Ultimate thickness to bandwidth ratio of radar absorbers

Analytic properties of the reflection coefficient of a multilayer metal-backed slab are considered. The result is a new form of the dispersion relationship, which characterizes the integral of the reflectance over wavelength in terms of the total thickness and averaged static permeability of the slab. The relation may be transformed to an inequality, which produces the least thickness to bandwidth ratio achievable for a physically realizable radar absorber. The particular cases of broad-band and narrow-band absorbers are discussed. The least thickness of a 10-dB broad-band dielectric radar absorber is shown to be 1/17 of the largest operating wavelength. The discussion also involves the results of a numerical study.     

Simple phase-locked loop with large pull-in range to noise bandwidth ratio

The little-known sawtooth phase comparator is shown to display frequency discrimination, allowing its pull-in range to be orders of magnitude greater than its noise bandwidth.     

频率步进太赫兹雷达的一维高分辨距离像

频率步进信号是一种较常用的距离分辨力高的雷达信号,常用于雷达的目标识别,而太赫兹波比微波信号波长短,更易于实现距离高分辨力。利用0.2 THz步进频率太赫兹雷达实现了高分辨一维距离像,分析了步进频率雷达系统中一维高分辨力距离像的成像原理,对0.2 THz步进频率雷达系统进行了介绍,最后,用Matlab对太赫兹雷达高分辨力进行了仿真,仿真结果表明,频率步进太赫兹雷达对静止目标达到了厘米级的高分辨力,而对于运动目标存在距离发散和耦合时移,速度越大,失真越大。     

低信噪比下雷达回波谱矩快速估计方法

针对在低信噪比下机载气象雷达回波多普勒参数（谱矩）估计不准确的问题，本文在气象目标的雷达回波频谱服从高斯分布的基础上，给出了一种利用协方差矩阵分解的快速参数化谱矩估计算法。通过理论分析，推导出雷达回波的协方差矩阵具有范德蒙结构特性，进而将用于谱矩估计的代价函数转化为类傅里叶变换结构，然后进一步通过快速傅里叶变换和高斯加权滑窗计算代价函数，实现快速的谱矩估计。仿真实验结果表明，该方法在信噪比低于5 dB时仍可以有效估计雷达回波的谱矩参数，同时运算复杂度大大降低，而且在谱宽值较大情况下仍能保持较好的估计性能。      

相控阵雷达波束资源管理

针对相控阵雷达波束资源管理问题进行了深入分析,重点研究了三坐标有源相控阵雷达自由波束的理论和实现问题,提出了适合于工程应用的算法,该方法能够依据数据处理对航迹的实时预测信息,解算高仰角目标的动态位置,通过波束调度完成对高仰角目标的跟踪,实现70°范围的仰角覆盖,通过在某定型产品中的应用,证明了该方法的有效性。     

高分辨单脉冲雷达距离像回波建模仿真

为了有效模拟和分析雷达目标回波特点,提出了一种数字仿真方法来建模和设计雷达目标回波。通过对高分辨单脉冲雷达的原理分析,设计雷达目标回波仿真系统框架,将系统分解成多个模块,针对每个模块建立相应的数字模型,并利用计算机软件实现,仿真表明该方法能有效建立雷达目标三通道一维距离像回波,并对后续单脉冲跟踪数据处理的研究具有指导意义。     

The effects of relative source strength and signal-to-noise ratio on angular resolution of antennas

High angular resolution is a desirable property of mapping and reconnaissance radar systems. The synthetic-aperture principle reduced the beamwidth of airborne radar by as much as two orders of magnitude. Notwithstanding the long interest in the subject, a quantitative relationship is lacking between beamwidth and resolution. This paper is an attempt to overcome this deficiency. Among its several results, it is shown that the angular resolution of synthetic-aperture radar can be considerably poorer than expected. It is also shown that a modest tapering of the synthetic aperture in those cases offers significant improvement.     

全极化频谱外推的合成孔径雷达成像分辨率增强方法

全极化合成孔径雷达可对不同极化通道分别独立进行频谱外推来增强分辨率,但分别独立处理难以利用极化信息的冗余性与互补性．将目标全极化数据分解到反映三种独立散射机理的Pauli基上,对分解后的全极化数据进行三维联合频谱外推处理,并利用实测数据进行了对比分析．结果表明：极化分解后,通过三维联合频谱外推的方法相比传统方法具有更高的预测模型匹配精度,可获得更好的分辨率增强性能．     

激光雷达三维距离像超分辨重构方法研究

针对目前激光雷达三维距离像分辨率低的问题,使用成本低且有效的图像处理方法获得高分辨三维距离像。首先,利用多传感器系统的特点,将低分辨率Gm-APD激光雷达与高分辨率ICCD激光雷达相结合,获得配准后的低分辨距离像和高分辨强度像,然后,提出了一种改进的图像引导算法实现低分辨图像超分辨重构。该方法使用马尔科夫随机场模型,定义了全局能量函数,该函数将距离保真项和正则化项相结合,通过求解优化模型获得高分辨三维距离像。通过对仿真图像和激光雷达距离像的超分辨重构处理,以主观视觉效果和图像质量客观评价指标来验证此方法。实验结果表明,该方法提高了距离像的分辨率,且很好地保护了图像的边缘结构,在无参考图像质量评价指标上较双三次插值、引导滤波和TGV取得更优值。     

相控阵雷达系统最大跟踪能力研究

相控阵雷达系统的最大跟踪能力是相控阵系统的重要指标,也是边跟踪边搜索（TAS）工作模式的研究基础。为了从工程应用的角度深入分析该性能指标,本文在Singer模型基础上,分析雷达跟踪的重访时间与工程测角误差的关系,并且分析在最小检测信噪比（SNR）情况下的跟踪驻留时间。通过对多目标时的统计分析,给出了平均重访时间和平均驻留时间,在此基础上,给出稳态时的最大跟踪能力闭和解析式。最后对非稳态的情况进行了分析,得到相应的雷达饱和状态解析式。基于上述分析,利用VC＋＋建立仿真平台,通过仿真验证了相关结论的正确性。     

基于高分辨率一维距离像雷达目标识别研究

基于一维距离像的目标识别是雷达目标识别的一种重要方法。本文利用最大相关系数法（MCC）和主分量分析方法（PCA）对目标一维距离像进行目标识别。针对一维距离像的目标姿态敏感性,分析了最大相关系数法和PCA特征提取方法的原理,并通过3种目标的实测数据进行分类实验,表明该算法的有效性。     

Degradation of signal-to-noise ratio due to amplitude distortion

The effect of filtering on the signal-to-noise ratio (SNR) of a coherently demodulated band-limited signal is determined in the presence of worst-case amplitude ripple. The problem is formulated as an optimization in the Hilbert space L₂. The form of the worst-case amplitude ripple is specified, and the degradation in the SNR is derived in closed form. It is shown that, when the maximum passband amplitude ripple is 2δ (peak-to-peak), the SNR is degraded by at most (1-δ²), even when the ripple is unknown or uncompensated. For example, an SNR loss of less than 0.01 dB due to amplitude ripple can be assured by keeping the amplitude ripple under 0.42 dB     

一种脉冲多普勒雷达解距离模糊的新算法

脉冲多普勒雷达在信号检测时存在距离模糊和速度模糊的问题，为了解决模糊问题，在体制上雷达一般采用多重脉冲重复频率（PRF）的工作方式。对于这种体制的雷达，人们已经给出了多种解模糊算法。本文主要阐述了一种解距离模糊的新方法及其实现步骤，并给出了利用该算法解距离模糊的仿真结果。     

宽调谐激光雷达亚毫米级距离分辨的实现方法

分析了单相干通道的宽调谐激光雷达虽具有超大带宽但不能实现符合理论值的距离高分辨率的原因,以及导致非线性调频相位误差的因素。构建了解决这一难题的双相干通道宽调谐激光雷达系统,啁啾带宽在THz量级,引入了具有固定延时的参考通道,采用了有效的信号处理方法,从参考通道中提取出相位误差,再利用此相位误差数据自适应地补偿掉目标通道中的相位误差。实验结果证明,该系统将距离分辨率由米级提高到了200μm左右,接近理论值120μm,实现了低至100 pW的最小可利用回波功率。且即使目标通道和参考通道的延时不相等时,该方法仍有效。     

提高高频雷达带宽的多载波技术研究

天波雷达工作在高频段,其工作带宽受电离层特性和人工信号干扰的限制,工程信号带宽一般只有十几千赫兹。利用多输入多输出(MIMO)原理,研究发射一组正交多载波调制的带宽为十几千赫兹的线性调频(LFM)信号照射目标,在接收端经匹配滤波和等效发射波束成形技术重建这一组回波信号成宽带信号,以增大雷达系统信号带宽。理论分析表明:在不考虑高频雷达多模多径情况下,发射N个频率间隔f_p=B的正交多载波调制LFM信号,在接收端采用匹配滤波和空时信号处理技术,将使接收信号带宽提高大约N倍。采用Watterson短波信道模型的仿真结果验证了理论分析的正确性。这表明在高频雷达多径环境不严重时,采用该方法可以提高雷达的距离分辨力。     

A 2-GHz analog-to-digital delta-sigma modulator for CDMA receivers with 79-dB signal-to-noise ratio in 1.23-MHz bandwidth

This paper presents the design of a second-order single-bit analog-to-digital continuous-time delta-sigma modulator (CT-/spl Delta//spl Sigma/M) that can be used in wireless CDMA receivers. The CT-/spl Delta//spl Sigma/M samples at 2 GHz, consumes 18 mW at 1.8 V and has a 79-dB signal-to-noise ratio (SNR) over a 1.23-MHz bandwidth. The CT-/spl Delta//spl Sigma/M was fabricated in a 0.18-/spl mu/m 1-poly 6-metal, CMOS technology and has an active area of approximately 0.892 mm/sup 2/. The /spl Delta//spl Sigma/M's critical performance specifications are derived from the CDMA receiver specifications.     

Simultaneous resolution of unambiguous range and doppler in a pulse-doppler radar using multiple PRFs

A method of simultaneously resolving both range and doppler ambiguities in a pulse-doppler radar is presented. The improvements over previous techniques are that only two PRFs are required and that the same number of doppler filters in each PRF is permitted.     

基于一维距离像序列的雷达目标微动参数估计

雷达目标微动参数估计是微动特征用于目标识别必须首先解决的一个问题。以典型的转动模型为例,分析了微动对一维距离像的影响,推导了不同情况下微动补偿需满足的精度要求,提出了利用自相关法、峰谷值检测法及单脉冲测角原理联合估计微动参数。仿真实验验证了所提算法在信噪比为-5 dB时仍有效。     

弹载宽带相控阵单脉冲雷达通道级STAP与ATBF研究

针对弹载宽带相控阵单脉冲雷达体制以及强海杂波背景,提出了一种基于通道级STAP与ATBF的杂波抑制、目标检测与角度测量方法。该方法交替使用两种发射方向图,首先采用常规方向图形成发射波束,利用和通道与俯仰差通道输出的距离-多卜勒图像进行自适应杂波对消与目标检测;然后根据目标单元处的对消因子获得等效的接收方向图,在需要抑制的杂波方向形成零点,根据收发互易原理将其转换为修正的发射方向图;最后按修正的方向图计算各阵元的加权因子,形成发射波束,采用常规的单脉冲方式测量目标角度。理论分析及仿真结果表明:该方法能有效抑制杂波及移位角闪烁、改善目标角度的测量精度,且运算量低、易于实现。      

On the possibility of high power gyrotrons for super range resolution radar and atmospheric sensing

High power gyrotrons have been developed recently; this makes a number of high power millimeter wave oscillators available. Currently their main application is the heating of fusion plasmas. This examines other potential applications for these RF sources. If used in multipulse radar mode, the pulses may be somewhat different from each other and this must be considered. A variant of coherent-on-receive data processing can be used. With this, the entire pulse, not only the phase, is renormalized to a reference pulse. The data are analysed off line. Possible applications of the quasi-optical gyrotron in a radar mode include exploiting its wide tuning range to achieve super range resolution and also remotely sensing the distribution of the size of ice crystals in cirrus clouds. Possible applications of a fixed frequency (94 GHz) gyrotron in the radar mode include studying the structure of clouds. In a forward scatter mode, these high power sources could provide the capability to remotely sense the structure of clear air turbulence. The tunability of the quasi-optical gyrotron could also be exploited to perform rapid path average measurements of relative humidity on the ground and in clouds, and to perform two way earth-to-space measurements of upper atmosphere trace element concentrations.