Range distance requirements for large antenna measurements

The dependence of the radiation patterns and antenna gains on the measurement distance when both transmitting antenna and receiving antenna have the same order of large dimensions is discussed. The antenna under test is the transmitting antenna. The near-zone radiation patterns (Fresnel pattern) and the antenna gains of various kinds of circular aperture distributions vs the measurement distances are calculated for an arbitrary size of the receiving probe antenna. It is found both theoretically and experimentally that the near-zone measurement error of the radiation patterns introduced when the receiving antenna is of comparable or the same dimension as the transmitting antenna is smaller than the error introduced when the receiving antenna is very small. Thus, it is concluded that as a range criterion 2D²_a/λ is more appropriate than 2(D_a+D_b)² /λ for pattern measurements (D_a and D_b are linear dimensions of the transmitting and receiving antennas, and D_a⩾D_b is assumed). It is shown that the gain error for any aperture distribution obtained by using a large receiving probe antenna is greater at any range distance than the error obtained by using a small antenna such as a dipole     

Efficient and accurate method for calculating and representingpower density in the near zone of microwave antennas

A method for computing and exhibiting Fresnel-region fields radiated by microwave antennas that uses plane-wave scattering matrix analysis is presented. Near-fields are calculated by numerically integrating the complex far-field antenna pattern. The predicted near fields are exhibited as relative power density contours lying in a longitudinal plane bisecting the antenna's aperture. With spatial-coordinate scaling, each set of contours becomes a function of the relative aperture distribution and the electrical size of the antenna. If the electrical diameter is much larger than any normalized transverse coordinate of interest, the contour set becomes invariant with respect to antenna size. The coordinate normalization can produce contours applicable to any antenna with the same relative aperture distribution, regardless of antenna size     

Gaussian beam techniques for illuminating reflector antennas

Simple design procedures are presented for use when a Gaussian beam is used to illuminate a classical reflector antenna. Displacement of the location of the beamwaist toward the focusing element in the case of electrically small antennas where the aperture is in the near field of the feed was calculated together with modification of the required beamwaist radius. Dual reflector antennas were discussed and design procedures appropriate for systems with large and small focal length to diameter ratio developed. Cases where a reflector or subreflector is electrically small, or in the near field of a feed, are readily treated. For elliptical beam antennas, a simple illumination system using only a scalar horn and a single cylindrical lens can generally be found; this has no ray optics analogue. A configuration of this type is discussed, with a practical case study of a 28-by-80-λ elliptical Cassegrain antenna operating at a wavelength of 3 mm. The design process for designing the feed system is discussed in detail. Despite the small size and relatively large aperture blockage, an aperture efficiency of 0.48 was measured, which compared quite well with the expected efficiency of 0.53, thus verifying the validity of the Gaussian beam design approach     

小型无线光通信终端大视场扫描捕获光学天线设计

针对小型、轻量化光通信终端,设计了一种大视场扫描捕获方案,并对该方案中所涉及的光学天线进行了详细研究。这种扫描捕获方案将MEMS反射镜作为伺服控制机构,进行天线指向控制;光学天线采用收发共口径体制,能够将MEMS反射镜的指向范围扩大3倍,且全视场畸变控制在了0.7%以内;最后对这种捕获方案的通信链路功率进行了核算,功率余量4.6 dB,较为充足。本文所提出的方案体小质轻,是无线激光通信领域中较为独特的形式,在无人机、单兵的应急建链、通信中具备良好的应用前景。     

Calcul du champ électromagnétique sur l’ouverture d’une antenne Cassegrain par la méthode des modes sphériques

The distribution of the electromagnetic field on the aperture of a Cassegrain antenna is obtained by applying the method of the spherical modes to the field diffracted by the auxiliary reflector according to the characteristics of the primary source. The simple case of the perfectly hyperbolic reflector and the more complex one of the pseudo-hyperboloid with a well shaped profile have been studied. The results obtained are confronted on the one hand with the standard methods of calculation and on the other hand with the experimental measures taken in a near field on a Cassegrain antenna operating on 40 GHz.     

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.     

通信网络的可靠性评估

通信网络的可靠性评估是一个难题。目前人们只对环型网和树型网进行可靠性分析。本文首先定义了通信网络的可靠性，依据图论提出了网络生成树的计算方法，以及网络可靠度的估算公式。最后给出了一个栅格型网的可靠度估算示例。     

Design and analysis of a folded Fresnel Zone Plate antenna

Based on the Kirchhoff-Huygens diffraction theory, a simple analytical method of a planar folded Fresnel zone-plate (FZP), that is the case when a planar reflector is placed behind the zone plates, has been developed. According to the numerical calculation results, the design procedure of the FZP antenna has been presented, and its focusing characteristics and gain-optimized conditions have been discussed. The variations of the focal field distribution with the antenna parameters such as zone numbers, focal length and antenna diameter and the radiation power patterns of the FZP have been simulated numerically. To take a good balance of both receiving and transmitting antennas, at 60GHz operating frequency, the focal length should be designed as a half of the antenna diameter and the zone number should be from 10 to 15. The results in this work show that the folded FZP has good focal characteristics and off-axis performance, and its antenna gain can be optimized by the suitable antenna parameter design. The possibility of applying the folded FZP as a low cost and high gain antenna without strict manufacturing requirement for millimeter-wave communications has been shown.     

近海激光通信分集技术对大气湍流扰动抑制的实验

为评估分集收发技术在近海面激光通信系统应用中对大气湍流扰动的抑制作用,设计了基于对多路1 550 nm激光光斑同步采集的验证实验方案。采用由时统终端触发的FPGA+多核DSP架构的实时图像处理系统实现目标中心位置的提取与目标灰度和的统计,进而得到激光从发射端至接收端的到达角起伏方差和闪烁指数。分别比较了等功率条件下单路发射和双路发射间、双孔径接收与等效单孔径接收间的到达角起伏方差和闪烁指数,同时比较了不同跨距下双孔径接收的效果。实验表明,在发射功率相同的情况下,与单路发射相比,双路发射能够有效地抑制因大气湍流扰动产生的到达角起伏和光强闪烁;在接收面积相同情况下,双孔径接收较单孔径接收所产生的到达角起伏与光强闪烁更弱,且在一定范围内,双孔径间的跨距存在最优值。     

地球同步轨道SAR天线约束分析与数字波束形成设计

针对地球同步轨道合成孔径雷达(GEO SAR)的对地观测需求,同时考虑到发射等其他因素的影响,基于GEO SAR天线的面积以及功率约束分析,在一定的系统参数下,设计了一种将数字波束形成(DBF)技术与反射面技术结合起来的天线.该天线在俯仰向采用DBF可以降低系统对于脉宽的限制,从而降低峰值发射功率;在方位向采用DBF可以减小系统实际工作的脉冲重复频率(PRF),增大测绘带宽.该设计方法为未来GEO SAR天线的发展提供了理论参考.     

双馈源双偏置结构星载通信多波束天线

为了使星载通信天线产生赋形波束的同时,又能辐射具有扫描特性的点波束满足特殊情形下的通信要求,提出了一种以单馈源赋形反射面天线为基础,利用另一个馈源进行副反射面赋形,补偿主反射面口径相位差的方法,从而形成高效率点波束,并通过副反射面及对应馈源横向偏焦实现点波束扫描的目的。为了检验方法的有效性,仿真实验了一副口径为2.2 m 的赋形反射面天线。实验结果表明:赋形波束在服务区内部的最小增益是30.0dBi,点波束在服务区内部及周边区域扫描时具有比赋形波束更高的增益,因此,所提方法是有效的。     

Optimization of microstrip feed geometry for prime focus reflectorantennas

The radiation characteristics of a circular microstrip antenna are studied numerically. Surface integral equations are used to formulate the problem from the boundary conditions and moment methods are used to reduce the integral equations to a matrix equation. An analytic method is used to design a microstrip feed and to achieve symmetric radiation patterns with low cross polarization and backlobe levels. The backlobe level is reduced by adding a quarter-wavelength choke to the side wall or the ground plane of the antenna and the bandwidth is improved by stacking two layers. The performance of the feed with the reflector antenna is also considered. One of the feeds was fabricated and tested. Satisfactory agreement between the computed results and the measurement data was obtained. The microstrip feed has a very small size which should reduce its blockage of the reflector aperture     

Optimum polarizations in the bistatic scattering from layeredrandom media

Investigates the polarimetric bistatic scattering characteristics of layered random media. On applying the Born approximation, the authors have calculated the bistatic Mueller matrix of a half-space random medium. The power received by a receiving antenna is the quantity chosen to optimize. The variables of the problem are the polarizations of the transmitting and receiving antennas. For the case when the polarizations of the transmitting and receiving antennas are identical, the authors have calculated the optimum polarizations and they have found that the optimum polarizations include both linear and elliptical polarizations. The conditions for maximum and minimum received power are also obtained. In the backscattering case, they have considered the situation when the transmitting and receiving antennas have independent polarizations. For a two-layer problem, they have observed the influence of the thickness of the layer in the classification of the optimum polarizations     

Shaped-beam horn-reflector antennas

A design method for a horn-reflector antenna, which has a beam of arbitrary cross section, is developed. To show the effectiveness of the design theory, the measured data of an electrical model of Japan's domestic communications satellite antenna of this type are shown in comparison with calculated results. The design theory is based on geometrical optics, and is applicable not only to a horn-reflector antenna, but also to any reflector antenna. At the first step of the design theory, the shape of the wavefront near the aperture is determined to correspond to desired beam shape. The shape of the reflector is then determined by the law of the optical path.     

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.     

Fresnel region power density levels from Earth station antennas

A method for predicting power density levels near transmitting parabolic Earth station antennas is described. The Fresnel region analysis applies to circular aperture antennas with an appropriate aperture amplitude distribution, and can be used to predict power densities along the antenna boresight or at off-boresight angles     

Ku频段卫星通信链路计算

卫星通信具有容量大、成本低、抗干扰性能强、覆盖面积广和通信距离远等优势,已成为舰船通信的重要手段。针对Ku频段卫星通信的特点,提出了一种链路计算方法,并给出了岸基发送站、卫星转发器和接收系统的参数,通过实例分析,计算上行发送站的EIRP、接收站天线的方位、链路降雨衰减、链路载噪比及链路余量等,从而设计出合理的链路预算。     

基于交叉接收的空时频编码高分辨率SAR处理方法

为了实现高分辨率宽测绘带SAR系统,需要在相对较小的天线孔径的约束下,提高系统的功率孔径积,并同时实现宽带信号的收发。针对上述问题,该文提出了一种基于交叉接收的空时频编码高分辨率SAR成像系统方案和处理方法,通过多子阵发射不同子带,不同波形的信号增大相控阵发射子阵的面积,提高了峰值功率,突破了传统SAR系统中功率孔径积的约束。采用交叉接收的频分方式实现大带宽信号合成,避免了复杂的后处理算法。理论和仿真验证了空时频编码的高分辨率SAR处理方法的有效性和可行性。     

UWB系统中天线性能对脉冲波形的影响

分析了超宽带无线系统中,天线在发射和接收过程中对基带脉冲信号波形的失真影响.采用了天线系统传递函数描述天线的辐射和接收特性,在暗室中对典型的超宽带印刷天线进行频域特性和时域特性的测量,给出了脉冲信号的辐射和接收过程.研究表明结合天线系统传递函数,可以设计出更符合FCC辐射功率掩蔽的脉冲信号,以及选取出波形保真系数最佳的本地模板信号,从而获得全局性能最优的超宽带系统.     

Subreflectarrays for Reflector Surface Distortion Compensation

With the increasing interest in the applications of large deployable reflector antennas operating at high frequencies, the requirement on the reflector surface accuracy becomes more demanding. Thermal effects inevitably cause certain reflector surface distortions, thus degrading the overall antenna performance. This paper introduces a novel reflector surface distortion compensation technique using a subreflectarray and presents detailed discussions. A microstrip reflectarray is used as a subreflector, illuminated by a primary feed. By properly adjusting the additional phase shift provided by the subreflectarray, the aperture phase errors caused by the main reflector surface distortions are compensated, resulting in a considerably improved antenna performance. As an example, a distorted 20-m offset parabolic reflector antenna operating at X-band is successfully compensated by a subreflectarray, and the simulation results are compared with those obtained by array feed and shaped subreflector compensation techniques. The microstrip subreflectarray is low-profile, lightweight, and cost-effective. Only one primary feed is required, and a reconfigurable design can be achieved if electronically reconfigurable reflectarray elements are adopted.