Showing papers on "Parabolic reflector published in 1976"

Some highlights in reflector antenna development

Abstract: Reflector antennas have been used since the radio pioneering era of Lodge, Hertz, and Marconi, but it took the exigent demands of radar in World War II to stimulate a real development in the reflector art. Subsequent interest in the science of radio astronomy and the inception of microwave ground communication links were responsible for a burgeoning growth in the field, so that in the 1940s and 1950s the design principles and requirements for prime focus fed systems were well established. Cassegrain, or secondary focus systems, and horn reflectors came into prominence in the early 1960s with the advent of satellite tracking and communication networks. The desire to maximize the gain, or the gain-temperature ratio, then led to development of sophisticated techniques for properly shaping the illumination over the reflector aperture in order to maximize efficiency and minimize spillover, among them being the shaping of the sub-reflector in Cassegrain systems and the use of multimode and hybrid mode feed horns. Not all reflector antennas utilize paraboloidal surfaces. Some recent developments in line source feeds make the spherical reflector attractive for scanning applications and the conical reflector for deployable, space-borne antennas. The large 1000-foot diameter reflector at Arecibo is a well known example of the former. Although some extremely large spaceborne reflector antennas have been proposed and studied, the largest now in use appears to be the unfurlable 30-foot reflector carried by ATS-6. Finally, some gain comparisons are given for a few of the (electrically) largest reflectors that have been built both for radio astronomy and for space communications. If some milestones in reflector development have been overlooked it is due to the limitations inherent in a review paper.

Solar energy reflector-collector

Abstract: A system including a non-tracking reflector-collector for the concentration and collection of solar energy. An energy-collecting plate is disposed upright along a substantially horizontal axis substantially coincident with the east-west direction of the earth. The collector plate is positioned within a semi-tubular reflector having parabolic sidewalls. The reflector surfaces on opposite sides of the collector plate are parabolic surfaces, each having a focal point approximately coincident with the upper terminal edge of the collector plate. The axes of the parabolas which define the respective surfaces are rotated about or diverge from their common focal point at a substantial angle. The reflector sides are of laminated construction having a base portion of a lightweight rigid plastic sheet, an underlayer of plastic corrugated board and a reflective film on the interior surface. The collector plate receives energy entering the aperture between the reflective surfaces. In one of the preferred embodiments, the plate elevates the temperature of a heat exchange medium flowing therethrough. The heat exchange medium provides for storage and use of the collected energy. In a second embodiment, the collector plate receives solar energy which is converted into electrical energy for storage and use.

Analysis of the radiation patterns of reflector antennas

Abstract: 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.

Manufacture of solar reflectors

Abstract: A tool is provided for manufacturing parabolic solar reflectors. The tool employs an improved smooth convex parabolic surface terminating in edges remote from the parabolic vertex which are preferably placed under elastic tension tending to draw the edges toward each other. The improved convex surface is a film of plastic coated with chromium metal on its exterior surface. A multiple layered thermosetting plastic reflector support is molded onto the convex surface of the tool. The reflector support is removed from the tool and a layer of aluminum is vacuum deposited onto the interior concave parabolic reflector surface.

The design of correcting secondary reflectors

Abstract: A computer program called DERIVE is described for the design of the reflecting surfaces of two-mirror radio telescopes. It calculates the shape of a secondary reflector to any given primary by use of geometrical optics, yielding zero path length errors for all paraxial rays. The only condition to be fulfilled is (for Cassegrain types) that incoming rays, after reflection at the primary, do not cross each other before reaching the secondary. Equations for this condition are given. This method can be used to improve existing telescopes at short wavelengths by correcting for the surface deviations of the primary reflector with a specially shaped secondary. The results of 17 calculated examples are described, for various types of deviations

Design considerations for parabolic-cylindrical solar collectors

Abstract: This report presents in some detail the various significant factors which influence the design of parabolic-cylindrical solar collectors.

Solar power system, with high concentration, linear reflective solar panels

Abstract: The solar power system with high concentration linear reflective solar panels of the linear parabolic type is intended to increase the electrical power output from conventional silicon solar cells, and heat water for steam power. Circular parabolic reflectors have been used for this purpose but there are not as flexible in application as the linear parabolic reflectors (L. P. R.'s). The solar power system may be arranged as an all electric type using continuous lines of silicon solar cells located at the apex or focal zone of the parabola, or may be designed as a dual solar conversion system with both solar photoelectric means and a water heating steam means, as an indirect or secondary power source. The key feature of the system is the geometric configuration of the linear parabolic reflectors (L. P. R.'s), with an unusually high reflective concentration ratio of 10:1 minimum, plus boosters, and the connection of these pivoted linear panels to a common oscillating linkage and timing unit for full sun following capability to maintain optimum direct solar exposure each day.

Use of a spherical concave reflector for jet‐noise‐source distribution diagnosis

Abstract: An account on the development of a directional microphone system for jet‐noise‐source strength distribution measurements is given The system selected is based on the imaging principle of a spherical concave reflector As expected, the system is diffraction limited; a loss of resolution results A special technique is discussed to recover the axial‐source strength distribution from the diffracted data Sample experiments are presented to show the successful application of such a system for jet noise measurementsSubject Classification: [43]2865; [43]5055; [43]8562

Calculation of radiation patterns of paraboloidal reflectors by high-frequency asymptotic techniques.

Abstract: Radiation pattern of a paraboloid is calculated by asymptotic physical optics and geometrical theory of diffraction and the two are compared.

Method and apparatus for tracking the sun for use in a solar collector with linear focusing means

Abstract: The invention introduces a coplanar rotational method of tracking the sun for use in a focusing solar collector that comprises of one or more linear focusing means such as cylindrical parabolic mirrors and linear lenses. Such a solar collector has one or more linear focal regions. It is particularly advantageous to use this tracking method in a large panel collector having multitude of linear focusing means. A plane parallel to the linear focal region or regions and perpendicular to the front plane of a solar collector is denoted as a focal plane. In applying the tracking method to the solar collector, the collector is rotated around an axis perpendicular to the front plane so that the sun'rays become parallel to the focal plane. The front plane remains substantially on the same plane during the tracking operation.

Sound pickup assembly

Abstract: A sound pickup assembly comprising a parabolic reflector in the focal point of which is mounted a pickup and wherein the reverse side of the parabolic reflector is formed as a binaural sound pickup having a pair of microphones mounted on opposite sides of the curved surface generally on a horizontal plane and including a pair of dummy external ears mounted near the pair of microphones such that the pickup can be used as a highly directive pickup utilizing the single microphone and parabolic reflector and wherein the unit can also be utilized for binaural pickup by utilizing the two antennas and dummy ears mounted on the back surface of the unit.

New method of measuring the shape of precise antenna reflectors

Abstract: The shape of the paraboloidal reflector surface is determined by making a large number of measurements of the reflector curvature along several radii of the surface. These measures of curvature are then integrated twice to give the reflector profile along each radius; the results from several radii then allow the reflector surface shape to be mapped in three dimensions. The curvature measurements are made by a three‐wheeled cart with a depth sensor resting on the surface at the midpoint of the wheels. Tests of the method on an 11 m diam antenna show an average repeatability of 0.037 mm in the measurement of the shape of the parabolic reflector.

Fields in the focal region of offset parabolic antennas

Abstract: An analysis which provides the electric field distribution in the focal region of an offset parabolic reflector as a function of small scan angle has been performed. Formulae which predict both the principal and cross polarized fields have been obtained. These formulae are relatively simple and compact, provide a useful design tool, and allow efficient computer calculation. The results obtained from these formulae compare favorably with results obtained by other authors.

Gregorian all-reflective optical system

Abstract: An optical heterodyne receiver comprises a system of reflectors forming a folded Gregorian configuration for collecting a signal beam, and an optical detector located at the focus of the system. The reflectors comprise a paraboloidal primary reflector and an ellipsoidal secondary reflector facing each other on an optical axis with the focus of the secondary reflector coinciding with the focus of the primary reflector. An auxiliary laser generates a local oscillator beam that is combined with the signal beam after the signal beam emerges from the exit pupil (which is also the aperture stop) of the system, and the resultant is impinged on the detector. A pair of image motion compensators is located as close to the exit pupil as possible for aligning off-axis inputs to the detector. The compensators also ensure that off-axis as well as on-axis inputs are substantially coaxial with the local oscillator beam, thereby maximizing signal detector efficiency. By utilizing a large f/number for the local oscillator beam, it effectively eliminates the need for critical alignment between the signal and the local oscillator beams at the detector.

Catoptric lens arrangement

Abstract: A family of catoptric lens arrangements is provided for focusing a maximummount of light from an omnidirectional source into a parallel or conical beam. A rear spherical-curvature reflector is inserted into a conventional forward spherical plus rear parabolic reflector arrangement, with its center of curvature and the light source both at the focal point of the parabolic reflector. In addition, a forward collimating lens is substituted for the central portion of the forward reflector. The theoretical 100% efficiency achieved by this arrangement is independent of the diameters of the forward and rear reflectors provided, of course, that the positions and curvatures are suitably compensated.

Intruder surveillance system optical detector - has light from several surveillance zones directed onto common photodetector

Abstract: The optical detector is used to monitor the light in a number of surveillance zones (E1, E2, E3) for intruder detection etc. The monitored light rays may be in the viible, UV, or IR ranges and light rays from each surveillance zone (E1, E2, E3) are directed on to a common photodetector via respective converging means (R1, R2, R3). The optical converging means (R1, R2, R3) have surfaces with two different radii of the curvature with the photodetector positioned at the focal point (F1) of the converging means (R1, R2, R3). Pref. the converging means (R1, R2, R3) comprise parabolic reflectors mechanically joined together so that they have an approximate common focal point.

Parabolic mirror assembly for sunlight concentration - has mirror coated plastics foil and rigid annular edge structure

Abstract: The parabolic mirror assembly is intended for concentration of sunlight for energy recovering by devices utilising light or heat, such as directly converting semi-conductor solar cells. The mirror (1) consists of a plastics foil for laminated plastics tissue, provided on one side with a mirror coating and having a shape of a paraboloid. The latter edge is connected to a rigid annular structure (3) supporting the mirror. The paraboloid is maintained in its shape by differences in air or gas pressure. Preferably a transparent foil or plate (12) is clamped in front of the mirror opening, which may be divided into smaller sectors by a support net. The annular structure is preferably mounted inside the parabolid edge.

Parabolic reflector including filament locating means

Abstract: A generally concave reflector member is provided with three or more bosses having flat outer surfaces The surfaces define a plane perpendicular to the axis of the parabola so that specific points within the parabola can be located with great precision By using the bosses as reference points, lamp filaments can be accurately placed within the lamp structure, regardless of variations in the reflector member which occur during the manufacturing process

Surface efficiency measurements on a high-modulus carbon fibre composite reflector antenna at L- and S-band frequencies

Abstract: The r.f. surface reflectivity of a parabolic antenna reflector fabricated from carbon fibre reinforced plastic with high modulus fibres, has been investigated at L- and S-band frequencies by a swept frequency gain comparison method. The gain of the antenna with the reflector uncoated was compared with that of the same unit but with a metal coating on the reflector.

Generation of hydrogen by solar energy - using concave parabolic mirrors and wave guides to concentrate and conduct energy

Abstract: An appts. for generating hydrogen by solar energy incorporates a number of concave parabolic mirrors distributed over a surface. Each mirror can be moved so that its surface is directed towards the sun and a flexible wave guide conducts the light from the focus of each mirror on to one end of a rigid wave guide. The other ends of the rigid wave guides are connected by flexible wave guides to a vessel through which steam is passed. The conc. solar energy raises the temp. of the stem enough to dissociate it into H2 and O2. The H2 and O2 are sepd. e.g. by a porous partition and the H2 is stored, and can be used to feed a gas turbine driving a generator of electricity. Each flexible wave guide consists of a bundle of optical fibres. The rigid wave guide has a sleeve and a core made from two glasses of different refractive indices, or it consists of a plastic sleeve contg. a liq. e.g. bromobenzene. The device provides a means of storing the energy derived from the sun, whereas existing appts. using e.g. the photovoltaic effect of pn semiconductor junctions, have very low efficiencies in winter and can be used only during daylight.

Solar energy unit for producing heat energy - maintaining minimum radiation, convection and conduction of heat

Abstract: Solar energy unit comprises a parabolic cylinder (1) for focussing sunlight onto a focal line (2) in which is disposed a pipe (3) for supplying a heat storage medium using a liquid such as water or a gas. The pipe may be coated with a radiation-absorbing material, e.g. nickel sulphide. Pref. the focal line of the cylindrical parabolic reflector forms the axis of rotation of the focussing system, and a straight line representing the line of the centre of gravity coincides with the focal line. The pipe may be mounted stationarily, and the height of the parabola may be 2.45 times the focal length of the parabola.

Cooker or heater with solar mirror - has parabolic reflector with split flow pipe running along its focal axis

Abstract: A device for application of solar energy to a cooking or heating installation by means of a reflector device has the reflector constructed as a high mirror finished parabolic curved metal plate with low radiation loss. The reflector is mounted in a rotating fashion about the axis of a matt black painted pipe (2) running at an angle in a southerly direction so that the pipe runs along the focus of the mirror. A separating wall is mounted within the pipe (2) to assist water circulation. The upper end of the pipe (2) can stand a pressure of 3 atmos. and is coupled to a double walled sealed insulated water container. The mirror is protected from influence of weather by a glass screen and a device is provided to rotate the mirror to receive maximum sunlight at all times.

High efficiency solar collector

Abstract: A novel type of solar collector apparatus is disclosed which comprises a generally planar, horizontally extending absorber having a radiation-accepting aperture in the lower surface thereof, and a duct extending therethrough for receiving a heat transfer fluid. A non-steered reflector is disposed directly beneath the absorber, the reflector exhibiting a cross-sectional configuration of a parabolic cylindrical nature.