喇叭反射器天线的电气性能

1.引言喇叭抛物面反射器天线分角锥形和圆锥形两种,这类天线的特点是频带宽、噪声低和便于操作,因此,卫星通讯地面站采用了这类天线。角锥形喇叭抛物面反射器天线是     

用于太阳模拟器光束调制的复合抛物面反射器设计

积分球出射光在远距离处的大辐照面上辐照均匀性及辐照度受出射光角度影响较大。针对这一问题，提出将复合抛物面聚光器逆用为复合抛物面反射器的积分球出射光角度调制方法。首先，研究复合抛物面反射器光束调制原理并推导抛物线方程；其次，分析复合抛物面反射器的参数对辐照面辐照均匀性及辐照度的影响，确定复合抛物面反射器的发散角与截取比等尺寸参数；最后，建立发散式太阳模拟器光学系统模型并仿真。仿真结果表明：复合抛物面反射器将积分球出射光半角由82°调制为25°；在太阳模拟器有效辐照面Φ1000 mm内，与未使用复合抛物面反射器相比，当复合抛物面反射器的截取比为20%时，辐照均匀性提高了0.24倍，为97.30%，辐照度提高了5.1倍，为553.54 W/m2，实现了远距离处高辐照均匀性的大辐照面模拟。     

偏置抛物面反射器天线:述评

<正> Ⅰ.引言偏置抛物面反射器的主要优缺点偏置抛物面反射器不论址在结构上,还是在分析上都很复杂,其主要优点是:(1)降低了口径遮挡影响,如图1所示;(2)能把反射器对初级馈源的反作用减至最小。其缺点是:当被线极化初级馈源照射时,偏置反射器在天线辐射场内产生交叉极化分量;当使用园极化时,虽不产生交叉极化分量,但使天线波束偏离电轴。对于小的偏置反射器,在线极化情况下,也能观测到这种偏置影响。     

前馈四喇叭抛物面反射器天线校正焦距的确定

本文主要应用几何光学原理,采用轴向散焦补偿横向散焦的方法,来确定比相、比幅兼用的前馈单脉冲抛物面反射器天线的校正焦距。利用馈源的轴向散焦导致的平方律相位差对横向散焦导致的线性相位差进行校正,获得了确定天线校正焦距的近似公式。计算结果与两种实际天线实测结果基本一致。     

典型角反阵列双基地一维距离像特性

角反射器在舰船目标防御中发挥着重要作用,如何有效对抗角反射器干扰是当前的研究难题.以典型八面体角反阵列为例,通过电磁计算和暗室测量获得了宽带双基地散射特性数据,分析了一维距离像随观测角和双基地雷达几何结构变化的规律.结果表明当双基地角达到一定角度条件下,角反射器散射强度急剧下降,这一特性可用于抗角反射器方法设计.     

新型变极化角反射器设计及散射特性分析

面向无源干扰灵活可调的发展需求,提出了一种基于极化栅加载的新型变极化角反射器,通过在金属角反射器内壁加载极化栅,以极低的成本实现了角反射器散射回波极化状态的灵活调控.以方形三面角反射器底面内壁加载圆形极化栅为例开展了仿真工作,分别对电磁波正入射以及宽角度入射两种不同场景下散射回波的极化特性进行了分析.仿真结果表明,所设计的变极化角反射器随着极化栅的旋转,回波出现显著的变极化响应,在Poincaré球上呈近似“8”字形,极化状态依次经历垂直线极化、左旋椭圆极化、水平线极化和右旋椭圆极化.此外,特定旋转角度下,经变极化角反射器调制的电磁回波在口面内呈现空域差异性.为验证所设计的新型角反射器的极化调控能力,利用PCB工艺加工制作了极化栅,并将其加载至角反射器内壁,开展了暗室测试,测试数据表明本文所提出的变极化角反射器在时间维和空间维上具备极化调控能力.因此,本文所提出的变极化角反射器在雷达对抗领域有广阔的应用前景.     

压缩天线测试场反射器的设计

应用几何绕射理论的结果,分析、介绍了两种压缩天线测试场(简称压缩场)反射器—滚边反射器和锯齿边反射器。导出了锯齿边反射器的边缘轮廓线方程,并根据J.B.凯勒的口径角点绕射系数公式,介绍了角点绕射场的计算式。给出了平面反射器模型的实验结果。     

基于旋转角反射器的ISAR干扰新方法

根据旋转角反射器的雷达回波特点,提出一种新的ISAR干扰方法.该方法利用角反射器的旋转控制产生的微多普勒效应对ISAR回波进行有效的调制,在方位向上形成干扰条带,同时利用旋转角反射器的距离向布阵实现距离维的压制干扰,从而达到遮盖ISAR目标的目的.对旋转角反射器的干扰建模、旋转角反射器的关键参数选择和布阵策略进行了详细的分析,对该干扰方法的工程实现具有一定的参考价值.最后,仿真数据和实测数据的处理结果验证了该方法的有效性.     

LED汽车前照灯高效抛物反射器的研究

根据非成像光学和光度学理论,针对LED光源的发光特性和汽车造型设计要求,分析了影响抛物反射器能量利用率的几何参数,导出了抛物反射器的光能利用率与反射器的口径、收光角及抛物镜主轴相对LED光源的角度的解析关系式.分析结果表明,反射器单位口径的光能利用率随口径的变化并非单调,而是存在着峰值,当收光角为70.53°时,单位口径收光效率最大值;对一定光学扩展量的抛物反射器,通过旋转LED光源,可以进一步提高光能利用率;抛物反射器的收光角不同,最佳的旋转角度也不同.TracePro仿真模拟结果与理论分析结论基本一致,所得结果为抛物反射器的优化设计提供了理论依据.     

基于极化分解的舰船和角反射器鉴别方法

使用角反射器是舰船电子对抗中常用的一种无源干扰方式,它在时域、频域和空域上与舰船的雷达回波都没有显著差异,因此传统单极化雷达很难有效鉴别舰船和角反射器。分析了舰船和角反射器在极化回波上的特性差异,并基于Krogager极化分解提取了单频点和多频点情况下的特征矢量,通过支持矢量机对舰船和角反射器进行了鉴别。电磁计算数据表明：该方法可以较好地对二者进行鉴别,且对单角反射器和阵列角反射器都有效,为解决舰船和角反射器的鉴别问题提供了一个可行的思路。     

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     

Radiation patterns of paraboloid with log-periodic dipole feed

The effect of axial displacement of phase centre on the secondary performance of a parabolic reflector is described, with particular reference to a log-periodic dipole-array feed. Computed and experimental results are presented.     

Lateral displacement of log-periodic paraboloid feed

The combined effect of lateral and axial displacement of the feed phase centre on the secondary performance of a parabolic reflector is described, with particular reference to a log-periodic dipole-array feed. Computed and experimental results are presented.     

On the accuracy of physical optics

The first-order correction to the physical optics (PO) solution for the axial radiation field from parabolic reflector antennas is found. The correction is of orderk^{-1}and is in quadrature with the PO solution. By means of the correction term the accuracy of the PO surface integral is round to be better than0.22(lambda/D)^{2}dB on axis, whereDis the diameter of the reflector. Thus, the PO solution for the directivity is extremely accurate for commun reflector sizes of several wavelengthslambda.     

基于最小二乘法的天线变形反射面的拟合

面天线变形反射面表达式的确立是计算其电性能的重要基础 ,提出的拟合方法就是用来精确确定变形反射面的数学方程的。其基本原理是通过分析天线结构 ,根据反射面节点位移 ,最小化整个曲面上采样型值点的轴向误差的均方根 ,从而求出用来确定变形抛物面几何位置的 6个参数 ,同时也就得到了基于最小二乘法的变形反射面方程。该拟合方法简单实用 ,易于程序实现 ,能够对天线机械结构设计人员提供了理论指导与帮助。     

Reflector materials for two‐dimensional low‐concentrating photovoltaic systems: the effect of specular versus diffuse reflectance on the module efficiency

Photovoltaic modules in two‐dimensional low‐concentrating systems with specular parabolic reflectors often experience high local irradiance that causes high local currents and cell temperatures. This generally results in power losses. The use of low‐angle scattering reflectors gives a smoother irradiance distribution, which results in a higher fill factor. In order to study how the choice of reflector material influences system performance, two different reflector materials (anodised aluminium and lacquered rolled aluminium laminated on a plastic substrate) were compared. The total and diffuse reflectance spectra of the reflector materials were measured, the integrated hemispherical and specular solar reflectance values calculated, and the angular distributions of scattered light investigated. Two geometrically identical 3× concentrating photovoltaic systems with semi‐parabolic over edge reflectors of the different materials were tested outdoors. While the anodised aluminium reflector, which had higher hemispherical and specular solar reflectance, resulted in a higher short‐circuit current, the low‐angle scattering lacquered foil gave a higher fill factor, due to a smoother image of the sun on the module surface, and an equally high calculated annual electricity production. Given its low price, the latter reflector should thus be more cost‐effective in low‐concentrating photovoltaic systems. Copyright © 2005 John Wiley & Sons, Ltd.     

Reflector surface deviations in large parabolic antennas

One of the important factors affecting the efficiency of parabolic reflector antennas is the degree to which the surface of the reflector deviates from the true parabolic shape. For a given reflector surface it is also important to locate the focal point of the best-fit paraboloid relative to the existing feed support structure. A simple method is presented for making these measurements, and results are given for a particular 60-ft diameter reflector. Static measurements were made with the antenna axis pointed vertically upwards, and changes were also measured as a function of elevation angle and wind. When the surface errors have a Gaussian distribution relative to the focal point, simple theory indicates that the received power relative to that from a perfect reflecting surface isP/P_{0} = exp -(2pi sigma / lambda)^{2}wheresigmais the standard deviation of the surface errors andlambdais the operating wavelength.     

Nd:YAG连续激光辐照铝合金旋转抛物面的温度效应

为了研究激光推进中激光作用反射面后的温度效应,采用自行设计的温度测量系统对不同激光功率辐照下的旋转抛物面铝合金靶的表面温度进行了测试,得到了不同条件下温度-时间关系曲线。结果表明,激光吸收率随激光入射角的增大而增大;罩面上的表面温度与位置相关,自辐照点至径向各点上的温度符合高斯分布,激光辐照点与其它各点呈现明显不同的升温和降温特点;激光辐照停止约数秒后,旋转抛物面表面上各点的温度趋于一致,之后按同一种热扩散方式和降温曲线变温。     

Radiation characteristics of a waveguide-excited short backfire-fedparabolic reflector operating in Q-band

Presents measured results at 31-38 GHz of the radiation characteristics of a 0.252 m diameter parabolic dish fed at the prime focus by a short backfire antenna. The feed consists of an experimentally optimised design of a short backfire antenna, having a conical main reflector of 15° slant angle. The measured radiation patterns of the reflector system generally agree quite well with the prediction based on aperture field integration     

The analysis of deployable umbrella parabolic reflectors

The radiation characteristics of an umbrella-type reflector are studied in detail. When the supporting ribs of the quasiparabolic reflector are parabolic in shape and the surface between any two adjacent ribs is the surface of a parabolic cylinder, the deviation of the surface from the true parabolic shape has the effect of spreading the focal point of the parabolic reflector into a focal region, the limits of which can be calculated from the knowledge of the reflector parameters. The best feed position can be accurately determined by requiring that the phase error over the surface be minimized. For the cosine to the powernillumination, numerical results showing the gain degradation, the shift in optimum focal point, and the change in secondary patterns, due to the deviation of the reflector surface from the true parabolic surface, are presented.