Dual Offset Reflector Antenna Research Articles

Laws of geometrical optics mapping in multi-reflector antennas with application to elliptical apertures

In shaped offset dual-reflector antennas, special care must be taken to prevent crosspolarisation for linear polarisation and beam squint for circular polarisation. This problem is addressed by deriving the laws that determine the mapping of the feed pattern onto the aperture of the reflector. There is a presentation of the conditions that must be satisfied for a GO mapping to be ideal without crosspolarisation and beam squint. The paper even present equations which allow the crosspolarisation and phase errors in the reflector aperture to be calculated directly from the mapping function. As an example, this theory is used to specify and characterise offset dual-reflector antennas with both circular and elliptical apertures. The equation for the crosspolarisation is generally valid only for dual-reflector antennas, but can in many cases also be applied to multireflector systems to obtain useful approximate results. This is shown by the application to a trireflector system; the proposed dual-reflector feed of the spherical reflector of the Arecibo Observatory.

Complete dual-offset reflector antenna analysis including near-field. paint-layer and CFRP-structure effects

The computer analysis of dual-offset reflector antennas fed by a circular corrugated horn, using an accurate feed model, is described. Near-field, thermal-paint, and carbon-fiber-reinforced plastic (CFRP)-structure effects are included in order to simulate a realistic design scenario and predict their impact on the radiation characteristics. The theoretical results have been verified by experiment for a near-field illuminated offset Gregory antenna. >

Geometric-optic synthesis of dual-reflector antennas with distributed sources

The problem of synthesising a dual offset reflector antenna system when illuminated by a distributed source, to satisfy prespecified conditions on power and phase distributions over the output aperture are examined under the assumptions of geometrical optics. The formulation shows that the synthesis hinges on solving a system of two coupled nonlinear partial differential equations, one of which is the Monge-Ampère equation. The relationship of this study with previous point-source treatments is examined in detail. Uniqueness properties of the design are extracted from the equations and new features introduced by the distributed source are indicated. Possible applications to contoured-beam reflector antennas fed by real sources are envisaged.

Optimum primary radiator tilt angle of a shaped offset dual reflector antenna

AbstractWhen we shape reflector surfaces of an offset dual reflector antenna for a given desired aperture distribution, we create a phenomenon in which the direction of the reflected ray by the shaped surfaces and an assumed direction of radiation by geometric optics do not coincide. Hence, the characteristics of cross‐polarized waves are degraded. If we shape the surfaces at a tilt angle of the main dish with respect to the direction of the main radiation pattern, we found that the directional errors become extremely small between the direction of the actually reflected ray and that of the assumed direction of radiation by geometric optics for an optimum tilt angle. At this tilt angle, we can shape the reflector surfaces satisfying almost all of the conditions imposed by geometric optics. When we shape the surfaces at the optimum tilt angle, we obtain continuous surfaces which generate a desired axisymmetric aperture distribution along the radial direction. We can design an offset dual reflector antenna with low sidelobes and favorable characteristics for cross‐polarized waves.Based on this theory, we built an experimental offset Gregorian‐type antenna with aperture diameter of about 50 λ. Measured results revealed excellent characteristics for cross‐polarized waves and those for sidelobes. Thus, we confirmed the validity of the theory of shaping reflector surfaces.

Comparative study of reflector antennas for small earth stations

For a small earth station, a detailed comparative study of three types of dual offset reflector antenna is presented. These are the shaped dual-reflector antenna, the sector-shaped paraboloidal reflector antenna and the spherical offset reflector antenna. The efficiency, the radiation patterns and the complexity of fabrication are some of the aspects considered.

Cross polarization in dual reflector antennas--A PO and PTD analysis

A physical optics (PO) and physical theory of diffraction (PTD) analysis of symmetric and offset dual reflector antennas is performed. It is shown that in most cases PO gives sufficient accuracy, but the PTD correction can be of importance to determine the depolarization, especially if the subreflector edge taper is low.

Dual offset reflector multibeam antenna for international communications satellite applications

Dual offset reflector antenna systems offer exciting possibilities for achieving both low scan losses and low cross polarization in geosynchronous communications satellite antennas providing narrow ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100 \leq D/\lambda \leq 400</tex> ) and multiple beam frequency reuse coverages over an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18\deg</tex> conical field of view. Novel geometrical configurations for the reflectors are characterized by simultaneously achieving: 1) blockage free apertures for all element beams within the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18\deg</tex> conical field of view, 2) compatibility with large planar feed arrays, 3) additional degrees of design freedom by orientation and shaping of reflector surfaces for depolarization and scan loss optimization, and 4) large effective <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f/D</tex> ratio achieved in compact and foldable geometries. A comparison of new front-fed offset Cassegrain (FFOC) and side-fed offset Cassegrain (SFOC) systems is made.

A simple derivation of the basic design equation for offset dual reflector antennas with rotational symmetry and zero cross polarization

A simple geometric derivation is given of the equation for designing an offset dual reflector antenna with perfect rotational symmetry and zero cross polarization.

Systematic design of a dual offset reflector antenna with an elliptical aperture

Systematic design of a dual offset reflector antenna with an elliptical aperture

Study of dual-offset reflector antenna with dielectric cone feed

Study of dual-offset reflector antenna with dielectric cone feed

Performance of offset reflector antennas with array feeds

The paper considers the radiation patterns of both single- and dual-offset reflector antennas excited by an array feed in which mutual coupling effects have been fully included. For the single-offset reflector antenna, the crosspolar pattern is dominated by the geometry of the configuration, but for a dual-offset reflector, whose geometry has been optimised to give low crosspolarisation, mutual coupling in the array becomes a dominant factor in influencing crosspolarisation. The influence of feed displacement is also reported. It is found that the change in crosspolar level is marked only for the optimised dual reflector. Then for small displacements mutual-coupling effects dominate, but for large displacements they can be neglected.

An offset dual-reflector antenna shaped from near-field measurements of the feed horn: Theoretical calculations and measurements

A synthesizing procedure for shaping dual-reflector offset antennas is described. The synthesis is based on geometrical optics and near-field measurements of amplitude and phase from the feed element. The procedure preserves good symmetry in mapping from feed to aperture which results in minimal distortions of the electrical characteristics of the antenna. A 1.8 m antenna has been manufactured and measured at 12 GHz. The radiation pattern is characterized by low sidelobes and cross polarization introduced by the offset geometry below -50 dB.

Offset spherical dual-reflector antenna

The dual offset spherical reflector antenna offers the advantage of a circularly symmetric main reflector together with a subreflector possessing an axis of symmetry. These features could lead to significant cost reductions in manufacture compared to existing offset designs. Initial results of a parametric study, using physical optics, show that 64% efficiency is possible with a peak crosspolar level below −35 dB, together with very low sidelobes.

Scan performance of dual offset reflector antennas for satellite communications

This paper summarizes the basic numerical steps employed to analyze dual offset reflector antennas. The technique is based on the application of the geometrical theory of diffraction from the subreflector and physical optics (PO) scattering from the main reflector. The PO integral is evaluated by using the Jacobi‐Bessel series expansion. Numerical results are presented for the off‐axis (scan) performance of an offset (clear aperture) Cassegrain antenna and comparison is made between a Cassegrain antenna and its equivalent paraboloid.

Numerical technique for shaping reflecting surfaces to synthesize antenna patterns

Algorithms for shaping offset dual reflector antenna surfaces are presented which use small areas of optimally tilted conic sections reported by Y. Mizugutch for starting up a numerical synthesis of reflector surfaces. A new ray ratio squared method is described for the precise control of antenna aperture amplitude distributions.

Evaluation of focal fields and radiation characteristics of a dual-offset reflector antenna

A receive-mode analysis of a dual-offset reflector antenna consisting of an offset paraboloid and an offset hyperboloid is presented. In this analysis the field scattered from the offset paraboloid is determined using a g.t.d. formulation involving two edge points and a reflection point, if one exists. A method is described for deciding whether there is a reflection point from the gradient of the path length at the edge points. The focal-region fields and the radiation characteristics are computed by numerical integration of the physical optics current on the offset hyperboloid. An experimental antenna operating at 35 GHz is described Results of measurements of radiation patterns and of the power coupled into a circular waveguide array feed are compared with theory. In each cae reasonable agreement is achieved for copolarised directed components. However, the experimental antenna produced higher crosspolarisation than expected.

Dual reflectors for shaped beams and zero cross polarisation

Offset dual doubly-curved reflector-antenna systems are designed on the basis of geometrical optics to produce a shaped beam (cosec2 pattern) in the vertical plane and a narrow beam in the transverse plane with zero cross polarisation. Two configurations of ray-path geometry are identified and the main parameters are investigated. Blockage effects can be removed by judicious choice of parameter values.

Multiple-beam dual-offset reflector antenna with an array feed

A computer simulation is described for the production of multiple beams by a dual-offset reflector antenna with a feed consisting of a circular waveguide array. It is shown that acceptable efficiencies and low crosspolar levels can be achieved for two sample beams of a multibeam configuration by deriving the array excitation from the focal-region fields of the double-offset antenna.