Showing papers on "Parabolic reflector published in 1970"

Analysis of reflector antennas

Abstract: Monograph on analysis of reflector antennas covering electromagnetic field equations, computer aided design, etc

Electronically controllable primary feed for profile-error compensation of large parabolic reflectors

Abstract: The paper shows that it is possible to compensate for the effects of mechanical profile errors in large parabolic reflectors, by means of a specially designed multielement feed array situated in the focal plane of the reflector. The factors relating the magnitude and period of these profile errors to the size and complexity of the compensating feed are discussed, and a novel method is described for achieving this compensation by controlling the phasing of the array. The system employs a spatial Fourier-transforming device, and its use is mainly restricted to long-period profile errors. Experimental results of this process, derived from a small-scale laboratory system employing a 1-dimensional 5ft parabolic reflector incorporating an 8-element feed, are presented. These results demonstrate compensation for profile errors up to π/2 radians. The possible application of this technique to existing and new reflectors is discussed.

The analysis of deployable umbrella parabolic reflectors

Abstract: The radiation characteristics of an umbrella-type reflector are studied in detail. When the supporting ribs of the quasiparabolic reflector are parabolic in shape and the surface between any two adjacent ribs is the surface of a parabolic cylinder, the deviation of the surface from the true parabolic shape has the effect of spreading the focal point of the parabolic reflector into a focal region, the limits of which can be calculated from the knowledge of the reflector parameters. The best feed position can be accurately determined by requiring that the phase error over the surface be minimized. For the cosine to the power n illumination, numerical results showing the gain degradation, the shift in optimum focal point, and the change in secondary patterns, due to the deviation of the reflector surface from the true parabolic surface, are presented.

Millimeter wave antenna system

Abstract: A millimeter wave antenna mounted on a satellite includes a parabolic reflector fabricated of carbon fiber reinforced plastic (CFRP) composite material to enable the parabolic shape of the reflector to be maintained to within three percent of a millimeter wave length despite possible temperature variations on the order of 300 DEG F. between portions of the reflector illuminated by the sun and in the umbra. Waveguides, fabricated from CFRP, for a feed positioned approximately at the focal point of the reflector are the sole mechanical supporting means for the feed. To take advantage of the physical properties of the carbon fiber reinforced plastic composite materials a honeycomb structure is sandwiched between layers of the CFRP. The surface of the reflector illuminated by the feed is coated with a thin film of aluminum which functions as a millimeter wave reflector. The waveguide CFRP interior is coated with a thin film of aluminum to provide the millimeter wave conducting surface.

Design of flared-horn primary feeds for parabolic reflector antennas

Abstract: The paper describes the derivation of a simple design procedure by which the dimensions of a rectangular flared-horn primary feed, operating in the TE10 mode, may be determined for parabolic reflectors, having any f/d ratio and with either a rectangular or circular contour, so that maximum aperture efficiency is obtained. The design technique is based on achieving a best match between the principal component of the reflector focal-plane electric field and that electric field existing in the horn mouth during transmission. In addition, the design procedure predicts the value of the spillover power, the reradiated power, the relative edge-field illumination, the resultant reflector aperture-field distribution and the value of the maximum aperture efficiency obtainable for the given combination of horn feed and reflector.

Matching focal-region fields with hybrid modes

Abstract: A previous anlysis of circularly symmetric reflectors has shown that the focal-region fields consist of an infinite spectrum of hybrid waves. This communication shows that these fields in the case of paraboloidal and spherical reflectors can be closely matched over the open end of a corrugated waveguide propagating a small number of hybrid modes.

Optical scanning seeker

Abstract: In an optical scanning target seeker, optical elements carried within a spinning gyroscopic mass scan the seeker field of view. The seeker spin axis is defined by the gyroscopic mass spin axis. The optical elements are positioned along the gyroscopic mass spin axis, or seeker spin axis, and include a parabolic reflector cut in a face of the gyroscopic mass, a slanted mirror mounted facing the parabolic reflector, and a focusing lens for focusing images reflected from the slanted mirror onto a detector. As the gyroscopic mass spins, energy beams from the seeker field of view are reflected off the slanted mirror and through the focusing lens in a circular sweep pattern. The novelty of this invention is in rotating a prism between the focusing lens and detector on an axis that is orthogonal to the seeker spin axis. The rotating prism changes the circular sweep pattern to curved radial beams and sweeps the beams over the detector. A target image is displayed on one of the beams when a target is present in the seeker field of view. Magnetic sensors react with magnets on the rotating gyroscopic mass and on the prism to indicate where a target is located in the seeker field of view when an image from the target is displayed on the detector.

Parabolic tripod feed support for parabolic dish antenna

Abstract: A tripod feed support structure for the front feedhorn of parabolic reflector antennas has curved members as the support structure which correspond to a paraboloid of revolution. The curved members reflect incident radio wave energy into a focal point having, for example, absorbent material. The structure substantially eliminates the residual effects of aperture blockage caused by the feed support structure.

Measurement of the electromagnetic field intensity in the focal region of a wide-angle spherical reflector

Abstract: In this communication an experimental study has been made of the intensity distribution in the focal region of a wide-angle spherical reflector illuminated by a linearly polarized plane wave of wavelength 12.5 mm. Intensity distributions with respect to the transverse field components were measured along the axis and in several transverse planes. The corresponding distributions for the longitudinal component were measured along directions parallel to the axis and along the same transverse directions. The peak of the longitudinal component was found to occur at a distance of about three wavelengths towards the reflector from the position of the peak of the transverse component. Experimental results have been found to compare well with the available theoretical calculations.

Radiation Field Limitation of Spherical Reflectors Using Gregorian Correctors

Abstract: Use is made of the Fourier integral to derive an expression for the radiation field of spherical reflectors which are corrected for spherical aberration with the use of a subreflector. Calculations for some cases of interest show the sidelobe radiation to be 5.6 dB higher than in a uniformly illuminated aperture.

The boresight sum gain and difference sensitivity of a Cassegrain reflector system fed by a four element array

Abstract: The casaegrain reflector, when fed by a four element array, finds very common usage as an amplitude comparison monopulse system. The boresight sum gain and difference sensitivity essentially determine the range and pointing accuracy of the system. Although much is known about the cassegrain reflector [1] and extensive work has been done on an idealized parabolic reflector monopulse system as a function of feed size and excitation [2], little has been published on the cassegrain monopulse system.