Main Reflector Aperture Research Articles

A Hybrid Reflector Antenna for Two Contoured Beams With Different Shapes

A hybrid reflector antenna is presented in this letter to generate two contoured beams with different sizes and shapes using a single feed for each beam. This antenna is a dual offset Gregorian design with the Mizuguchi condition and is fed with two horns. One horn illuminates the main reflector and the other one illuminates the subreflector. In this antenna configuration, the main reflector aperture is shared by two contoured beams and the shapes of these two contoured beams are determined by main reflector surface and subreflector surface, respectively, and the electrical performances can be optimized independently. There is, therefore, minimal loss of gain in this dual coverage antenna as compared with a single/dual reflector dedicated to a single coverage. This method has many advantages such as providing two different shaped beams, good aperture efficiency, simple mechanical structure, light weight, and low complexity. The antenna design procedures are described in detail. The Ku-band Earth deck antenna prototype with dual shaped beams is designed, fabricated, and measured. A good gain performance is demonstrated for two different shaped regions. The difference between the predicted edge-of-coverage gain results and the measured results is less than 0.2 dB.

Homology Parameters for Large Axisymmetric Shaped Dual-reflector Antennas

We extend the concept of best-fitting paraboloids for large single and dual reflectors with conic-section surfaces to best-fit shaped surface for large dual reflectors shaped for uniform amplitude distribution. The point focus of the paraboloidal main reflector is replaced by focal lines for the main reflector and the primary subreflector focus, whereas the secondary subreflector point focus at the feed is kept. The reflector surfaces are shaped, and all rays from the main-reflector aperture to the feed meet an equal-path-length condition. This condition may be represented by a set of “homology parameters” determined by a least-squares method. Finally, we calculate the homology parameters and the root mean square of surface errors for an 8-m dual-reflector system including gravity effects for the antenna pointed toward zenith and the horizon.

A New Method of Designing Circularly Symmetric Shaped Dual Reflector Antennas Using Distorted Conics

A new method of designing circularly symmetric shaped dual reflector antennas using distorted conics is presented. The surface of the shaped subreflector is expressed using a new set of equations employing differential geometry. The proposed equations require only a small number of parameters to accurately describe practical shaped subreflector surfaces. A geometrical optics (GO) based method is used to synthesize the shaped main reflector surface corresponding to the shaped subreflector. Using the proposed method, a shaped Cassegrain dual reflector system is designed. The field scattered from the subreflector is calculated using uniform geometrical theory of diffraction (UTD). Finally, a numerical example is provided showing how a shaped subreflector produces more uniform illumination over the main reflector aperture compared to an unshaped subreflector.

Ka대역 위성통신용 타원형 이중옵셋 그레고리안 안테나 설계

In this paper, we have designed the elliptical dual offset gregorian antenna which can use Ka band earth station antennas in the fixed-satellite service. The structure of antenna is increasing the antenna gain by decreasing blockage areas and decreasing wind effects by shortening height of the antenna. The corrugate horn antenna for this antenna has symmetric radiation patterns and low side lobe levels that can meet ITU-R envelope. The distribution of electric field on a aperture of main reflector is calculated by an ray-tracing method that use the radiation pattern of the feed horn. The final geometric of antena is decided by choosing the distribution that comply with antenna requirement. The FEKO analysed electrical performance of this antenna. The fabricated antenna has 45.0dBi(@30.0GHz)/41.7dBi(@20.2GHz), high efficiency and low side lobe level that meet ITU-R S. 580-6 envelope.

About a New Procedure for Offset Bifocal Reflector Antennas Synthesis

This letter presents a novel procedure for designing of three-dimensional offset bifocal reflector antennas (BFRAs). This procedure allows us to determine the reflector surfaces in analytical form as functions of two parametric variables. Initial design considerations are described. Two BFRA example designs with aperture dimensions of about 60 wavelengths are presented. One of them has a field of view of 47 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex> </formula> for the whole main reflector aperture efficiency greater than 50%. Thus, the proposed procedure is suitable for designing scanning and multibeam reflector antennas with a wide field of view in one plane.

Zooming and Scanning Gregorian Confocal Dual Reflector Antennas

The zooming and scanning capabilities of a Gregorian confocal dual reflector antenna are described. The basic antenna configuration consists of two oppositely facing paraboloidal reflectors sharing a common focal point. A planar feed array is used to illuminate the subreflector allowing the antenna to scan its beam. The resulting quadratic aberrations can be compensated by active mechanical deformation of the subreflector surface, which is based on translation, rotation and focal length adjustment. In order to reduce the complexity of the mechanical deformation, least squares fit paraboloids are defined to approximate the optimal correction surface. These best fit paraboloids considerably reduce scanning losses and pattern degradation. This work also introduces two different zooming techniques for the Gregorian confocal dual reflector antenna: the first consists of introducing a controlled quadratic path error to the main reflector aperture; and the second is based on reducing the size of the radiating aperture of the feeding array.

Polarization properties of offset dual-reflector antennas

For an offset dual-reflector antenna design of zero geometrical optics cross polarization, the diffraction-induced cross polarizations calculated from the differential phase shift between the fundamental TEM/sub 00/ and higher order TEM/sub 01/ Gaussian beam modes, which represent principal and cross-polarization components, respectively, are in agreement with measured data. Since this residual cross polarization in the main reflector aperture is in approximate phase quadrature with the principal polarization, the far-field cross polarization is in phase with the principal polarization. Thus, both principal polarizations exhibit the same slight rotation for a given far-field direction. An important consequence is the preservation of orthogonality between two orthogonal linear polarizations from the feed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Antennas employing conical-dielectric horns. Part 2: The Cassegrain antenna

A design theory is presented for Cassegrain antennas employing dielectric-cone feeds. A modal approach is used to describe the aperture field over the subreflector, while a ray-optics method is employed to determine the sub-reflector profile and main-reflector aperture distribution. Experiments have been made with antennas designed for operation over bands centred near 11 and 18 GHz, and results are in generally good agreement with theory. These antennas are shown to have high efficiency, good main-beam symmetry and low mutual coupling.

Proposed high-efficiency spherical-reflector antenna

A technique is proposed for raising the efficiency of sphereical-reflector antennas embodying the Gregorian method of phase correction. The method is based on the Galindo-Williams modified Cassegrain antenna. An additional subreflector is introduced between the Gregorian corrector and the spherical reflector, in order to cause the power rom the feed horn to be uniformly distributed over the main reflector aperture. Equations are presented which enable the co-ordinates of the subreflectors to be computed. Two examples are given and a theoretical effieciency of 93% is predicted in one case.