Reflector effects on the performance of a retrodirective antennaarray

This paper presents modeling strategies to determine the operating characteristics of a heterodyne phase-conjugate retrodirective Van Atta (1959) array in the presence of a plane reflector. The models used are based on physical and geometrical optics principles. Predictions of the operating characteristics of the array due to the close proximity of a plane metallic reflector are compared with experimental measurements. It is shown that provided the reflector is positioned at a distance greater than 1.25 times the separation distance between the transmitter and the retrodirective array its effect on the performance of the retrodirective array appears to be negligible     

Radiation pattern of a test reflector antenna from near-fieldmeasurements over focal region of a coupled lens or offsetreflector

A novel scheme has been investigated by which the radiation pattern of a test reflector antenna is determined by rescaling a plot of the electric field distribution in the focal plane of a large lens or in the offset focal plane of a large offset reflector placed in front of the transmitting antenna under test. The major advantage of the technique is that it permits a direct plot of the desired radiation pattern from near-field amplitude data without requiring any phase measurements. The test method is simpler and the test data more accurate than for pervious test methods     

扩束系统设计与分析

随着光电传感技术的快速发展,对于红外干扰技术的要求也越来越高,常规系统已经无法满足能量高度集中、隐蔽性好的新要求.基于此原因,提出了一种离轴双反射式激光干扰扩束系统的设计方案,并对系统主要部件包括离轴双反射式镜组、平面反射镜及固定支撑结构进行了详细的设计与分析.为了缩小系统尺寸,采用了一种新的平面反射镜支撑结构;为减小镜面变形,离轴双反射式镜组及平面反射镜均采用微应力固定设计.仿真实验结果显示,系统一阶固有频率为45.68 Hz,其固定支撑结构应力远小于材料屈服强度.测试结果表明,系统的两轴一致性误差小于等于0.3 mrad,并可以实现1:12.01的扩束比,满足设计指标要求.     

Beam squint in a linearly polarised offset reflector antenna

A beam squint has been found to occur in the field radiated by an offset paraboloid antenna illuminated by a feed with linear polarisation in the plane of offset. The squint, whose existence has been confirmed by computed and measured radiation patterns, occurs in the offset plane, and is typically 0.03 of a beamwidth for a reflector of 6-wavelengths diameter. An assessment is given of the likely effect of the squint on the performance of an offset reflector radiating a circularly polarised field     

一种新型的介质反射面天线

提出了一种新型的多层介质结构的反射面天线，反射平面上所需要的相位补偿通过选择合适的介质厚度来实现，使用几个多层圆形介质即可满足条件。与传统的高增益天线相比，该结构设计简单，加工方便。验证了几种不同层数的结构和一个等口径的抛物面反射面天线。加工并测试了一个采用Vivaldi做馈源的4层结构的反射面天线。仿真和测试结果均表明该天线具有良好性能。     

Compact range reflector analysis using the plane wave spectrumapproach with an adjustable sampling rate

An improved method for determining the test zone field of compact range reflectors is presented. The plane wave spectrum (PWS) approach is used to obtain the test zone field from knowledge of the reflector aperture field distribution. The method is particularly well suited to the analysis of reflectors with a linearly serrated rim for reduced edge diffraction. Computation of the PWS of the reflector aperture field is facilitated by a closed-form expression for the Fourier transform of a polygonal window function. Inverse transformation in the test zone region is accomplished using a fast Fourier transform (FFT) algorithm with a properly adjusted sampling rate (which is a function of both the reflector size and the distance from the reflector). The method is validated by comparison with results obtained using surface current and aperture field integration techniques. The performance of several serrated reflectors is evaluated in order to observe the effects of edge diffraction on the test zone fields     

Analysis of one-dimensional zonal reflectors

A one-dimensional zonal reflector is a conducting surface which is uniform in one direction and has a zonal profile in the other. Similar to a cylindrical reflector, it converts a cylindrical wave from a line-source into an outgoing plane wave. The radiation performance of such reflectors with TM-wave illumination is analyzed by the method of moments (MoM). The influence of corner diffraction and zoning on the sidelobe level is investigated. Three types of configurations are considered, which include the parabolic zonal reflector and two stepwise zonal reflectors of different configurations. It is found that corner diffraction makes a significant contribution to the sidelobe level, but zoning intrinsically raises the far-out sidelobes. Numerical results show that the near-in sidelobes of the stepwise zonal reflector can be significantly decreased by adjusting the geometrical configuration     

Effect of aperture feed and reflector configuration on the time- and frequency domain radiation patterns of reflector impulse radiating antennas

The prompt off-boresight radiation from an arbitrary reflector impulse radiating antenna (IRA) is considered in both the time and frequency domains using a time-domain physical optics formalism. The theory is used to compare the performance between reflector IRAs with common transverse electromagnetic feed configurations that have been designed to maximize the boresight fields. It is found that moving the feed arms of reflector IRAs toward the vertical helps to reduce sidelobe levels, as reflector IRAs with their feed arms oriented at 60/spl deg/ from the horizontal have sidelobes that are 4-5 dB lower in the H plane and 1-2 dB lower in the E plane than more traditional reflector IRAs with feed arms oriented at 45/spl deg/. The lower sidelobes are accompanied by a higher peak gain, albeit with a wider beamwidth. There are corresponding significant differences in the time domain waveforms that result. The theory is verified by comparison with experimental data from a half IRA with feed arms at 45/spl deg/. The peak fields, pulse widths, and overall waveform shapes agree well between theory and experiment, though there are temporal asymmetries in the measured data that are not predicted by the theory.     

Ground-plane-backed hemispherical Luneberg-lens reflector

A spherical Luneberg-lens reflector provides excellent passive wideband and wide-angular radar-signature augmentation, and has been widely used. Much of its signature-enhancement performance over half of its angular coverage can potentially be achieved by using a corresponding low-profile, hemispherical Luneberg-lens reflector, mounted on a reflective ground plane. This paper presents a quantitative study of a practical design of an off-the-shelf hemispherical Luneberg-lens reflector to gain insight and to fully explore its performance limits. Extensive wideband and wide-angle measurements were carried out for this lens configuration, and a comprehensive numerical analysis was also conducted, using the finite-element method combined with a boundary integral equation to complement the test data. The effect, in practice, of a finite-sized ground plane, and the resulting vertically polarized traveling-wave interference to the direct lens reflector's return, were demonstrated. Key design issues are discussed, and potential solutions are suggested.     

Stray signal requirements for compact range reflectors based on RCSmeasurement errors

The authors present a performance criterion for compact range reflectors such that their edge diffracted stray signal levels meet a reasonable radar cross section (RCS) measurement error requirement. It is shown by example that one of the significant error sources is the diffracted fields emanating from the edges or junctions of the reflector. This measurement error is demonstrated by placing a diagonal square flat plate in the target zone and rotating it to appropriate angles. These angles are determined by bisecting the plane wave and stray signal directions. This results in a peak bistatic measurement of the edge diffracted stray signal. It is proposed that the diagonal flat plate be used to evaluate new reflector designs as well as existing systems. A reasonable stray signal performance level has been developed so that new reflector systems can be characterized in terms of an RCS measurement error requirement     

An efficient plane wave spectral analysis to predict the focalregion fields of parabolic reflector antennas for small and wide anglescanning

An efficient approach is described for calculating the field distribution in the focal region of an electrically large, symmetric or offset parabolic reflector antenna with an arbitrary rim contour, when the concave reflector surface is fully illuminated by an obliquely incident arbitrary electromagnetic plane wave. The dominant contribution to the focal-region fields is found by transforming the physical-optics integral over the reflector surface into a plane-wave spectral (PWS) integral. The PWS integral is evaluated rapidly via the fast Fourier transform (FET) algorithm to furnish, in only a single computation, the field for every place in the focal plane (or any plane parallel to it) within the focal region for a given direction of the incident wave. The correction to the physical-optics field is relatively small in the focal region and may therefore be neglected. Numerical results based on this PWS approach are presented, and their accuracy is established by comparison with results based on other approaches     

改善单偏置天线交叉极化劣化的C-band馈源

描述了用波纹喇叭中的 HE_(21)模抵消单偏置抛物面天线非对称平面交叉极化分量的基本原理,介绍了 TE_(21) 模激励器、波纹喇叭的设计方法和展宽馈源抑制单偏置天线交叉极化分量频带宽度的设计方法,给出了 C 波段 2．4m 单偏置抛物面天线的实验测试数据,单偏置抛物面天线非对称平面交叉极化电平改善了10dB,抑制交叉极化分量的馈源相对工作频带宽度大于8％。这种 TE_(21)模激励技术和与主模 TE_(11)模相位差的调整方法,对馈源的电压驻波比几乎没有影响。     

The ohio state university compact radar cross-section measurement range

The ElectroScience Laboratory at The Ohio State University has recently installed a new radar cross-section measurement system. The system uses a Scientific Atlanta compact range reflector (an offset parabolic reflector) to generate a far-field plane wave in the confines of a40 times 20 times 60ft anechoic chamber. The system uses a computer controlled microwave frequency synthesizer and a multichannel computer controlled receiver. The target support/positioning system and an optical target alignment system are also interfaced to the computer. The parameters of the system are 1) operation from 1 to 30 GHz (eventual operation to 96 GHz has been confirmed by field probing); 2) a plane wave volume (test area volume) of 1.3 m diameter; and 3) a sensitivity of -50 dBsm. Of particular importance is the ability of the system to measure phase as well as amplitude. This permits vector subtraction of the background and system calibration using a reference (sphere) target. The development of this system and the performance characteristics obtained so far will be discussed. Some results which demonstrate the system performance will be shown. Of particular interest is the broad-band measurement of both amplitude and phase. This permits conversion of the results to the time domain. Examples will be shown in which the various system components (antennas, reflector, walls, ceiling, etc.) are separated in the time domain by this technique. The development of the range is continuing and planned future improvements will also be discussed.     

用PTD分析双弯曲反射面天线形变和穿孔的辐射特性

该文根据模型反射面天线的爆炸实验测试结果建立了反射面天线形变的数学模型,应用物理光学(P0)法和物理绕射(PTD)理论计钟:了一种赋形反射面天线形变后的辐射特性,同时还计算了反射面天线表面被爆炸破片穿孔后的辐射特性,结果表明,由于反射面的局部形变,直接导致辐射方向图的恶化,并且随着形变部分面积的增大,水平面的副瓣抬高很大,穿孔也会使水平面的副瓣抬高。     

星载大口径太赫兹反射面天线设计与实现

为解决大口径太赫兹反射面天线工程实现的难题,提出了一套口径2.5 m的星载太赫兹天线系统。该天线由大口径反射面天线和准光学馈电网络组成,可以接收183 GHz微波电磁信号。详细介绍了天线系统电性能仿真分析与大口径反射器的结构方案,对加工完成的大口径太赫兹天线系统进行了电性能测试,实测天线主波束效率达到90.2%,能够满足静止轨道卫星载荷的应用需求。     

Offset dual-shaped reflectors for dual chamber compact ranges

The application of the theory of the synthesis of offset dual-shaped reflectors to the design of compact ranges is examined. The object of the compact range is to provide a uniform plane wave with minimum amplitude and phase ripple over as large a volume as possible for a given size reflector. Ripple can be lowered by reducing the edge diffraction from the reflector producing the plane wave. This has been done either by serrating or rolling the edge. An alternative approach is to use dual offset-shaped reflector synthesis techniques to produce a reflector aperture distribution that is uniform over most of the aperture, but with a Gaussian taper near the edge. This approach can be used together with rolling and/or serration if desirable. The amount of phase and amplitude ripple obtained with two different dual-shaped reflector designs is studied as a function of position in the plane wave zone and reflector size in wavelengths. The amount of both transverse and longitudinal (z-component) cross polarization is studied     

A high aperture efficiency, wide-angle scanning offset reflectorantenna

A unique single offset reflector antenna has been designed which provides as much as ±30° of scanning in azimuth while maintaining a much higher aperture efficiency than a torus antenna. Like a torus antenna, different portions of the reflector are illuminated for each scanned beam. The reflector profile curve in the plane of scan is found by least squares to minimize the error for the beams with the greatest scan angle, and then polynomial terms of up to sixth order which minimize nonplanar phase errors are added to produce a three-dimensional reflector surface. Numerical simulation indicates very good results for all 0.5° beams in the ±30° azimuth field of view, with peak gain no more than 0.3 dB below ideal and highest side-lobe levels no worse than 13.3 dB below the peak gain. Additionally, comparable performance can be extended to the elevation plane out to 15°/-30°, although full azimuth performance becomes compromised at extreme elevation scan angles. By using an offset design, there is no blockage of the outgoing beam by the feed array assembly for azimuth scanning. With better feed performance than comparably sized paraboloids, and being more compact than similar torus reflectors, this novel antenna should find numerous uses in spacecraft and terrestrial applications     

Fan beam generated by a linear-array fed parabolic reflector

The theoretical background and the results of computer simulations and experimental studies for a parabolic reflector fed by a linear array are detailed. The concept of using a parabolic reflector antenna fed by a small linear array to generate fan-beam patterns is validated. Large angle scan along the broad-beam direction of the fan beam can be achieved by offsetting the linear array laterally. It is both empirically and numerically demonstrated that the array feed must be displaced in the reflector's axial direction to an optimum location from the focal plane in order to achieve the best antenna gain performance. As a result, the linear-array fed parabolic reflector can be used in place of a long planar array in a multifunctional reflector antenna system     

Étude paramétrique du rayonnement d’une antenne unipolaire placée sur une surface conductrice gauche

The Geometrical Theory of Diffraction is used to predict the pattern of a monopole antenna situated on the axis of a circular ground plane. The moderate pattern dependance versus ground plane diameter is shown. Then, the computation is enlarged to a monopole situated on a skew reflector. The pattern obtained with a reflector showing an outside round shape is nearly the pattern of monopole vertically located in an infinite ground plane.     

Improvements to a surface-wave antenna measurement range with troublesome site effects

A surface-wave antenna measurement range used for ship antenna modelling work has been improved by the development of a novel source antenna. The antenna, a large `half-truncated? corner reflector, has reduced unwanted range reflections to allow phase measurements to be made to an accuracy of approximately ±2°. Also, the screening effect of the reflector allows an adjacent range on the same reflecting ground plane to be operated simultaneously without noticeable effect on the surface-wave range performance.