电子工程信息

天线阵列是一类由许多天线单元规则或随机排列并适当激励获得预定方向图的特殊天线。为满足不同天线阵列方向图的要求，通过某种手段，获取天线阵列理想口径分布的过程，即为天线阵综合。经典的可用解析式表示的口径分布有Taylor、Chebyshev、Hamming、Gauss和余弦分布等等，也可用各种数值方法获取所需的口径分布。 天线阵综合从其方法或手段上来区分大致可分为解析法和数值法两种；从口径分布的种类上来看有三种：即口径幅相分布综合、仅幅度分布综合和仅相位分布综合；根据天线波束形状，又可区分为锐波束、宽或扇形波束、赋形波束（如余割平方波束）等。在天线与微波技术领域，天线阵综合一直是热门的研究课题，经久不衰，IEEE、IEE等国外杂志与会议文献以及国内众多期刊与会议文献经常发表此类的论文。 原子函数理论用于天线分析和综合由俄罗斯专家克拉夫奇果于1996年提出，在国内乃至西方现有的教课书中鲜有表述。原子函数理论的出现拓展了天线阵综合的研究领域。作者基于原子函数理论的基本概念，阐述了线阵天线、平面阵列一些综合问题的新的研究方法；利用原子函数理论，构造了许多新的口径幅度分布，并将它们与Taylor、Gauss和余弦等传统幅度分布进行比较。原子函数理论对于许多读者来说，是一个崭新的理论，基于以上考虑，本刊以增刊形式发表“天线综合问题及其新的求解方法”一文，希望对读者有所裨益。     

编者按语

天线阵列是一类由许多天线单元规则或随机排列并适当激励获得预定方向图的特殊天线。为满足不同天线阵列方向图的要求,通过某种手段,获取天线阵列理想口径分布的过程,即为天线阵综合。经典的可用解析式表示的口径分布有Taylor、Chebyshev、Hamming、Gauss和余弦分布等等,也可用各种数值方法获取所需的口径分布。     

超宽带超低副瓣相控阵天线时域远场辐射特性研究

本文首先研究了天线时域辐射远场的基本原理,建立了计算公式.在此基础之上,分析了相控阵天线工作在窄脉冲条件下的时域辐射场,发现其时域方向性(如:时域远场峰值方向图、时域远场平均功率方向图)与频域方向性(频域远场方向图)并不一致,这种不一致性随着天线口径的增大或脉冲宽度的变窄而愈加明显,并且在天线注满时间之内表现得尤为突出.文章由此指出:对于超宽带超低副瓣相控阵天线来说,其性能用时域指标去衡量胜于用频域指标去衡量的新观点.     

椭圆口径天线的一种新的设计方法

利用口径坐标变换，比较了圆口径和椭圆口径天线方向函数的差异，得出了将圆口径分布方向图特性映射到椭圆口径的条件，并将圆口径天线最佳综合方法圆Taylor综合应用于椭圆口径天线的设计。将这一条件应用于椭圆离散阵设计，给出了设计实例，比较了连续圆口径分布与椭圆离散阵的特性，扩展了椭圆阵列的常规设计方法。     

基于遗传算法的阵列天线方向图综合

本文介绍了用遗传算法对阵列天线方向图进行综合的方法。首先利用泰勒及切比雪夫幅度分布的方向图作为优化目标进行幅度优化,验证了遗传算法用于阵列天线方向图综合的可行性。然后给出了某S波段成像雷达天线阵遗传优化结果的幅相分布曲线。最后将优化方向图与标准遗传算法综合的结果比较。结果证明文中所述方法能更好的逼近目标方向图。     

近场测量相控阵天线的全息成像方法

研究了一种利用近场测量技术全息成像相控阵天线口径幅相的方法。该方法是把近场测量获得的方向图函数与由单元形式及幅相分布表示的方向图函数进行比较,采用FFT算法和空间域的Fourier重构法,可以快速、精确地成像出相控阵天线口径的“全息图”,进而诊断出阵中单元幅相的奇异程度。通过仿真实验,检验了该方法的成像分辨率和精度,并考察了不同口径区域的成像误差对辐射方向图的影响程度,说明该具有非常好的应用前景。     

恒阻抗TEM喇叭天线设计关键问题研究

恒阻抗TEM喇叭天线具有沿轴线方向特性阻抗为一恒定值的特点,所以喇叭内的反射损耗非常小,常用于超宽带电磁脉冲的辐射与接收。为了提高恒阻抗TEM喇叭天线远场主射方向脉冲峰峰值,通过数值仿真和实验测试研究了天线口径以及特性阻抗值与远场主射脉冲的关系。研究发现,天线沿主轴方向长度一定时,脉冲源通过50Ω同轴线直接向天线馈电,远场主射方向脉冲峰峰值先随天线口径增大而迅速增加,当口径达到某一值时,脉冲峰峰值达到最大值,如果继续增大口径,脉冲峰峰值开始缓慢下降。对于各个特性阻抗值不同的TEM喇叭天线,当它们分别选取上述峰峰值最大对应的口径时,280Ω的恒阻抗天线远场主射方向脉冲峰峰值最大。     

宽带仅幅度测向天线方向图评估

<正>科罗拉多大学电气与计算机工程系的Dejan S.Filipovic在《IEEE Antennas and Wireless Propagation Letters》2018年17卷3期上介绍了一种天线方向图质量评估方法,带有2个偏斜天线实现毫米波宽带仅幅度测向(AODF)。文章提出了几项参数标准,从方向图平滑度和波束宽度随频率变化的稳定性两方面评估了独立天线单元的辐射性能。然后对这些标准进行计算分析,确定目标(喇叭)天线获得弹性AODF性能所需     

基于天线-罩体综合设计的反射面赋形设计方法

介质夹层式天线罩在保护内部天线的同时,使得透过罩体后天线口径场的幅度和相位分布发生变化,其中相位分布的变化是引起天线远场方向图畸变的主要因素.文章从天线罩体综合设计的角度出发,提出一种反射面赋形设计方法,通过赋形反射面来改变天线口径场的相位分布,使其与天线罩引起的相位分布的趋势相反,以保证透过天线罩后的口径场仍为同相场.对某地面卫星通信站的9.14m口径天线罩进行了数值实验,结果表明:所提方法可有效改善带罩天线系统的电性能,对于方向图畸变导致的副瓣和零深变化其效果尤为显著.     

锥削分布圆形口径场的瞬态辐射

利用电磁脉冲的口径瞬态辐射场计算公式,针对锥削分布圆形口径的同相口径场及线性相移、平方律相移等非同相口径场情况,计算了辐射高斯脉冲时的E面能量方向图、半能量波瓣宽度及面积利用系数等参数。计算表明,对于锥削分布圆形口径场,其辐射场特性与口径面半径、激励脉冲宽度及口径面锥削分布指数有着密切的关系。     

Ground-based measurements of inflight antenna patterns for imagingradar systems

An approach is presented for determining the inflight antenna pattern in the cross-track direction for air- and spaceborne synthetic aperture radar (SAR) systems. In the 1991 Oberpfaffenhofen DC-8/E-SAR calibration campaign, ground-based measurement, equipment comprising 18 precision calibration receivers and nine polarimetric active radar calibrators, all operating in C-band, were tested. These instruments are capable of handling various pulse lengths and repetition frequencies, and they have a very high dynamic range. Together with precise internal clocks, these instruments are suitable for recording the actual radar transmit pulse shape for the later evaluation of the desired inflight antenna pattern. Lining up these devices in the cross-track direction, each receiver yields an azimuth cut of the three-dimensional antenna pattern. The elevation pattern was then obtained by time correlation of these azimuth cuts. Further results concerning pulse shapes, squint angles, and H-V pattern misalignment are presented     

Transmit patterns for active linear arrays with peak amplitude andradiated voltage distribution constraints

Distribution functions used in array antenna design typically synthesize specified pattern characteristics without consideration for either the peak amplitude of the radiating elements or the aperture radiated power. There do exist applications, however, in which the pattern synthesis must employ such constraints. In the transmit mode of active array antennas, for example, it is desirable to radiate as much power as possible subject to a per-element peak amplitude constraint while simultaneously suppressing the outer sidelobes. This paper discusses the design considerations of the constrained least squares (CLS) distribution function. In the CLS distribution, most of the radiating elements near the array center are set to their maximum value while only a few of the outer elements are tapered. A method for generating CLS distributions given constraints on both the peak element amplitude and the total effective radiated voltage (ERV) is discussed. The design involves specifying the desired ERV and a weighting function that allows selectively suppressing sidelobes in specified regions. The effects of these design parameters on the far-field patterns are explored     

Radiation pattern synthesis for circular aperture horn antennas

A set of radiation pattern functions, suitable for synthesis of radiation patterns from circular aperture horn antennas, is obtained by assuming an aperture distribution consisting of the fields of cylindrical waveguide modes. A technique is presented for using a linear combination of the radiation pattern functions to approximate a desired radiation pattern. Linear combinations of the radiation pattern functions resulting in maximum secondary gain, when used to illuminate a paraboloidal antenna, are obtained empirically. Using spherical wave theory, maximum performance theoretically obtainable from an antenna is derived as a function of the aperture size of the feed system; the feed efficiency resulting from these theoretical limits on performance is compared to the feed efficiency of patterns obtainable from circular aperture horn antennas, and to experimental results of attempts to realize optimum circular aperture horn patterns.     

A scattering matrix-based beamformer for wide-angle scanning in hybrid antennas

This paper presents a new approach to beamforming in hybrid antennas. Using a scattering matrix model for the hybrid antenna system, a bidirectional transformation is developed that relates the signals at the hybrid system feed to the signals that would be present in a planar array at the location of the reflector aperture. For example, the received fields at the feed of a hybrid antenna system may be transformed into the fields at the reflector aperture, and these reflector aperture fields may then be processed as if they were received by a planar or linear array. Similarly, the desired field or current distribution across the reflector aperture when transmitting may be transformed into the required field or current distribution at the hybrid system feed. This method allows standard linear or planar array analysis and synthesis techniques to be used with the hybrid system. Examples are provided for transmit and receive weight synthesis.     

Scanning of sector and cosecant beams generated by a circular aperture

A method of scanning a one-dimensional shaped pattern generated by a circular aperture is presented. It is shown that the desired beam shape can be retained in the desired scan plane by superposing on the nonlinear phase distribution applied along and parallel to the meridian plane, a linear phase progression along the perpendicular direction. Analysis carried out using the stationary phase method of evaluating the integral reveals that the gradient of the linear phase progression is a function of position along the meridian plane of the aperture. Expressions for the phase functions are derived. Computed results on the phase distribution and the radiation pattern are presented.     

Optimization of the geometry of a TEM-horn for radiation of ultrashort pulses used as an element of an antenna array with controlled position of the main lobe

The finite-difference time-domain method is used to build the model of a TEM-horn with exponential longitudinal distribution of the characteristic impedance along the axis. This model is used to calculate the antenna energy pattern and the shape of the ultrashort pulse of the electromagnetic field in the far zone. Geometrical parameters of the antenna aperture are selected so as to increase the width and the uniformity of the energy pattern in the direction of radiation as well as minimize the level of the backward radiation.     

On the characterization of a reflector impulse radiating antenna (IRA): full-wave analysis and measured results

There is a growing demand for impulse radiating antennas (IRAs) to receive and transmit short pulses. The basic concepts of IRA are reviewed and the far-field pattern versus frequency of an ideal IRA is characterized based on the fundamental properties of IRA. It is shown that the transmitted pulse is ideally in the form of a time derivative of the input pulse. The physical optics simulation results show that the far-field characteristics of a parabolic reflector are very close to an ideal IRA if it is fed properly. The reflector IRA was constructed, analyzed and measured at UCLA. The near-field and far-field characteristics of the reflector IRA are studied using both the method of moments (MoM) full-wave simulations and the frequency domain measurements. In this paper, the radiation mechanism of the reflector IRA is studied using a detailed current distribution on the parabolic reflector and the feeding structure at different frequencies. Applying either the calculated current distribution on the reflector IRA or the measured near-field results, it is seen that the aperture field intensity of the parabolic reflector is not the same in the two principle planes and as a result the beam-widths in the two principle planes are different. The far-field patterns of the antenna are measured and the calculated far-field patterns support the measured results. The calculated current distribution results provide a guideline on how to properly change the feeding structure to achieve a more uniform aperture field and increase the antenna radiation efficiency.     

Rapid method for obtaining footprint patterns for very large antenna arrays

A new antenna pattern synthesis technique that allows the design of large planar antenna array radiating footprint patterns of a specified boundary with controlled ripple and sidelobe levels is presented. The method synthesises the desired footprint as a composition of a set of circular Taylor patterns appropriately weighted with the samples of the pattern obtained after stretching or shrinking a continuous circular aperture distribution developed by the Elliott-Stern method. A footprint of continental Europe radiated by a planar array with a large number of elements shows the technique's performance. The synthesis procedures were completed in about 1 s using a desktop computer.     

基于HPSO的波束扫描反射阵天线设计

提出一种基于混合粒子群算法(HPSO)的低旁瓣波束扫描反射阵天线设计方法。在该方法中,首先利用天线实际方向图和渐变的理想方向图构建了加权的适应度函数。然后通过优化口径面相位分布搜索适应度函数的最小值,最终达到降低旁瓣的目的。同时,设计并制作了一副中心频率为12GHz 的圆极化波束扫描反射阵天线。实测结果与仿真结果较为吻合,天线在56°扫描范围内,旁瓣电平均小于-15dB,且带宽达到11. 67%。     

基于孔径长度域重采样的快速恒定束宽波束形成

为解决宽带阵列天线波束宽度抖动的问题,在分析阵元权系数和阵列方向图傅里叶变换关系的基础上,提出了一种基于孔径长度域重采样的快速恒定束宽宽带波束形成方法。该方法通过期望方向图的傅里叶反变换获取孔径长度域上的权系数曲线,然后用不同的采样间隔对该权系数曲线进行重采样得到不同频率下的阵元权系数。由于仅需进行一次积分运算,该方法具有运算量小、速度快的特点。为使阵列方向图在恒定束宽的基础上具有更好的方向性,通过对孔径长度域拟合度的分析给出了期望方向图的设计方法。仿真结果表明所提方法可以快速形成方向性较好的宽带阵列恒定束宽方向图。