Showing papers on "Parabolic reflector published in 1980"

Shaped reflector antenna analysis using the Jacobi-Bessel series

Abstract: The physical optics approximation is employed to derive the radiation integral for a doubly curved offset reflector antenna illuminated by an arbitrary source. A novel procedure is presented for expressing the radiation integral in terms of a summation of Fourier transforms of an "effective" aperture distribution which includes the effect of the curvature of the surface. The Jacobi-Bessel series is used to evaluate the Fourier transforms. The vector nature of the far-field pattern is studied by evaluating its three Cartesian components in a unified fashion. The rapid numerical evaluations of the expressions obtained are demonstrated via extensive test cases. In particular, the scattering characteristics of symmetric and offset parabolic, spherical, and shaped reflectors are studied in detail, and comparisons are made with other available data.

Collection of solar energy

Abstract: Apparatus for collecting solar energy comprises one or more solar energy collectors attached to a frame which floats on a pool of water, and means for orienting the frame relative to the azimuthal direction of the sun. The solar energy collectors are horizontal elongate parabolic reflectors which also float on the pool of water and which can be rotated about their longitudinal axes to orient them relative to the elevation of the sun. Solar rays reflected by such reflectors are absorbed by elongate absorption devices placed at the focal points of the parabolic reflectors. The absorption devices are preferably of a novel design which provides for removal of the energy of the absorbed rays by means of a working fluid which passes through the device. The parabolic reflectors preferably have body portions composed of a novel constructional material which comprises a plurality of hollow glass bodies which are connected together through randomly coalesced wall portions.

Microwave antenna system having enhanced band width and reduced cross-polarization

Abstract: The antenna system employs a parabolic reflector fed by an offset feed array of circular wave guides located substantially at the focus of the parabolic reflector, but offset from the axis thereof. A plurality of aperture tuning mechanisms disposed at the mouths of the circular waveguides of the waveguide feed array, and having physical lengths much shorter than one wavelength at the frequencies involved, are provided to reduce cross-polarization and mutual coupling between adjacent feeds. The short resonant length of these tuning mechanisms, and their shape which is chosen to generate the TM11 mode E-field contour line ensures that they are effective over a broad bandwidth of as much as 20% or more. Within this bandwidth, they act as inductive suppressors to control both cross-polarization and mutual coupling between adjacent feeds.

Some important geometrical features of conic-section-generated offset refelector antennas

Abstract: Geometrical characteristics of conic-section-generated offset reflectors are studied in a unified fashion. Some unique geometrical features of the reflector rim constructed from the intersection of the reflector surface and a cone or cylinder are explored in detail. It is found that the intersection curve (rim) of the rotationally generated conic-section reflector surface and a circular cone with its tip at the focal point is always a planar curve and has a circular projection on the focal plane only for the offset parabolic reflector. Furthermore, in this case, the line going through the center of the circle, parallel to the focal axis, and the central axis of the cone do not intersect the reflector surface at the same point. Numerical results are presented to demonstrate some unique features of offset parabolic reflectors.

Cavity enhancement by controlled directional scattering

Abstract: The interest in efficient solar collection design has stimu­ lated investigation of 2-D (troughlike) cavity structures. In fact, it was recently shown that such cavities can be designed to produce absorption enhancement in the solar collector.' In this Letter we describe a novel principle for designing cavity enclosures. The new method can be applied to advantage to nonimaging concentrator design. Thus, it is by now well known that radiation collimated within an angular divergence ±θ can be concentrated on a receiver by the factor Cmax = sinθ and without transmission loss by the use of reflectors of the CPC type. To meet strictly both requirements (i.e., maximum concentration and no transmission loss) the re­ flector should touch the receiver. In cases where it is not practical for reflector and receiver to touch, a solution is available that maintains flux concentration Cmax but intro­ duces some transmission loss. The present method main­ tains high transmission albeit at the expense of some con­ centration in the presence of a gap between reflector and re­ ceiver. The slight loss of concentration may be partly offset by enhanced absorption of radiation by the receiver, resulting from the cavity effect. The idea is to immerse the receiver in an enclosure with special properties. Small elements of the enclosure wall have the specific property that radiation incident on the element from outside the angular subtense of the receiver is scattered (or redirected) onto the receiver in the manner shown in Fig. 1(a). Assuming that such elements are realizable in practice (this will be shown to be the case later), it is easy to see how to construct the cavity. The enclosure is composed of a chain of such scattering elements. The receiver R is immersed as shown in Fig. 1(b) sufficiently deep so as to block the effective aperture ABCD of the cavity from seeing itself.The con­ centration ratio of the enclosure for diffuse radiation is just the area of the effective aperature divided by the receiver area,

Combined radar and infrared scanning antenna

Abstract: An antenna system has a parabolic reflector mounted so that it points generally downwards and a primary aerial is located at the focus of that reflector. Waves from the primary aerial are reflected back by the parabolic reflector to a reflector plate through an aperture in which the primary aerial projects. Scanning in both elevation and azimuth is effected by movement of the reflector plate.

Rim loaded reflector antennas

Abstract: A general theory of reflector antennas loaded by surface impedances is presented. Spatial variation of primary illumination is taken into account using a generalized slope diffraction coefficient. The theory is experimentally checked on surface loaded square plate scatterers and then used for computing the radiation diagram of parabolic and hyperbolic dishes. Computer programs and computed diagrams refer to the case of focal illumination and negligible tapering of primary illumination.

Deflection and stress analysis of a 4.2-m diam primary mirror of an altazimuth-mounted telescope

Abstract: Large finite-element mathematical models are developed to calculate the deformations induced by the supports of a 4.2-m aperture 3.2-focal ratio primary mirror of an optical telescope. It is supported axially on three rings of pneumatic cylinders and radially by a system of transverse level weights, an arrangement only possible in a telescope that uses an altazimuth mounting. The stress distributions in the mirror when lifted by a central lifter and when resting on its axial flotation system are shown. A comparison is made between the results using classical flat-plate theory and the finite-element models.

Solar energy collector

Abstract: A solar energy collector comprising a collector core located within a longitudinal parabolic reflector and formed of a series of spaced tubes exposed to the direct rays of the sun and to rays reflected by the reflector and arranged in a cylindrical array extending longitudinally to form a fluid path between two end annular manifolds connected at opposite ends of a storage tank located within the array.

The Pursuit Of Symmetry In Wide-Angle Reflective Optical Designs

Abstract: The design of wide-angle reflective optical systems has been to a large degree a pursuit of symmetry. Major systems developed in the 1970s can be broken down as modular design combinations of three classical systems--Schmidt, Schwarzschild, and Baker. These configurations are based on the following four constructional principles: 1) aperture stop and correction at the center of curvature of a spherical mirror, 2) confocality of two parabolic mirrors working at infinite conjugates, 3) concentric mirrors, 4) polar strip field coverage. Five notable wide-angle reflective systems developed in '70s are: 1) Two-Axis Baker, 2) Hughes WALRUS, 3) Honeywell Wide-Angle Conical Scanner, 4) Perkin-Elmer Ring Telescope, 5) Corrected Schwarzschild.

Geometric modeling and analysis of large latticed surfaces

Abstract: The application of geometrical schemes, similar to geodesic domes, to large spherical antenna reflectors was investigated. The shape and size of flat segmented latticed surfaces which approximate general shells of revolution, and in particular spherical and paraboloidal reflective surfaces, were determined. The extensive mathematical and computational geometric analyses of the reflector resulted in the development of a general purpose computer program capable of generating the complete design parameters of the dish. The program also includes a graphical self contained subroutine for graphic display of the required design.

Camera Viewfinder Using Tilted Concave Mirror Erecting Elements

Abstract: The camera viewfinder would consist of a two-element objective lens, a field stop, a tilted concave mirror, an aperture stop, a second tilted concave mirror, and a two-element eyepiece. This forms a Z shaped configuration with the mirrors at the corners of the Z. The two mirrors, with the aperture stop midway between them, form a 1:1 telescopic erecting relay system. Two types of mirrors are studied: spherical and parabolic. The main problems encountered in the spherical mirror system are axial astigmatism and field tilt, both caused by the tilted mirrors. By using confocal, coaxial, decentered parabolic mirrors, with the aperture stop at the common focal point, the axial astigmatism can be eliminated; however, the field tilt problem is aggravated. By rotating the axis of the second parabolic mirror about the common focal point, the field tilt can be minimized, and the astigmatism in all beams eliminated. This last configuration is, however, plagued by distortion and coma. We conclude that none of these systems is satisfactory for image quality.

Modified Zone-plate Interferometer for Testing Aspheric Surfaces

Abstract: A new type of common path interferometer using a modified zone-plate developed for testing aspheric surfaces is described The modified zone-plate is made by combining two kinds of zone-plates; the semicricular part of the plate produces the spherical wave, and the remainder the desired aspheric wave These are synthesized by digital computation A method of computation for synthesizing the modified zone-plate and some experimental results of the test of parabolic mirrors are given

Method and device for measuring physical characteristic of target surface

Abstract: PURPOSE:To make the rapid and highly reliable surface inspection possible by radiating electromagnetic radiations to the portion to be inspected of an object surface and the portions existing in the adjoining positions on both sides thereof and comparing the intensities of the radiations reflected from both. CONSTITUTION:A searching part 13 which is movable in the arrow A direction is inserted into the inside surface of a pipe 12 such as hydraulic brake cylinder. Light from a light source 19 is radiated to a parabolic mirror surface 16 by way of a lens 20 to form a circular ring-foam focus on the surface 11. The reflected light is imaged on a photo detecting array 22 by way of the mirror surface 16 and spectroscope 24. If here there are flaws such as porous concave pits 27, they are detected as a region differing in intensity on the array 22. The intensities of the reflected light from these flawed portions and other normal surface are input as electric signals 28 from the detector array 22 to an automatic processing unit 29. In the unit 29, comparative operations are accomplished by the specified circuits, thus the surface inspection may be performed rapidly and highly reliably.

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

Abstract: 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.

Portable folding microwave antenna

Abstract: A microwave directional antenna in which a parabolic reflector is mounted on a portable base. The parabolic reflector is constructed in two semicircular sections that are hinged to each other and to a supporting pedestal for rotation about a common horizontal hinge axis. The two sections can be rotated in opposite directions to move the sections between a folded position during transit and an extended position when in operation. In the extended position the two sections are locked together and rotated as a unit to change the elevation of the antenna.

Signal lamp for two-wheeled vehicle - has reflector and lamp cover divided into corresponding zones for max. light output

Abstract: The signal lamp for a two-wheeled vehicle incorporates a reflector with a number of parabolic reflector zones of differing focal widths and a common focus at which the light bulb is positioned. The reflector zones deflect light in differing directions and each is associated with a corresponding prism or lens zone of the lamp cover. The latter zones cause the incident light rays to be totally internally reflected before exit from the signalling direction. Pref. the lamp cover zones each have a number of prism surfaces which are at least partially curved. The lamp exhibits a max. light intensity in the signalling direction.

Parabolic telescope and spectrometer combination

Abstract: The properties of a nonfocusing collimating parabolic telescope are studied in detail by a ray-tracing method. The best optical quality with respect to coma and astigmatism is calculated for rays close to the optical axis of the telescope. For rectangular fields of view the borders are not sharp because of the aberration. A combination of a parabolic telescope and an echelle-type spectrometer gives very high spectral resolution. Wadsworth, Ebert-Fastie, and other types of spectrometers are equally well suited to be combined with this telescope. For some cases spot diagrams demonstrate the optical performance. In addition, diffraction by the aperture and its implications are discussed.

Single element spherical surfaced optics insensitive to wavelength and temperature

Abstract: These thick elements are all corrected for third order spherical aberration and they are also corrected for spherochromatism (i.e. chromatic variation of spherical aberration) or longitudinal color or both. Most are preferably made of materials of low index of refraction less than 1.55, such as BK-7 or fused silica. Most elements corrected for third order spherical and spherochromatism exhibit longitudinal color, but this poses no problem when they are used with a single wavelength laser. Such systems can be used to focus a laser beam to provide a very fast f number diffraction-limited point source, or used in optical testing, experiments, and the like. The designs are characterized by an extremely low sensitivity of performance to wavelength changes and thus to uniform temperature changes (thermal soaks). A temperature change of several hundred degrees centigrade--from cryogenic temperatures up to near the melting point of the optics, has essentially no effect on the predicted performance. Since the systems have no aspheric surfaces, they are substantially less expensive than fast f number parabolic mirrors, which would also provide point sources. The systems are also less alignment sensitive than parabolas of the same f number. Several systems have low fifth order spherical aberration which can be fully corrected if divided into two elements. Other systems useful in interferometric testing with lasers are described. Some employ multiple passes through a single optical element. These may be corrected for third spherical aberration, longitudinal color, and spherochromatism. Such an element with an index of 1.71 is described.

A Cross-Shaped Horn and a Square Waveguide Polarizer for a Circularly Polarized Shaped Beam Antenna for a Broadcasting Satellite

Abstract: A cross-shaped horn and a square waveguide polarizer for a circularly polarized antenna for a broadcasting satellite are designed using a finite difference method and a beam contour of an offset parabolic reflector fed with three cross-shaped horns is given.

Light fitting for elongated lamp - has reflecting strap, carrying on its upper side tooth-shaped reflectors, parallel to lamp axis

Abstract: The light fitting has a reflector grille underneath the elongated lamp. The grille strips are of V-shaped cross section and connect two mutually inclined, parabolic reflector sheets. The strips upper side is covered with a reflecting strap (41) which carries reflectors (43), parallel to the lamp axis and of toothed-shaped cross section. Pref. two sections (41'), with oppositely directed reflectors, are provided on the strap approximately from vertical axis of the elongated lamp (2). The angle of inclination of the reflector surfaces, facing the lamp side, are smaller than that of the rear sides. The reflectors may be stepped according to the Fresnel principle in the approach to the arcuated mirror sections.

Stationary phase method for far-field computation of defocused reflector antennas

Abstract: Computation of the far field of a defocused reflector antenna using the stationary phase method is described. The positions of the stationary phase points are determined, to eliminate one of the two numerical integrations of the radiation integral. Examples of scan patterns and computational time saving are presented.

Cassegrain excitation wave guide arrangement for parabolic antenna - uses glass fibre reinforced insert piece as secondary reflector carrier

Abstract: A waveguide (1) which passes axially through the parabolic reflector (5) is terminated in an insert piece consisting of a sharp end (6), a cylindrical portion (2) and an expanding portion (3) made in one piece of a dielectric material having a dielectric constant of 2,5 to 3,5. The front end is intended so as to form a triangular cross section with an azimuth angle (alpha) of 150 deg. the surface of which is metallised and acts as a reflector. The sharp end (6) faces incoming radiation propagated in the waveguide (1) and reduces partial reflection at the transition to the dielectric material. The merit of this arrangement is that a ray element (1) which in a traditional construction would be lost in that it would bypass the auxiliary reflector, is through double reflection from the inside of the insert piece (3) and the metallic surface (4) included in the beam emitted by the reflector (5). Also, the construction is robust and does not require auxiliary mirror support struts which in older designs disturb the homogeneity of the emitted beam.

Photo coupling device

Abstract: PURPOSE:To make possible coupling of the output light of miniature and multiple optical fibers to one optical fiber at low losses by combining a curved face mirror or plural plane mirros and lenses for collimating. CONSTITUTION:1 thru 4 are optical fibers for input, 11 thru 14 are focusing type rod lenses for collimating, 30 is a glass substrate, 31 is a parabolic mirror formed at the end face of the glass substrate 30 and 100 is an optical transmission fiber which is placed in the position of the focus of the parabolic mirror 31. The output light of the optical fiber 1 is made to parallel beams by the rod lens 11. The parallel beams then enter the glass substrate 30 and are reflected by the parabolic mirror 31. The light beams reflected by this parabolic mirror 31 are reduced in diameter and are coupled to the optical fiber 100. Since the device is constituted in this way, coupling to the multiple optical fibers is made possible.

Analysis of the influence of geography and weather on parabolic trough solar collector design

Abstract: The potential performance of single-axis tracking parabolic trough solar collectors as a function of optical energy distribution and receiver size has been calculated for eleven sites using typical meteorological year input data. A simulation based on the SOLTES code was developed which includes the three-dimensional features of a parabolic trough and calculates the thermooptical tradeoffs. The capability of the thermooptical model has been confirmed by the comparison of calculated results with the experimental results from an all-day test of a parabolic trough. The results from this eleven-site analysis indicate a potential performance superiority of a north-south horizontal axis trough and, in addition, a high quality (optical error, sigma/sub system/ less than or equal to 0.007 radian) collector should be of the same geometric design for all of the sites investigated and probably for all regions of the country.

Optical analysis of point focus parabolic radiation concentrators

Abstract: A simple formalism is developed for analyzing the optical performance of point focus parabolic radiation concentrators. To account for off-axis aberrations of the parabola, an angular acceptance function is defined as that fraction of a beam of parallel radiation incident on the aperture that would reach the receiver if the optics were perfect. The radiation intercepted by the receiver of a real concentrator is obtained as a convolution of angular acceptance function, of optical error distribution, and of angular brightness distribution of the radiation source. For numerical calculations this method is more accurate and less time-consuming than the ray-tracing method.

An experimental investigation of the parabolic reflector as a nearfield calibration device for underwater sound transducers

Abstract: Results are presented of an experimental investigation of the use of thin metal parabolic reflectors to form underwater quasiplane wave regions in the nearfield of the reflector. This quasiplane wave volume is then used to calibrate underwater sound transducers in terms of directivity and sensitivity. Such reflectors, mass produced for use with electromagnetic wave devices, are readily available, inexpensive, and rugged. Experiments were conducted with reflectors ranging from 45 to 122 cm in diameter at frequencies from 30 to 300 kHz. It might be noted that at the higher frequencies the acoustic wavelength is approximately an order of magnitude shorter than that for which the reflectors were designed. Test transducers, typically half the size of the reflectors, were calibrated both in the nearfield of the reflector and in the farfield (using conventional techniques) and the results were compared. It was found that for the major lobe there was excellent agreement and that the levels of the minor lobes were...

Laser Beam Expander-A New Design

Abstract: In 1978 the author described a laser beam expander that was unobscured, corrected for spherical aberration, coma, and astigmatism, and consisted of four spherical mirrors. It was not corrected for Petzval curvature, however; therefore the expanded laser beam would defocus slightly if the input beam were not aligned to the system correctly. This paper describes a new design that has just three mirrors, one an aspheric, and that is corrected for spherical aberration, coma, astigmatism, and Petzval curvature. It is also unobscured, and has the very nice feature that the one aspheric mirror is used in a centered fashion: no off-axis section of an aspheric mirror needs to be made. The new design can be realized in any beam expansion ratio that is desired, but performance suffers at very high magnifications. Two representative designs, 4X expansion and 8X expansion, will be shown and discussed, and their performance numbers will be given.