单脉冲双极化天线阵列设计

文章研究了单脉冲双极化天线阵列。天线阵混合馈电微带单元由共面微带线馈电和缝隙耦合微带线馈电两者结合形成,"十"字形微带单脉冲比较器与天线阵同面,具有结构紧凑、加工方便和成本低的优点。经仿真验证,在工作频带内其辐射单元双端口隔离度高于34dB;并且2个极化端口在其对应主平面方向的副瓣电平均低于-20dB。天线可适用于新一代多极化雷达系统。     

星载全空间可见GPS接收系统定位精度分析及验证

针对低轨空间科学卫星在轨任意姿态无固定对天面造成的无法连续GPS(Global Positioning System,全球定位系统)定位的问题,在HXMT(Hard X-ray Modulation Telescope,硬X射线调制望远镜)卫星中提出了星载全空间可见的GPS接收系统,并指出了双天线多径干扰对定位精度的影响。建立模型,对双天线下主瓣直达信号和后瓣镜像干扰信号叠加合成的信号进行定位精度分析,结果表明,空间中83.3%以上的GPS卫星信号对该系统带来的定位误差影响不大于单天线的定位误差影响。通过半物理动态仿真验证以及外场试验进行验证,实际工程测试数据结果表明采用剔星策略后定位精度提高约13.4%。从而证明了星载全空间可见的GPS接收系统方案的正确性,并可广泛应用于工程实际。     

Ranging airport pseudolite for local area augmentation

This paper discusses the integration of an airport pseudolite (APL) into a local area augmented differential GPS based precision approach system. A prototype architecture is described that is being used to develop requirements for the local area augmentation system. Key features of this prototype system are presented along with its current performance. Key features discussed include the use of a multipath limiting antenna, APL signal structure factors, a unique APL automatic gain control, and GPS blanking technique to maximize APL tracking performance, while minimizing the electromagnetic interference to nominal DGPS performance     

Multipath-adaptive GPS/INS receiver

Multipath interference is one of the contributing sources of errors in precise global positioning system (GPS) position determination. This paper identifies key parameters of a multipath signal, focusing on estimating them accurately in order to mitigate multipath effects. Multiple model adaptive estimation (MMAE) techniques are applied to an inertial navigation system (INS)-coupled GPS receiver, based on a federated (distributed) Kalman filter design, to estimate the desired multipath parameters. The system configuration is one in which a GPS receiver and an INS are integrated together at the level of the in-phase and quadrature phase (I and Q) signals, rather than at the level of pseudo-range signals or navigation solutions. The system model of the MMAE is presented and the elemental Kalman filter design is examined. Different parameter search spaces are examined for accurate multipath parameter identification. The resulting GPS/INS receiver designs are validated through computer simulation of a user receiving signals from GPS satellites with multipath signal interference present The designed adaptive receiver provides pseudo-range estimates that are corrected for the effects of multipath interference, resulting in an integrated system that performs well with or without multipath interference present.     

Multicomponent receiver architectures for GPS interference suppression

The global positioning system (GPS) is a one-way satellite-based navigation system employing spread-spectrum techniques that is widely used for commercial and military applications. Although the very low signal-to-noise ratio (SNR) is handled by the large spreading gain, GPS is susceptible to high-power interference signals and various types of jammers. We propose multicomponent receiver architectures for GPS interference suppression. A conventional antenna system is first considered which utilizes a minimum-variance distortionless-response (MVDR) beam former and assumes that the GPS signal angle of arrival (AOA) and the antenna model are known at the receiver. However, this receiver is sensitive to AOA estimation errors and can have a high computational complexity. This sensitivity problem is eliminated by a multicomponent system based on a multistage matched filter (MF). Since this MF receiver also has a high computational complexity because the jammer AOAs must be estimated, we introduce a blind interference canceler based on the constant modulus (CM) array that is insensitive to AOA estimation errors and has a low computational complexity. Computer simulations are provided to illustrate the performance of the various systems for interference suppression in example signal scenarios.     

阵列旋转对功率倒置算法性能的影响分析

针对卫星导航抗干扰中,功率倒置算法下导航信号载噪比受干扰来波方向的影响,通过理论推导和数值计算的方法研究了天线阵列旋转与功率倒置算法抗干扰性能的关系。分析结果表明:天线阵列旋转会使功率倒置算法下的阵列增益在最大值和最小值之间呈现连续的、周期性的变化。相比固定天线阵不变的载噪比,阵列旋转能够使信号在一段时间内获得更大的载噪比,对于四阵元Y型阵列,阵列旋转理论上对载噪比的最大提升程度可以达到14dB左右。仿真结果验证了理论推导的正确性。     

Analysis and Design of Antennas for Air Traffic Collision Avoidance Systems

The analysis and design procedure of an antenna for a CW Doppler radar system being developed for pilot warning of midair collision hazards is presented. The antenna consists of two vertical arrays of half-wavelength dipoles mounted near a circular conducting cylinder. Each vertical array is composed of three vertical dipoles. Each array provides relatively uniform illumination (2-3 dB) in the forward 180 angular segment of the horizontal plane and approximately + 10-150 coverage in the vertical plane. The antenna could be used in a two-mode operation, either in a standard monopulse radar system (sum and difference amplitude patterns) or in a system where amplitude and phase are the measurable quantities.     

Comparison of Superresolution Algorithms for Radio Direction Finding

The problem of high-frequency radio direction finding (HFDF) has perennially been compounded by the interference effects of multicomponent wavefields. The wavefields are generally produced by ionospheric multipath or cochannel interference from other transmitted signals. Because HFDF sytems must operate on short duration signals and are usually restricted to limited antenna array apertures, modern techniques of superresolution spectral analysis are applied to resolve the constituency of multicomponent wavefields. This paper presents a performance comparison of five superresolution spectral algorithms in solving the HFDF wave interference problem.     

Artificial Site Shielding for Communications Satellite Earth Stations

A method of reducing the possibilities of interference between earth stations and microwave radio-relay stations by the use of pit shielding has been investigated. A pit was constructed containing a 32-foot diameter antenna. Measurements are reported which indicate a shielding advantage of at least 25 dB. A siting example under actual conditions is given.     

一种利用功率反演和线性约束最小方差算法的自适应天线

介绍了一种新的基于功率反演和线性约束最小方差的算法,以高度抑制GPS接收机的干扰信号。这种结构通过提调整天线阵列的权值,实时地接收并改变来自各方向的GPS信号,同时对不同方向的干扰信号有高的抑制比。对固定和移动的干扰都做了仿真,仿真表明这种结构有很深的零点,对固定干扰信号的抑制比可达到115dB,对移动干扰信号的抑制比可达到94dB。     

Wideband cancellation of interference in a GPS receive array

We have demonstrated that by using an adaptive space-time array the interference from multiple, strong interferers plus multipath can be canceled down close to the noise floor without producing serious loss or distortion of a GPS signal. Design criteria are presented and limitations are examined. We also compare space-time processing with suboptimum space-frequency processing, and demonstrate by simulation that for equal computational complexity space-time processing slightly outperforms suboptimum space-frequency processing     

Effects of test vehicle patterns on cellular coverage measurements

Mobile test systems intended for cellular phone coverage measurements suffer from uncertainties, which are caused by the unpredictable radiation pattern of the measuring antenna installation. Not only do adjacent structures and very common multiple antennas disturb the characteristics, but also in the case of an ideal position does the vertical lobing introduce errors exceeding 10 dB. The problems are likely to be worse in dense urban areas, where multipath from surrounding buildings is the dominating propagation mode     

基于阵列天线的一种GPS多径抑制方法

为了抑制多径效应对GPS的严重影响，在分析了多径效应对伪码跟踪环路影响的基础上，提出了一种基于空间平滑的改进稳健波束形成算法来抑制GPS多径效应。以直线阵为基础，采用前后向空间平滑算法对阵列接收信号进行预处理，针对各种失配，采用改进的稳健波束形成算法进行处理。该方法既可以有效地抑制GPS多径效应，又可以有效地改善伪码跟踪环路的跟踪精度。仿真实验结果验证了所提方法的正确性和有效性，具有较高的工程实践价值。     

Azimuth-Elevation Estimation Performance of a Spatially Dispersive Channel

A model is presented for the estimation of azimuth and elevation in a dispersive media where the signals come from a continuum of directions. These bounds depend upon the array ambiguity patterns and the channel spread function. Specific cases are discussed showing how the result reduces to an easily tractable analytical tool in many cases of interest. The model discussed is applicable to angular estimation performance in the presence of such interference as diffuse multipath, chaff clouds, vertical angle of arrival spread in sonar systems, and turbulent and multiply scattered optical channels.     

卫星导航接收机空间自适应调零抗干扰技术研究

比较了两种自适应调零抗干扰天线系统方案的优缺点,根据实际应用场合,确定抗干扰天线方案设计为中频输出的数字调零系统.对自适应调零的信号处理进行了理论研究,建立了阵列信号的模型,根据导航卫星信号远小于干扰信号等因素,选用了基于线性约束的功率倒置算法,通过调整权值系数使得天线阵的方向图零点对准干扰信号方向,实现干扰零陷.仿真结果表明:通过零陷处理可达到干信比为77dB的抗干扰能力,验证了算法的有效性.     

Cancellation of jammers and jammer multipath in a GPS receiver

It is demonstrated by simulation that jammers and jammer multipath can be cancelled using an adaptive space-time array, leading to nearly ideal GPS performance     

Results from a Four-Element Adaptive Antenna Experiment

Experimental results from a four-element, linear, half-wavelength spacing, adaptive-array antenna under the control of the least mean square (LMS) algorithm are presented. The array is found to be capable of nulling a 70-MHz signal to -35 dB below a desired signal over a 5-MHz bandwidth. The antenna processing gain is constant over a desired signal-to-jammer signal power ratio range from -20 dB to 5 dB. A sharp reduction in processing gain is observed for angular separations between jammer and desired signal of less than 10°. Antenna patterns taken with weights set in 300 iterations of the LMS algorithm show that the one strong, one weak jammer combination has a longer weight convergence time and reduced processing gain compared with a two strong jammers combination. Contours of constant desired signal-to-jammer signal power ratio, after adaptive antenna processing, reveal a complex shape for communication between air and ground due to the finite angular resolution of the adaptive antenna.     

Clutter and jammer multipath cancellation in airborne adaptiveradar

Airborne surveillance radars must detect and localize targets in diverse interference environments consisting of ground clutter, conventional jamming, and terrain scattered jammer multipath. Multidimensional adaptive filtering techniques have been proposed to adaptively cancel this interference. However, a detailed analysis that includes the effects of multipath nonstationarity has been elusive. This work addresses the nonstationary nature of the jammer multipath and its impact on clutter cancellation and target localization. It is shown that the weight updating needed to track this interference will also modulate sidelobe signals. At the very least, this complicates the localization of targets. At the worst, it also greatly complicates the rejection of clutter. Several techniques for improving cancellation of jammer multipath and clutter are proposed, including 1) weight vector interpolation, extrapolation, and updating; 2) filter architecture, constraint, and beamspace selection; 3) prefilters; 4) 3-D STAP architectures; and 5) multidimensional sidelobe target editing     

Omnidirectional Instantaneous Direction Finding System

A system for providing near-instantaneous determination of the azimuthal angle of arrival of a received signal has been designed and fabricated at L band. Direction is determined by phase measurement of the outputs of a multimode antenna, which has no moving parts. Effects of multipath interference are reduced to a minimum through a combination of signal processing techniques. The position of the transmitting source is presented on a PPI display.     

Low altitude target model for radar simulation

A simulation model of antenna array signals from a low altitude target is considered. Explicit expressions for statistical and spectral characteristics of the scattered signals are obtained in the Kirchhoff approximation. The model permits to evaluate the efficiency of different techniques of low altitude target tracking. It benefits the comprehension of the influence of multipath propagation on tracking radars