低旁瓣小口径天线口面场分布函数的研究

小口径反射面天线主反射面电尺寸较小、副反射面遮挡较大,经典的口面场分布函数已经不再适用于小口径天线的赋形设计。针对0.9 m Ku频段天线低旁瓣、高效率的要求,用多目标遗传算法优化了其口面场分布。经几何光学赋形设计,利用Grasp软件计算了该天线的辐射性能,在Ku收发频段的口面效率可达60%以上,第一旁瓣低于-18 dB,并且±20°范围内的广角旁瓣满足INTELSAT IESS-601要求。利用一种二阶贝赛尔函数描述了该类口面场分布,分析了小口径天线口面各区域的能量分布对其效率和旁瓣的影响。     

赋形双反射面天线口面场分布的优化

口面场分布函数是反射面天线赋形的主要参数之一,对反射面天线辐射性能起着决定性作用。针对采用分析方法确定口面场分布函数的缺陷,提出了一种优化口面场分布函数的方法。通过分析口面场分布函数与天线辐射场之间的关系,构造了基于遗传算法优化口面场分布函数的数学模型,并分别给出以天线效率和灵敏度为优化目标的2个优化实例。计算结果显示,在优化天线效率的实例中,在满足第一旁瓣电平低于-20 d B的要求下,天线效率高于88%;在优化天线灵敏度的实例中,天线G/T值提高了0.2 d B/K以上的,所提方法达到了预期效果。     

赋形双偏置天线口面场分布函数研究

针对目前关于双偏置反射面天线的无遮挡形式口面场分布函数的研究较少的情况,研究了赋形双偏置天线的几何参数变化对口面场分布的影响,进而深入分析了口面场分布对辐射方向图的影响。针对平方公里阵天线(Square Kilometer Array,SKA)高效率低旁瓣的要求,提出了一种改进型余弦口面场分布函数。计算结果表明,天线第一旁瓣电平低于-20 dB,天线效率高于85%。     

Ku/Ka四波段共馈低剖面赋形天线设计

针对传统切换式多馈源的低剖面反射面天线结构复杂,不能多频段同时工作的问题,介绍了一款四波段单馈源低剖面环焦反射面天线及设计方法。该天线工作在四波段14~14.5 GHz, 11.45~12.75 GHz,19.6~21.2 GHz,29.4~31 GHz。整体天线采用双槽深波纹喇叭单馈源、通过口面场分布和多项式拟合过渡函数的方法构造的赋形副反射面和主反射面。用电磁仿真软件进行了建模仿真和验证。实测结果表明,整体天线较传统天线的效率提高12%以上,第一旁瓣<-14 dB,指标满足设计要求。     

双偏置格里高利天线赋形方法的研究

针对双偏置格里高利天线的赋形技术进行了研究, 给出了一种双偏置格里高利天线的赋形方法.通过全微分条件推导出了副反射面和主反射面的映射关系, 并结合能量守恒定律、反射定律和等光程条件, 求取天线主、副反射面的轮廓曲线.最后给出了一个设计实例, 仿真结果表明:利用文中的赋形方法能够有效控制口面场幅度分布, 实现预期的天线方向图.     

一种用天线电流设置抛物线方程初始场的新方法

主要研究了对数周期天线在电波传播过程中初始场的设置问题。提出了一种用天线电流来设置抛物线方程初始场的新方法,解决了传统初始场设置方法在天线架高较低时口面难以支撑所需要的初始场的问题,建立了抛物线方程初始场设置与天线电流分布之间的直接联系。利用该方法,计算了两组对数周期天线不同条件下的传播因子,验证了该方法的可行性和有效性。     

高效率低旁瓣天线口面场分布函数研究

在赋形双反射面天线中,口面场分布函数对天线电气性能起到至关重要的作用。口面场分布函数妆接影响天线的增益和近角旁瓣。在传统卫星通信地面站中,要求天线第一旁瓣电平在-14dB以下,口面利用率在90%左右,而射电天文望远镜要求天线第一旁瓣电平小于-20dB,口面利用率要求在85%以上。研究并给出了一种整个口面能量均匀分布而外边缘低锥销的口面场分布函数,可以满足高增益,低旁瓣的要求。     

毫米波赋形偏馈双反射面天线技术

为了实现一种具有高口面辐射效率、斜波束出射能力的口径天线,采用几何光学方法设计了一种偏馈双反射面天线.天线主反射面采用赋形设计,副反射面的设计过程中采用Snell定理作为约束条件.通过理论公式、数值模拟仿真和实验测试研究,实现了一种出射波束口径为110 cm、天线口面场分布为抛物形分布、波束出射方向与竖直方向成20°夹角的赋形偏馈双反射面天线.在中心频率95 GHz下,实测天线增益为59.7 dB,第一副瓣电平为-19dB,天线口径效率达到78%.     

基于NURBS建模的椭圆波束赋形天线设计

基于非均匀有理B样条曲面建模,提出一种低剖面椭圆波束赋形天线设计方法。利用馈源喇叭的辐射方向图和主反射面口面场分布函数,对φ=0°面的主副反射面曲线赋形,计算任意φ平面的主副反射面赋形曲线,利用非均匀有理B样条曲面建模技术对主副反射面建模并用全波仿真软件进行仿真优化。仿真结果表明,用该方法设计的椭圆波束天线在12.5 GHz和14.5 GHz时效率分别为67.82％和65.38％,第一副瓣电平均小于-14 dB,该天线实现了低剖面和高效率的优良性能。     

偏轴卡塞格伦天线的二次赋形

针对采用旋转副镜方式切换频段的大型卡塞格伦天线,提出根据等光程条件和主反射镜的射线描迹对副反射镜进行二次赋形,以修正偏轴对光程造成的影响。通过物理光学法计算了二次赋形后的卡塞格伦天线及正馈和偏焦的对称型卡式天线远场方向图,并比较了馈源相心在不同横偏距离时二次赋形后的天线方向图。结果表明:副反射镜的二次赋形有效地修正了偏轴对天线辐射方向图的影响。     

Aperture feed for a spherical reflector

The problem of designing a feed system for illuminating a spherical reflector is examined. A method is proposed for specifying the required field distribution over the aperture of the feed system, and the primary illumination and gain resulting from this distribution are derived. The results indicate that a significantly smaller feed aperture can be employed than would be indicated by conventional ray tracing methods. Specific numerical results are obtained by taking the Arecibo antenna as an example, for which a calculated aperture efficiency of 67.5 percent is possible with approximately a 38-foot-diameter aperture feed.     

一种Ku波段帽型组合馈源设计分析

针对船载小口径天线的馈源设计需求,对一种新型组合馈源的馈电结构进行了模式分析,给出了一个环形口面辐射场的计算方法。通过优化提出了一个Ku频段线极化工作的组合馈源设计实例。经过CST优化仿真,组合馈源的反射板不到3个波长,且在馈源辐射波束半张角为90°时,主面边缘照射电平约为-10 dB。同时由于该组合馈源具有自支撑结构优点,因此非常适合应用于小口径、小焦径比的反射面天线。     

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.     

Improvement of prompt response from impulse radiating antennas by aperture trimming

Reflector impulse radiating antennas (IRA) traditionally have been constructed by terminating a self-reciprocal, transverse electromagnetic (TEM) transmission-line feed structure into a paraboloidal reflector. The section of the paraboloid used is usually circular in cross-section, with the outer boundary coinciding with the circle of symmetry of the TEM feed. The reflector converts the spherical TEM mode on the feed line into an approximate plane wave in the near field by geometric optics. The prompt radiated electric field in the direction of focus is given in the physical optics approximation in terms of the integral of the electric field of the TEM mode over the aperture plane inside the reflector boundary. Balanced feed structures have TEM modes that provide both positive and negative contributions to this integral in the aperture plane. Determination of the contour where the principal component of the electric field in the TEM mode is zero identifies portions of the aperture that contribute destructively to the integral. These portions are removed, thereby increasing the prompt radiated field without altering the feed structure or the applied voltage waveform. Furthermore, decreasing the size of the TEM feed relative to the aperture size, followed by appropriate aperture trimming, allows an even greater increase in radiated field. Results are presented that predict an increase in prompt radiated fields for all electrode configurations. Improvements are largest for electrode angles that are large (with respect to the vertical). The trends predicted by the numerical results are verified by an experiment conducted on a time-domain antenna range.     

SABOR: description of the methods applied for a fast analysis ofhorn and reflector antennas

The program presented in this paper is intended to provide a valuable aid for teaching antennas to electrical engineers, and to provide fast and accurate pre-designs for professionals. This paper covers the theory and numerical techniques used in SABOR. In summary, this program computes the radiated field of an aperture antenna (horn or reflector), using a common engine based on the Gauss-Legendre quadrature method for evaluating the radiation integrals. For horn, the aperture fields are the usual dominant modes of the feed waveguide, with a quadratic phase correction. For reflectors, the aperture fields are computed using geometrical optics ray tracing from the feed horn. Also, equivalent-reflector concepts are applied for dual-reflector antennas. The paper includes some examples to demonstrate the most important features of the program     

圆口径正馈抛物面天线的近场分析

分析了圆口径正馈抛物面天线的近场.采用口径场绕射积分求取了天线的近场及远场方向图,绘制了波束宽度、方向性和最大副瓣电平三个关键参数随场点距离的关系曲线.通过与物理光学法的计算结果对比,验证了该方法的正确性.仿真结果是:随场点距离的减小,波束宽度展宽,方向性减小,最大副瓣电平在一定范围内波动.场点在D2/λ外,远场近似的波束宽度误差小于1%;在0.5D2/λ外,远场近似的波束宽度误差小于10%;在0.5D2/λ内,不能采用远场近似.     

反射面天线焦面场采样研究与相控阵馈源设计

为了设计高性能的相控阵馈源(phased array feed,PAF),通过反射面天线焦面场最优采样的研究,给出了PAF参数与天线口径效率之间的关系,总结了PAF的最优采样范围和单元间距,导出了PAF单元数量的计算公式.给出了一个9 m天线的PAF设计实例和性能分析,在4～7 GHz频率范围内,扫描范围为±3°时,天...     

Scalar horn with shaped lens improves Cassegrain efficiency

It is shown that the aperture efficiency of a classical Cassegrain antenna can be considerably improved if the radiation pattern of the feed is optimally shaped. The corresponding optimum field distribution Over the aperture of the feed consists of a circular main lobe which is surrounded by concentric sidelobe rings. This optimum field distribution with one sidelobe ring included is realized by shaping of a dielectric lens which is positioned in the aperture of a corrugated horn antenna. The design can provide a theoretical aperture efficiency of 90.5 percent when subreflector diffraction and aperture shadowing are neglected, i.e., an improvement of 0.4 dB compared to an optimum conventional feed. Measurements of a model at 22.8 GHz gave a practical result of 85.6 percent. If the model is used to feed a 30 m radiotelescope the overall antenna efficiency becomes about 71 percent.     

A comparison among 1-, 3-, and 7-horn feeds for a 37-beam MBA

A very common multiple beam antenna (MBA) configuration consists of a collimating device illuminated by an array of feeds. The collimating device is usually a reflector or a lens. The feeds are usually horn antennas with a circular aperture. The reflector is usually offset-fed to eliminate aperture blockage; the lens is center fed. The antenna's feeds are excited to produce a finite number of beams, so as to provide contiguous coverage of the field of view. The designer is forced to minimize the angular spacing between adjacent beams in order to maximize the minimum gain over the antenna's field of view. On the other hand, the feed horn's aperture gain is maximized when the feed horn spacing and its aperture diameter are equal. This results in antenna efficiency of the order of 30% when a single feed horn is excited to produce a beam. When a cluster of 3 or 7 adjacent feed horns are excited to produce a single beam, antenna efficiency can be increased to 50%. When it is tolerable, several identical antenna apertures can be used to replace a single aperture configuration. In this case, each of M apertures produces approximately N/M beams of an MBA that produces N beams. Horns producing adjacent beams do not illuminate the same aperture. This permits the use of a much larger horn aperture for a given beam spacing. This results in reduced spillover, higher gain of each beam, and increased antenna efficiency of each aperture. This paper investigates the maximization of gain for several lens antennas. It shows that antenna gain is increased as its focal length is decreased. That is, a focal length-to-diameter ratio (F/D) less than 1 is preferred     

Dual parabolic cylindrical reflectors employed as a compact range

Compact ranges using dual parabolic cylindrical reflectors are investigated, and the dependence of the aperture field on the feed pattern and system geometrical parameters is studied. A uniformity factor is defined to indicate the aperture field uniformity and the significance of the diffracted fields is explored. Offset configurations are also considered and studied. It is shown that their feed location and orientation can be optimized to minimize the geometrical-optics cross polarization. The effects of offset angle on the edge diffraction and aperture shape are also studied