A scanning spherical tri-reflector antenna with a moving flatmirror

Spherical reflector systems can achieve pattern scanning without rotation of the main reflector through the use of multiple subreflectors that can move. Also, two subreflectors can be shaped to correct for spherical aberration and to control the aperture distribution on the spherical main reflector. In a previous paper (see ibid., vol.41, p.778, no.6, 1993) we introduced a method that offers both aperture phase and intensity control and scans the main beam without an accompanying movement of the illuminated area over main reflector. The method can overcome the poor aperture utilization problem common in spherical reflector antenna systems; however, it requires motion of the entire subreflector system, including the feed, during scan. In this paper we discuss a method that does not require motion of the subreflector system during scan. This method employs a flat mirror that creates a virtual image of the subreflector system. The motion of the subreflector system in the previous design is replaced by the motion of the virtual image that is controlled by the motion of the flat mirror. The new design offers simplified mechanical motion, while maintaining beam efficiency performance comparable to that of traditional spherical tri-reflector scanning antennas, but with some sacrifice in aperture efficiency and cross-polarization performance     

K频段斐波那契网格稀疏阵列分析与设计

针对低轨宽带卫星通信网、5G通信网应用中对K/Ka频段多波束有源相控阵天线的需求,对斐波那契网格阵列进行改进,提出一种大规模低旁瓣稀疏阵列的高效设计方法。首先从数学上对斐波那契网格阵列的栅瓣抑制特性进行解释,进而对阵列进行数值计算和全尺寸三维电磁仿真,最后结合实际工程应用给出一种K频段高密度集成有源相控阵多波束天线的阵面及射频芯片的布板方案。这种大间距阵列在大扫描角域和大带宽内具有低副瓣、无栅瓣、高增益等优良特性,非常适用于通信应用中的高密度集成有源相控阵天线。     

基于极小极大值算法的多波束天线优化设计*

为了以多个性能近似一致的点波束覆盖服务区,提出了一种新型赋形多波束天线设计方法。优化过程中将天线口径投影面内的相位分布和各个馈源的位置作为优化变量,然后以不同位置波束的增益和旁瓣作为目标函数,最后利用极小极大值算法获得高增益低旁瓣多波束覆盖。数值仿真结果表明了优化设计的有效性,解决了传统标准单口径单馈源多波束天线旁瓣电平高、波束交叠增益低的问题。     

基于方向图可重构天线的新型宽角度扫描相控阵

提出了一种基于方向图可重构天线单元的新型相控阵,并分别研究了其均匀、非均匀相控阵的扫描特性。通过重构天线单元的工作状态和各单元的激励,其均匀阵可以获得低副瓣电平等较好的辐射性能,其非均匀阵的主波束扫描范围达到±80°,在扫描平面内3dB 主波束覆盖可达176°,且栅瓣电平很低。研究表明了重构天线在相控阵天线研究中 的广阔应用前景。     

Nonmechanical Beam Steering by Scattering from Ferrites

A small aperture radiating circularly polarized energy is loaded with a spherical ferrite to produce an electronic beam directing system. The ferrite is immersed in a static magnetic field which is in general at an oblique angle with the unreflected direction of radiation. It is shown that radiation is principally in the direction of the magnetic field when the polarization is in the negative sense. From symmetry this allows beam deflection with two degrees of freedom. To consider an application for such a device, it is proposed that this deflection system be used in conical scan. A mechanization is shown, which solves the problem in principle, but it is not competitive with present mechanical scanners from the point of view of side lobes, etc.     

阵列天线的遗传优化

非均匀稀布阵通常具有较高的旁瓣。为降低旁瓣,本文对传统遗传算法进行了改进并用于阵元位置的优化。对于一个孔径为50,由25个阵元组成的阵列天线,本文获得了比已有文献更低的旁瓣。     

A shaped offset-fed dual-reflector antenna

A shaping scheme based on geometric optics for offset-fed dual-reflector antennas is presented. A ray tube emerging from a symmetric feed horn is transformed, after reflections, into a circular beam with a uniform phase and a prescribed radial power distribution on the aperture. In this scheme, Snell's law was not imposed on the main reflector. Based on this approximate solution, computer runs were taken for a 5.5-m dish baseline system, and very satisfactory results were obtained. The system so designed not only gives very low sidelobes but also provides a very high aperture efficiency. At 12 GHz an estimated 84 percent of aperture efficiency was achieved in spite of the severe constraint that the ray intersecting the edge of the main reflector meet a -10-dBi criterion.     

望远超分辨成像中的视场光阑影响及补偿机理

根据衍射光学理论,分析了基于瞳函数调制的望远超分辨成像系统中,用于视场选择和过滤旁瓣影响的视场光阑的衍射效应对于成像效果的影响机理,并给出了补偿原理和方案。微孔视场光阑和四环带阶跃型位相滤波器分别放置在系统一次像面和出瞳位置。理论分析和仿真表明:视场光阑口径越小,最终像面光斑主瓣越宽甚至失去超分辨效果,旁瓣光强峰值与主瓣光强峰值之比也越高。对此时出瞳处的光场振幅、位相场分别进行多项式拟合,求解进行修正的复振幅型光瞳滤波器设计参数,可以有效抑制视场光阑的衍射效应,获得良好的超分辨成像效果,且超分辨成像与光阑效应补偿合二为一,不会增加系统光路的复杂度。并进行了实际实验,验证了以上设计方法的有效性。以上研究结果可为应用在天文观测、空间探测等方面的超分辨成像系统设计提供依据。     

低副瓣有源相控阵天馈系统中的一体化设计

该文提出低副瓣有源相控阵天馈系统中的一体化设计方法,从几个主要方面阐述如何进行一体化设计,在248元天线阵上试验,实测波瓣的峰值副瓣电平和差波瓣零深均在-31dB以下,当波瓣扫描至60时,其峰值副瓣电平不高于-26.5dB,表明一体化设计的必要性。     

Optimum optical limited scan antenna

An optical limited scan antenna system is considered for applications such as spot coverage of a small portion of the earth from a satellite. The optimum criterion relating aperture efficiency, number of control elements, and angular coverage is revisited briefly. The optical scheme advocated utilizes a bootlace aperture lens, a generalized Luneberg lens focused to the near field, and a small array of active elements. The operation of the system is described first in terms of geometrical optics and elementary diffraction principles. The subarray viewpoint is then developed using simplified diffraction concepts. These results form the basis of a design procedure for the synthesis of high performance limited scan systems. An accurate solution necessary for the analysis of small antennas is developed using a modal decomposition and the wave equation. Numerical computations for a case of practical interest verify the expectation of near optimum performance.     

采用DFP-BFGS优化大间距子阵级非周期八角阵

采用DFP-BFGS变尺度算法优化分析了非周期八角阵的子阵中心位置,使栅瓣得到抑制,且阵列的辐射特性达到良好的效果。由于阵列辐射单元之间间距选取大于1个波长,天线方向图必定有栅瓣出现,所以,选择优化子阵中心位置,分散栅瓣能量,使周期八角阵变形为非周期八角阵布阵形式。若该阵列采用高效阵列单元,就可以实现有限相控扫描,且可以获得更低的副瓣要求。     

一种高效率的四脊喇叭馈源

以天线口径效率为目标,研究了四脊喇叭口径对馈源波束等化、波束宽度恒定和天线口径效率等性能的影响,得到了一种3∶1带宽高效率圆四脊喇叭馈源的设计。该馈源在整个频带内具有较低的电压驻波比,三个主平面的主极化方向图波束等化较好,-10d B波束宽度基本恒定,且天线口径效率达到55%以上。     

基于差分进化算法的宽频带扫描不等间距直线阵设计

设计了宽频带波束扫描不等间距直线阵列天线。在阵列天线孔径尺寸、带宽和最大波束扫描角度给定的情况下, 采用DE 算法极小化直线阵在工作频带内扫描方向图的峰值副瓣电平,求得最优的阵元间距分布。仿真结果表明,不等 间距排布方式可在工作频带内有效地抑制直线阵方向图的栅瓣。采用Ansoft HFSS 软件对优化后的直线阵进行了建模仿 真,HFSS 仿真结果与优化计算结果基本吻合。     

Focal region characteristics of focused array antennas

The effects of focused aperture amplitude tapering, both direct and inverse, on axial forelobes and aftlobes are investigated. Taylor tapers give low sidelobes but high forelobes and aftlobes, plus a modest gain degradation. Inverse tapers give low forelobes and aftlobes but high sidelobes and large gain degradation. Uniform excitation gives comparable axial and transverse subsidiary lobes, and is probably the best choice. Focal shift, where the peak axial power density occurs between the aperture and the phase (geometric) focus, due to the1/R^{2}factor, is accurately calculated for a uniform square aperture. Since peak axial power density available from a focused aperture depends only on aperture size in wavelengths and on distance, these focal shift results allow system trade-offs to be made.     

同频大时宽雷达干扰特性研究

针对现代低功率发射和大时宽、高工作比体制雷达工作时受到的同型临近雷达干扰或敌方欺骗干扰,分析和仿真了雷达间主瓣与主瓣、主瓣与副瓣和副瓣与副瓣的同频干扰及其对雷达的目标回波功率、信号频谱、探测概率和信噪比等方面影响所表现出来的特征,给出了同频干扰对雷达接收机前端的损伤分析结果,为雷达抗同频干扰技术和方法研究提供必要的理论和分析基础。     

Synthesis of unequally spaced arrays by simulated annealing

Simulated annealing is applied to the synthesis of arrays in order to reduce the peaks of side lobes by acting on the elements' positions and weight coefficients. In the case considered, the number of array elements and the spatial aperture of an unequally spaced array are a priori fixed. Thanks to the high flexibility of simulated annealing, the results obtained for a 25-element array over an aperture of 50λ improve those reported in the literature     

一种新型双极化口径耦合微带天线单元的研究

本文在比较了一些微带天线实现双极化思路后,提出了一种新型高极化隔离度和低后向辐射的双极化微带贴片结构:即在口径耦合单元的馈线上增加一对对称寄生微带线调节枝节,进行匹配阻抗和实现高极化隔离度,并利用H形口径耦合,减小贴片单元的后向辐射,提高天线的辐射效率。该结构简单,调节简便,馈线网络占有面积较小,且易做成更大规模的双极化天线阵,非常适合现在高分辨率双极化合成孔径雷达和抗多径干扰高的移动通讯系统的需要。文中给出了仿真和实测结果,吻合较好,从而证明了设计的有效性。     

Circularly polarized dielectric-loaded planar antenna excited bythe parallel feeding waveguide network

A new receiving planar array antenna for DBS (direct broadcasting satellite) is proposed. The element antenna is a short waveguide aperture mounted in the ground plane, loaded with a dielectric and polarizers, and excited through its side wall by another feeding rectangular waveguide. The gain of the element antenna loaded with a dielectric is so high that the grating lobes can be reduced sufficiently even if the element spacing in the array is wider than the wavelength in free space. Therefore we can reduce the number of the array elements, and parallel feeding by the low loss waveguide network can be feasible to provide a planar array antenna. This paper describes the experimental results of several kinds of the circularly polarized dielectric-loaded element antennas and the planar antennas fed by the waveguide network. In the 12 GHz band the planar antenna with 64-element radiators has a maximum gain of 31.9 dBi with an aperture efficiency of 94.7%, the 1 dB-down frequency bandwidth of the gain is about 800 MHz (6.7% for a center frequency of 11.85 GHz), and the frequency bandwidth of the axial ratio is less than 1 dB of 850 MHz (7.2%)     

High efficiency and low sidelobe design for a large aperture offset reflector antenna

A design method giving high efficiency and low sidelobes is discussed for large aperture offset reflector antennas. A new reflector shaping technique using the subreflector and the beam waveguide reflector with the parabolic main reflector is proposed to simplify the main reflector manufacturing process. The effectiveness of the technique is confirmed by the model experiments. One problem with this reflector shaping technique is that the subreflector edge level cannot be controlled independently of the main reflector edge level. By investigating the relation between the gain reduction and the subreflector edge level, which affects the wide-angle sidelobe levels, the realizable characteristics of antennas are studied. In order to decrease the subreflector edge level without reducing the aperture efficiency, a technique using an extended reflector is also proposed. Its effectiveness is shown by theoretical and experimental investigations.     

Finite difference analysis of electrically large parabolicreflector antennas

A reflector antenna is analyzed using the finite-difference method (FD). The induced current densities on an axially symmetric parabolic reflector are rigorously calculated. The measured equation of invariance (MEI) is used to terminate the FD mesh very close to the reflector surface. To take advantage of the axial symmetry, the theory of coupled-azimuthal potentials (CAPs) is employed. Illustrative results are obtained for reflector antennas with different aperture dimensions. Results by physical optics (PO) approximation are also included for comparison. The purpose of this paper is not to replace ray optics (RO) and PO in the design of reflector antennas, but to demonstrate the advancement in the FD method, which hitherto was limited to low-frequency and closed-boundary regime. The calculated surface current densities of a reflector antenna do show that the normal component of the current densities at the edges exhibits high standing waves which are missing in PO, and which we know should be there. The standing wave of current densities may not affect the main beam, but certainly will have an effect on side lobes and have a major impact in estimating the loss of the antenna