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     

A shaped single reflector offset antenna with lowcross-polarization fed by a lens horn

A novel compact primary-fed offset reflector antenna with the potential of radiating circular as well as elliptical beams with low cross-polarization, is proposed. The reflector is fed by a horn with a phase-correcting lens in the aperture. Compared to the dual-reflector offset antenna, the concept is easier to assemble and mechanically more robust. The antenna has been synthesized and analyzed by computer programs resulting from modifications of corresponding PO programs for dual-reflector offset antennas. The synthesized antenna exhibits similar cross-polarization, side-lobe level, and aperture efficiency as those of dual-reflector offset antennas, although the one-to-one correspondence between zero cross-polarization and conformal mapping from the feed to the aperture, is not exactly valid for this approach     

A first-order treatment of aberrations in Cassegrainian and Gregorian antennas

The decrease in aperture efficiency caused by small aberrations in a reflector antenna is determined. The important case of a Cassegrainian (or Gregorian) antenna with a feed placed in the vicinity of the focal point is treated in detail. For this case the various aberration components due to astigmatism, coma, etc., are derived explicitly, their effect on aperture efficiency is shown, and the conditions that optimize performance are given. The results are useful for the design of multibeam antennas in ground stations and satellites.     

Application of rectangular and elliptical dielcore feed horns toelliptical reflector antennas

The pattern characteristics of elliptical reflector antennas are investigated when they are fed by rectangular and elliptical horns partially filled with a dielectric. The bandwidth characteristics of these dielcore horns are superior to those of their corrugated horn counterparts. Representative reflector patterns are computed to properly demonstrate the utility of these feeds for reflector antennas with elliptical apertures. This reflector antenna exhibits high efficiency and low cross polarization, and may be suitable for radar and satellite antenna applications. The antenna configuration may become useful in relatively small antennas where more than 10% cross-polar bandwidth is required. The efficient dielcore horns may also be used as feeds for elliptical nonshaped dual-reflector antennas     

Characterization of tapered slot antenna feeds and feed arrays

A class of feed antennas and feed antenna arrays used in the focal plane of paraboloid reflectors and exhibiting higher than normal levels of cross-polarized radiation in the diagonal planes is addressed. A model which allows prediction of element gain and aperture efficiency of the feed/reflector system is presented. The predictions are in good agreement with experimental results. Tapered slot antenna (TSA) elements are used as an example of an element of this type. It is shown that TSA arrays used in multibeam systems with small beam spacings are competitive in terms of aperture efficiency with other, more standard types of arrays incorporating waveguide type elements     

一种T形太赫兹成像系统的设计

为了获得较高的帧速率以及降低成本,提出了一种带有波束扫描功能的T形太赫兹成像系统.系统包含两个共极化扇形波束扫描天线,它们以T字形正交摆放.收发天线具有基本相同的内部结构,由角锥喇叭馈源、产生扇形波束的椭圆主反射体以及用于实现波束扫描功能的旋转次反射体构成,而所有这些元件都镶嵌在两个平行金属板之间.给出了T形太赫兹成像系统的具体设计,提出了设计高性能扇形波束扫描天线的系统化方法,最后给出了一些实验的成像结果,以论证系统的功能.     

Performance and design procedure of dual parabolic cylindricalantennas

The radiation characteristics of dual parabolic cylindrical antennas are studied, and the dependence of the principal plane beamwidths and the peak cross-polarization on their geometrical parameters is determined. The antenna aperture is rectangular in shape and generates an elliptical beam pattern, with a beamwidth ratio that can be controlled by the main and subreflector focal lengths. The far-field patterns are determined by an extended aperture integration method that includes the contributions of the reflected and the main diffracted rays. It is found that the cross-polarization depends of the offset angle between the axis and the direction of the normal to the subreflector surface and can be minimized by optimizing the relative angle between the reflectors. Other pattern characteristics are controlled by the antenna geometrical parameters and the feed illumination. A procedure for the design of these antennas and the expressions for determining the reflector geometries are provided     

Classical axis-displaced dual-reflector antennas for omnidirectional coverage

The aim of this work is to discuss the synthesis and performance of classical dual-reflector antennas suited for an omnidirectional coverage. The reflector arrangements are axially symmetric with surfaces of revolution generated by axis-displaced conic sections, established from geometrical-optics (GO) standpoints to achieve omnidirectional radiation characteristics. Closed-form equations are derived for the design of all possible reflector configurations. The vector GO aperture field is also obtained, yielding an approximate analysis by the aperture method. Some pertinent geometrical characteristics and efficiency curves are then presented and discussed for several antenna configurations fed by transverse electromagnetic coaxial horns (for vertical polarization). A practical antenna design is conducted and analyzed by the method-of-moments technique, demonstrating the accuracy of the efficiency analysis yield by the aperture method for moderately large antenna apertures.     

一种星载通信混合反射面天线的设计方法

为了使星载通信天线产生1个赋形波束覆盖服务区,同时产生1个固定点波束和1个有限扫描点波束,该文提出一种由2个赋形反射面和3个馈源组成的混合反射面天线。该天线是以赋形主反射面共用为基础,等效为2副单馈源单偏置反射面天线和1副双偏置格里高利型赋形反射面天线,分别产生赋形波束、固定点波束和有限扫描点波束。通过对一副口径为1.2 m的天线各个波束进行仿真实验,赋形波束在Ku收、发频段时波束覆盖区边缘(EoC)方向性系数为27.5 dBi,固定点波束在C收、发频段时天线口径效率高于70%,通过将赋形副反射面及对应馈源横向偏焦实现Ka收、发频段的点波束在服务区内外的扫描。仿真结果表明,该混合反射面天线可实现C/Ku/Ka频段的同时通信任务。     

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。     

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.     

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     

Logiciel de conception d’antennes à deux réflecteurs. application aux systèmes conformés elliptiques à alimentation décalée

To facilitate the design of dual reflector antennas, the interactive, graphic CA2R software package handles centrally or offset-fed structures with quadric or shaped reflectors. Surface shaping, based on geometrical optics, improves the antenna’s efficiency and the sidelobe level. Existing techniques are applied to an offset-fed antenna with an elliptical projected aperture. An original numerical method to minimize crosspolar components is also presented.     

Design of scanning spherical trireflector antennas with highaperture efficiency

It is frequently desirable to scan the main beam of a large antenna system without moving the main aperture structure. Spherical reflectors have excellent potential in this application. However, they are not commonly used because of poor aperture efficiency and high side lobes in traditional implementations. This work introduces a new dual-subreflector feed system design which does not require oversizing the spherical main reflector to accommodate scan and yet permits a controlled aperture illumination. The design yields high aperture efficiency, low cross-polarization, and low side lobes     

Novel Gaussian beam method for the rapid analysis of largereflector antennas

A relatively fast and simple method utilizing Gaussian beams (GBs) is developed which requires only a few seconds on a workstation to compute the near/far fields of electrically large reflector antennas when they are illuminated by a feed with a known radiation pattern. This GB technique is fast, because it completely avoids any numerical integration on the large reflector surface which is required in the conventional physical optics (PO) analysis of such antennas and which could take several hours on a workstation. Specifically, the known feed radiation field is represented by a set of relatively few, rotationally symmetric GBs that are launched radially out from the feed plane and with almost identical interbeam angular spacing. These GBs strike the reflector surface from where they are reflected, and also diffracted by the reflector edge; the expressions for the fields reflected and diffracted by the reflector illuminated with a general astigmatic incident GB from an arbitrary direction (but not close to grazing on the reflector) have been developed in Chou and Pathak (1997) and utilized in this work. Numerical results are presented to illustrate the versatility, accuracy, and efficiency of this GB method when it is used for analyzing general offset parabolic reflectors with a single feed or an array feed, as well as for analyzing nonparabolic reflectors such as those described by ellipsoidal and even general shaped surfaces     

An Efficient FDTD Model for Resistively Loaded Cylindrical Antennas With Coaxial Lines

A full coarse-grid based finite-difference time-domain (FDTD) model is proposed for an efficient analysis of resistively loaded cylindrical antennas driven by coaxial feed lines. In the case of the electrically thin resistive antenna, the thin-wire approximation is applied to the near fields around the antenna. The resistive antenna is equivalently represented by a series connection of piecewisely lumped resistors along the antenna axis. And the coaxial line is replaced by an equivalent source over the feed aperture of the line. Then the corresponding FDTD update equations make it possible to implement the full coarse-grid model without additional grid refinements for the antenna and the feed line. The transient reflected feed voltage and the input impedance of resistive antennas are calculated numerically and compared with those of a full fine-grid.      

Aperture-coupled microstrip antenna with a perpendicular feed

A new technique is described for feeding printed antennas. A microstrip antenna on one substrate is coupled through an electrically small aperture to a microstrip feed line on a perpendicularly oriented substrate. No direct connection is made to the patch. Such a geometry allows two separate substrates to be used for the antenna and feed functions. Measurements of a prototype design are presented.     

亚毫米波段折叠光路的准光近场照射天线设计与应用

介绍了一种新颖的折叠光路近场准光照射天线设计方法,并成功应用在微波黑体定标源微弱散射的双站测量中. 在双站测量中,传统的小口径天线适用于低频范围,被测目标足够小才能保证远场条件. 与传统基于远场条件出发的小口径天线设计不同,本文所提出的准光照射天线的设计目的是在目标区降低链路衰减,实现相位平坦、幅值边缘衰减的聚焦照射,并可在近场区域内测得目标的远场散射特征. 设计基于准光学设计方法:由主反射镜和平板反射镜共同构成紧凑的折叠光路,首先确定馈源喇叭天线的等效高斯波束参数,然后基于高斯波束传播理论设计主反射镜,再通过全波仿真验证其折叠路径. 仿真分析表明即使馈源采用基本的圆锥喇叭馈源,也可实现良好的聚焦效果. 双站实测数据表明该天线设计达到了设计目的,为亚毫米波近场双站散射测量的开展提供了关键性的波束控制,具备广泛的应用价值.     

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.     

Diffraction analysis of line feeds for spherical reflectors

The diffraction limitations of the line feeds for spherical reflector antennas are analyzed by means of an asymptotic transition region theory (TRT). It is shown that diffraction from the ends of the line feed causes a broad 6-dB-deep central dip in the aperture field of the reflector. The corresponding reduction in aperture efficiency and increase in spillover are also calculated by means of the TRT. The accuracy of the theory is checked by numerical evaluations of the array sum expression for the radiation field and of the secondary aperture-field and spillover integrals. The results are applicable to the line feeds of the spherical reflector antenna of the Arecibo Observatory