory and mechanical realization of an ideal scanning methodfor a single-channel imaging microwave radiometer

The scan path of an imaging microwave radiometer is determined so that the desired area is totally covered, while the overlap between successive sweeps is minimized. This minimizes the number of redundant data points, which, in turn, leads to faster and more economical postprocessing. Different scanning methods and sampling techniques are discussed in brief. Conical scan is chosen and three different approaches are presented. A theory that relates the flight velocity to the angular velocity of the antenna beam to provide an ideal scan pattern is formulated for pendulum scan. Results of each scan method are presented and compared, and the best one is chosen. Some considerations about the mechanical realization and an outline of the instrument are presented     

An overview of ultra-wideband microwave imaging via space-time beamforming for early-stage breast-cancer detection

Ultra-wideband (UWB) microwave imaging has recently been proposed for detecting small malignant breast tumors. In this article, we review the current research status of this approach. First, we introduce the concept of microwave imaging via space-time (MIST) beamforming and related signal-processing algorithms. The objective of these signal-processing techniques is to form a spatial image of scattered microwave energy, and to identify the presence and location of malignant lesions from their scattering signatures. Next, we present numerical studies based on finite-difference time-domain simulations to demonstrate the efficacy of MIST beamforming for detecting small malignant breast lesions in both prone and supine configurations. Finally, the experimental feasibility of UWB microwave imaging is demonstrated using an initial imaging prototype and multilayered breast phantoms.