Aperture blockage in reflector antennas

The aperture blockage effects on both the copolarized and the cross polarized components of the front-hemisphere pattern of a typical quadrupod supported primary-feed paraboloidal reflector antenna are evaluated. A detailed numerical model of the scattering process which involves the feed, the feed supporting struts, and the reflector itself is employed to compute the blockage effect.     

Off-axis cross-polarization and polarization efficiencies of reflector antennas

Cross polarization in reflector antennas is related to the polarization efficiency. Simple approximate expressions for the peak cross polarization are derived in terms of the polarization efficiency. Front-fed, Cassegrainian, and offset antennas are considered. It is shown that symmetrical antennas have lower peak sidelobes than offset antennas with the same polarization efficiency by approximately 2.5 dB. Excellent agreement between the present method and other methods is achieved. Formulas for the off-axis angle at which peak cross polarization takes place are also given for symmetrical and offset reflectors. It is found that for reflectors with the sameD/lambdaratio, symmetrical antennas have larger off-axis angles (1.6 times larger) for peak cross polarization in comparison with offset antennas.     

Design of wide-band corrugated conical horns for Cassegrain antennas

Design procedures based on extensive theoretical and experimental investigations are given for hybrid-mode corrugated conical horns having near-constant beamwidth, low cross-polarized sidelobes and low reflection for continuous bandwidths up to 2.1:1. The design techniques are applicable for horn flare semi-angles to about30deg, which includes most feed horns in dual-reflector antennas.     

Biconical antennas and conical horns with elliptic cross section

The mode-matching technique is applied to the problem of radiation from a conical antenna with elliptic cross section including the degeneration to a sector antenna. In the `guiding region' of the antenna the transverse electromagnetic wave is considered as well as higher-order waves which are described by products of Lame functions which satisfy the boundary conditions. In the exterior region, the field is expanded into products of Lame polynomials. Antenna input impedances and far-field patterns are shown as results. In addition to computing the far-field patterns of a conical horn with elliptic cross section by the aperture field method, the authors analyze the radiation field by a multipole expansion to the mode-matching technique     

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     

Passive intermodulation on large reflector antennas

In this work, an analytical model for the study of passive intermodulation (PIM) on large reflector antennas is presented. Passive intermodulation, in the scattered field, arises when the scatterer is nonlinear, or when it presents junctions connecting linear materials. Its presence causes a degradation of some antenna parameters and, especially, the cross-polar level, which may rise by several tens of dB. It would then be useful to develop a technique to predict its influence, in order to take appropriate steps during antenna design. A heuristic model for the junction problem has previously been derived and validated with measurements in a time-domain physical optics (TD-PO) framework. These results are applied here to a TD-PO analysis of reflector antennas, in particular, for a satellite-communication antenna and for a radio-astronomy antenna.     

Microwave holographic metrology of large reflector antennas

A microwave holographic technique for the determination of amplitude and phase of the principal and cross-polarized aperture fields of large reflector antennas is described. The hologram formation process utilizes the elevation over azimuth scanning system normally associated with these antennas, and, in this respect, appears to be unique among other proposed methods of field probing. The present work describes the means used to obtain vital information on the antenna structure such asE- andH-plane phase centers of the feed, and rms values of the reflector surface profile errors. Accurate prediction ofE- andH-plane radiation patterns in the near- and far-field is also demonstrated.     

Radiation from conical horns with large flare angles

Radiation patterns of conical horns with large flare angles excited in theTE_{11}mode are calculated from a simple solution for horn modes using the vector diffraction formula. Radiation patterns are expressed in closed form when the half-flare angle is less than30deg. Patterns obtained by experiment show close agreement with calculated results.     

An active surface for large reflector antennas

We present a solution adopted for the Noto antenna (Sicily) in order to overcome the degradation of antenna efficiency due to the gravitational deformation of the structure of large antennas. This new setup allows a substantial increase in the operating frequency, and eliminates the dependence of the antenna efficiency on elevation.     

Design of multiple-edge blinders for large horn reflector antennas

Attaching blinders to the sides of pyramidal horn reflector antennas and other large aperture antennas is one method of controlling high sidelobes for horizontal polarization. This paper describes analysis and design procedures for arriving at a useful multiple-edge blinder for reducing undesirable sidelobes of a pyramidal horn reflector antenna. Several blinders have been designed and tested for use with a pyramidal horn reflector antenna. They are directed at reducing a high sidelobe near90degin the azimuth plane where levels (referred to the main lobe) of -52 dB at 3.74 GHz and -58 dB at 6.325 GHz are presently typical. A 14-edge blinder designed using these techniques reduced these levels by 20 dB at 3.74 GHz and 12 dB at 6.325 GHz and did not significantly degrade antenna performance for other angles and other polarizations.     

Application of moment method to large cylindrical reflector antennas

For a cylindrical reflector, illuminated by a line source, the induced surface current is assumed as the sum of the physical optics and an unknown difference current. This difference current is then found by an application of the moment method. It is shown that such an assumption increases the accuracy of the computations and reduces the required computer time.     

大型面天线CAE分析与电性能计算的集成

研究了CAD/CAE集成建模技术和天线组合结构理论,基于反射面位移场并采用PO法分析天线远区电场,解决了由背架、反射面和中心体组成的组合结构网格自动划分难题,开发了面向大型雷达天线结构的集成分析系统.此系统可辅助结构设计人员对天线结构参数进行修改,对结构形状、分布方式进行调整,对天线加工精度、装配精度提出合理要求.工程案例的应用结果证明了该系统的有效性与准确性.     

Gain of corrugated conical horns

The absolute gain of a corrugated horn which is designed as a 100-GHz gain standard for the Crawford Hill 7-Meter offset reflector has been calculated and measured. The measured gain is determined from "three horn" transmission measurements. The other two horns are a TRG Model W869 corrugated horn and a dual mode horn. Correction factors were computed from the near field power transmission formula. The measured gain of the gain standard is30.8 pm 0.16 dB. Comparison between measured and calculated gains indicate very low ohmic loss in a corrugated horn. The condition of maximum gain for a given length has been found to be a half wavelength phase deviation in the horn aperture. Calculated gain data as well as near field correction factors for two identical corrugated conical horns are given here as reference information.     

Spurious signals generated by electron tunneling on large reflector antennas

Large reflector antennas are currently fabricated by assembling a large number of small light aluminum panels onto a superstructure. A large number of aluminum-to-aluminum joints are inherently exposed to RF radiation on such an antenna. It is shown in this paper that the natural oxide layer on aluminum is of the correct thickness to permit electron tunneling through the Al-Al2O3-Al junctions. The nonlinearity due to the junctions then generates spurious signals when these antennas are used for simultaneous transmission and reception of signals at different frequencies. Moreover, the large number of junctions (rivets) on an antenna can combine to produce serious inteference in these diplexed systems.     

Scanning capabilities of large parabolic cylinder reflector antennas with phased-array feeds

Two methods of scanning large parabolic cylinder antennas are examined: one method moves a small array across the focal plane to form a scanning beam; the other method employs a larger stationary array which is capable of electronically scanning the beam. With conventional single-element feeds, the maximum possible scan angle decreases with increasing reflector size. With array feeds, however, the scan limits are shown to be independent of reflector size and antenna gain. Antennas with movable array feeds are found to have high performance (high gain and low sidelobes) even when scanned more than ten degrees off axis; antennas with stationary array feeds degrade rapidly beyond about one degree of scan because of aperture blockage. Off-axis designs which eliminate the aperture blockage are shown to extend the coverage of antennas with stationary feeds to aboutpm 5degrees.     

Bandwidth properties of corrugated conical horns

It is shown that the aperture fields of circumferentially corrugated conical horns remain virtually unchanged over a very wide frequency range, and that the bandwidth improves as the length of the horn is increased. The theory is applicable over a large range of flare angles.     

Astigmatism in reflector antennas

The characteristics of the astigmatic phase error in large parabolic reflector antennas are described. A procedure for focusing an antenna and diagnosing the presence and degree of astigmatism is given.     

Diffraction-optimised shaped-beam reflector antennas

An iterative method is presented to find the reflector profile which minimises the mean-square error between a scattered and a desired field, thereby achieving pattern synthesis. This technique is applied to 3-dimensional circulary symmetric systems for either field- or power-pattern synthesis. Theoretical and experimental results are given for the problem of synthesising a uniform-amplitude sector beam between 20° and 66°.     

Diffraction by wide-flare-angle corrugated conical horns

Expressions for the diffracted far field of a wide-flare-angle corrugated conical horn (operating on the HE11 mode) have been obtained making use of a simpler expression for the aperture field. Expressions for the radiation pattern and gain reduce to a closed form when the flare (semivertical) angle is less than 30°. The theoretical results are in close agreement with experiment.     

Hybrid modes in corrugated conical horns

A simpler solution for spherical hybrid modes in corrugated conical horns has been shown to have a deviation from the rigorous solution of less than 0.7 dB for the case considered by Clarricoats. Expressions for the radiation pattern and gain of such a horn with small flare angle have been obtained under balanced hybrid conditions.