Back-to-Back Reflector Antennas With Reduced Moment of Inertia for Spacecraft Spinning Platforms

A back-to-back reflector antenna system with reduced moment of inertia is proposed in order to address the demanding problem of supporting large reflector antennas on spinning platforms. The configuration provides additional potential advantages, such as reducing the spinning speed by half for a given sampling rate when both back-to-back reflectors are utilized. Geometrical parameters of the reflector are determined such that the moment of inertia of the rotating system is reduced. It is shown that these back-to-back reflectors suffer from a high cross-pol level in the asymmetrical plane due to the large feed offset angle. Two different methods are explored to alleviate the high cross-pol level problem. In the first method, a sub reflector is utilized to minimize the cross-pol level by satisfying the Mizugutchi condition. In the second method, a tri-mode matched feed horn is suggested to achieve a similar result. The suppressed cross-pol level puts forward the gravitationally balanced back-to-back reflector antenna systems as a potential candidate for future spacecraft antennas on spinning platforms.     

Effect of defocus on the prompt response of a reflector IRA

Impulse radiating antennas (IRAs) are an emerging class of antenna that are designed to radiate extremely short electromagnetic pulses with multiple decades of instantaneous bandwidth. The most common IRAs are made with a transverse electromagnetic (TEM) transmission line feeding a paraboloidal reflector. The IRA is usually constructed so that the electrical feed point of the TEM transmission line coincides with the focal point of the paraboloid. The paraboloidal reflector converts the spherical wave emanating from the feed point into a plane wave (i.e., a spherical wave centered at -/spl infin/). In many practical cases, the feed point and focal points are not exactly aligned, producing some defocus of the reflector. In this paper, we model the case of hyperbolic defocus because of its analytic form and compare this model with experimental measurements. A hyperboloidal reflector fed from one focus converts the expanding spherical wave into a second expanding wave which appears to emanate from the second focal point of the hyperboloid (which is behind the reflector). Hyperboloidal defocus is roughly equivalent to moving the electrical feed closer to the reflector than the optical focal point. Previous theoretical results from in-focus IRAs predicted that the E- and H-plane temporal responses should be symmetric with respect to the temporal center of the response. The results shown here demonstrate that the defocusing causes these responses to become asymmetric. The new results are in better agreement with experimental measurements of IRAs and provide a physical explanation for experimental results that differ from the original theory.     

Center-fed parabolic reflector antenna cross polarization due to slightly right-left asymmetric feed patterns

Slightly right-left (R-L) asymmetric feed pattern effects on a center-fed parabolic reflector antenna cross polarization have been described with some numerical computation examples, noting that measured feed patterns, both in theEplane and in theHplane, are generally not completely R-L symmetric and have a slightly different R-L field intensity which produces asymmetrical reflector surface currents. It is shown from the numerical computations that even a slight feed asymmetry, in both amplitude and phase, gives rise to a cross polarization in the secondary prinicpal planes and that, in particular, phase R-L asymmetry incurs two-dimensional movement of principal- and cross-polarized patterns resulting in the rapid increase of principal-plane cross polarization as well as the maximum cross polarization, principal-pattern beamshift, and the sidelobe variations.     

反射面天线馈源喇叭边缘照射电平的分析

反射面天线设计的关键就是通过选择合适的喇叭馈源边缘照射电平以追求天线的高性能（增益,旁瓣电平, 效率等）。本文主要利用实例验证了标准反射面天线馈源喇叭的优选边缘照射电平,分析了赋形反射天线馈源喇叭的优选 边缘照射电平,给出了标准反射面和赋形反射面在设计中各自馈源喇叭的优选边缘照射电平。从而可以在设计工作中对 于不同形式的反射面天线有针对性的设计馈源喇叭的边缘照射电平。     

用FDTD和物理光学混合法分析毫米波抛物面天线

抛物面天线通常的分析方法是几何光学法和物理光学法,对于电大尺寸的抛物面天线这两种方法都可以得到较好的结果,对于电小尺寸馈源的抛物面天线,馈源方向图不仅取决于辐射器本身的辐射特性,其馈电结构对馈源方向图也有较大的影响,在此情况下,用上述方法得到的结果与实验结果之间有较大的误差.利用FDTD可以把整个馈电结构纳入计算域中,得到辐射器完整的近区场,由等效原理可求出抛物面上电流分布,从而用物理光学方法计算抛物面天线远区场.本文用这种混合方法分析计算了毫米波波导裂缝作为辐射器的抛物面天线,计算结果和测试结果相当吻合,证明了方法的有效性.     

预测反射面天线馈源毁伤效应的混合算法

提出了一种预测反射面天线系统在馈源毁伤状态下辐射特性的混合算法.采用时域有限差分法(FDTD)分析了波导开口辐射器馈源穿孔毁伤时的初级辐射特性,利用物理光学法(PO)和物理绕射理论(PTD)分析了反射面天线的次级辐射特性.并采用非场分裂式完全匹配层(UPML)吸收边界条件、共形网格(Conformalmesh)技术提高计算精度和效率,取得了良好的效果,充分验证了混合算法的有效性.     

Pattern synthesis of the offset reflector antenna system with lesscomplicated phased array feed

The performance degradation of an offset reflector antenna with off-axis scanning feed and distorted reflector surface can be improved by using a phased array feed. Generally, both analog attenuators and phase shifters are used in phased array feed. Yet, it seems to make the feed system very complicated. In this paper, a phase-only gradient search (POGS) algorithm is developed to optimize the performance of offset reflector antenna systems using phased array feed that is equipped with phase shifters only. This technique not only can greatly simplify the complexity of phased array feed, but also can provide the reflector antenna with better antenna gain and sidelobe level control capability. Simulation and experimental results are presented to illustrate the excellent performance of offset reflector, with limited beam scanning capability, can be obtained by using this less complicated phased array feed     

A method for producing a shaped contour radiation pattern using asingle shaped reflector and a single feed

Eliminating the corporate feed network in shaped contour beam antennas will reduce the expense, weight, and RF loss of the antenna system. One way of producing a shaped contour beam without using a feed network is to use a single shaped reflector with a single feed element. For a prescribed contour beam and feed, an optimization method for designing the reflector shape is given. As a design example, a shaped reflector is designed to produce a continental-United-States (CONUS) coverage beam. The RF performance of the shaped reflector is then verified by physical optics     

Synthesis of the fields of a transverse feed for a spherical reflector

The problem of designing a transverse feed for a spherical reflector is considered and a method is presented for synthesizing the fields on a surface of a sphere enclosing a feed that will produce a specified reflected field at the surface of a spherical reflector. The method identifies the reflector and a spherical surface enclosing the feed as a boundary value problem and uses a finite set of spherical waves to approximate the boundary conditions. A feed designed to excite this field will in turn produce the desired reflected field at the surface of the reflector, under the condition that that portion of the reflected field which is scattered by the feed may be neglected. It is shown that the feed need produce only a small part of the synthesized field to obtain an antenna efficiency of more than 70 percent. Some typical field distributions will be shown so as to indicate a method for designing a feed and to point out the correlation between the polarization of the synthesized field and the polarization of the reflected field at the surface of the reflector.     

A small dipole-fed resonant reflector antenna with high efficiency, low cross polarization, and low sidelobes

The computer-aided optimization of a small five-wavelength diameter reflector antenna with a center-supported dipole-disk feed is described. The primary radiation is controlled by using a patented beamforming ring to give low cross polarization and low sidelobes due to spillover. The efficiency is maximized by controlling and taking advantage of the multiple reflections between the feed and the reflector. This has inspired the name "resonant reflector antenna." The gain from the feed reflector resonances is so large that it compensates almost completely for the about 1 dB loss due to center blockage of the aperture.     

Effect of surface distortions on the crosspolarisation performance of paraboloidal reflectors

The effects on the crosspolarisation and the radiation patterns of circular paraboloidal reflectors produced by (a) reflector distortions which are periodic in the circumferential direction and (b) a lateral offset of the feed have been evaluated for a wide range of reflector and feed parameters. It is shown that the use of a balanced hybrid-mode feed minimises crosspolarisation introduced by reflector distortions.     

共反射面双频段单脉冲馈源设计

叙述了共反射面双频段单脉冲馈源的一种设计方法，该馈源采用了各自频段的喇叭馈电，实现了双频共面馈电的技术要求。根据馈源的理论方向，计算了天线的理论方向图。     

An equivalent focused reflector feed in place of any generalised defocused or extended feed

A procedure is presented whereby generalised reflector feeds with near-field and/or defocused properties can be replaced by an equivalent point-source feed located at the origin. The equivalent feed induces identical reflector currents and consequently yields identical scattered fields. Thus all physical optics reflector analysis can be carried out in terms of a focused point-source illumination function.     

Scale model development of a high efficiency dual polarized line feed for the Arecibo spherical reflector

The experimental development of a 1:6.535 scale model line feed for the Arecibo spherical reflector is described. The 14.7-ft long model at 2810 MHz simulates a 96.6-ft feed at 430 MHz capable of illuminating the full 1000-ft aperture of the reflector. The feed design requirements are discussed and an experimental program is outlined in which the necessary line source parameters were established using a number of leaky cylindrical test sections. Experimental measurements of both the near and far fields of the model feed are described and typical results are quoted and discussed. Finally, some results obtained after installation of a full size feed in the reflector are given and compared with predictions based on the model data.     

Analysis of the radiation patterns of reflector antennas

The development and application of a numerical technique for the rapid calculation of the far-field radiation patterns of a reflector antenna from either a measured or computed feed pattern are reported. The reflector is defined by the intersection of a cone with any surface of revolution or an offset sector of any surface of revolution. The feed is assumed to be linearly polarized and can have an arbitrary location. Both the copolarized and the cross polarized reflector radiation patterns are computed. Calculations using the technique compare closely with measured radiation patterns of a waveguide-fed offset parabolic reflector. The unique features of this technique are the freedom from restrictive feed assumptions and the numerical methods used in preparing the aperture plane electric field data for integration.     

Effect of aperture feed and reflector configuration on the time- and frequency domain radiation patterns of reflector impulse radiating antennas

The prompt off-boresight radiation from an arbitrary reflector impulse radiating antenna (IRA) is considered in both the time and frequency domains using a time-domain physical optics formalism. The theory is used to compare the performance between reflector IRAs with common transverse electromagnetic feed configurations that have been designed to maximize the boresight fields. It is found that moving the feed arms of reflector IRAs toward the vertical helps to reduce sidelobe levels, as reflector IRAs with their feed arms oriented at 60/spl deg/ from the horizontal have sidelobes that are 4-5 dB lower in the H plane and 1-2 dB lower in the E plane than more traditional reflector IRAs with feed arms oriented at 45/spl deg/. The lower sidelobes are accompanied by a higher peak gain, albeit with a wider beamwidth. There are corresponding significant differences in the time domain waveforms that result. The theory is verified by comparison with experimental data from a half IRA with feed arms at 45/spl deg/. The peak fields, pulse widths, and overall waveform shapes agree well between theory and experiment, though there are temporal asymmetries in the measured data that are not predicted by the theory.     

Focal shifts in parabolic reflectors

Given a parabolic reflector, the maximum directivity is not always achieved by placing the feed at the focal point. Depending on the nature of the feed, the maximum directivity can be obtained by axially displacing the feed either toward or away from the reflector. For low-tapered feeds, the shift should be toward the reflector. This result is similar to an optical phenomenon called the focal shift. We find that this positive shift depends mainly on the Fresnel number of the reflector. For highly tapered feeds, the shift should be away from the reflector. This negative shift becomes significant when the reflector aperture is small, in units of wavelength. A unified view is presented to explain both the positive shift and the negative shift in terms of spillover, aperture illumination efficiency and phase asynchronism. For a system with optimum aperture edge taper, no focal shift can exist.     

A retrodirective microstrip antenna array

A Van Atta retrodirective reflector was designed and developed, using an aperture-coupled microstrip antenna array. This reflector possesses the advantage of reflecting high fields to the source point over a wide range of incidence angles and, owing to the low cost and conformability of the structure, is suitable for applications in intelligent vehicle highway systems (IVHS). An approximate theory associated with the reradiation and scattering principles of the reflector is presented for the purpose of understanding and designing the reflector. The utility of the retrodirective reflector was demonstrated by comparison with a plate reflector and a microstrip antenna array without a feed structure. Finally, a reflector with switches in the middle of the microstrip feed lines was investigated for possible applications in communications and remote identification     

双频共面单脉冲天线研制

论述了双频共面单脉冲天线的设计方法。天线口径较小时,馈源的遮挡口径相对较大,这对天线的性能影响很大,选择口径较小的双频馈源是实现双频共面的关键。天线低频段馈源采用4喇叭单脉冲形式,高频段馈源采用单口多模单脉冲喇叭,通过各自的馈电网络实现单脉冲功能。天线采用卡塞格伦形式,通过对天线和馈源的优化设计,可实现天线双频段工作性能,实测结果与计算结果基本吻合。     

Maximization of the directive gain of a parabolic reflector antenna

The directive gain of a parabolic reflector antenna is maximized by optimizing the feed aperture distribution. The feed aperture distribution is specified by a set ofNbasis functions weighted by coefficients to be determined. This approach is different from the conventional method where, given a particular feed, the directive gain is maximized by subjecting the reflector aperture parameters to optimization.