Showing papers on "Parabolic reflector published in 1989"

Optical system of collimation notably for helmet display unit

Abstract: The system is designed to be mounted in a air pilot's helmet. It uses a confocal assembly with a first parabolic mirror and a second parabolic mirror, placed downline of a collimation objective which gives a collimated radiation. The first mirror is totally reflective and the second mirror is semi-transparent to simultaneously transmit, by reflection, the collimated radiation and, by transparency, for example the view of the external landscape. These two mirrors are integrated into the ends of a plate with two parallel faces. The collimated radiation penetrates the plate by one of the parallel faces, gets reflected on the first mirror, undergoes a succession of total reflections on the parallel faces and then gets reflected on the second mirror before leaving the plate, still doing so through one of the two faces.

A parabolic mirror time‐of‐flight electron energy analyzer

Abstract: We have designed and built a high‐efficiency time‐of‐flight electron spectrometer which has the potential to record accurately the angular distribution of the photoemitted electrons This analyzer uses an electrostatic analog of an optical parabolic mirror to collimate, in an isochronic fashion, half of the electrons emitted from an isotropic point source and measure each electron’s energy by time‐of‐flight Results are presented which demonstrate that the spectrometer operates near its design collection efficiency and energy resolution

Simple primary focus feeds for deep reflectors

Abstract: The radiation characteristics of the coaxial cavity feed antenna are computed numerically. Excellent agreement between the computed and measured radiation patterns is obtained. The numerical method is used to optimise the performance of the antenna as a feed for deep parabolic reflectors (f/D < 0.35). The crosspolarisation level is reduced from −16 dB to below −30 dB. The circular waveguide is filled by a dielectric rod to reduce the feed aperture size and consequently increase the radiation patterns beamwidth. The dielectric rod end is shaped to reduce the cross-polarisation level.

Lighting unit with variable flood to spot capability - has twin fixed and moving lenses with matching concentric convex and concave prisms enabling selection of light beam

Abstract: The lighting unit with parabolic reflector (1) has two plastic or glass lenses (4,6) mounted in front of and co-axial with the reflector (1). The lens (4) nearest the reflector (1) has concentric circular prisms of convex form (5) and is fixed, whilst the front lens (6) has matching concentric prisms of concave form (7) and can move axially over a distance (a). When the two lenses (4,6) are touching a parallel spotlight beam is obtained, whilst a floodlight beam of variable divergence is obtainable as soon as the lenses (4,6) are separated. USE/ADVANTAGE - In pocket torches, shopwindow or theatre lighting. Economic to manufacture and various lighting characteristics are possible by changing prism dimensions or including planar regions in make-up of lens, does not produce dark spots of rings when beam is divergent.

An improved method for manufacturing accurate and cheap glass parabolic mirrors

Abstract: We have developed at CERN a cheap method for manufacturing accurate parabolic mirrors. These mirrors were needed for imaging to a ring the light generated by the Cherenkov radiation in the Ring Imaging Cherenkov detector (RICH) proposed by the DELPHI Experiment [1] at CERN. These mirrors are numerous (300). They are cut from a parabola 800 mm in diameter and have focal lengths ranging from 370 to 400 mm. The focal point needs to have a diameter smaller than 1.2 mm. They should have a good reflectivity in the UV region above 80% at 160 nm. A very good surface quality was required (an average roughness below 1 nm). In order to comply with these requirements and to produce these mirrors as cheaply as possible the conventional heat forming technique had to be thoroughly restudied and improved.

Pactruss support structure for precision segmented reflectors

Abstract: The application of the Pactruss deployable structure to the support of large paraboloidal reflectors of very high precision was studied. The Pactruss concept, originally conceived for the Space Station truss, is shown to be suitable for use in a triangular arrangement to support a reflector surface composed of hexagonal reflector panels. A hybrid of Pactruss structural and deployable single-fold beams is shown to accommodate a center body. A minor alteration in the geometry is in order to avoid lockup during deployment. To assess the capability of the hybrid Pactruss structure, an example truss supporting a full-scale (20 meter diameter) infrared telescope was analyzed for static and dynamic performance. A truss structure weighing 800 kilograms gave adequate support to a reflector surface weighing 3,000 kilograms.

Light with wide angle radiation pattern

Abstract: A warning light having a wide angle radiation pattern and the ability to accept either an incandescent lamp or gaseous discharge tube as the light source is disclosed. The wide angle radiation pattern is, in part, achieved through the use a reflector having three separate surfaces which define parabolas with different axes and a common focal point, two of these parabolic reflector surfaces being spacially separated from one another and extending from the third reflective surface. The light emitter is supported from the third parabolic reflector surface such that the lamp filament or the gaseous discharge tube will extend through the common focal point.

Radiation properties of parabolic torus reflector

Abstract: General radiation-pattern formulas for a torus reflector antenna have been developed using physical optics. These expressions are valid at arbitrary feed locations not only within the primary focal arc but also for beam scanning with squinted feed horn illuminations. Numerical results were obtained at 22 GHz for an experimental 1.25 m*2.5 m torus reflector in both elevational beam scanning and extended azimuthal scanning outside the primary +or-15 degrees field of view. An elevation scanning range of 7 degrees showed only a 1 dB gain reduction. The 20 degrees azimuth beam (i.e. 5 degrees extended azimuth scanning) showed a 1.4 dB gain reduction. Comparison between calculated and measured patterns showed agreement in beamwidth and most pattern features. The discrepancy between calculated and measured sidelobe levels in the azimuthal plane is attributed to imperfection enhancement by the horizontal oversize of the reflector. >

Mid range UV communications

Abstract: Mid-range communications are improved with a transmitter having an elongate omni-directionally radiating tube of UV energy that are focussed by a compound parabolic reflector to within a designated azimuth and/or elevation. The configuration of the reflector gives a broad beam directivity over a receiver target area to the exclusion of other bearings and elevations such that selected receiving stations can be designated between moving or unstable communication platforms, such as aircraft or ships. Because scattering occurs at angles larger than the direct beam, the requirement for accurate tracking mechanisms is further relaxed. Furthermore, these extra scattered photons increase the link distance. The need for very small divergence transmitters, like lasers, is eliminated permitting inexpensive, efficient UV lamps to be used with compound reflectors as transmitter sources.

Passive infrared detection system with substantially uniform sensitivity over multiple detection zones

Abstract: A passive infrared detection system includes a reflective optical system comprising a focusing element (e.g. an elliptical or parabolic reflector) having an apparent focal length dependent upon the displacement of incident rays from the optical axis of such element, and a plurality of planar reflectors arranged at different angles with respect to such optical axis to provide the detection system with a plurality of different zones of detection, each having a different maximum detection range associated with it. According to the invention, the planar reflectors are arranged with respect to the focusing element so that each planar reflector cooperates with a different portion of the focusing element to project onto an IR detector located at the focus of such focusing element a relatively constant size image of a given target located at the maximum detection range associated with that planar reflector. Such an optical system provides the detection system with more uniform sensitivity from one zone of detection to another.

How To Align An Off-Axis Parabolic Mirror

Abstract: The alignment of an off-axis parabolic mirror can be discussed mathematically in terms of third order optics using Zernike polynomials. While this discussion can add insight to the theory of alignment, it doesn't provide an easy means of knowing what to do in a "Hands-On" laboratory situation. As can be inferred from the title of this paper, a "How-To" method of alignment will be discussed. As for the theory of alignment, let it suffice to say that it can be shown that an off-axis parabola is a surface which departs from a best fit sphere in terms of spherical aberration, coma, and astigmatism.

Wide angle warning light

Abstract: A dual emitter light assembly employs a reflector having a pair of concave reflector dishes. Each dish is associated with a lamp socket. Each concave dish comprises at least three parabolic reflector surfaces having a common focal point. The axes of the parabolas of revolution which define the reflector surfaces are non-parallel and lie in a common plane, the axis of both dishes lying in the same plane.

A comparison of reflector antenna design for wide-angle scanning

Abstract: The authors compare the ability of six single- and dual-reflector designs to scan up to 300 beamwidths in order to determine the feasibility of wide-angle scans using reflector antennas. The single reflectors are either parabolic symmetric dishes with f/D=2 or f/D=1 or an offset reflector with f/D=2. Scanning is accomplished for the first two designs by tilting the reflector dish. The third design is scanned electronically. The dual reflectors are Cassegrain designs. All designs have a circular diameter of 1000 wavelengths. Results obtained are presented and discussed. >

Reflector for high-intensity lamps

Abstract: A parabolic reflector differs from a standard paraboloid configuration by defining a relatively small, reflective cone on its reflective surface which is axially aligned with the longitudinal axis of the parabolic reflector. The reflective surface of the cone in any cross section taken through the conical axis and is so contoured that light impinging from a light source disposed forwardly of the reflector on the longitudinal axis thereof will strike the concave reflective surface of the cone, and reflect against the main parabolic reflecting dish, where it is re-reflected forwardly and parallel, thus eliminating the light from the lamp passing close to the longitudinal axis which would otherwise reflect back through the lamp rather than alongside it. This reflector is designed for use with high power HMI lamps from 1200 to 18 kw which are used for motion picture and television set lighting. Cone angle is from 15 degrees to 45 degrees maximum.

Multicoverage shaped reflector antenna designs

Abstract: The application of the hybrid shaped reflector/array feed approach to the design of multiple contoured antennas is examined. The results show that a hybrid antenna can achieve coverage gain performance comparable to that of a conventional array-fed parabolic reflector design but with a significantly reduced number of feed elements. Increasing the number of feed elements results in a reduced amount of reflector shaping, which in turn leads to better control of the sidelobes and roll-off characteristics. For single and dual beam coverages, improvements can be achieved by imposing constraints on these parameters during the optimization process. For multiple coverages, however, the need to share the reflector shape between several beams restricts the freedom to control the spurious radiation. It appears that for such requirements the sidelobes can be improved only by increasing the number of feed elements to reduce the amount of reflector shaping. This design approach has been used to deal with different multicoverage scenarios including dual-beam AFSAT coverage (C-band), the seven-beam EUROPESAT coverage (Ka-band), and the modified five-beam EUROPESAT supercoverage. >

Optical Testing Of Off-Axis Parabolic Segments Without Auxiliary Optical Elements

Abstract: The traditional optical test for an off-axis segment of a parabolic mirror utilizes an autocollimation flat and requires considerable test-bay space. Several other test configurations that will minimize space requirements are described. One method involves a null corrector, and three others require no auxiliary test optics. Combinations of the methods described will be useful in providing full independent evaluation of the figure of the segment under test.

Parabolic mirror for electromagnetic waves - with inflatable space bounded by specified plastics foils

Abstract: Parabolic mirror for electromagnetic waves is made of a first foil (3) of flexible inextensible material which has been preformed to a parabola and has its edges joined to a second foil (4) to form a fluid-tight internal space (I) An annular frame (10) holds the edge (6) of the first foil Both foils are pref made of PVC and have been welded together along the edge (6) When the interior (I) is inflated by a gas admitted through the connection (11), the foil (4) is stretched plane ADVANTAGE - Mirror is easy to transport and to erect and is less costly than presently available parabolic mirrors

A comparison of reflector antenna designs for wide-angle scanning

Abstract: Conventional reflector antennas are typically designed for up to + or - 20 beamwidths scan. An attempt was made to stretch this scan range to some + or - 300 beamwidths. Six single and dual reflector antennas were compared. It is found that a symmetrical parabolic reflector with f/D = 2 and a single circular waveguide feed has the minimum scan loss (only 0.6 dB at Theta sub 0 = 8 deg, or a 114 beamwidths scan). The scan is achieved by tilting the parabolic reflector by an angle equal to the half-scan angle. The f/D may be shortened if a cluster 7 to 19 elements instead of one element is used for the feed. The cluster excitation is adjusted for each new beam scan direction to compensate for the imperfect field distribution over the reflector aperture. The antenna can be folded into a Cassegrain configuration except that, due to spillover and blockage considerations, the amount of folding achievable is small.

Lighting device for a liquid crystal screen

Abstract: Lighting device for the liquid crystal screen of a portable television. This device comprises at least one fluorescent tube 9, 10 which is eccentric or "off-axis" with respect to the reflector 11, 12, the latter consisting of a segment, known as a "Herschel" segment, of a parabolic reflector.

Antenna arrangement and process for its use

Abstract: Antenna arrangement for high-frequency electromagnetic radiation with a parabolic reflector (2) and a housing arrangement (6) in the shape of a spoked wheel or a disc. Said housing arrangement is secured to the parabolic reflector (2) by means of a securing device (4). Said housing arrangement (6) in the shape of a spoked wheel or a disc has on its radial edge a plurality of exciters (8) for sending or receiving high-frequency signals. Said housing arrangement (6) is mounted rotatively on the securing device (4) in such a way that each exciter (8) can be rotated or positioned in the focal point (26) of the parabolic reflector (2). The latter is mounted on a supporting device (18). The antenna arrangement can be set on a particular transmitter or receiver by means of an adjusting device (28).

Fresnel lens type complex reflection system having a lens function

Abstract: The present invention pertains to a Fresnel lens type complex reflecting system in which a set of parabolic mirrors are utilized to function as a convex lens. This is accomplished through incident light rays impinging on concave surfaces of the parabolic mirrors. In this way, the focal point of the complex reflecting system will be on an opposite side of the complex reflecting system as the direction of incident light. Another feature of the present invention is an orientation of a set of parabolic mirrors which function to operate as a concave lens. This is accomplished through incident light rays impinging on convex surfaces of the parabolic mirrors.

Projection lamp has a parabolic reflector and polyacrylic deflector - for enhanced electro=optical efficiency and reduced weight for directional illumination beacon or signal lamps

Abstract: A lamp (1) for projecting a beam of light from two or more electroluminescent diodes (4) includes a combination of parabolic reflector (3) and of a coaxial deflector in the form of a conical profile (10) of transparent material (I) which will transmit some (deflected) rays R 3 directly while reflecting others (R1) so that the latter emerge (R4) after subsequently encoutering the reflector (3). Pref. the coaxial deflector (4) is approximately centred on the focal point of the other reflector (3). The wall thickness of (10) may vary, pref. increasing as the wall diverges and not necessarily of constant annular thickness. Pref. (I) comprises 'plexiglass' (RTM - an acrylic or methacrylic polymer). Pref. the emitters (4) are mounted directly on a transverse printed circuit board carried on a threaded stud for adjusting the positions of the lamps (4) or the deflector (10) relative to each other and to the reflector (3). USE - Esp. for projection lamps for illumination of selected areas, such as a road obstruction, or a (railway) signal lamp, or a runway beacon. Use of the electroluminous energy, the combination of the type of emitter and the semi- and total reflector profiles makes efficient, e.g. by halving the power consumption necessary for a railway wagon rear lamp and reducing its weight from typically 7 kg to 5 kg through saving weight and size on battery capacity.

Electron scanning antenna

Abstract: PURPOSE: To make the structure compact, and improve the precision and mechanical strength by providing an array of element sources, an electronic element for feed control, and a reflector which converges energy, and arranging the array in the focus area of the reflector. CONSTITUTION: The parabolic reflector 10 which is fed by the plane source array 11 arranged nearby the focus F of the reflector 10, the array 11 of element sources, and the electronic element for feed control are included. The electronic element for feed control includes hybrid couples corresponding to the element sources respectively, an amplifying circuit 21, and a beam forming circuit 24 which comprises an adjustable phase shifter 25 and an adjustable attenuator 26 which are controlled individually by a control unit 27. Further, at least one synthesizing unit 28 is included which consists of a set 29 of hybrid joins for sending out an effective output signal corresponding to a given beam. Consequently, the antenna can be made compact and improved in precision and mechanical strength.

Test of a two-dimensionally focusing quasi-optical antenna using a gyrotron

Abstract: A quasi‐optical antenna having one elliptical reflector and one parabolic reflector has been built for millimeter wave scattering measurements on the TORTUS tokamak plasma at the University of Sydney. This letter reports the first demonstration of the properties of such an antenna using a gyrotron millimeter wave source. Its advantages are (1) good two‐dimensional focusing (along the major radius and the toroidal directions) and (2) easy movement of the focus across the diameter of the plasma by changing the orientation of the parabolic reflector.

Experimental investigation of the wavefronts formed by computer optics components

Abstract: Plane phase optical components generating complex wavefronts from a spherical wave were made and investigated experimentally. The shape of a new wavefront was compared experimentally with the surface of a parabolic mirror.

Mesh pillow in deployable front-fed umbrella parabolic reflectors

Abstract: An analytical solution for the umbrella reflector surface shape, including the pillowing contribution, is presented. The solution is simple and sufficiently accurate for most antenna applications, and apart from being useful as a design tool, it can be easily incorporated into an existing computer code, allowing for more realistic evaluations of the umbrella reflector electrical characteristics. The analytical solution was tested by numerically solving the equations using a successive overrelaxation procedure. The gain degradation and the gore-related sidelobes clearly show the significance of pillowing on the antenna radiation characteristics. >

Penetration of a focused electromagnetic pulse into a biological material and its application to hyperthermia

Abstract: A localized temperature distribution inside a biological material (human muscle) is obtained through the use of a parabolic reflector to focus an electromagnetic pulse. With the point-matched time-domain finite-element method, the focused field and its penetration into the biological material are found, then the temperature profile in the material is calculated. The temperature is localized so that it can heat a specific spot without overburning the surrounding tissue. Attention is given to the factors which influence the localization characteristics, including the applied frequency, the associated electric parameters of the biological material, and the size of the parabolic reflector. The penetration depth and localization volume can be controlled by the adjustment of the applied frequency and the parameters of the reflector. >

Infrared detecting device

Abstract: PURPOSE:To prevent the detection efficiency of infrared rays from decreasing by arranging a light emitting element on the optical axis of a parabolic mirror where the detection efficiency of infrared rays is not decreased, and moving the parabolic mirror. CONSTITUTION:The parabolic mirror 1 is drawn out in the direction of the optical axis. In this state, the light emitting element 4 meets the focus of the parabolic mirror 1 and the light beam emitted by the light emitting element 4 is reflected by the parabolic mirror as shown by an arrow to become parallel light in the optical axis direction which travels to a reflecting mirror 3. This light beam is reflected by the reflecting mirror and projected in the opposite direction from the incidence direction of the infrared rays. The position of a detection area is confirmed with this light. A support frame 5 is supported by a frame 6 and so fixed not to move down. The power supply to the light emitting element 4 is controlled by a switch (not shown in figure) which operates when the support frame 5 fitted with the parabolic mirror is stored, and then the light emitting element 4 is lighted only when necessary.