Calibration of a polarimetric imaging SAR

Calibration using point targets is discussed. The fourport network calibration technique is used to describe the radar error model. The processor ambiguity function and the radar distortion matrices are combined to form a generalized polarimetric ambiguity function. The polarimetric ambiguity function of the SAR is found using a single point target, namely a trihedral corner reflector. Based on the resultant polarimetric ambiguity function, an estimate for the backscattering coefficient of the terrain is found using a modified version of the single target calibration technique (STCT). A radar image recorded by the JPL aircraft SAR, which includes a variety of point targets, is used for verification of the new calibration method. The calibrated responses of the point targets are compared both with theory and responses based on the POLCAL technique     

An adaptive impedance tuning CMOS circuit for ISM 2.4-GHz band

The difficulties encountered in matching an antenna to its optimal impedance are reduced with an adaptive 0.35-/spl mu/m CMOS circuit based on several switched shunt capacitors arranged in capacitor banks and on a few external series inductors. As high-quality inductors are difficult to obtain in CMOS, the inductors are placed either in an low-temperature cofired ceramic (LTCC) substrate or is a lumped component outside the core circuit. The circuits, presented here through a range of simulations, are optimized to function within the ISM 2.4-GHz band, but the general approach employed to improve matching can be used for other frequency bands as well. The circuits discussed provide a VSWR/spl les/2 match for every impedance with VSWR/spl les/5. There is a 1-dB power loss for a perfect 50 /spl Omega//spl rarr/50 /spl Omega/ transformation, a break-even point at VSWR=1.5, and a 3-dB increase in delivered power for VSWR= 4.3.     

Linear transformations of the ambiguity function

The radar ambiguity function is useful as a criterion of goodness for modulation signals used to discriminate the range and range-rate of point targets. It is often desirable to change existing ambiguity functions to meet new specifications of resolvability. One way of accomplishing this task is by using linear transformations of the ambiguity function. A review of the properties of ambiguity functions pertinent to the paper is included. Sufficient conditions for linear transformations to result in new ambiguity functions are presented in several forms. Then, necessary and sufficient conditions for kernels of the linear transformations to correspond to linear signal transformations are derived.     

New calculation methods for echo-ranging ambiguity

In correlation echo ranging the ambiguity, or square of the signal autocorrelation envelope, is important, and two new approaches are presented that speed up general ambiguity calculations. Some signals such as linear FM can be represented by lines in a frequency-time plot, and for two such lines the cross ambiguity is associated with the point of crossing and depends on the angle of crossing. This method is extended to curved lines, including lines that touch rather than cross. Other signals have a noiselike modulation, and may be conveniently described by a distribution of spectral intensity in the frequency-time plot. For two such noise signals the mean value of the cross ambiguity depends very simply on the overlap of the two distributions. In the limit the two approaches are shown to give answers consistent with one another. In one illustrative application it is shown that, with symmetrical pulse forms, a high ambiguity at the extremes of the ambiguity diagram is always accompanied by an ambiguity concentration near the origin. In another example the ambiguity diagrams and general behavior are calculated for straight and slightly curved lines (FM pulses), for both the narrowband and wideband cases.     

Geometrical optics prediction of surface scattering statistics

A composite-roughness formulation of the geometrical optics approximation is applied to study the statistics of near-nadir electromagnetic scattering from the sea surface. For scattering from Gaussian random surfaces, the scattering cross section is dependent only on the probability density of surface slopes. The statistical distribution of the scattered intensity depends on both the slope probability density function and <|/spl Omega/|> $the mean absolute value of the surface curvature. The curvature is of interest because it provides a measure of capillary wave spectra. Numerical results are obtained for scattering from isotropic surfaces for a fixed number N of specular scatterers and for N Poisson distributed. Obtaining viable estimates of <|/spl Omega/|>, and hence of capillary wave spectra, from backscatter data at microwave frequencies may not be practical. Optical measurements for which individual point scatterers can be identified may, however, yield estimates of the surface curvature.     

副载波对广播信号的频谱和模糊函数的影响

根据调频立体声广播中副载波的产生原理,针对广播信号的频谱和模糊函数图进行分析,指出:有副载波的广播信号的模糊函数图的零距离切面在导频信号的二分频的整数倍上出现相关峰、多普勒切面则由无副载波的广播信号的模糊函数图的多个多普勒切面加权相加而成;同时带宽较窄的有副载波的广播信号的模糊函数图的相关峰呈现多峰.最后给出了消除多峰的方法和实录信号的处理结果.     

The unification of differential encoding and decoding algorithm for various signals

Many monographs point out that differential encoding and decoding is necessary for ef- fectual information transmission against phase ambiguity while seldom discuss the reason why phase ambiguity will emerge inevitably.Available algorithms are specially designed for certain modulation scheme;these algorithms cannot satisfy the requirement of soft-defined radio,which perhaps demands a uniform algorithm for different modulations.This paper proposes a new opinion on phase ambiguity from the view of probability.This opinion believes that modulating symbol sequence can affect,at optimum sampling epoch,the modulated waveform as oscillating carrier has done,and so the stochastic sequence leads to phase ambiguity.Based on a general signal model,this paper also puts forward a novel universal algorithm,which is suitable for different signals,even some new ones,by configuring several parameters.     

Fine‐Motion Estimation Using Ego/Exo‐Cameras

Robust motion estimation for human–computer interactions played an important role in a novel method of interaction with electronic devices. Existing pose estimation using a monocular camera employs either ego‐motion or exo‐motion, both of which are not sufficiently accurate for estimating fine motion due to the motion ambiguity of rotation and translation. This paper presents a hybrid vision‐based pose estimation method for fine‐motion estimation that is specifically capable of extracting human body motion accurately. The method uses an ego‐camera attached to a point of interest and exo‐cameras located in the immediate surroundings of the point of interest. The exo‐cameras can easily track the exact position of the point of interest by triangulation. Once the position is given, the ego‐camera can accurately obtain the point of interest's orientation. In this way, any ambiguity between rotation and translation is eliminated and the exact motion of a target point (that is, ego‐camera) can then be obtained. The proposed method is expected to provide a practical solution for robustly estimating fine motion in a non‐contact manner, such as in interactive games that are designed for special purposes (for example, remote rehabilitation care systems).     

一种基于平行辅助基线的干涉仪测向算法

针对平面阵测向中存在的相位模糊问题,提出一种基于平行基线的干涉仪测向算法。该算法利用平行基线中短基线相位差可能的模糊数获得长基线的一系列可能相位差,通过相关运算实现解模糊,并利用最小二乘解确定最终的入射信号方向。算法中引入的平行基线有效降低了解模糊运算量,而最小二乘解则提高了算法测向精度。计算机仿真结果验证了算法解相位模糊的正确性和测向的高效性。     

基于固定模糊度技术的精密单点定位性能分析

模糊度固定是影响精密单点定位精度和快速收敛的主要问题之一,而相位偏差的有效分离是模糊度固定的关键因素,采用包含相位偏差的钟差和与之耦合的轨道来完成模糊度的固定,基于全球分布的5个IGS连续跟踪站5 d的观测数据,采用采样间隔为30 s的高精度精密钟差产品,研究精密单点定位(PPP)的整周模糊度在固定解模式和浮点解模式下...     

The Omega navigation system--An overview

The Omega worldwide VLF radio navigation system is discussed. Following a brief historical perspective, the current and projected system configurations are described with emphasis on the operational characteristics of transmitting station equipment. The Omega positionfixing process is examined and the available user equipment is reviewed. The characteristics of VLF radio wave propagation, which have a significant impact on Omega navigation accuracy, are discussed. Finally, the various elements of the Omega user community are described along with the likely nature of future increased applications of the Omega navigation system.     

Maintainability Applications Using the Matrix FMEA Technique

The Matrix Method of Failure Modes and Effects Analysis (FMEA) provides an organized and traceable analysis from the piece-part failure-mode through all indenture levels to system-level failure effects. This paper describes a methodology for reversing the buildup process for maintainability analysis. The output of this reverse process identifies each system-failure effect individually and the related indentured, lower-level composition of contributing sources of failure. The results of this technique provide source data for identifying different levels of ambiguity for fault isolation, evaluating test point adequacy, formulating replacement level criteria, developing maintenance diagnostic charts and procedures, validating maintenance concepts, and segregating most-probable faults for spare parts requirements.     

基于模糊平面的信号识别方法

将一维信号变换到二维坐标平面往往更有利于描述信号的时变特征,从而实现信号的分类识别。基于离散时频分布的信号识别方法,将时频核设计问题转化为以信号自模糊函数为原始特征的特征选择问题,以实现特征降维和信号识别。时频核设计孤立考察模糊平面上各个特征点,且降维空间中存在着识别信息冗余。将核设计的原理推广,直接基于模糊平面进行信号识别,利用K—L展开和线性变换对自模糊函数进行特征提取,在降维空间内综合了各原始特征共有的分类信息,并去除特征之间的相关性,从而比时频核设计方法具有更优的信号识别性能。     

星载合成孔径雷达不同工作模式下的PRF优化选取研究

星载合成孔径雷达中,脉冲重复频率（PRF）是非常重要的参数。它的选择受到很多因素的影响,尤其是受到发射干扰、星下点回波、距离模糊以及方位模糊的影响,也正是受到这些因素的影响,导致在不同的工作模式下,PRF的选取有很大的差异。这里在研究常用的条带工作模式下PRF选取的基础上,讨论了聚束和滑动聚束模式下PRF选取的特殊性,给出了这两种工作模式下PRF选取的方法,并进行了仿真验证其有效性。     

Selfaligned AlGaAs/GaAs HBT grown by MOMBE

The very low parasitic resistance n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBT) grown by metal organic molecular beam epitaxy (MOMBE) using all gaseous source dopants are reported. The carbon and tin dopants were introduced through the uses of trimethygallium (TMGa) and tetraethyltin (TESn). To achieve the low parasitics, the graded InGaAs emitter cap layer was doped with tin to 5*10/sup 19/ cm/sup -3/ and the doping level in the subcollector was 3*10/sup 18/ cm/sup -3/. The emitter and collector sheet resistances were 25 Omega / Square Operator and 10 Omega / Square Operator , respectively. The 800 AA thick base layer was carbon doped to a level of 7*10/sup 19/ cm/sup -3/. The base contact resistance and sheet resistance were 0.1 Omega mm and 180 Omega / Square Operator , respectively. With a thin AlGaAs surface passivation layer for the emitter-base junction, the common emitter DC current gain was maintained up to 25, even for 2*5 mu m/sup 2/ emitter size devices. The unity short circuit current gain cutoff frequency f/sub T/, and maximum oscillation frequency f/sub max/, were 48 and 63 GHz, respectively.<>     

Reconsideration of Azimuth Ambiguities in SAR

The traditional method of specifying and controlling azimuth ambiguities in SAR is through integrated energy balance measures. However, the most frequently observed azimuth ambiguities arise from ensembles of strong point reflectors in the principal sidelobes of the antenna, which in turn are aliased into the processed Doppler bandwidth by the radar PRF. This paper considers the dependence of these ambiguities on radar wavelength and PRF. It is shown that such ambiguous image elements are strengthened in proportion to ? 2 and PRF-1. The theoretical structure is based on orbital SAR geometry, including Earth rotation. The work is applied to a SIR-B L-band radar scene in which azimuth ambiguities are clearly observed. The level and spatial position of these ambiguities are measured in the digital image. The results are extrapolated to higher frequency radars such as ERS-1 and Radarsat. It is concluded that for these C-band radars the point azimuth ambiguity restraint is more relevant (and more binding) than the traditional energy balance method.     

GPS姿态测量中的整周模糊度的实时解算方法

GPS 实时姿态测量的核心问题是整周模糊度解算。本文提出了一种适合实时姿态测量的模糊度解算方法,它利用单差平滑伪距进行解算,与传统的模糊度解算方法相比具有许多优点。该方法的有效性和实用性通过仿真实验进行了验证。     

基于编码跳频图案的DS/FH测控信号性能分析

为了研究跳频图案的不同编码方式对DS/FH测控信号的性能影响,从模糊函数的角度出发,推导了DS/FH测控信号的模糊函数表达式,得到了不同切面的距离模糊图和速度模糊图。仿真结果表明,采用步进编码形式跳频图案的DS/FH测控信号,出现距离和速度耦合;采用随机编码形式跳频图案,则没有距离和速度耦合,且具有良好的目标分辨性能和测量精度性能。     

基于栅格投影的地基合成孔径雷达三维地形匹配俯仰角模糊处理方法

近距离对高大建筑物进行监测时,基于栅格投影的地基合成孔径雷达(ground-based synthetic aperture radar,GB-SAR)三维地形匹配过程中易出现俯仰角模糊现象,影响投影结果的解译.针对此问题,文中提出一种俯仰角模糊现象的处理方法.首先推导了任意GB-SAR观测几何条件下的图像距离-方位坐...     

An Accurate Approximation of the Impedance of a Circular Cylinder Concentric with an External Square Tube

The problem of determining the characteristic impedance of a concentric coaxial transmission line having a circular inner conductor and a square outer conductor is reexamined. The Green's function for a rectangle is used to determine the geometrical capacitance of a series of structures ranging from 1-46 Omega with an error less than 10 -5. The method of analysis is illustrated in detail for the 1-Omega case. The resitlts are presented in terms of the "outer shield factor" R/sub eff/, which is defined as the ratio of the diameter of an outer circle, having the same capacitance as the outer square, to the side of the outer square, Values of this ratio are tabulated for impedances ranging from 1-46 Omega. These values are also plotted on a curve which can be read with an error of the order of 0.02 Omega for impedances greater than 3 Omega.