Showing papers on "Reflector (antenna) published in 1995"

Geodesy using the Global Positioning System: The effects of signal scattering on estimates of site position

Abstract: Analysis of Global Positioning System (GPS) data from two sites separated by a horizontal distance of only ∼2.2 m yielded phase residuals exhibiting a systematic elevation angle dependence. One of the two GPS antennas was mounted on an ∼1-m-high concrete pillar, and the other was mounted on a standard wooden tripod. We performed elevation angle cutoff tests with these data and established that the estimate of the vertical coordinate of site position was sensitive to the minimum elevation angle (elevation cutoff) of the data analyzed. For example, the estimate of the vertical coordinate of site position changed by 9.7±0.8 mm when the minimum elevation angle was increased from 10° to 25°. We performed simulations based on a simple (ray tracing) multipath model with a single horizontal reflector which demonstrated that the results from the elevation angle cutoff tests and the pattern of the residuals versus elevation angle could be qualitatively reproduced if the reflector were located 0.1–0.2 m beneath the antenna phase center. We therefore hypothesized that the elevation-angle-dependent error was caused by scattering from the horizontal surface of the pillar, located a distance of ∼0.2 m beneath the antenna phase center. We tested this hypothesis by placing microwave absorbing material between the antenna and the pillar in a number of configurations and by analyzing the changes in apparent position of the antenna. The results indicate that (1) the horizontal surface of the pillar is indeed the main scatterer, (2) both the concrete and the metal plate embedded in the pillar are significant sources of scattering, and (3) the scattering can be reduced greatly by the use of microwave absorbing materials. These results have significant implications for the accuracy of global GPS geodetic tracking networks which use pillar-antenna configurations identical or similar to the one used for this study at the Westford WFRD GPS site.

EMAT probe and technique for weld inspection

Abstract: A method and apparatus of inspecting for flaws in a specular reflector, where the flaws having an expected length and the reflector is electrically conductive. The method includes directing a beam of an electromagnetic acoustic transmitting transducer along a beam axis toward the specular reflector for producing a reflected electromagnetic acoustic beam. The transmitted beam has side lobes with zero points therebetween, at least some of the side lobes being major side lobes. The reflected beam is received using an electromagnetic acoustic receiving transmitter set at an angle to the beam axis, the angle being selected to be at one of the zero points and past all of the major lobes of the transmitted beam to eliminate root and crown signals of the weld, in the reflected signal.

A generalized diffraction synthesis technique for high performance reflector antennas

Abstract: Stringent requirements on reflector antenna performances in modern applications such as direct broadcast satellite (DBS) communications, radar systems, and radio astronomy have demanded the development of sophisticated synthesis techniques. Presented in the paper is a generalized diffraction synthesis technique for single- and dual-reflector antennas fed by either a single feed or an array feed. High versatility and accuracy are achieved by combining optimization procedures and diffraction analysis such as physical optics (PO) and physical theory of diffraction (PTD). With this technique, one may simultaneously shape the reflector surfaces and adjust the positions, orientations, and excitations of an arbitrarily configured array feed to produce the specified radiation characteristics such as high directivity, contoured patterns, and low sidelobe levels, etc. The shaped reflectors are represented by a set of orthogonal global expansion functions (the Jacobi-Fourier expansion), and are characterized by smooth surfaces, well-defined (superquadric) circumferences, and continuous surface derivatives. The sample applications of contoured beam antenna designs and reflector surface distortion compensation are given to illustrate the effectiveness of this diffraction synthesis technique. >

Apparatus for switching optical signals and method of operation

Abstract: The present invention provides an apparatus (74 and 200) for switching an optical signal from an input optical fiber (210) to one of a plurality of output optical fibers (214 and 216). The apparatus (74 and 200) includes a collimator (76) for collimating an input optical signal into a collimated beam (216) at an angle with respect to a reference and a decollimator (78) for focusing the collimated beam to an output optical signal (220). The present invention also includes a reflector (92, 208, 218 and 222) for reflecting the collimated beam. The reflector (92 and 208) has a plurality of positions for changing the angle of the collimated beam (216) with respect to the reference so that the output optical signal (220) is focused on one of the plurality of output optical fibers (214 and 216).

Solar energy plant

Abstract: A solar radiation concentrating system (1) comprises at least two reflectors (12, 16) successively arranged along an optical path (4) of the system (1) so that a first (12) of the two reflectors (12, 16) reflects the radiation towards a second (16) of the two reflectors (12, 16). The reflectors (12, 16) have such spectral characteristics as to be capable of highly reflecting the radiation in a reflection range of wavelengths and absorbing the radiation in an absorption range of wavelengths, wherein the absorption range of wavelengths of the first reflector (12) substantially includes the absorption range of wavelengths of the second reflector (16).

Optical device with low electrical and thermal resistance bragg reflectors

Abstract: A compound-semiconductor optical device and method. The optical device is provided with one or more asymmetrically-graded heterojunctions between compound semiconductor layers for forming a distributed Bragg reflector mirror having an improved electrical and thermal resistance. Efficient light-emitting devices such as light-emitting diodes, resonant-cavity light-emitting diodes, and vertical-cavity surface-emitting lasers may be formed according to the present invention, which may be applied to the formation of resonant-cavity photodetectors.

Wavelength-stabilized, high power semiconductor laser

Abstract: A wavelength-stabilized, semiconductor laser having a light amplifying diode heterostructure with a flared gain region in an external resonant cavity. The flared gain region has a narrow aperture end which may be coupled to a single mode waveguide and a wide output end. A light emitting surface of the heterostructure proximate to the wide end of the flared gain region is partially reflective and combines with an external reflector to form a resonant cavity that is effectively unstable. The intracavity light-emitting surface proximate to the narrow aperture end is antireflection coated. The external reflector may be a planar mirror or a grating reflector. A lens or an optical fiber may couple the aperture end of the flared gain region to the external reflector. Frequency-selective feedback is provided by orienting the grating reflector or providing a prism in the cavity in front of the external planar mirror. Other filtering elements may also be placed in the external cavity. The flared gain region and waveguide may be differentially pumped or modulated with current provided by separate contacts.

Sensitivity and transient response of microwave reflection measurements

Abstract: Microwave reflection measurements are widely used for the characterization of minority‐carrier lifetimes in semiconductors. A theoretical description of the technique is presented. The approach is based on a dielectric multilayer model that accounts for experimental parameters such as microwave frequency, sample thickness and doping, and the distance to an optional reflector behind the sample. With a new definition of the sensitivity in transient microwave reflection measurements, the most sensitive configuration is investigated for a given semiconductor thickness and conductivity. Good agreement between the theoretical simulation and measurements is demonstrated. The model is also used for calculating microwave reflection transients from the excess carrier decay after pulsed laser excitation. It is found that the reflected microwave power mirrors the carrier decay if three criteria are fulfilled: The carrier generation must be homogeneous; low‐injection conditions are required; and the reflector must be positioned appropriately for linear dependence of the microwave reflection on the carrier density.

Deployable satellite antenna for use on vehicles

Abstract: A deployable satellite antenna system permits an antenna with elevation and azimuth control to be mounted to the roof of a vehicle. The elevation control assembly for the antenna system has a base with two parallel tracks and a slider that moves along these tracks. The antenna is connected to a support frame pivotally attached to the slider. Pivot arms are pivotally attached between the reflector and the base adjacent to the parallel tracks. The elevational position of the antenna is adjusted by a motor that controls the position of the slider along the parallel tracks between a stowed position in which the antenna is stowed facing the vehicle and a deployed position in which the antenna is rotated to a maximum elevational angle. The azimuth of the antenna is controlled by a rotating assembly mounted to the roof of the vehicle beneath the base of the elevation control assembly.

Broadband optical reflector—an application of light localization in one dimension

Abstract: A broad‐band optical reflector based on the localization of light for one‐dimensional disordered systems is proposed and demonstrated both theoretically and experimentally. The binary disordered multilayer reflector consists of alternating random layers of two coating materials. Its high reflection range is much wider than that of standard λ/4 stacks and can be obtained by a conventional coating method and ordinary materials. This kind of reflector will have significant applications in laser technology and optical equipment.

An antenna system having a choke reflector for minimizing sideward radiation

Abstract: A antenna system of the present invention comprises a radiating means for radiating a radio frequency, which is converted from electric power, and which has a impedance matching unit and a power divider; a first reflecting means for reflecting and filtering said radio frequency; and at least one second reflecting means for filtering said radio frequency radiated in the sideward direction of said antenna system, which is vertically attached to said first reflecting means, and is able to be moved in a horizontal direction.

Electrostatically-controlled cantilever apparatus for continuous tuning of the resonance wavelength of a fabry-perot cavity

Abstract: An electrostatically controlled cantilever apparatus for continuous tuning of the resonance wavelength of a Fabry-Perot cavity is disclosed. A resonant cavity is formed between two distributed Bragg reflector (DBR) mirrors. The top reflector is composed of a movable top DBR supported in a freely suspended cantilever, a variable-thickness air spacer layer and a fixed DBR. The bottom reflector is fixed on the substrate. By applying a tuning voltage to create electrostatic attraction, the cantilever may be deflected towards the substrate, thereby changing the thickness of the air spacer layer and consequently the resonant wavelength of the Fabry-Perot cavity.

Ultrasound detection techniques

Abstract: A method for separating a liquid and in particular a liquid metal from heterogeneous constituents therein, comprises the steps of providing a passage for a flow of liquid containing heterogeneous constituents and directing ultrasound waves into the passage. The ultrasound waves are made to form standing waves in the liquid using a reflector and by tuning the frequency of the ultrasound waves. The standing waves cause extraneous particles in the liquid to coagulate at the nodes. The reflector is also designed to direct some of the ultrasound waves upwardly into the passage. The flow of the liquid metal through the passage and the ultrasound in the passage carry the coagulated particles into the slag on the surface of the liquid metal for removal. The ultrasound waves also cause cavitation effects which degas the liquid metal. An ultrasound particle detection device is also disclosed which includes a transmitting delay line, a receiving delay line and a reflector immersed in a liquid. The reflector reflects ultrasound from the transmitting delay line to a focal volume. The receiving delay line receives ultrasound reflected by extraneous particles in the focal volume allowing for their detection.

Electromagnetic absorption in the human head from experimental 6-GHz handheld transceivers

Abstract: We have used a new millimeter-resolution MRI-based model of the human body to calculate the electromagnetic absorption in the head and neck for three experimental Yagi antennas suggested for handheld transceivers of a proposed 6-GHz personal communication network (PCN) system. The SAR distributions are obtained with a resolution of 1.974/spl times/1.974/spl times/1.5 mm for transceivers that are held against the ears and tilted forward by 33/spl deg/. The finite-difference time-domain technique is used to calculate the EM fields and SARs for the transceiver, antenna, and head and neck coupled region that is divided into 158/spl times/84/spl times/188 or nearly 2.5 million cells. The highlights of the numerical calculations are verified by means of a head-shaped experimental model made of tissue-equivalent materials simulating the electrical properties (/spl epsiv//sub r/,/spl sigma/) of the skull, brain, muscle, eyes, and ears developed for use at 6 GHz. Because of the proximity to the antenna, the highest SARs are obtained for the upper part of the ear. For a planned radiated power of 0.6 W, the peak SARs averaged over any 1 g of tissue defined as a tissue volume in the shape of a cube are on the order of 0.5-1.0 W/kg for two of the proposed antennas and considerably higher (2.06 W/kg) for the third antenna using a narrower off-axis reflector. Low SARs for the first two antennas are likely due to the shielding provided by the relatively wider strip reflector plates used for these antennas.

Electrodeless fluorescent lamp.

Abstract: An electrodeless fluorescent lamp having an envelope with an improved shape. The invented shape is shorter and the light-trapping area near the neck is substantially reduced or eliminated. The ratio of the operational width to the operational height of the envelope is preferably at least 1.5 and the reflector face angle is preferably less than 40°.

Accurate simulation of reflector antennas by the complex source-dual series approach

Abstract: The radiation from circular cylindrical reflector antennas is treated in an accurate manner for both polarizations. The problem is first formulated in terms of the dual series equations and then is regularized by the Riemann-Hilbert problem technique. The resulting matrix equation is solved numerically with a guaranteed accuracy, and remarkably little CPU time is needed. The feed directivity is included in the analysis by the complex source point method. Various characteristic patterns are obtained for the front and offset-fed reflector antenna geometries with this analysis, and some comparisons are made with the high frequency techniques. The directivity and radiated power properties are also studied. >

AlN-GaN quarter-wave reflector stack grown by gas-source MBE on (100) GaAs

Abstract: A 15 period, wurtzite-structure AlN-GaN reflector stack has been grown on (100) GaAs by gas-source molecular beam epitaxy. A peak reflectance of over 90% has been realised, in agreement with a matrix-method computer simulation. Our results support the feasibility of vertical Fabry-Perot cavity optoelectronics using nitride materials.

Omni-directional LED lamps

Abstract: Omni-directional LED lamps are disclosed in three embodiments. In a first embodiment, two LEDs are mounted side by side in a miniature bayonet base that can fit into a conventional miniature bayonet socket. The side-by-side LEDs face semi-spherical mirror reflectors that distribute the unidirectional light emitted from the LEDs over an omni-direction. A second embodiment has two LEDs facing one another with a spherical mirror reflector between to cause unidirectional light to be omnidirectional. In a third embodiment, a semi-spherical reflector is mounted in the top of a lens cover above an LED. The components are housed in a sealable casing for marine applications where the casing can be mounted to a dock piling.

Method for switching optical signals

Abstract: The present invention provides an apparatus (74 & 200) for switching an optical signal from an input optical fiber (210) to one of a plurality of output optical fibers (214 & 216). The apparatus (74 & 200) includes a collimator (76) for collimating an input optical signal into a collimated beam (216) at an angle with respect to a reference and a decollimator (78) for focusing the collimated beam to an output optical signal (220). The present invention also includes a reflector (92, 208, 218, & 222) for reflecting the collimated beam. The reflector (92 & 208) has a plurality of positions for changing the angle of the collimated beam (216) with respect to the reference so that the output optical signal (220) is focused on one of the plurality of output optical fibers (214 & 216).

Reflector antenna, especially for a communications satellite

Abstract: The invention provides a reflector antenna, especially for a communications satellite, having at least one fixed main reflector (102) with an essentially circular aperture. A fixed feed system (118) includes a horn radiator (108) with a rotationally symmetric radiation diagram and a fixed polarization direction. An auxiliary reflector may be arranged to be rotationally positionable around a main axis (E) and has a reflecting surface that is shaped as a partial surface of a nonrotationally symmetric ellipsoid with a low numerical eccentricity, which illuminates main reflector (102) elliptically with an ellipticity that is essentially constant regardless of the rotational position.

Spatial light modulator

Abstract: A spatial light modulator includes a reflector which is electrostatically deflectable out of a normal position, whereat a supporting beam is unstressed, into a deflected position, whereat a portion of the mirror contacts a portion of a landing electrode at the same electrical potential as the reflector. An inorganic layer or solid lubricant is deposited on the contacting portions. After the modulator is operated for a period of time, the tendency of the reflector to stick or adhere to the landing electrode is diminished or eliminated by the layer so that the reflector is returned to its normal position without any reset signal or with a reset signal having a reasonably low value. Preferred materials for the layer are SiC, AlN or SiO 2 .

Scanned antenna system

Abstract: Compact, microwave scanned antennas include combinations of a radiator, a reflector and a mirror. The radiator is formed by plating a shaped dielectric core. It generates an antenna beam at an output aperture in response to a microwave signal at an input port. The wavefront orientation of the antenna beam is a function of the wavefront orientation of the microwave signal at the input port. Changing the angular relationship between the path of the microwave signal and the input port changes the wavefront orentation of the antenna beam and, therefore, its beam axis. Pivoting the reflector realizes the desired angular change in the microwave signal path. Alternatively, the reflector can be fixed and the mirror pivoted to vary the microwave signal path. Antenna embodiments can be physically realized with a single moving part, the shaped dielectric is easy to form and when configured to operate at a high frequency, e.g., 77 GHz, the antenna is small enough to fit behind an automobile license plate.

Phase correcting zonal reflector incorporating rings

Abstract: An array of conducting elements printed on a grounded dielectric substrate functions as an electromagnetic phase shifter. With a fixed substrate and a given operating frequency, the phase shift is determined by the array parameters. In the paper, the spectral domain moment method model for analyzing homogeneous reflective phase shifters with conducting rings as elements is presented, and numerical and experimental results are given. A novel phase correcting Fresnel zonal reflector based on this model is reported. A 43% maximum antenna efficiency and -22 dB sidelobe level were measured in X-band. The bandwidth of the reflector is estimated to be greater than 10%. >

Nonimaging optical concentrators and illuminators

Abstract: A nonimaging concentrator (or illuminator) of light. The concentrator (or illuminator) has a shape defined by dR/dφ=Rtanα where R is a radius vetor from an origin to a point of reflection of a light edge ray from a reflector surface and φ is an angle between the R vector and an exit aperture external point of the concentrator (illuminator) and coordinates (R, φ) represent a point on a reflector curve and α is an angle the light edge ray from an origin point makes with a normal to the reflector curve. The reflector surface allows the light edge ray on the reflector curve to vary as a function of position. In the concentrator an absorber has a shape variable which varies with position along the absorber surface.

Superdirective antennas with passive reflectors

Abstract: A brief introduction to the problem of superdirective radiation in antenna theory, and a solution to the problem of wave scattering from a structure, formed by resonant scatterers, is presented. The paper describes construction of a two-dimensional superdirective antenna with one active element, and a reflector made of resonant scatterers-unclosed cylinders proposed by Veremey and Shestopalov (see Radio Science, vol.26, no.2, p. 631-636, 1991). Physical phenomena, which cause the effect of superdirective radiation, are studied in detail. It is shown that the interaction between the resonant elements leads to the possibility of exciting a mode characterized by a high level of reactive power, in the vicinity of a passive structure. Particular attention is paid to the sensitivity of the superdirective antenna, and to tolerance constraints. It is shown that changes of the angular width of a slot in an unclosed cylinder (or in several unclosed cylinders), within /spl plusmn/1%, do not lead to the destruction of the superdirective resonance. >

Dual reflector high bay lighting system

Abstract: A dual reflector lighting system having a housing, a ballast and a lamp socket connected to receive a gaseous discharge or high intensity discharge (HID) lamp. An outer reflector is mounted to the housing to reflect a portion of light from the lamp. An inner or auxiliary reflector is mounted coaxially with the lamp to reflect a substantial amount of light from the lamp downwardly. The auxiliary reflector is preferably adjustable relative to the lamp. The invention also covers a dual reflector assembly, including an outer reflector and an inner reflector, adjustable relative to each other which is adapted to be mounted to a HID fixture. The invention also covers an auxiliary reflector having a predetermined size and shape adapted to fit within an outer reflector of a HID fixture and preferably includes facilities for adjusting the auxiliary reflector relative to the outer reflector. The invention also covers a retrofit kit which includes a ballast, an auxiliary reflector and facilities for connecting the auxiliary reflector to an existing HID fixture and for adjusting the auxiliary reflector so that a substantial portion of light is concentrated downwardly.

Integrated antenna for satellite and terrestrial broadcast reception

Abstract: A compact and flat antenna that provides both Direct Broadcast Satellite and local off-air reception. The flat reflector is made of a composite material with multiple reflective radiating surfaces. The multi-stepped reflector combines both diffraction and refractive principals to collimate Radio Frequency signal waves to a short focal point. At the focal point a phase correcting splash plate and lens direct the RF signal through a low loss axis-fed circular waveguide and then to a low noise amplifier. This compact design reduces space, cost and over-all structure, which presents an aesthetically pleasing satellite communication antenna. The antenna aperture includes a VHF/UHF antenna element for reception of local and/or off-air broadcast TV signals eliminating the need and cost to install a separate antenna.

Resonant cavity light emitting diode with an alxoy/gaas reflector

Abstract: A resonant cavity light emitting diode is fabricated which makes use of a Ag mirror/contact and a buried AlxOy/GaAs Bragg reflector. The buried AlxOy is formed by the selective conversion of AlAs. The differential light output efficiency is measured and found to be ∼5.5% when the AlxOy/GaAs reflector is present versus ∼2.5% for a control device without the AlxOy/GaAs mirror. The measured efficiencies are compared with calculations.

Light for motor vehicles comprising a reflector including a plurality of reflecting areas

Abstract: Light (10) for motor vehicles which comprises a container body (11) containing one or more reflectors (12-112) defining specialised sectors having specific functions, each reflector (12-112) having at least one incandescent lamp (14) associated with a lamp holder (15), the reflector (12-112) cooperating at its front with an outer transparent element (13), the reflector (12-112) being defined by a plurality of concave or convex reflecting areas (16-116) distributed substantially evenly on a surface of the reflector (12-112), the reflecting areas (16-116) being visible through the outer smooth transparent element (13) as a mated plurality of apparent luminous images (19).