Showing papers on "Parabolic reflector published in 1982"

Secondary pattern and focal region distribution of reflector antennas under wide-angle scanning

Abstract: A new numerical method, Fourier-Bessel series techniques, has been developed to investigate the far-field pattern and focal region distribution of reflector antennas under wide-angle scanning. In this Fourier-Bessel series technique, the current on the reflector surface is first expanded in terms of elementary sinusoidal functions via the well established fast Fourier transform (FFT) algorithm and the surface integration involved in physical optics integration is then carried out analytically. The derivation of Fourier-Bessel series and its convergence as applied to parabolic reflectors are described. The secondary patterns and focal region distributions of a parabolic reflector with F/D = 0.48 and scanning up to 48 beamwidths are presented.

Radiation cones from feed-support struts of symmetric paraboloidal antennas

Abstract: Wide-angle radiation associated with the plane-wave component of the field in the focal space of a paraboloidal reflector is computed by integrating the currents induced on the feed-support struts. This component of radiation is locally maximum on radiation cones which lie along the axis of each strut. Comparison with data measured for the Dwingeloo radio telescope indicates good agreement for the position, width, and intensity of these cones, even at levels 50 dB below the peak of the main beam.

Light-rotation coupling for a plurality of channels

Abstract: For the transmission of a plurality of light channels between two parts which rotate relative to each other, an optical transmission element is arranged with its optical axis OA coaxial to the axis of rotation and light transmitters in different radial regions. By convex lenses or mirrors the bundles of rays coming from the light transmitters are parallelized and impinge on the optical transmission element which individually focuses the bundles of rays. In order to obtain an imaging scale of 1:1 a synchronously rotating rhomboid prism or a parabolic mirror can be used. In addition, HF channels can be transmitted.

Solar energy collecting apparatus

Abstract: A non-tracking elongated evacuated tube solar energy collector employing compound parabolic reflectors. An energy absorber is positioned at the focal points of the parabolas and is supported by one or more support members along its length. Each support member is a length of resilient wire in the form of a coil encircling the energy absorber with arms extending from each side of the coil. Each arm bears against the inner walls of the evacuated tube at two spaced-apart contact regions.

Sunrays focusing apparatus

Abstract: A sunrays focusing apparatus for obtaining highly condensed solar energy. The apparatus includes a first trough-shaped parabolic reflector mounted for rotation about both vertical and horizontal axes. A first elongated refractor is mounted to the first parabolic reflector along or adjacent to the focal axis of the first parabolic reflector. A second trough-shaped parabolic reflector is also mounted to the first parabolic reflector in such a way that focal axes of both first and second parabolic reflectors are disposed at right angles to each other. A second reflector is mounted to the first parabolic reflector along or adjacent to the focal axis of the second parabolic reflector. Mounted on the second parabolic reflector is a sun tracking device responsive to sunrays for directing the first parabolic reflector towards the sun.

Comparison of Fresnel lenses and parabolic mirrors as solar energy concentrators

Abstract: This paper compares the gain that can be achieved with a one- or two-stage concentrator, when the first stage is a Fresnel lens or a parabolic mirror, as a function of the luminosity of the concentrator. The results show that the achievable gain using a parabolic mirror is greater than that obtained using a flat or roof lens but is lower than that obtained using a curved lens.

A transform technique for computing the radiation pattern of prime-focal and Cassegrainian reflector antennas

Abstract: An efficient numerical method based on the use of the fast Fourier transform (FFT) algorithm is developed for computing radiation patterns of aperture antennas with given aperture distributions. The method is also readily applicable to the problem of computing the radiation pattern of paraboloidal reflector antennas when the induced surface currents on the surface of the reflector are known. Using an efficient launching and scanning scheme for subreflector analysis, the method is extended to a Cassegrainian reflector antenna system.

Theoretical Investigation Of Millimeter Wave Propagation Through A Clear Atmosphere-II

Abstract: A general model that describes beam wave propagation through a dispersing and absorbing, clear, turbulent, heterogeneous atmosphere is extended and related to common experimental quantities, viz, intensity covariances, angle-of-arrival, and the mutual coherence function. These experimental quantities are assumed to be measured via parabolic reflector antennas; aperture averaging is taken into account. Explicit expressions for the second and fourth order coherence functions for a general beam wave are derived; it is found that log-amplitude! Phase correlations play an important part in the derivation of these two auantities. A brief review of reflector antenna theory is given. Three experimental situations are considered: the quasi-optical method; intensity covariance via two reflector antennas; the long base-line interferometric method.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Surface tolerance loss for dual-reflector antennas

Abstract: A formula is derived to evaluate the relative influence of subreflector and main reflector surface errors on overall tolerance loss for a dual-reflector antenna. Comparisons are made with the results of random-number simulation of surface errors in a Gregorian system.

Auxiliary unit for carrying out reflection measurements using an IR spectrometer

Abstract: An auxiliary device enabling reflection measurements to be carried out by an IR spectrometer designed for the performance of transmission measurements comprises two deflecting mirrors (22, 23) to be positioned in the straight beam section of the spectrometer and two focussing reflector arrangements (26, 2, 27) of which the first forms at the location of the sample (16) to be investigated by the reflection method a reduced image of the focus (30) situated within the ray of beams (28) deflected by the first deflecting mirror (22) while the said second focussing reflector arrangement forms an enlarged image of the said reduced focus at a distance before the said second deflecting mirror (23) so that the beam of rays (33) emitted by the said second deflecting mirror forms a prolongation of the beam of rays inciding upon the said first deflecting mirror just as if the auxiliary device did not exist. Each reflector arrangement comprises a collimator mirror (26, 27) for parallelizing the divergent beam of rays emitted by the associated deflecting mirror (22, 23) and sections of a common parabolic mirror (2), the beams of rays (29, 31) emitted by the said collimator mirror (26, 27) extending in parallel to the axis of the said parabolic mirror (2) and the sample being arranged at a point coinciding with its focal point (16).

Rotary light coupling for a plurality of channels

Abstract: In order to transmit a plurality of optical channels between two parts rotating relative to one another, an optical transmission element is arranged with its optical axis (OA) coaxial with respect to the axis of rotation, and there are optical transmitters in various radial regions. Convex lenses or mirrors are used to parallelise the ray bundles, which emanate from the optical transmitters and impinge on the optical transmission element which focuses the ray bundles individually. A synchronously rotating rhomboid prism or a parabolic mirror can be used in order to achieve an image scale of 1:1. In addition, HF channels can be transmitted.

Good Imaging With Very Fast Paraboloidal Primaries: An Optical Solution And Some Applications

Abstract: Attention is given to the imaging performance improvement obtainable in telescopes with fast parabolic primaries by means of two-mirror correctors of the Paul-Baker type. Images with 80 percent of the energy concentrated within 0.2 arcsec are projected for an f/1 primary relaying to an f/2 final focus, over a 1 deg-diameter field. It is noted that the mechanical structure and enclosure of a large telescope built with these fast optics should be significantly smaller and less expensive than those for conventional optics. The application of the Paul-Baker corrector system is explored for such diverse telescope types as those employing six off-axis primary mirrors, UV astronomy telescopes with no chromatic aberration, a low emissivity IR astronomy instrument with an off-axis f/1 parent primary mirror part, and thin rectangular aperture telescopes which are useful for spectroscopy and photometry.

Infrared ray image pickup device

Abstract: PURPOSE:To obtain high reflectances with only one sheet of reflecting surface and maintain the distinctness of images by providing an off-axis parabolic mirror as the detector optical system of the infrared ray image pickup device condensing the infrared rays which the target object radiates. CONSTITUTION:The infrared rays 1 which the image pickup target radiates are captured with an afocal system 2 as incident light and said rays are scanned horizontally by a rotary polyhedral mirror 4, after which the rays are vertically scanned with a vertical scanner 5 in synchronization to a fixed partial period, by which the infrared rays 1 from each instantaneous field of vision are converted to parallel luminous fluxes 1'. Here, an off-axis parabolic mirror 6 is provided and the parallel luminous fluxes 1' are condensed to the infrared ray detector 7 placed in the focus of said mirror. The output of said detector 7 undergoes video amplification 8 then signal processing 9 and forms the video in display 10. The use of one off-axis parabolic mirror in this way necessitates only one sheet of required polishing surface and enables high reflectances virtually free from wavelength dependency to be provided and the images to be made distinct.

Optical scanning device

Abstract: PURPOSE:To attain straight line flat scanning with a simple constitution, by rotating or vibrating a light source, reflecting an optical beam from the light source on a parabolic mirror, and projecting the beam on the surface of a photoreceptor. CONSTITUTION:An optical beam irradiated from a light source 1 is made to an optical beam in parallel with an optical axis cl on a parabolic mirror 4, reflected as a reflected light 5 and irradiated vertically on the photosensitive plane of a photosensitive drum 6. In vibrating the light source 1 with a rotary drive means 2 toward the arrows (a) and (b) alternately at a prescribed period, the optical beam irradiated from the light source 1 is reflected on the mirror 4 while the direction is being changed momently. Since the light source 1 is placed on the focus of the mirror 4, the reflected optical beam is always in parallel with the optical axis cl, regardless of the rotary angle of the light source 1, this is reflected as a reflected light 5, which is irradiated on the photosensitive plane of the drum 6 for horizontal scanning.

Imaging performance of mirror pairs for grazing-incidence applications: a comparison.

Abstract: The eight distinct reflection configurations for pairs of toroidal mirrors are investigated by numerically calculating their aberration patterns for on- and off-axis source points. The best performance is obtained for a Z-shaped configuration where the two mirrors deflect in opposite directions across a common interior sagittal and tangential focus. Imaging properties can be improved significantly in some cases by replacing the toroidal elements with their elliptical or parabolic equivalents. The best overall performance is obtained with parabolic mirrors in a U-shaped configuration.

Solar concentrators with immovable receiver for solar energy.

Abstract: The invention provides a high-concentration solar optical system which has a receiver, particularly a cavity light receiver, which is disposed in a stationary position and into which the concentrated light pencil of a small aperture angle falls from a constant direction, particularly in the axis of symmetry of the cavity light trap, irrespective of the position of the sun. This is achieved by using a concave mirror whose shape results from a plane intersection with a paraboloid of revolution enclosing an angle of 45 degrees to the axis of the paraboloid. This elliptically delimited paraboloid section is rotated, oppositely to the rotation of the earth, about the sidereal polar axis coinciding with the solar receiver axis and passes through the centre of the elliptical parabolic mirror. This parabolic mirror is obtained in accordance with the invention by elastic or plastic deformation of an originally plane mirror foil which is exposed to an elevated air pressure while clamped along the elliptically rigid frame.

Catoptric light source for vehicle headlamp - uses filament lamp in parabolic reflector to direct light along an internally reflecting duct shaped to concentrate light beam

Abstract: The catoptric light is useful for motor vehicle headlamps providing a flat topped beam with better beam concentration to give more effective illumination for a given lamp power. The catoptric light has a filament lamp with its filament mounted slightly beyond the focus of a parabolic reflector. The direct and reflected light passes through a circular section converging duct with reflecting walls. The duct then turns through an angle of approx. 120 degs. and the outside of the bend is shaped to focus the light rays just inside the end of the square section internally reflective duct through which the light emerges. The square duct is directed downwards at approx. 20 degs. below the horizontal so the highest light ray emerging is horizontal.

Bicollimated near field gregorian reflector antenna

Abstract: : A bicollimated near-field Gregorian reflector is structurally similar to a classical confocal parabolic reflector, but its surfaces are shaped to have better scan capability. A geometrical optics procedure is used in designing the reflector surfaces. A three-dimensional ray tracing procedure is used in analyzing the aperture phase errors as the beam is scanned to different angles. The results show that the bicollimated configuration has about 45% greater angular scanning range than the corresponding confocal parabolic dual-reflector system.

Ideal second stages in tandem with parabolic concentrators

Abstract: Expressions for the concentration capability of parabolic reflectors are derived and extended to include additional ideal second-stage concentration. The ultimate concentration of a parabolic reflector (primary) alone is shown to achieve one-half of the ideal limit in 2-D geometry; the respective two-stage configuration is shown to approach the ideal limit itself at large f/Nos.

Testing the figure of parabolic reflectors for solar concentrators.

Abstract: A novel method for testing the optical quality of large parabolic solar concentrators is presented, based on autocollimation. An optical system continuously scans the reflector along a fixed reference axis. At each position along the axis, the spread function is obtained. Analysis of the location, width, and intensity changes of this function gives quantitative information about the reflector’s defects. A figure of merit describing the performance of parabolic trough reflectors is proposed.

Acurex Parabolic Dish Concentrator (PDC-2)

Abstract: The design approach, rationale for the selected configuration, and the development status of a cost effective point-focus solar concentrator are discussed The low-cost concentrator reflective surface design is based on the use of a thin, backsilvered mirror glass reflector bonded to a molded structural plastic substrate The foundation, support, and drive subassembles are described A hybrid, two-axis, Sun tracking control system based on microprocessor technology was selected Coarse synthetic tracking is achieved through a microcomputer-based control system to calculate Sun position for transient periods of cloud cover as well as sundown and sunrise positioning Accurate active tracking is achieved by two-axis optical sensors Results of the reflective panel demonstration tests investigating slope error, hail impact survivability, temperature/humidity cycling, longitudinal strength/bending stiffness, and torsional stiffness are discussed

Continuous measurement of properties of particles in flow

Abstract: The arrangement determining rheological properties of microscopic objects, e.g. erythrocytes in a flow medium, has a light source directing rays vertically to the focal point of a parabolic mirror, through which passes a transparent capillary tube. The latter contains the flow medium, which is pumped from a supply container and is of constant cross-section except in the focal point, where it has a cross-section with a convergence-divergence area for circulation of the cells. Light reflected by the mirror reaches an image analyser, which has an optical, mosaic-like flat receiver an anamorphoser, a rotatable detector associated with a single photo-electric receiver and a device to process the signals delivered by the analyser. Pref. the anamorphoser comprises conductors whose heads form the receiving points of the mosaic-like receiver and whose other ends are arranged in the form of a circular track to work with the rotating detector.

Focal surfaces of offset dual-reflector antennas

Abstract: An analytical technique is described for finding the best focal surfaces for offset-fed dual-reflector antennas. A ray tracing procedure traces the loci of rays incident on the main reflector onto a plane or 'screen' situated perpendicular to a central ray of the antenna system. Given, then, by computer graphics, the best feed locations for azimuth and elevation plane patterns, an aperture diffraction method is used which can compute the sidelobe levels and beamwidths resulting from aperture phase errors on scanned or multibeam patterns. High-magnification Cassegrain or Gregorian antennas, with tilt angles optimised according to Japanese criteria, produce excellent radiation diagrams many beamwidths from the central, unaberrated pattern direction.

Solar energy condensing device

Abstract: PURPOSE:To obtain a condensing device which is manufactured easily at a low cost, and has a high condensing ratio, by opposingly placing two through parabolic reflectors so that the respective focal lines meet at right angles. CONSTITUTION:The first and second through parabolic reflectors 3, 4 are reflectors obtained by processing a plywood of 3mm. thick to a parabolic surface, and sticking a polyester film which has vapor-deposited Al in a vacuum to approx. 8,000Angstrom thick on the surface, onto the surface of the plywood. These two parabolic reflectors 3, 4 are fixed to fixed frames 9, 10 so that the respective focal lines meet at right angles. A solar beam which has been made incident to the first through paraboilc reflector 3 are reflectors by two reflectors 3, 4 and are condensed to almost one point. In this way, a condensing device which is manufactured easily at a lost cost, and has a high condensing ratio is obtained.

Beam scanning and focal surfaces for parabolic cylinder reflectors

Abstract: The location of the focal surfaces for parabolic cylinder reflectors with Gaussian tapered illumination is investigated and compared with that obtained by numerical simulation. It is found that an idealized surface that holds approximately in most practical cases is the circle described on the vertex-focus line as diameter. Formulas are derived for the change of gain and beamwidth with scan angle.

Bandwidth capabilities of array-fed parabolic cylinders

Abstract: The bandwidth of hybrid phased-array/reflector antennas, in which a large parabolic cylinder reflector is fed by a relatively small phased array, is investigated. Two types of array feeds are considered: one employs only phase-amplitude matching, the other employs amplitude and time-delay matching. In the case of phase-amplitude matching, the on-axis hybrid array/reflector designs are shown to have substantially higher bandwidth than pure phased arrays. A form of time-delay compensation is described which removes the bandwidth limitations of hybrid array/reflectors, but introduces interfering signals. This interference can be avoided by either locating the feed outside the caustic zone or by using off-axis array feeds.

Simple infrared telescope with stray-light rejection.

Abstract: A very simple telescope is described that consists of a parabolic mirror, a small spherical mirror, and a single germanium lens. This three-element telescope is unobscured, is corrected for spherical aberration, coma, astigmatism, and Petzval curvature, and has stray-light rejection features. The good aberration correction makes it suitable for covering a substantial field of view on a flat image surface. The stray-light rejection features are: no obscuration, an aperture stop, a field stop, and a Lyot stop. The key to this new design is the novel use of two separate optical axes in the same system. The parabolic mirror and the spherical mirror have the same optical axis, but the axis of the lens is displaced and parallel. The theory of the design will be explained.

Sound collector mounted on car

Abstract: PURPOSE:To form a sound collector having excellent directivity and sensitivity by combining a parabolic reflector with the steering wheel of a car and by arranging a microphone at its focal point. CONSTITUTION:A parabolic reflector 2 made of a transparent material is fitted inside of the steering wheel 1 of a car, and a microphone 4 is arranged at its focal point. The voice of a driver who is driving the car is collected to the focal point by the reflector 2 and inputted to the microphone 4. The voice signal inputted by the microphone 4 is recognized by a voice recognizing device 5, which outputs a signal corresponding to the voice. The signal is sent to respective driving circuits 6, 7- to perform prescribed operation. Thus, the sound collector having excellent directivity and sensitivity is formed without spoiling the driving performance of the car.