Exact sampling approach for reflector antennas analysis

A new method for computing the far field of a possibly shaped or deformed reflector antenna based on a sampling representation of the radiation integral is presented. Using a projection technique the required samples can be efficiently computed using a two-dimensional fast Fourier transform (FFT), whereas the radiated field is reconstructed via standard sampling expansion. Numerical examples and computation time analysis are reported showing the effectiveness of the approach particularly for deformed reflectors and/or plane-cut field evaluation.     

New approach to compact measurements on reflector antennas

The letter describes a novel scheme for very compact measurements on reflector antennas. The measurement configuration involves a plane reflector located just beyond (and parallel to) the aperture plane, so that radiated power is reflected and refocused back into the feed. Measurement of return loss can then give information on antenna efficiency and gain. The basic concept is described and its performance confirmed by means of experiments on a 10 ft (3.048 m) diameter reflector. Possible methods of extending the performance of the scheme are briefly discussed.     

Electronic scanning by ferrite-loaded corner reflector antennas

The measured performances of the antennas which consist of a90degcorner reflector, a horn, a core wire of a coaxial line, two or three ferrite rods, and electromagnets magnetizing the respective ferrites are presented. The following are made clear for the antenna with two ferrite rods. The load of the ferrites yields the asymmetric power pattern owing to the anisotropy of the ferrites, though the antenna geometry and the magnetization of the ferrites are symmetric. Moreover, the remarkably sharper main lobe and the higher gain are obtained by loading the ferrites. The main lobe can be turned to the direction reflected about the symmetric plane of the antenna by reversing all the dc magnetic fields applied to the ferrites, that is, electronic lobe switching in theH-plane is realized. It is shown that the antenna loaded with three ferrite rods makes the continuous scan of the main lobe possible by applying the suitable magnetic fields to the ferrites. The direction of the main lobe of these antennas is turned by electronically changing the currents of the electromagnets, that is, by changing the tensor permeabilities of the ferrites. The reciprocity for antennas composed of isotropic media does not hold for these antennas. The receiving power pattern coincides with the transmitting pattern reflected about the symmetric plane when the same dc magnetic fields are applied for both cases. Hence, these antennas permit us to receive from a direction and simultaneously to transmit in the direction reflected about the symmetric plane.     

A new series representation for the radiation integral with application to reflector antennas

Given the true or any approximate current on a reflector, the radiated far-field is determined from a rapidly convergent series representation of the radiation integral. The leading term is a well-shapedJ_{1}(x)/xbeam pointing in a desired direction. Higher order terms provide perturbations to the leading term. The coefficients of the series are independent of the observation angles. Hence, once they are computed, the field may be determined very rapidly at large numbers of points. Initially, a suitable small angle approximation is made that places the radiation integral in the form of a Fourier transform on a circular disk. The theory is then extended such that the results are valid in both the near and the wide angle regions. Application to a rotationally symmetric paraboloid is presented herein. Other applications include the offset and dual reflectors and near- to far-field integrations. A modified form of the series can also be used for Fresnel zone computations.     

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.     

Rim loaded reflector antennas

A general theory of reflector antennas loaded by surface impedances is presented. Spatial variation of primary illumination is taken into account using a generalized slope diffraction coefficient. The theory is experimentally checked on surface loaded square plate scatterers and then used for computing the radiation diagram of parabolic and hyperbolic dishes. Computer programs and computed diagrams refer to the case of focal illumination and negligible tapering of primary illumination.     

Offset parabolic reflector antennas

The paper provides a tutorial review of a number of offset parabolic reflector configurations including both single and double-reflector geometries. The author commences by describing some basic techniques which can be applied to predict the vector radiation fields and provides some indication of the validity of these methods. The formulation of a relatively simple analytical model for the offset reflector antenna is described based upon the physical-optics approximation. The electrical performance of the single-offset reflector is examined by comparison of predicted and measured data. The particular problems arising from the choice of polarisation and reflector dimensions are highlighted, and some practical applications involving multiplebeams, shaped and contoured beams, monopulse tracking and low sidelobes are briefly reviewed. Practical primary-feeds for offset-reflector antennas are discussed and the matched-feed concept is outlined, the matching of the electric fields in the primary-feed aperture to the reflector focal fields being illustrated. The advantages and disadvantages of dual-reflector antennas are then examined, with particular emphasis upon the open Cassegrainian configuration and the optimised doubleoffset configuration which offers, in principle, both freedom from blockage and low levels of cross-polarised radiation.     

Pattern measurements of reflector antennas in the compact range andvalidation with computer code simulation

The measurements were performed at the University's compact range facility. They demonstrated: (1) the excellent dynamic range that can be achieved with antenna pattern measurements in a compact range facility; and (2) the excellent validation achieved for the calculated patterns of two 8-ft diameter reflector antennas. The compact range has a rolled edge modification to its reflector and uses a pulsed radar system to eliminate the clutter interference such that a dynamic range of more than 80 dB can be obtained. The measured far field patterns of two 8-ft reflector antennas, a prime focus fed antenna and a Cassegrain antenna, at 11 GHz were compared with those calculated by Ohio State University's Reflector Antenna Code. The computer code simulation's approach is also briefly described     

Polarization losses in reflector antennas

Various definitions for polarization-loss efficiency of Cassegrainian and front-fed reflectors are compared. The effects of flare angle, feed taper and the feed pattern asymmetry on the polarization-loss efficiency are investigated. The definitions based on aperture fields are shown to be inadequate and far fields must be used for calculating the polarization losses.     

Double spherical cassegrain reflector antennas

There is a need for high gain antennas that are capable of rapid scanning and multibeam operations. This paper presents a study of the double-spherical Cassegrain reflector to ascertain whether this antenna is practical for these purposes. Aperture blocking, spread of the field, and phase and amplitude distributions are examined using geometric optical techniques. Some radiation patterns are calculated to show the effects of illumination taper, aperture blocking, and phase errors.     

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.     

Evanescent-wave tracking: new approach to the analysis of large reflector and aperture antennas

A new method based on local evanescent-wave tracking is proposed for the analysis of large reflector and aperture antennas.     

Depolarization properties of offset reflector antennas

The cross polarized radiation for linearly polarized excitation and the beam displacement for circularly polarized excitation have been investigated for offset reflector antennas. Numerical calculations are given to illustrate the dependence upon the angletheta_{0}between the feed axis and the reflector axis as well as upon the half-angletheta_{c}subtended at the focus by the reflector. In the casetheta_{0} = theta_{c} = 45deg, measured results have been obtained for both linearly and circularly polarized excitations with a dual mode feed illuminating an offset paraboloid. The cross polarized radiation of horn reflector and open Cassegrainian antennas rises sharply to rather high values off the beam axis; however, in general, the maximum cross polarized radiation of offset reflector antennas can be made small by using a small angle between the feed and reflector axes. The cross polarization caused by offset is compared with that caused by an unbalanced feed pattern. The effect of the longitudinal current distribution and of departure of the surface from a paraboloid on cross polarization are also examined. The clarification of these cross polarization properties is found to be valuable in the design of reflector antennas.     

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.     

Cylindrical and three-dimensional corner reflector antennas

Two reflector antennas are proposed. The first is constructed by adding a cylindrical reflecting surface of suitable radius to theV-shaped corner reflector antenna. The feeding element is a half-wavelength dipole. The resulting cylindrical corner reflector provided a 2 dB increase in gain, minimum sidelobe level, low input reactance, and uncritical dependence of performance on frequency. The second antenna is constructed by adding a cylindrical surface to the three-dimensional corner reflector. This extension provided an increase in gain of at least 6.5 dB, an input resistance compatible with the commercially available 50- or75-Omegacoaxial cables, low input reactance, and uncritical dependence of performance on frequency. A grid-type cylindrical corner reflector antenna, and a three-dimensional corner reflector antenna with a cylindrical subsurface of finite reflecting surfaces were designed, and the measured input impedances, gains, and field patterns showed excellent agreement with the theoretical results for both 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.     

An integrated control and structural design approach for mesh reflector deployable space antennas

An integrated control and structural design approach for mesh reflector deployable space antennas is presented in this paper. The coupled relationship of the antenna structure, deployment trajectory, and control system is discussed, and then the integrated design model is proposed. A multi-objective function is set to simultaneously minimize the antenna mass, the impact on antenna, and the energy dissipation of control system. The cross section areas of links, Bezier control points, and controller gain parameters are selected as the design variables. With the eigenfrequency, rigidity, stability, rapidity and accuracy constraints, the optimal integrated design is achieved. The highly nonlinear characteristic of this problem is discussed and corresponding solving strategy and methodology are described. Experiments are carried out to verify the rationality and validity of the structural analysis models and the control algorithm. Numerical simulations demonstrate the feasibility of the proposed design method.     

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.     

Focal region fields of dual reflector antennas

A simplified analytical method to predict the field distribution in the focal region of dual reflector antennas having circular symmetry is presented. The method is used to study the field distribution at the subdish and in the focal plane, and hence the ability of the antenna in focusing the incident wave. Experimental results obtained on a 2.6-m spherical Gregorian reflector operating at 9.0 GHz agree well with theoretical ones.