Artificial Beam Sharpening Technique for Radar Beacon Systems

A method of improving angular discrimination artificially in radar beacon systems, without going to extremely high frequencies of operation or using unreasonably large interrogator antennas, involves the use of a null-type antenna pattern superposed on a normal directional beam. The effective are over which replies are obtained is determined by an amplitude discriminator circuit within the beacon which compares the amplitude of the pulse signals received on the null pattern with those received via the directional beam. Only if the latter exceed the former by a predetermined amount does the beacon produce a reply. The method, which has been tried experimentally and its theory verified, produces an increase in traffic handling capacity, as well as improved angular resolution, by reducing unwanted triggering and, hence, clutter on the display and the over-interrogation of transponder beacons. An antenna is described which eliminates triggering on sidelobes by providing the proper current distribution to the radiating elements to cause the null pattern to cover the sidelobes of the normal beam. Triple-pulse amplitude discriminators have been built and tested in a double-pulse interrogation system. Some theoretical considerations and design curves and equations for use in designing nulltype antennas are given in the Appendix.     

On the Perfomance of Air Traffic Control Radar Beacon System

The sidelobe suppression and improved sidelobe suppression mode performance of terminal and enroute air traffic control radar beacon systems using the existing antenna and a typical improved antenna in the presence of perfectly dielectric flat ground are investigated theoretically. Necessary analytical expressions for various quantities characterizing the system performance have been derived. A general purpose computer program has been developed for the computation and tabulation of these quantities as functions of the elevation angle of the observation point and for different combinations of heights of the directional and omnidirectional antennas of the beacon. Although the discussions given here apply to some specific antenna configurations, the theoretical method developed has more general application in evaluating quantitatively the performance of the beacon system in a given situation.     

Electronic Search Beam Stabilization

Compensating for ship's motion (roll and pitch) is a problem fundamental to shipboard radars. The more traditional aproach has been to mechanically stabilize the antenna structure. The alternative approach of stabilizing only the antenna beam is far from being new conceptually, but is more realizable with today's technology. The basic elements are a planar array with an elevation scan capability that rotates continuously in azimuth combined with a high speed digital processor. Electronic stabilization of such an antenna is inherently more challenging than that of a two-axis phase-scanned array. An algorithm is derived for surveillance beam positioning as the antenna rotates. The implementation of this algorithm provides hemispheric search beam stabilization.     

Performance Analysis of a Dwell-Time Processor for Monopulse Beacon Radars

Performance of a monopulse air traffic control radar beacon system (ATCRBS) target data extractor is analyzed via an analytical approach. Results refer to a statistical analysis of the section of the receiver which associates replies sent by the desired aircraft during the antenna dwell-time. Some numerical results are reported which refer to the ATCRBS section to be devised in the discrete address beacon system (DABS).     

一种雷达模拟器天线系统设计

该系统采用角锥喇叭天线组成比幅测角系统,介绍了一种用于雷达模拟器的天线系统设计,解决了方位波束宽度大和天线增益高之间的矛盾,具有结构简单、易于实现、天线增益和测角精度高等特点。经测角误差分析和电磁仿真,证明天线系统的增益系数、测角范围和测角精度等主要技术指标满足雷达模拟器设计要求,具有推广应用价值。     

SEVERAL PROBLEMS IN DESIGNING DBS SYSTEMS FOR AIRBORNE PULSE DOPPLER RADAR

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Detection of moving targets in wideband SAR

A likelihood ratio is proposed for moving target detection in a wideband (WB) synthetic aperture radar (SAR) system. WB is defined here as any systems having a large fractional bandwidth, i.e., an ultra wide frequency band combined with a wide antenna beam. The developed method combines time-domain fast backprojection SAR processing methods with moving target detection using space-time processing. The proposed method reduces computational load when sets of relative speeds can be tested using the same clutter-suppressed subaperture beams. The proposed method is tested on narrowband radar data.     

The untold Pearl Harbor radar story

Ever wonder what happened to the radar set that detected the Japanese aircraft before the raid on Pearl Harbor? This article reveals the fate of that SCR-270 radar set; describes some of the radar development background; and includes typical results of a World War II command, control and communications system that used the SCR-270 as its backbone radar. The SCR-270 was a radio-echo detection and direction finding set for locating aircraft. It operated by transmitting a short-duration pulse of high frequency radio waves, which would be reflected or re-radiated by any metallic or conducting surface within the field of the directive transmitting antenna; therefore, one or more aircraft within the antenna field appeared as a source of reflected radio waves. Rotating the antenna which also served as the receiving antenna, provided a means for determining the azimuth or direction of aircraft. The system measured the time it took a blip or reflected return from the target to appear on a cathode ray tube indicator, to give the distance or range to the detected aircraft. The maximum range of the radar was about 250 miles up to 50,000 feet under all atmospheric conditions including rain, mist, smoke or fog, and during daylight or darkness. The azimuth and range data supplied by the set permitted the plotting of the location of detected aircraft on maps. Major performance characteristics of the radar are provided in the included table     

波束波导馈电系统在深空探测天线应用中的关键技术研究

针对波束波导馈电系统在深空探测天线应用中存在的电小尺寸镜面绕射引起波束波导传输效率降低,不同极化工作时波束指向不一致,以及TE21模跟踪时坐标转换等问题,进行深入研究并给出相应的解决方案或数学模型.通过优化椭球镜M5的曲率,解决了电小尺寸镜面绕射使波束波导传输效率下降问题,使S频段的传输效率提高约4％,35 m天线副反射面的截获效率增加约11％,天线增益提高0.7 dB;给出天线束峰值位置随方位、俯仰角变化的数学模型,提出了中值补偿方法,使天线左右旋极化峰值不一致增益损失减小约0.16 dB,并给出TE21模跟踪时的坐标转换数学模型.这些方法和数学模型已成功应用于实际工程中,并取得了良好的效果.     

The Effect of Ground Reflections and Scattering on an Interferometer Direction Finder

The azimuth and elevation angles of an airborne beacon transmitter can be determined using a direction finder comprised of two orthogonal interferometers located near the earth's surface. In this paper we consider the reflection of the incident electromagnetic field by the earth's surface and the resultant effect on the direction-finding system. The analysis yields an upper bound or limit to the interferometer phase error and the corresponding error in bearing angle that can result because of specular reflection and diffuse scattering.     

Optimum Alignment of an Inertial Autonavigator

The performance of an inertial autonavigator can only be as good as the accuracy to which the system is initially aligned. Optical methods of alignment can be performed with high precision; however, this technique requires external equipment and is subject to some physical constraints, such as land-based operation. The general problem discussed here is the use of an automatic azimuth alignment technique known as gyrocompassing. In the use of the gyrocompassing technique to obtain azimuth alignment, accuracies are degraded considerably by two dominant error sources, the level axis controlling gyro drift rate and the imperfections of reference or independent velocity information. Consequently, an optimum performance controller is developed for driving the system in this mechanization and is based on a priori knowledge of the second-order statistics of the system error sources. The performance criteria will be to minimize the mean square azimuth error.     

Electronically steerable plasma mirror based radar-concept andcharacteristics

An alternative to using a phased array to steer a radar beam is to electronically control the orientation of an inertialess broadband microwave reflector. Recent experiments have demonstrated that a planar plasma mirror immersed in a magnetic field can be formed with electron densities high enough to reflect X-band microwave beams. A plasma mirror performs like a metal mirror, but it is inertialess. Compared to high performance phased array systems, a plasma mirror based radar system is much simpler and is therefore more affordable. Electronic steering of microwave beams using a plasma mirror permits the use of wide instantaneous bandwidth waveforms. Potential areas of application for a plasma mirror based antenna system include ship self-defense, high-resolution radar imaging, target identification, electronic countermeasures, high data rate communications, spread spectrum links and remote sensing. As a reflector, the plasma mirror exhibits extremely low loss and the reflectivity is very nearly 100%. Since a perfectly reflecting object cannot radiate, the noise temperature contribution of the plasma mirror to the antenna temperature is likely to be small. The plasma sheet can be steered in elevation by tilting the magnetic field, and steering in azimuth may be accomplished by designating cathode initiation sites. Switching times between successive mirror orientations may be less than 20 μs     

一种稳健的利用分布式小卫星获取宽域、高分辨SAR图像的方法

 传统星载合成孔径雷达(SAR)受最小天线面积条件的限制，其横向分辨率与测绘带宽度相矛盾，采用编队飞行的分布式小卫星SAR体制，可解决这一矛盾，即能够同时获得大测绘带、高分辨率的地面场景的SAR图像。主要研究如何在误差环境下抑制由小天线引入的多普勒模糊的信号处理方法。该方法利用子空间投影技术对导向矢量进行精确估计，在小卫星存在基线及其他误差时仍然能够稳健地恢复高分辨的二维SAR图像。     

Reply Correlation Test Analysis in Monopulse Beacon Radars

The statistical behavior of the position data furnished by single air traffic control radar beacon system (ATCRBS) reports is analyzed. Some statistical models are correspondingly derived in order to be employed for the performance evaluation of the dwell-time section of the ATCRBS monopulse receiver. The expression of the failure probability is derived for the range and azimuth tests performed by the association algorithms operating in the monopulse ATCRBS target data extractor. Some numerical results are reported referring to the evaluation of the above failure probabilities in different conditions.     

TDRSS中用户星的星-星天线跟踪规律深入研究

应用坐标转换，得到用户星的星-星天线基本跟踪规律。针对几种情况，并考虑地球的隔断影响和天线的自身限制，对星一星天线的方位角和俯仰角表达式进行了修正和补充。最后，针对某用户星，应用Matlab进行数学仿真。结果表明，根据得出的跟踪规律，可以使用户星的星一星天线最大范围地跟踪中继卫星。     

弓网电弧辐射特性及对机场下滑信标的影响

为获得弓网电弧辐射特性及从理论上分析其对机场下滑信标的影响。选择典型电气化动车线路,首先基于CISPR16-1标准,利用电磁干扰接收机对电分相和普通点处的弓网电弧电磁辐射进行点频测试,获得了其在下滑信标台频谱内的辐射特性,然后基于电波传播理论,以电气化轨道平行跑道为例,分析了弓网电弧电磁辐射对飞机导航的影响。结果表明：电弧电磁辐射具有一定的随机特性,普通点处产生的电磁辐射场强小于电分相处;普通点的电磁辐射不会对飞机的导航产生干扰;当轨道距跑道中心的距离分别为700、120和60 m时,电分相拉弧点距下滑信标台天线的距离应分别小于3 291、546和249 m时才不会对飞机的导航产生干扰。本结果能够为轨道电气化和民用航空这两大工业体系在机场区域的电磁兼容性设计提供依据。     

空分加时分(空时分集)通信天线的跟踪问题研究

在时分多址通信体制下,采用相扫天线是抗截获、抗干扰的最有效途径。在时分多址通信体制下解决相扫天线节点间相互跟踪和通信是关键问题。文中详细地阐述了计算补点的方法,分析了方位角、航向角、舷角与扫描跟踪角之间的关系,并给出了相应的数学模型和补点算法的过程。     

An Application of Radiometric Techniques to Precision Angle Tracking Radar Systems

A new technique is described which provides for precision angle tracking of celestial radio sources with a conventional monopulse antenna receiving system. It is shown that this technique is readily adapted to angle tracking radars. The features of conventional monopulse operation are preserved while permitting precise angle tracking of noise sources when signal to noise ratios are much less than unity. Measurements, using a four-horn monopulse feed with a 28-foot parabolic reflector and a "monopulse radiometer" produced the characteristic monopulse angle detection functions when using the sun, the moon, and Cassiopeia A as boresight reference sources. Precision measurements were made to 8 arc second under varying weather conditions using 28-foot radio astronomy antennas. The accuracy of the measurements were limited by the antenna angle encoders, consequently no conclusions are drawn with regard to the absolute accuracy of the measurements. The celestial coordinates of four discrete radio sources and the equations for coordinate transformation to local elevation and azimuth are contained in the Appendixes.     

Interferometer Design for Elevation Angle Estimation

Radars that are developed for the purpose of monitoring aircraft landings in the terminal air traffic control system can be designed to exploit the relatively high signal-to-noise ratio that characterizes the power budgets calculated for such a link. An interferometer using a pair of low gain antennas can be used to obtain passive coverage over a targe azimuth and elevation sector. A large baseline can be used to obtain the desired elevation angle estimation accuracy. In this paper an optimal tradeoff between the width of the subarray aperture and the width of the interferometer baseline is performed that achieves a specified elevation angle estimation error while minimizing the overall height of the interferometer configuration. The algorithm searches through the class of antenna patterns that can be synthesized from so-called finite impulse response, linear phase digital filters. For the specific problem of designing an elevation sensor for monitoring landing aircraft on final approach, the elevation angle can be estimated with no more than 1-mrad rms error when the aircraft is within ± 60° azimuth, 2.5° to 40° elevation, using two 7-wavelength subarray antennas spaced 8 wave-lengths apart. The design of a separate sensor for resolving the interferometer ambiguities is formulated as a hypothesis testing problem and solved using statistical decision theory. A bound on the probability of an ambiguity error is derived that accounts for the effects of ground reflection multipath and receiver noise.     

机载脉冲多普勒雷达DBS技术

 本文从多普勒谱分辨理论出发,分析了DBS成象的基本原理,实现DBS成象的实时信号处理过程,提出了DBS实时数字信号处理方案。通过计算机模拟试验表明,在雷达天线保持匀速扫描状态时,系统的多普勒波束锐化比可达17.4:1左右,并可对载机前方±15°—60°方位范围内提供一幅大面积的,高分辨力的扇形雷达图象。