Showing papers on "Reflector (antenna) published in 1994"

Microwave Horns and Feeds

Abstract: This book is devoted to describing the theory, design, performance and application of microwave horns and feeds for reflector. The first general treatment of feeds for reflector antennas, it describes design principles and methods of analysis.

Antenna pattern synthesis: a new general approach

Abstract: The antenna pattern synthesis problem is of the utmost importance in almost every kind of antenna applications. Therefore, a very large number of contributions have appeared on this subject. But virtually all of them deal with simplified versions of the complete synthesis problem, wherein the degrees of freedom available in principle are strongly reduced, and/or idealized design criteria or requirements are considered. In this paper we present a formulation which allows us to overcome this fragmentation of the synthesis problem. A clear and direct description of the performance actually required by the antenna and a representation of the radiating properties of the antenna as a system allows us to formulate the synthesis problem as an intersections finding problem, i.e., to find a common element between a number of sets, each one containing elements fulfilling part of the requirements. This allows a completely general and flexible formulation of the problem, independent of the actual structure of the antenna. Then the practical implementation of this formulation is widely discussed, showing how an efficient solution procedure can be devised. The implications of the well-known ill-conditioning of the synthesis problem are also discussed. In order to show how the approach works and to assess its flexibility and power, a couple of significant examples are included, namely, a phase-only reconfigurable array and a shaped reflector synthesis. These examples are unconventional since no a priori choice of the intensity distribution (for the array case) or of the feed cluster (for the reflector case) is required. The method presented is able to exploit all the available degrees of freedom in order to fulfill the design requirements. >

Multiple-element driven array antenna and phasing method

Abstract: An antenna array for direction-agile applications, such as r.f. packet mesh networks, employs a plurality of quarter-wave radiators disposed normally to a ground plane on a dielectric backing and switching elements for selecting a desired receiving direction and transmission direction and minimizing interference from signals in opposing directions. A control system selects and switches direction rapidly enough to receive and transmit digipeating signals in selected different directions using the phasing and switching elements. A specific embodiment employs eight radiators of 0.2625 electrical wavelengths (quarter wave plus 5%) disposed equidistant along a circle within a circular ground plane in a pattern which is 1/4 wavelength from the outer boundary of the ground plane, each radiator being disposed at least 0.15 wavelengths to about 0.25 wavelengths from adjacent radiators in a circular pattern. The antenna is characterized by eight electronically switchable radiating directions (at 45° intervals) with at least 20 dB front to back ratio and a 3 dB beamwidth of 64°. Pairs of radiators form parasitic elements, driven elements and reflectors with spacing selected as a modest compromise from the ideal spacing to allow electronically selectable directionality using identically-spaced elements acting as driven elements, parasitic elements and reflector elements. The driven elements are slightly reactively fed.

Composite multi-beam and shaped beam antenna system

Abstract: A composite antenna for use in satellite communication provides both the functions of multiple beams and a shaped beam radiated from a single radiating aperture. The radiating aperture may employ a mirror or a lens. Transmitted radiation from an array of radiators is coupled via a subreflector to the main reflector or lens which constitutes the radiating aperture of the antenna system. During reception of radiant-energy signals, signals received by the main reflector or lens are coupled via a separate subreflector to a separate array of receiving radiators operated at a frequency band different from that of the transmit array. The two subreflectors are combined into a single subreflector assembly employing a metallic concave reflector covered by a layer or coating of frequency selective optical material which allows for propagation of radiation at one frequency to the metal reflector while reflecting radiation in the other frequency band from a surface of the coating. Separate beamformers are employed for receiving and transmitting radiant-energy signals, the beamformers combining signals of clusters of radiators to provide for multiple beams wherein each of a plurality of the beams is formed by a cluster of radiators. Additional connection is provided via diplexers to the beamformers to select radiators to be employed for generation of shaped beams for both reception and transmission. The reflecting surfaces have diameters much larger than the diameters of the radiators to provide for individual beams from each of the radiators.

Analysis and design of a microstrip reflectarray using patches of variable size

Abstract: In a great number of microwave applications a highly directive antenna with a main beam scanned to a certain angle is required. To achieve this a certain aperture illumination with progressive phasing is used. The two primary ways to do this are reflectors and arrays. The reflector antenna uses its geometry to create the desired phase across the aperture, while the array employs distinct elements fed with progressive phasing. Reflector antennas are advantageous in the fact that they typically exhibit large bandwidth and low loss. The main disadvantage of the reflector is the geometrical constraint it imposes on the design. The most popular reflector, the parabolic reflector, also exhibits inherently high cross polarization levels. Microstrip patch arrays are lightweight, low-profile antennas that are capable of low cross polarization levels but typically have small bandwidth and fairly large loss at microwave frequencies. The more attractive features of reflectors and arrays are combined in the reflectarray. The steps taken in the design of a microstrip reflectarray using patches of variable size are outlined. Measured and theoretical results are shown for the finished design, and several important performance criteria are compared with the microstrip reflectarray.

A simple FDTD model for transient excitation of antennas by transmission lines

Abstract: A simple FDTD model is developed for use with antennas that are fed from transmission lines. The model is especially designed for use with transient excitations, where the incident and reflected waveforms within the transmission line are of interest, and the latter is determined directly in the FDTD calculation. The model is verified for both transmission and reception of transient waveforms by comparison with measured results for a cylindrical monopole antenna with a plane reflector. >

Time-domain physical-optics

Abstract: The authors extend the concept of the frequency-domain physical-optics approximation to the time domain, and use it to determine some significant properties of large reflector antennas. When this method is used to determine the equivalent surface-current density on the reflector, the effects of time-delayed mutual coupling between points on the surface are ignored. Consequently, many of the numerical limitations found in other conventional time-domain techniques are avoided, e.g. boundary-truncation error, interpolation error, numerical dispersion error, numerical instability, error accumulation with time marching, etc. More significantly, this method requires relatively small amounts of computer memory and CPU time. Several applications to the transient analysis of pulsed radar systems are given. >

A curved field reflectron time‐of‐flight mass spectrometer for the simultaneous focusing of metastable product ions

Abstract: The ability to simultaneously focus a wide mass range of metastable fragment ions formed after the initial ionization event in a matrix-assisted laser desorption/ionization time-of-flight mass spectrometer has been made possible by the development of a new type of ion reflector. This coaxially designed time-of-flight instrument employs a modified single stage reflector whose axial voltage gradient rises differentially in order to produce an alignment of energy focal points for product ions. In contrast, product-ion focusing in conventional constant field reflectors occurs over a broad range of distances from the reflectron exit. Approximately 90% of the product-ion mass spectrum can be collected without adjustment, thereby eliminating the need to scan the reflector voltage. Design considerations of the curved field reflectron, its calibration properties and representative metastable spectra of several peptides are discussed.

Tailored edge-ray reflectors for illumination

Abstract: The edge-ray principle can be used to tailor a reflector. However, one set of edge rays already fully determines the reflector profile. We present a design method for tailoring compact compound elliptical concentrator (CEC)-type reflectors to a given source and a desired angular power distribution. Two reflected images of the source, one on each side of the source, contribute together with the direct radiation from the source to produce the desired power distribution. We determine the reflector profile by numerically solving a differential equation. No optimization is required. Beyond the angular region in which the power distribution can be strictly controlled, the power drops to zero in a finite decay range. This decay range becomes narrower as the reflector increases in size. We show a reflector for producing a strictly constant irradiance from −43 to 43 deg from a cylindrical source of constant brightness. The reflector extends to a maximum distance of 8 source diameters. No power is radiated beyond ± 50 deg.

Apparatus and method for concentrating radiant energy emanated by a moving energy source

Abstract: A device efficiently collects energy from a moving source without having to actively track the source. The device includes a primary concentrator, a secondary reflector and a target position. The primary concentrator is positioned to receive energy from the moving energy source and to direct the energy toward the secondary reflector. The secondary reflector has a concave surface which is covered by a number of convex reflecting surfaces. These convex reflecting surfaces direct the energy toward the target position regardless of the relative angle between the energy source and the primary concentrator.

Interferametric measuring system with air turbulence compensation

Abstract: An improved interferometric measuring system wherein the system projects a first beam of light at a first measurement wavelength along a reference path to a reference reflector and a second beam of light at a second measurement wavelength along a measurement path to a measurement reflector, and determines a change in position of the measurement reflector from an interference pattern produced between a first light beam reflected from the reference reflector and a second light beam reflected from the measurement reflector, and wherein the system can measure atmospheric disturbances along the measurement path, concurrently with measuring a change in the position of the measurement reflector.

Condensing and collecting optical system using an ellipsoidal reflector

Abstract: An off-axis optical system for collecting and condensing electromagnetic radiation utilizes an ellipsoidal reflector configured to minimize the effects of magnification and optical aberrations. An ellipsoidal reflector (M1, P) having primary and secondary focal points (F1, F2) along the major axis (8) is illuminated by a light source (S) and subtended by an acceptance cone (16) of the target (T). In one embodiment, a single ellipsoidal reflector is configured with its major axis non-coincident with its geometric optical axis (12) and with the optical axis (14) of the target at an angle greater than zero degrees so as to reduce substantially the distance at which a focused image is formed and to achieve an average magnification near unity thereby maintaining the brightness of the source at the target. The radiant flux at the location of the target is increased by incorporating a retro-reflector (M2) of toroidal or spherical design.

Probe for monitoring a fluid medium

Abstract: A probe (60) for monitoring a fluid medium employing at least one electromagnetic wave reflector (8) and at least one fiber optic (4 and 5) for analysis of the fluid medium. The probe includes a base (2) having a hole (68), a window (1) covering the hole of the base, wherein the window transmits electromagnetic waves and an electromagnetic reflector, spaced apart from the window, disposed to reflect at least part of the electromagnetic waves toward the window. The probe collects the reflected waves through one or more fiber optics placed behind a window to a fluid medium and transmits the waves to a spectrometer connected to a computer which analyzes the fluid medium on a real time on-line basis. Piezoresistive and temperature sensing elements are deposited on the window which also may function as a force collector diaphragm of thin refractory or a semiconductor materials. The piezoresistive elements are on the unsupported part of the diaphragm and at least part of the diaphragm is transparent to electromagnetic waves.

A design procedure for classical offset dual reflector antennas with circular apertures

Abstract: A geometrical optics procedure for designing electrically optimized classical offset dual reflector antennas with circular apertures is presented. Equations are derived that allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The procedure, together with these equations, yields an optimized design, starting from general system requirements. The procedure is demonstrated by designing both an offset Cassegrain and an offset Gregorian antenna, and is validated by analyzing their radiation patterns using physical optics surface current integration on both the main and subreflectors. >

Optical measuring apparatus

Abstract: Laser light from LD (laser diode) is guided through a fiber to be projected onto a reflector. A receiver detects a return beam of modulated light reflected by the object and outputs a signal reflecting a phase difference between the laser light and the modulation signal. The frequency of the modulation signal is changed based on the signal value so as to finally achieve phase lock. When the phase lock fixes the frequency of the modulation signal, the frequency always corresponds to a distance from LD to the reflector or a group index of a substance filling the optical path. Thus, the distance to the object or the group index of the substance filling the optical path at the time of phase lock can be determined in a simple manner and with a high accuracy, based on the output frequency at the time of phase lock.

Reflector design for illumination with extended sources: the basic solutions

Abstract: The goal of the optical design of luminaires and other radiation distributors is to attain the desired illumination on the target with a given source while minimizing losses. Whereas the required design procedure is well known for situations in which the source can be approximated as a point or as a line, the development of a general analytical design method for extended sources began only recently. One can obtain a solution for extended sources by establishing a one-to-one correspondence between target points and edge rays. Here the possible solutions in two dimensions (cylindrical sources) are identified, based on only one reflection for the edge rays. The solutions depend on whether the "image" on the reflector is bound by rays from the near or the far edge of the source. For each case there are two solutions that could be called converging and diverging by analogy with imaging optics. Counting the topological choices for the boundaries of the "image" we obtain a complete classification of the buildingblocks from which luminaires can be designed. One can construct interesting hybrid configurations by combining these building blocks. Thus one can gain a great deal of flexibility for tailoring designs to specific requirements. The differential equation for the reflector is shown to have an analytical solution. Explicit results are presented for symmetric configurations with the target at infinity.

Light emitting optical device with on-chip external cavity reflector

Abstract: A 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.

Enhanced fluorescence detection of samples in capillary column

Abstract: A simple device for collecting a greater amount of fluorescent emission from a minute sample in a capillary column. An axially symmetrical paraboloid reflector is implemented to collect fluorescent emission from the capillary column. The reflector also serves as a simple bracket for positioning and aligning the capillary column. Fluorescent emission is collimated by the paraboloid reflector which allows more effective use of band pass filters in blocking scattered radiation from detection. The scattered and transmitted radiation can be used to facilitate alignment of the capillary with respect to the detection optics. The paraboloid reflector also facilitates the implementation of simultaneous multiple-channel detection.

Single-growth-step GaAs/AlGaAs distributed Bragg reflector lasers with holographically-defined recessed gratings

Abstract: A ridge waveguide GaAs/AlGaAs quantum well DBR laser fabricated with a simplified grating recess-technology and a third order grating is described. The reflector is fabricated on top of a recessed waveguide using holographic exposure followed by reactive ion etching. The laser operates on a single longitudinal and lateral mode with threshold current as low as 20 mA, output power 5 mW per facet and is intended for monolithically integrated interferometer applications.

Directional antenna, in particular dipole antenna

Abstract: In order to produce a directional antenna which is superior to those of the prior art, and especially a dipole antenna which is easier to manufacture and of simpler design, and also has enhanced electrical properties, the dipole with its circuit balancing element (7) according to the invention is made of the material of the reflector (5). The dipole and the circuit balancing element (7) project from the reflector wall (5) through corresponding areas which are cut out and/or punched out, up to a region (11) where they join with the remaining material of the reflector wall (5), and are preferably bent outwardly in relation to the plane of the reflector wall in the region of the point (11) where they immediately join with the remaining material of the reflector wall (5).

Flourescent lighting fixture retrofit unit and method for installing same

Abstract: A retrofit unit for a fluorescent lighting fixture having a housing with an open face and a method for installing same. The retrofit unit includes a reflector plate for covering the open face of the housing and brackets for attaching the reflector plate to the housing. The reflector plate has slots formed therein which cooperate with the brackets for adjusting the reflector plate to fit the housing. At least one of the brackets acts as a hinge allowing the reflector plate to rotate away from the open face of the housing. The method includes providing the reflector plate and brackets, as well as inserting a bracket in a slot, adjusting the brackets relative to the slots, and adjusting fasteners relative to the brackets.

Digital image system for determining relative position and motion of in-flight vehicles

Abstract: The system includes a reflector assembly mounted on a first one of a pair of spacecraft. The reflector assembly includes a mirror around which are positioned a mirror and retroreflectors. A light source mounted on the second spacecraft illuminates the assembly the reflections from which are directed into a radiometer which is also mounted on the second spacecraft. The mirror has a known curvature, and the known curvature in conjunction with the retroreflectors allow calculation of the position and motion parameters of the first spacecraft relative to the second.

A comparison between techniques for global surface interpolation in shaped reflector analysis

Abstract: Usual geometrical optics based syntheses of shaped reflectors provide numerically defined surfaces which must be interpolated for subsequent evaluation of the antenna secondary field to check against design specifications. The implementation of three techniques capable of performing global interpolations of numerically defined (3D) surfaces, namely, the quintic pseudosplines, polynomial Fourier series, and Jacobi polynomial-sinusoidal expansions, is explored. The relative superior stability of the first is demonstrated for the synthesis of shaped reflectors presenting critical behavior of their principal curvatures. >

Gradient reflector location sensing system

Abstract: A multi-band high-speed videometric head tracking system (10) having a gradient reflector array (12) attached to a helmet (13) on a person's head, ultraviolet light source (14) emitting light which is reflected by the reflector array to a video camera (11) which provides an image to a spot location estimator (29) providing accurate locations of spots in the image representing the reflectors' reflecting light to image location accuracies within a pixel of the image. The location information from the spot location estimator goes to a track point 3-D location and helmet LOS estimator (33) that provides location and orientation information to a Kalman Filter (15) that accurately estimates and predicts the helmet position at faster rates than would be possible for a process that uses just the image-based measurements of the helmet.

Device for ultrasonic flow measurement

Abstract: An ultrasound flow measuring tube includes an ultrasound transmitter transmitting ultrasound energy toward a reflector in the tube, which reflects the ultrasound energy so that it is reflected from a side of the tube before reaching a second reflector. The second reflector directs the ultrasound energy to an ultrasound receiver. The reflectors direct the ultrasound energy along a spiral path in the tube.

Antenna reflector reconfigurable in service

Abstract: An in-service reconfigurable antenna reflector having a rigid support structure, a deformable reflective surface having radio reflection properties and actuators operating on the deformable reflective surface to deform it. The reflective surface is elastically deformable with stiffness in bending and the actuators operate at control points of the deformable reflective surface, transversely thereto.

Design parameters and measured performance of the IRAM 30-m Millimeter Radio Telescope

Abstract: The "Millimeter Radio Telescope" (MRT) is operated by the Institute for Radio Astronomy in the millimeter range (IRAM) and is located at 2850-m altitude in the Sierra Nevada, near Granada, Spain It is a reflector antenna of 30-m diameter with a surface accuracy of 008 mm and a pointing accuracy of better than 2 arcsec The telescope is equipped with sensitive receivers for the atmospheric windows between 08- and 7-mm wavelength The authors describe the optics layout of the receiver and calibration system, which allows simultaneous observations at a number of frequencies The special design aspects of the antenna, in particular the control of thermal deformations and the achievement of a high reflector and pointing accuracy are described The authors compare the design computations with the characteristics of the telescope, derived from several years of operation and optimization The success of the design is demonstrated by observational experience The authors conclude the paper with a short review of some of the astronomical results obtained with the telescope >

Apparatus for detecting proper positioning of objects in a holder

Abstract: The positions of objects in a holder, such as a cassette containing semiconductor wafers, are determined by a system that projects a pair of coplanar light beams through the cassette from one side. A reflector on the opposite side reflects both light beams back though the cassette and onto separate photodetectors on the one side. A computer analyzes signals from the photodetectors as the cassette is moved through the light beams. As the cassette moves the light beams are interrupted by the wafers. The relative widths and timing of pulses in the signals indicate the location of wafers in the cassette and whether a wafer is misaligned.

Circularly polarized microcell antenna

Abstract: A circularly polarized microcell antenna (10) that requires only a single feed-line to radiate circularly polarized electromagnetic energy therefrom. The antenna (10) comprises a reflector box (14) having a bottom (15) and side walls (17) to which an electrical connector (20) is mounted. The center conductor (24) of the connector (20) is electrically connected to a conductor bar (22) upon which a first dipole assembly is mounted at a designated one-quarter wavelength location. The shell of the connector (20) is electrically connected to the reflector box (14) upon which a second dipole assembly is mounted at a designated one-quarter wavelength location. Each dipole assembly comprises a primary dipole arm (52) and a secondary dipole arm (68) which are electrically connected by a phasing loop that introduces a 90° phase shift between the primary dipole arm (52) and the secondary dipole arm (68). Thus, a single feed-line is capable of feeding both the primary and secondary dipoles so as to allow circularly polarized electromagnetic energy to radiate therefrom.

Recessed lighting fixture

Abstract: A recessed lighting trim comprises a reflector, a circular frame connected to the reflector, and a circular translucent plate mounted in the frame. The translucent plate is retained in the plate by tabs of the frame which are bent onto the translucent plate. The frame includes hooks adapted to be received in slots formed in the reflector to enable the frame to be installed and removed by being rotated relative to the reflector. A chain connects the frame to the reflector to prevent the frame from falling after being removed from the reflector.