Design and performance of the monopulse control system

Ka-band (32 GHz) monopulse tracking has been chosen for the upcoming NASA missions. This decision requires an increased pointing accuracy for the Deep Space Network antenna servo systems that can be maintained in a noisy environment. The noise sources include wind gusts, encoder imperfections, and receiver noise. This article describes the selection of the position and monopulse controllers for the improved tracking accuracy, and presents the results of linear and non-linear simulations to confirm that servo performance will meet the requirements     

单脉冲跟踪接收机的设计

随着微电子技术和计算机技术的进步,电子线路的集成化已经成为中高频电路发展的一个重要方向,根据工程需要,采用进口集成芯片AD6459、MAX2605、AD633等设计了70 MHz基于锁相环的单脉冲跟踪接收机,相比原来的接收机,集成度高,硬件电路大大简化,成本低,调试方便,现已应用于某卫星通信地球站天线跟踪系统,大量的动态性能实验表明接收机参数稳定,同时使跟踪系统的可靠性也得到较大的提高。     

Design and analysis of a multimode feed horn for a monopulse feed

The design of a multimode feed horn for use in a monopulse feed system is summarized. Both amplitude and phase patterns have been obtained and compared with measurements. The far-field amplitude and phase patterns are computed in consideration of achieving the desired aperture distributions for the sum and difference beams. The phase center of the horn is discussed in relation to the multimode excitation and frequency dispersion. It is shown that the phase center location moves as the mode content changes, and proper adjustment of the mode content will result in design optimization. Some tradeoff curves are also presented for design optimization     

Cross coupling in a five horn monopulse tracking system

A model is developed which explains the observed effects of secondary pattern crosstalk in a five horn circularly polarized monopulse tracking system. The model predicts unstable operation and loss of track for sufficiently depolarizing targets as well as polarization dependent uncertainties in the angular location of off-axis targets. The cross coupling is characterized by two complex coupling coefficients between adjacent horns in the monopulse feed system. This characterization is assumed to be valid irrespective of whether the observed secondary pattern effects are the result of mutual couplings within the feed structure itself or caused by cross-polarized backscatter from the paraboloidal reflector. A "ridge" and "nonridge" polarization terminology is adopted which is physically related to the fact that the error horns in a five horn circularly polarized system are heavily ridge loaded for one linear polarization and not the other.     

Partial adaptive nulling on a monopulse phased array antenna system

A partial phase-only nulling (PPON) algorithm has been developed and evaluated on a 496-element monopulse phased array antenna system which employs five-bit phase shifters. Using this PPON algorithm allows nulls in the far-field pattern to be steered to the desired directions for a phased array equipped with low-resolution phase shifters to perform simultaneous nulling in the sum and two difference patterns in the environment of multiple jammers. Simulated and experimental patterns are illustrated     

SAR成像质量指标评估软件系统的设计

合成孔径雷达(SAR,Synthetic Aperture Radar)是一种应用广泛的微波遥感成像雷达,能够全天时、全天候对地观测成像,并且图像有着高方位分辨率。SAR图像研究是遥感方向最为重要的前沿领域之一。目前没有一套专门的软件系统工具来对SAR成像进行指标的计算与测量,都是建立在通用的辅助工具如MATLAB上,计算效率低且不方便。文中设计了一种SAR成像的质量评估系统软件,该系统中包含一套比较完备的SAR成像质量指标,然后以这套指标为主要出发点,设计开发出SAR图像质量指标评价的软件。该软件以C/C++语言为基础,以OGRE和CEGUI等开源库为框架。该系统能够实现对数据文件的读取、图像的基本操作、图像和数据的质量指标测定、指标的测定和计算等,并且有着友好的人机交互功能。     

A bit system that guarantees better accuracy for monopulse antennadetection systems

Accurate integration and calibration of well-designed components can compensate for time-varying errors in a monopulse antenna system. A switchable four-port bit system, using a balanced four-way splitter and four balanced, electronically controlled, fast switches, make it possible to know the signal location measured by the monopulse antenna with very great accuracy in the presence of these errors     

Optimum beamformers for monopulse angle estimation usingoverlapping subarrays

We here derive the optimum sum and difference beamformers for monopulse target localization using a linear array. The beamformers are constructed, treating as superelements two overlapping subarrays. Removing the common factor associated with the superelement pattern from the angle error function leads to a closed-form target angle estimator independent of any adaptive nulling performed. Performance analysis of the angle estimator is conducted, and a procedure is developed to construct the beamformers, which achieve the minimum estimation variance under Gaussian noise. It is shown that the optimum angle estimator using the maximum overlapping subarrays is efficient for a moderately high signal-noise ratio (SNR) and a small off-boresight angle. The proposed method can be easily modified to incorporate interference cancellation     

Hybrid approach for sub-arrayed monopulse antenna synthesis

A computationally effective hybrid approach to define the 'optimal' compromise between sum and difference patterns in monopulse arrays is presented. First, the partitioning into sub-arrays is performed by exploiting the knowledge of independently optimal sum and difference excitations. Then, the sub-array gains are computed by means of a gradient-based procedure, which takes advantage from the convexity of the problem at hand. Selected results are shown and compared with those from state-of-the-art methods in dealing with representative test cases.     

对单脉冲末制导雷达距离欺骗分析

反舰导弹末制导雷达越来越多地采用单脉冲角跟踪技术,舰艇方须结合自身特点,采取有效的对抗措施。本文根据单脉冲雷达基本原理,建立了距离波门拖引干扰模型,推算出实施距离波门拖引干扰的成功率和干扰机所需功率,并在此基础上提出了一种较为可行的干扰方法。     

Motion error determination from the signum-coded SAR raw data

The authors explore the determination of motion errors of an aircraft platform from the signum-coded synthetic-aperture-radar raw signal (SC-SAR data). The SC-SAR has a one-bit representation. In fact it only provides information about the sign of SAR recorded data. Displacement from the line-of-sight (LOS) direction and nominal forward velocity of SAR platform are estimated from this signal by using the reflectivity displacement method (RDM), which allows motion error determination directly from SAR raw data. The theory of the motion error estimation from the signum-coded raw data is presented and supported by experimental results. Comparison is made between the motion parameters computed by the original and the SC-data in order to show that the motion errors can be also determined by applying the RDM to the SC-signal     

低DNL的SAR型模数转换器的设计

保证DAC中元器件的精度、减小DNL误差是提高SAR ADC性能的关键。通过对SAR ADC内部DAC的结构进行综合分析,针对传统的C-R混合式结构中的集总电容阵列进行了优化设计。电容阵列由相同的非集总的单位电容组成,并通过数字逻辑的控制来实现对单位电容连接点的选择。验证结果证明设计有效,ENOB、SFDR和SINAD等参数都得到明显的提高,保证了SARADC的单调性,实现了低DNL的SAR型模数转换器的设计。     

An advanced system for the automatic classification of multitemporal SAR images

A novel system for the classification of multitemporal synthetic aperture radar (SAR) images is presented. It has been developed by integrating an analysis of the multitemporal SAR signal physics with a pattern recognition approach. The system is made up of a feature-extraction module and a neural-network classifier, as well as a set of standard preprocessing procedures. The feature-extraction module derives a set of features from a series of multitemporal SAR images. These features are based on the concepts of long-term coherence and backscattering temporal variability and have been defined according to an analysis of the multitemporal SAR signal behavior in the presence of different land-cover classes. The neural-network classifier (which is based on a radial basis function neural architecture) properly exploits the multitemporal features for producing accurate land-cover maps. Thanks to the effectiveness of the extracted features, the number of measures that can be provided as input to the classifier is significantly smaller than the number of available multitemporal images. This reduces the complexity of the neural architecture (and consequently increases the generalization capabilities of the classifier) and relaxes the requirements relating to the number of training patterns to be used for classifier learning. Experimental results (obtained on a multitemporal series of European Remote Sensing 1 satellite SAR images) confirm the effectiveness of the proposed system, which exhibits both high classification accuracy and good stability versus parameter settings. These results also point out that properly integrating a pattern recognition procedure (based on machine learning) with an accurate feature extraction phase (based on the SAR sensor physics understanding) represents an effective approach to SAR data analysis.     

Angle measurement with a phase monopulse radar altimeter

It is possible to enhance the conventional satellite radar altimeter in such a way that the range measurement is accompanied by an angle measurement. This is useful if the radar applications of these altimeters are to be expanded to include phase nonlevel surfaces such as continental ice sheets and land. The angle measurement can be made in one or two directions through the inclusion of one or two additional antennas and receiver channels and the integration of complex “cross-channel” waveforms whose phase indicates the angle to the point of first reflection from the scattering surface. This paper develops the measurement concept and establishes the precision of the resulting elevation measurement through an analysis of the dominant sources of error within the instrument. It is shown through analysis and numerical simulation that elevation errors over a flat tilted diffusely scattering surface can be maintained below the 1-cm level. The impact of antenna pointing and surface roughness are considered     

Design of ATM AAL1 SAR for circuit emulation

The asynchronous transfer mode (ATM) adaptation layer type 1 (AAL1) segmentation and reassembly (SAR) are designed and implemented by the field programmable gate array (FPGA). The SAR header is generated and processed in the FPGA and the SAR payload is stored in an external first-in-first-out (FIFO) device. A method to recover the source clock, called synchronous residual time stamp (SRTS), is implemented. The designed AAL1 SAR FPGA is properly tested in a prototype circuit board     

Synthesis of adaptive monopulse patterns

A procedure is developed to simultaneously synthesize sum and difference patterns for space-time adaptive processing (STAP) in such a way that a specified monopulse slope after adaptation is achieved     

一种单端10-bitSARADCIP核的设计

本设计通过采用分割电容阵列对DAC进行优化,在减小了D／A转换开关消耗的能量、提高速度的基础上,实现了一款采样速度为1MS,s的10-bit单端逐次逼近型模数转换器。使用cadencespectre工具进行仿真,仿真结果表明．设计的D／A转换器和比较器等电路满足10-bitA／D转换的要求,逐次逼近A／D转换器可以正常工作。