Showing papers on "Parabolic reflector published in 1979"

Imaging reflector arrangements to form a scanning beam using a small array

Abstract: To obtain the performance of a large aperture phased array, a small phased array is combined with a large main reflector and an imaging arrangement of smaller reflectors to form a large image of the small array over the main reflector. An electronically scanable antenna with a large aperture is thus obtained, using a small array. An attractive feature of the imaging arrangement is that the main reflector need not be fabricated accurately, since small imperfections can be corrected efficiently by the array. As an application, a 4.2-m diameter antenna is discussed for a 12–14 GHz satellite with a field of view of 3 degrees by 6 degrees required for coverage of the continental United States.

An efficient technique for the computation of vector secondary patterns of offset paraboloid reflectors

Abstract: A series approach for the rapid computation of the vector secondary pattern of offset paraboloid reflectors wherein the feed is displaced is presented. We show that the Jacobi polynomial series method, which has been demonstrated to provide an efficient means for evaluating the radiation integral of symmetric paraboloid reflectors, can be extended to the case of an offset paraboloid without compromising the ease or speed of computation. The analysis leading to the series formula is also useful for deriving an analytic expression for the optimum scan plane for the displacement of the feed. Representative numerical results illustrating the application of the method and the properties of the offset paraboloid are presented.

Solar concentrator flux distributions using backward ray tracing.

Abstract: Flux distributions produced by parabolic and circular cylinder solar concentrators subject to surface slope errors and defocusing are determined. The technique developed traces a set of rays from a point on the absorber back through the concentrator optics to the sun. The solar flux at the absorber point is the sum of the flux associated with each ray. Various models of the solar disk are introduced by weighting the flux associated with each ray as a function of where it strikes the solar disk.

Method of making precision parabolic reflector apparatus

Abstract: An improved method of making a high precision trough shaped parabolic reflector apparatus is described. A smooth surfaced sheet of flexible material is bent and formed over a convex mold comprising a number of precision shaped parabolic arcs mounted to a base. Means are provided for clamping the flexible sheet of material and drawing it into close conformity with the convex mold. The backside or convex side of the sheet of material is then cemented to a support framework comprising a number of approximately parabolic, but not necessarily precision formed web or rib members which are joined together by a torsion tube or similar structural stiffening means. The type of cement utilized accurately fills any discontinuities and/or inaccuracies in the arcuate shape of the approximately parabolic ribs so that the ribs and the flexible sheet are bonded rigidly together as a unit without distortion or strain on the sheet. The approximately parabolic, but non-precision ribs and stiffening means thereafter serve to maitain the sheet of flexible material in a highly accurate and precision parabolic contour produced by the precision parabolic mold.

Scan limits of off-axis fed parabolic reflectors

Abstract: The scan limits of point-fed paraboloidal and line-fed parabolic-cylinder reflector antennas are derived for large reflectors of arbitrary focal-length-to-diameter ratio ( F -number). A numerical approach is employed which incorporates the effects of all higher order spatial distortions (ray aberrations) normally neglected in previous analyses. The results demonstrate that paraboloids of large F - number have substantially less scan capability than could be inferred from earlier analyses.

Reflector system having sharp light cutoff characteristics

Abstract: A light fixture comprising parabolic reflector segments therein, the lamp being located at the focal point of the segments. One segment has an arc preferably more shallow than the other segment. The window opening is angled preferably at an angle of 60 degrees to the elongate axis of the parabolic segments to provide sharper light cutoff or less spill light from one reflector segment than from the other. A shield positioned parallel to the elongate axis and on the side of the axis within the reflector segment where the cutoff characteristics are the greatest, permits primary reflected light from the lamp, while preventing direct light from the lamp to pass above the shield. The specular underside of the shield enhances light reflection therefrom while the darkened top shield surface blocks secondary reflection above the cutoff angle.

The cosmic microwave background radiation.

Abstract: Radio Astronomy has added greatly to our understanding of the structure and dynamics of the universe. The cosmic microwave background radiation, considered a relic of the explosion at the beginning of the universe some 18 billion years ago, is one of the most powerful aids in determining these features of the universe. This paper is about the discovery of the cosmic microwave background radiation. It starts with a section on radio astronomical measuring techniques. This is followed by the history of the detection of the background radiation, its identification, and finally by a summary of our present knowledge of its properties. II. RADIO ASTRONOMICAL METHOD S A radio telescope pointing at the sky receives radiation not only from space ,but also from other sources including the ground, the earth’s atmosphere, and the components of the radio telescope itself. The 20-foot horn-reflector antenna at Bell Laboratories (Fig. 1) which was used to discover the cosmic microwave background radiation was particularly suited to distinguish this weak, uniform radiation from other, much stronger sources. In order to understand this measurement it is necessary to discuss the design and operation of a radio telescope, especially its two major components, the antenna and the radiometer 1 . a. Antennas An antenna collects radiation from a desired direction incident upon an area, called its collecting area, and focuses it on a receiver. An antenna is normally designed to maximize its response in the direction in which it is pointed and minimize its response in other directions. The 20-foot horn-reflector shown in Fig. 1 was built by A. B. Crawford and his associate? in 1960 to be used with an ultra low-noise communications receiver for signals bounced from the Echo satellite. It consists of a large expanding waveguide, or horn ,with an off-axis section parabolic reflector at the end. The focus of the paraboloid is located at the apex of the horn, so that a plane wave traveling along the axis of the paraboloid is focused into the receiver, or radiometer, at the apex of the horn. Its design emphasizes the rejection of radiation from the ground. It is easy to see

Solar energy collector

Abstract: A solar collector comprising a plurality of direction adjustable elongated parabolic reflectors (16,18) side by side Along the focus of the reflectors tubes (8) for a heat collecting medium extend, which are connected to heat exchangers or the like In order to enhance the versatility and efficiency of the solar collector each reflector consists of reflector wall portions (16,18) movably connected to each other and operable from an open parabolic reflector condition to a non-reflector condition, in which later they entirely enclose the tubes (8)

Infrared intrusion detection system

Abstract: A passive infrared intrusion detection system including a mirror assembly having an array of plane mirrors disposed at respective angular positions to provide a wide field of view. A parabolic mirror confronts the plane mirror array and is disposed with an infrared detecting element at its focal point. Radiation received in the field of view is directed by one or more of the plane mirrors to the parabolic mirror which focuses the received radiation onto the detecting element which provides an electrical signal which is processed to provide an alarm indication of intruder presence.

Energy control device

Abstract: First and second reflectors, having a parabolic concave reflective surface and a conical reflecting surface, respectively, are vertically spaced on co-linear axis. An energy source, such as a loudspeaker mounted atop the frusto-conical second reflector near the apex of the conical reflective surface thereof is at or proximate the focal point of the concave reflective surface of the parabolic reflector. It is desirable for the major diameters of the reflectors to be approximately twice the wave-length of the lowest frequency sound for which the device is applicable. The shapes of the reflective surfaces are established to provide essentially equal path lengths of energy radiated from the source to a wave front to provide coherent omnidirectional energy propagation from the assembly or, in an alternative use of the apparatus, receive radiant energy and focus it on target instead of a loudspeaker at the focal point of the parabolic reflective surface.

The cosmic microwave background radiation

Abstract: Radio Astronomy has added greatly to our understanding of the structure and dynamics of the universe. The cosmic microwave background radiation, considered a relic of the explosion at the beginning of the universe some 18 billion years ago, is one of the most powerful aids in determining these features of the universe. This paper is about the discovery of the cosmic microwave background radiation. It starts with a section on radio astronomical measuring techniques. This is followed by the history of the detection of the background radiation, its identification, and finally by a summary of our present knowledge of its properties. II. RADIO ASTRONOMICAL METHOD S A radio telescope pointing at the sky receives radiation not only from space ,but also from other sources including the ground, the earth’s atmosphere, and the components of the radio telescope itself. The 20-foot horn-reflector antenna at Bell Laboratories (Fig. 1) which was used to discover the cosmic microwave background radiation was particularly suited to distinguish this weak, uniform radiation from other, much stronger sources. In order to understand this measurement it is necessary to discuss the design and operation of a radio telescope, especially its two major components, the antenna and the radiometer 1 . a. Antennas An antenna collects radiation from a desired direction incident upon an area, called its collecting area, and focuses it on a receiver. An antenna is normally designed to maximize its response in the direction in which it is pointed and minimize its response in other directions. The 20-foot horn-reflector shown in Fig. 1 was built by A. B. Crawford and his associate? in 1960 to be used with an ultra low-noise communications receiver for signals bounced from the Echo satellite. It consists of a large expanding waveguide, or horn ,with an off-axis section parabolic reflector at the end. The focus of the paraboloid is located at the apex of the horn, so that a plane wave traveling along the axis of the paraboloid is focused into the receiver, or radiometer, at the apex of the horn. Its design emphasizes the rejection of radiation from the ground. It is easy to see

Imaging properties of off-axis parabolic mirrors.

Abstract: Geometric optics is used to find the shape of the image and the irradiance cast on a spherical target by a circular beam after reflection by a far off-axis paraboloidal mirror. For moderately large f/No. the image is found to be nearly circular with its center shifted slightly from the beam axis. However, the target irradiance can be highly asymmetric unless the beam intensity falls off rapidly with radius. An expansion in powers of inverse f/No. is used to obtain closed form expressions for the image shape and the target irradiance. Numerical studies are carried out for parameters relevant to the design of a laser fusion reactor. Limits are placed on allowable tilt errors by means of a naive analysis of ray aberrations. A useful formula is derived for the perturbed target irradiance under small tilt errors, based on a new expression for the caustic. These simple formulas allow one to carry out detailed design studies without recourse to ray tracing codes.

Carrier plate for parabolic solar energy collector - supports parabolic reflectors and is reinforced at rear and is supported by several spaced struts

Abstract: The solar energy collector has a carrier plate (27) on which one or more parabolic reflectors (26) are mounted. The opposite surface of the carrier plate (27) carries a zig-zag metal or plastics reinforcing element (28). The surface of the carrier plate (27) on which the reflectors (26) are mounted pref. has a number of spaced struts (29), each with a parabolic support face (30), on which the parabolic reflectors rest. The carrier plate (27) may have the form of a rotational paraboloid and be carried by a pivot mounting for focussing the solar energy collector.

Support structure for a large dimension parabolic reflector and large dimension parabolic reflector

Abstract: The reflector support structure 12 includes a plurality of rod-like elements 13 which are secured together at their respective ends, forming joints 14, in such an arrangement so as to describe a generally paraboloidal shape comprised of a plurality of open triangles. Elongated standoff elements extend outwardly from at least the joints 14 of the reflector support structure 12 and have secured thereto positioning elements for supporting the apexes of triangular-shaped reflecting sections 11. A plurality of reflecting sections 11 are arranged to substantially mate along their respective edges, and are held in place by the supporting elements, to form a large, substantially parabolic, reflector 10. When the reflector 10 and reflector support structure 12 are used as part of a solar collection system, a tracking support structure supports the reflector support structure off the ground and in a correct orientation relative to the sun.

Semi-tubular parabolic multiple core helix solar concentrator

Abstract: A device for improving the radiant solar energy collection efficiency of a helix shaped solar collector-concentrator by concentrating the sun's rays on a plurality of specifically positioned energy absorber collecting cores as the sun moves through its solar day without the use of active tracking devices, is provided. By using a helix shaped semi-tubular parabolic collector-concentrator with multiple specifically positioned collecting cores crossing and intersecting the shifting sharp focal axis of the reflective surfaces of the helix shape at a slight angle to the focal axis, rather than being exactly on the focal axis, at least one or more of the collecting core surfaces is in sharp focus at all times, thus optimizing the sun's radiant solar energy collection capacity of said device. Further increased primary direct and non-reflective incident solar energy is collected on a plurality of collecting cores providing additional collection efficiencies. The helix shaped semi-tubular parabolic reflector and the energy absorber cores are enclosed by a transparent, relatively air-tight covering which causes the device to be resistant to environmental factors such as snow, rain, wind, pollution and other atmospheric degradants. The additional confined heat energy generated and trapped within the covered helix shaped semi-tubular parabolic reflector further increases the device's collecting efficiency. In one embodiment the heat energy thus collected may be transferred to a heat absorbing medium to be utilized in a useful manner. In another embodiment the solar energy impinging on the energy absorber collecting cores may be converted by other means such as photoelectric conversion into electrical energy to be utilized and stored.

Multiple stage optical system for creating high-intensity solar light beam

Abstract: An optical system concentrates solar light energy or energy from another light or electromagnetic radiation source into a low-diverging, collimated, high-intensity beam. The optical system has several stages, each including an input collimating lens, a fresnel-like reflecting surface, and a parabolic reflector; and prior to the first stage is an input objective lens and at the output of the last stage is a pinhole aperture and an output collimating lens.

Solar heat reflector unit - comprises mirror adjustably clamped in supporting frame shaped to correspond to mirror surface geometry

Abstract: The reflector is for a solar heat collector, and comprises a mirror (11) adjustably clamped in a supporting body (12) The body can be a frame equipped with elastic and adjustable clamping studs or bolts (13), and shaped to match the mirror shape, being formed by a series of strips (15) The reflector which may be of glass or metal In the case of a parabolic reflector, the frame may have two straight and two curved supports

Electrical and thermal energy generator - uses laser and directs solar radiation onto converter via system of mirrors

Abstract: An electrical and thermal energy generating system is used, which does not require any raw material and does not pollute the environment It uses a device to convert the light of a laser into electrical or thermal energy The laser (6) is fed from solar radiation (1) and directs a light beam (7) on to the convertor The output of the laser is directed on to a convex mirror (10), where it is deflected on to a parabolic mirror (8) with photocells (11)

Receiving and transmitting properties of small grid paraboloid by moment method

Abstract: The receiving and transmitting properties of a grid paraboloidal reflector of aperture diameter 273λ and f/D ratio 0395, operating at 410 MHz, are analysed using the moment method For the receiving situation, with a normally-incident plane wave illuminating the reflector, the distributions of current, obtained in the inner grids only, show a close resemblance to those predicted by the physical optics approximation It is shown that neither maximum scattered nor maximum total electric field on axis is received at the geometrical focus, but at a point between this focus and the vertex This result is in agreement with that calculated by the physical optics method for small solid paraboloids of the same f/D ratio Contours of scattered off-axis fields are also presented in the geometric and true focal planes of the paraboloid as well as in longitudinal planes of such a reflector In the transmitting situation, the grid paraboloid is excited by a centrally driven couplet feed, positioned at different points along the axis It is shown that the feed position affects considerably the distributions of current in the feed elements but not in the reflector grids, and confirms that defocusing the couplet feed results in an increased forward power gain

Parabolic mirror made by the rotation method: its fabrication and defects.

Abstract: One possible method of making a large screen display is to use a virtual image system with a large concave mirror. A concave mirror with a high quality surface can be made inexpensively. A resin, such as an epoxy resin which hardens at room temperatures, is formed into the parabolic shape by a rotating dish. A mirror with a 920-mm diam and a 1150-mm focal length is made, which has sufficiently good characteristics for a virtual image display system. The fabrication and defects of mirrors made by this method are described.

New approximate method for computing the radiation properties of reflector antennas: application to cylindrical reflector antennas

Abstract: A new approximate method for computing the current distribution on reflector antennas is presented. It employs the modified Kirchhoff approximation and leads to a vector integral equation of the second kind for the current distribution. The integral in this integral equation can be interpreted as a current due to the curvature of the reflector surface. The method is applied to a cylindrical parabolic and a cylindrical corner reflector antenna. The integral equation is solved numerically, and the computed current distributions and directive gains are compared with those obtained by solving the exact integral equation as well as with the results that follow from the application of the physical-optics approximation.

SHADE - A computer model for evaluating the optical performance of two-axis tracking parabolic concentrators

Abstract: A computer model SHADE (Selection of Heliostat Arrangement for Distributed Engines) has been developed at the Pacific Northwest Laboratory to aid in determining the optical performance of two-axis tracking parabolic concentrators The shading of individual mirror assemblies in a field of parabolic dishes determines the optimal field arrangement and the most efficient method of plant operation SHADE provides a simple and inexpensive analytical tool for examining certain design aspects of solar thermal power systems using a network of point-focusing parabolic concentrators

Collector installation for solar energy - has skeletal structure with rows of adjustable reflectors focussed on common absorbers

Abstract: The complicated and expensive erection work connected with the assembly of a large number of collectors for the energy of the sun, esp. e.g. the large number of pipe joints necessary, is simplified and reduced considerably. A collector platform formed from light structural details is set up, inclined to the vertical and free to rotate on a vertical axis. In this the reflectors are arranged in rows side by side; the focussing line of the reflectors in one row lying in a straight line, in the proximity of which a common absorber for the row is positioned. The row of reflectors thus forms a long parabolic mirror with a length which is the multiple of a single mirror and instead of separate abosrobent tubes, one long tube can be used.

Image transfer device using mirror moving on spherical focal surface

Abstract: An apparatus for transferring a portion of an image from the spherical focal surface of a telescope to a fixed viewing area. A spherical parallelogram type linkage has means for selectively positioning a mirror in the spherical focal surface of the telescope and constrains the mirror to move within the contour of the spherical focal surface of the telescope. The parallelogram type linkage includes means for transferring the image reflected by the mirror to a remote viewing area.