Showing papers on "Cassegrain antenna published in 2000"

Reflector antenna and method of producing a sub-reflector

Abstract: A reflector antenna is disclosed with a main reflector and a rotatable sub-reflector that significantly reduces vibrations in the sub-reflector. The sub-reflector includes a reflecting surface located in front of the main reflector between the main reflector and a radiation source as well as a cylindrical shaft that extends in a direction parallel to a main axis of the main reflector. The sub-reflector is made of two connected parts, wherein one part includes the reflecting surface, and the other part is made of a non-reflecting material and formfittingly engages with the reflecting surface. The sub-reflector is rotatably supported on the cylindrical shaft and has a rotation speed of between approximately 1500 to 3500 rpm.

Deployable phased array of reflectors and method of operation

Abstract: A deployable phased-array-of-reflectors antenna includes individual reflectors and feed arrays. Each feed array is disposed above a corresponding individual reflector. The individual reflector antennas are preferably disposed adjacent to one another (e.g., on a hexagonal lattice) to form a phased array antenna using the individual reflectors antennas as elements. Phase and amplitude control electronics are coupled to each reflector antenna to provide steering for the signal energy coupled between the reflectors and the feed arrays. Switching electronics are coupled to the feed arrays and selectively activate and deactivate beam forming clusters of feeds in the feed arrays. A method for generating a steerable antenna pattern couples signal energy through a beamforming section to form steered signal energy. Next, the method couples the steered signal energy between a phased array of reflector antennas. The method selectively activates a first feed cluster for a first reflector, a second feed cluster for a second reflector, and so on, until feed clusters are activated in all of the reflectors in the array. The method then couples the steered signal energy between the first and second feed clusters. The method subsequently activates and deactivates the feed clusters to reduce the impact of grating lobes in the total antenna pattern, or when a particular cluster attenuation has been reached.

Multi-beam reflector antenna system with a simple beamforming network

Abstract: An antenna system and method for generating a desired contiguous spot beam pattern, and a signal is disclosed. The contiguous spot beam generating antenna system comprises a reflector system configured in a side-fed Cassegrain (SFOC) configuration, an array of feed horns comprising at least a subset of feed horns for illuminating the reflector system, and a beamforming network, communicatively coupled to the array of feed horns, for controlling an excitation of the subset of the feed horns in the array of feed horns. The method comprises illuminating a side fed offset Cassegrain reflector system with an RF signal emanating from an array of feed horns, and controlling an excitation of the subset of the feed horns. The present invention provides a beamformer network that can produce uniform performance over wide scan angles, is easier to integrate and test, that can change the beam pattern on orbit, and that provides a more complete utilization of space assets without dramatically increasing the cost of manufacturing and operating a satellite. The use of a SFOC configuration or other wide scanning antenna permits the use of a simple beamforming network while maintaining excellent beam beam scanning characteristics.

Multi-band and polarization-diversified antenna system

Abstract: A multiple band, polarization diversified antenna system that accommodates a plurality of independent and separate antenna subsystems that share a common aperture and boresight. The antenna system includes a first low-band antenna subsystem for one polarization mode in a low frequency band, a second low-band antenna subsystem for another polarization mode in the low frequency band and a high-band, dual-polarization, dual-reflector antenna subsystem for two high-frequency antenna subsystems having orthogonal polarization modes. The dual-reflector antenna subsystem includes a main reflector, a sub-reflector and a support cone. The two low-band antenna subsystems and the high-band, dual-polarization feed subsystems are all positioned behind the main reflector of the high-band dual-reflector antenna subsystem. The signals transmitted by the high-band antenna are directed towards the sub-reflector and are reflected therefrom to be directed towards the main reflector. The signals are reflected from the main reflector to be emitted toward free space from the antenna system through the support cone. The low-frequency signals pass through the main reflector, the sub-reflector and the support cone. The main reflector, the sub-reflector and the support cone are suitable frequency selective surfaces so that the main reflector and the sub-reflector are reflective to the high-frequency signals and are transparent to the low-frequency signals, and the support cone is transparent to both the high-frequency and low-frequency signals.

Method and apparatus for eliminating keyhole problem of an azimuth-elevation gimbal antenna

Abstract: The present invention provides two approaches for eliminating a keyhole problem associated with an azimuth-elevation gimbal antenna which is a problem that occurs when the antennae is tracking a satellite vehicle that is substantially directly overhead, i.e., the satellite vehicle is near the zenith position. At such a point, the azimuth motor of the gimbal antenna must turn very rapidly when the satellite passes through such near zenith position. A first approach involves tilting up one of the elevation axis joints when the antenna points at or near its zenith position such that the pointing angle may be altered by a predetermined angle, for example around 0.5° to 1°, from the zenith position. A second approach involves tilting the secondary reflector of the cassegrain antenna such that the pointing direction of the antenna may be altered by a predetermined angle.

An omnidirectional dual‐shaped reflector antenna

Abstract: A dual-shaped reflector antenna with an omnidirectional pattern and vertical polarization is presented. A radial-mode conical feed illuminates a rotationally symmetric dual-shaped reflector system able to drive the main beam in a nearly horizontal direction and able to control both the main lobe direction and its pattern. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 27: 371–374, 2000.

Cylindrical antenna coherent feed system and method

Abstract: Systems and methods are disclosed for illuminating multiple columns of antennas to provide a desired wave front without introducing non-coherent combining. The preferred embodiment feed network provides elevation scanning for a multiple beam antenna system on a per antenna beam basis. In a preferred embodiment columns of antenna elements are divided into phase-centers having a relative phase shift introduced there between. Phase differentials are introduced into the antenna beam signals of each phase-center of antenna elements in order to provide a phase progression which steers the antenna beam a predetermined angle from the broadside. The phase differentials are independently provided for each antenna beam signal to thereby allow independent steering of each antenna beam.

Parabolic reflector antenna

Abstract: This specification discloses a parabolic reflector antenna, which is used as an antenna for signal transmission between the radio communication base station and the mobile terminals By determining the curvatures and relative positions of a main-dish with a main reflecting surface and a sub-dish with a sub-reflecting surface and means of determining the size of the feedback device and relevant distances in between, the present invention improves the signal reception and emission of the parabolic reflector antenna

Intermediate and far fields of a reflector antenna energized by a hydrogen spark-gap switched pulser

Abstract: Previously, the design, fabrication, and testing of a pulser with a parabolic reflector antenna, known as a prototype impulse-radiating antenna (IRA), had been presented in the IEEE Transactions on Plasma Science in 1997. The radiating system has now been more fully characterized with additional measurements and computations of near-field, intermediate, and far fields on bore sight.

Satellite antenna enhancer and method and system for using an existing satellite dish for aiming replacement dish

Abstract: An easily installable enhancement for replacing the reflective surface area for a satellite dish and method for using an installed dish as a reference, allowing the installation of a dish with added features without re-acquiring the satellite signal or reaiming the dish. In one variation, the enhancement includes a reflector addition, which is fitted with fasteners that locate the reflector against the existing dish. This variation includes use of the original feed horn, which is relocated using a feed horn support extension. This variation is also designed to avoid the “shadow” of the feed horn and its support arm, and to minimize the reflective surface area at the lower end of the dish, which reduces collection of such interfering material as snow, rain, and debris. In variations using increased reflector size, the enhancement reduces loss of signal during inclement weather or in other situations in which the satellite signal is partially blocked. In one variation, the added reflector is a standard parabolic reflector, such as a 24-inch dish, superimposedly installed over the original reflector. In a second variation, the added reflector is a custom designed parabolic surface that extends the existing dish surface only at the original reflector's circumferential edge. In a third variation, the added reflector is ring-shaped and similarly attached at the outer edge of the original reflector. Also disclosed is a system for attaching and making additional adjustments for applications using a more complex replacement reflector, such as for receiving signals from multiple satellites.

Array fed multiple beam array reflector antenna systems and method

Abstract: Array fed multiple beam antenna systems and methods for use on an orbiting spacecraft carrying a communication system. The antenna systems include a reflector and a relatively small array feed compared to the reflector. The array feed has feeds (radiators) that illuminate the reflector and that are disposed in a focal plane of the reflector. A power division network excites the radiators of the feeds. The antenna system is capable of very wide scan angle operation and may be used to provide multiple spot beam coverage over the surface of the Earth viewed from a synchronous orbit spacecraft. Phase aberration normally associated with scanning is corrected by adjusting excitation coefficients of each array feed. The spot beams are scanned across a field of regard by controlling the position of each feed in the focal plane and using the appropriate amplitude and phase distribution associated with a particular spot beam (array feed). The amplitude and phase distributions may be fixed or varied during operation. A dual band system includes a second array feed and a frequency selective surface disposed between the array feeds that optimizes the respective array feeds. Use of the frequency selective surface in dual band implementations produces a very efficient communication system.

Antenna alignment configuration

Abstract: An antenna that has an alignment configuration for aligning the antenna with a satellite. In one embodiment, the antenna includes an antenna reflector that has a centerline and a front surface and a rear surface. A reference plane is defined on the rear surface that is perpendicular to the centerline of the reflector. The reference plane is used in connection with alignment devices for orienting the antenna reflector in desired azimuth, elevation, and skew orientations.

Deployment of an ellectronically scanned reflector

Abstract: A deployable reflector for an electronically scanned reflector antenna is provided. The deployable reflector may be confined to a relatively small volume for transportation of the reflector to a deployment site. Upon deployment, the reflector of the present invention forms a relatively large reflector surface, having a precisely controlled surface geometry. The reflector generally includes a plurality of panel members interconnected to a plurality of ribs interconnected to an extendable boom. The antenna reflector of the present invention is particularly well suited for a space-based antenna, where a reflector that can be collapsed into a small volume for transport and deployed to form a large reflector surface having high gain is desirable.

A Novel Inverted Trapezoidal Antenna Fed by a Ground Image Plane and Backed by a Reflector

Abstract: This paper presents a new ultrawide band inverted trapezoidal antenna. The antenna is fed by a 50 ? coaxial cable through an image ground plane and backed by a reflector for the radiation and detection of ultra-short electrical pulses. A 50 ? input impedance was achieved over a wide bandwidth by the use of a 3D microstrip line feeding concept. The input bandwidth of the antenna was calculated from simulation and verified by experiment to be more than 4 GHz. The metallic reflector is introduced to eliminate radiation back lobes. Maximum pulse radiation occurs at an elevation angle of 40° and 60° for broadside and edge radiation, respectively.

Beam waveguide antenna with independently steerable antenna beams and method of compensating for planetary aberration in antenna beam tracking of spacecraft

Abstract: An antenna assembly for forming and directing a transmit beam, and for controlling receive and transmit beam tracking of a spacecraft in the presence of planetary aberration. The assembly includes a main reflector, a sub-reflector centered along an optical axis of the main reflector, and a moveable transmit feed for directing electromagnetic radiation along a longitudinal axis thereof. The assembly also includes an intermediate beam waveguide assembly arranged between the moveable transmit feed and the main reflector, wherein the intermediate beam waveguide assembly includes fixed and moveable optical components for guiding electromagnetic beam energy between the moveable transmit feed and the main reflector. A beam steering mechanism is coupled with the moveable transmit feed for angularly displacing the transmit beam from the optical axis by displacing the moveable transmit feed in a direction substantially orthogonal to the longitudinal axis of the transmit feed.

A measurement of the coupling between close-packed shielded cassegrain antennas

Abstract: Design and performance details are given for a 0.9-m diameter shielded cassegrain antenna, which will be used in a 13-element close-packed array, The array is designed to make images of brightness fluctuations in the cosmic microwave background radiation. Coupling between a pair of the shielded cassegrain antennas with a separation of 1 m is in the range -110 to -130 dB over the 26- to 36-GHz band.

Multi-feed multi-band antenna

Abstract: A multi-feed, multi-band antenna includes a parabolic dish reflector, a plurality of four-port feeds, and may also include one or more orthomode two-port feeds. Each four-port feed is constructed to conduct multiple frequency bands and multiple polarized RF signals within each of the bands. A mounting structure mounts each of the feeds at a different position in a line and in a plane parallel to the rim of the reflector. The four-port feeds are of a size which allows them to be mounted adjacent each other and two degrees apart. The mounting structure positions the feeds at a distance F from the reflector. The diameter D of the reflector and the distance F have a relationship such that F/D is less than approximately 0.5.

The Large Adaptive reflector : A 200-m diameter, wideband, cm-m wave radio telescope

Abstract: The Large Adaptive Reflector (LAR) is a concept for a low-cost, large aperture, wideband, radio telescope, designed to operate over the wavelength range from 2 m to 1.4 cm. It consists of a 200-m diameter actuated-surface parabolic reflector with a focal length of 500 m, mounted flat on the ground. The feed is held in place by a tension-structure, consisting of three or more tethers tensioned by the lift of a large, helium-filled aerostat-a stiff structure that effectively resists wind forces. The telescope is steered by simultaneously changing the lengths of the tethers with winches (thus the position of the feed) and by modifying the shape of the reflector. At all times the reflector configuration is that of an offset parabolic antenna, with the capability to point anywhere in the sky above -15° Elevation Angle. At mid-range wavelengths, the feed is a multi-beam prime-focus phased array, about 5 m diameter; at meter wavelengths, it is a single-beam phased array of up to 10 m diameter. Simulations have shown that in operating wind conditions (10 m / s average speed with 2.5 m / s gusts), the position of the feed platform can be stabilized to within a few cm over time scales of -20 s. Research indicates that the telescope concept is feasible and that an order of magnitude improvement in cost per m 2 of collecting area over traditional designs of large parabolic antennas can be achieved.

The large adaptive reflector: a 200-m diameter wideband centimeter- to meter-wave radio telescope

Abstract: The Large Adaptive Reflector (LAR) is a concept for a low- cost, large aperture, wideband, radio telescope, designed to operate over the wavelength range from 2 m to 1.4 cm. It consists of a 200-m diameter actuated-surface parabolic reflector with a focal length of 500 m, mounted flat on the ground. The feed is held in place by a tension-structure, consisting of three or more tethers tensioned by the lift of a large, helium-filled aerostat -- a stiff structure that effectively resists wind forces. The telescope is steered by simultaneously changing the lengths of the tethers with winches (thus the position of the feed) and by modifying the shape of the reflector. At all times the reflector configuration is that of an offset parabolic antenna, with the capability to point anywhere in the sky above approximately 15 degree Elevation Angle. At mid-range wavelengths, the feed is a multi-beam prime-focus phased array, about 5 m diameter; at meter wavelengths, it is a single-beam phased array of up to 10 m diameter. Simulations have shown that in operating wind conditions (10 m/s average speed with 2.5 m/s gusts), the position of the feed platform can be stabilized to within a few cm over time scales of approximately 20 s. Research indicates that the telescope concept is feasible and that an order of magnitude improvement in cost per m2 of collecting area over traditional designs of large parabolic antennas can be achieved.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Two-lens and lens-fed reflector antenna systems for MM-wave wireless communications

Abstract: In this paper, the characterization and design of 30 GHz two-lens and lens-fed reflector antenna systems is presented. In this approach, a hyperhemispherical substrate lens feeds either a larger but thin hyperbolic lens or a parabolic reflector. The attractive feature of these two-antenna systems is that it leads to a 75% reduction of the lens material, while maintaining about the same length and on-axis characteristics as the single lens antenna. In these two-antenna systems, limited scan capability is possible which can lead to relaxed alignment requirements between a receiver and a transmitter for line-of-sight broadband wireless links.

Reflector effects on the performance of a retrodirective antenna array

Abstract: This paper presents modeling strategies to determine the operating characteristics of a heterodyne phase-conjugate retrodirective Van Atta (1959) array in the presence of a plane reflector. The models used are based on physical and geometrical optics principles. Predictions of the operating characteristics of the array due to the close proximity of a plane metallic reflector are compared with experimental measurements. It is shown that provided the reflector is positioned at a distance greater than 1.25 times the separation distance between the transmitter and the retrodirective array its effect on the performance of the retrodirective array appears to be negligible.

Broadband antenna has spiral coil set above reflector surface to provide a low profile antenna

Abstract: The broadband antenna has a spiral arm (2) that is parallel to a reflector (3) that has a dielectric layer (3b) and a metallic surface (3c). The separating distance (d) is set to suit the frequency range. The metal surface is organized as an array of elements.

Using offset parabolic reflector antennas for free space material measurement

Abstract: This paper reports on using a dual reflector antenna to improve the bandwidth of a free space material measurement system that was based on dielectric lens horn antennas. Low-cost offset parabolic dishes, intended for the domestic satellite TV market, are used to generate the required focused beam. Results show that, for a system that costs less, the operating frequency band of the lens system may be doubled.

Limited field of view antenna for space borne applications

Abstract: A hybrid parabolic reflector phased array antenna system which is stowable in a space vehicle and is deployable in space. The antenna includes a large torus which acts as a support structure for a plurality of small reflector cells called super elements, each including its own reflector and an array of feed elements. The torus supports a stretched reflector mesh and matching back-up catanary wires that provide a mechanism for pulling the reflector surface of the cells down to an exact paraboloid. A set of rigid corner posts for stretching the mesh fabric for forming multiple reflectors is also provided. The torus is also used to support individual super element feed arrays for each reflector. The super elements incrementally scan the beam by group selection of feed elements in each feed array with time delay phase control being used to steer the array factor so as to achieve fine steering. Each of the super elements scans incrementally with a selected group of feed elements varying between three and twelve, which are varied in position relative to the focal axis of the feed array. The groups of feed elements of the feed arrays are also controlled so as to mitigate any undesired grating lobe problem.

Analysis, design and measurements on an active focal array fed reflector

Abstract: ALCATEL develops reflector antennas with multifeed arrays for civil and military communications satellites. In this paper, an X band, high gain spot beam antenna with accurate beam steering and shaping, and low sidelobe levels is presented. The selected antenna is comprised of an offset parabolic reflector with overlapping feed cluster. Pattern synthesis is performed with an active beamforming network (BFN). Design rules are gained from a detailed analysis of the antenna architecture. A demonstrator is designed and measured. Low sidelobes (-25 dB), accurate steering (0.05/spl deg/), and good agreement between theoretical and experimental spots are demonstrated. Attention is paid to optimizing the design of constitutive elements (lightweight planar focal array, shaped reflector).

Gregorian antenna system

Abstract: An antenna system comprising a feed array, a subreflector and a main reflector which are oriented to define a offset gregorian antenna geometry. The feed array is comprised of a plurality of separate feeds which are aligned on a predetermined contour. Each feed array is coupled to a feed network which acts to combine the illumination beams of clusters of a preselected number of feeds to produce a plurality of composite illumination beams. Each composite illumination beam is directed to be incident upon a separate predetermined location on the subreflector which directs the composite illumination beams and directed towards the main reflector. Each composite illumination beam is reflected by the main reflector in a preselected direction so that each composite illumination beam forms an antenna beam that impinges a predetermined coverage area on the Earth. Each antenna beam defines a separate coverage cell in the coverage area, wherein the position and orientation of the feeds, the subreflector and the main reflector provides antenna beams over a full Earth field of view coverage area where each antenna beam is approximately symmetrically shaped.

Focuser-based hybrid antennas for one-dimensional beam steering

Abstract: In this paper, an approach to the synthesis of FHA for limited field of view in one plane is developed. From the considered examples, it can be seen that in the case of limited field of view, the FHA allows us to appreciably reduce the feed array size and the controlled element number as compared with the HA with parabolic cylindrical reflector. The considered approach to FHA synthesis can be generalized in several directions: (a) offset system with no blockage, (b) dual-reflector system with ordinary (commercial) main parabolic reflector and a small focuser-subreflector, (c) HA with a divergent reflector for extended field of view, etc.

Experimental results on multi-beam receiving antenna for satellite broadcasting

Abstract: Satellite broadcasting services are currently provided in Japan using four orbital positions, one operates in the BSS band (11.7 to 12.2 GHz) and the other operates in the FSS band (12.2 to 12.75 GHz). A number of satellites located in different orbital positions will be provided in the future. A commonly used dish antenna can receive signals from only one satellite at a time. A multihorn-feed reflector antenna can receive signals simultaneously from several satellites in different orbital positions, but the number of satellites may be limited by the arrangement of the feed horns. A multi-beam phased-array antenna can receive signals simultaneously from a great number of satellites in different orbital positions. This paper describes the fundamental design of a multi-beam receiving antenna and measured results of an experimental model.

Scanning continuous antenna reflector device

Abstract: A method and a device are disclosed for the generation of a surface, the reflection phase gradient of which will be varied by means of a controllable static electric field. The present solution takes into account, instead of mainly the transmissive properties, also the reflection properties of an arrangement comprising a ferroelectric material. Such a reflecting surface may contribute to an entire antenna aperture, a portion of an antenna aperture or an element in a conventional array aperture. In a general case N lobes and M nulls are to be controlled at the same time. In such a case the surface will preferably be designed as a curved surface, for instance a rotation symmetric parabola, while in other cases the reflector element may be designed just as a plane mirror. An antenna comprising such a reflector element of ferroelectric material can also form a polarization twisting Cassegrain antenna with a flat or curved main reflector element. The reflector element in a typical embodiment consists of a plate ( 50 ) of a material presenting ferroelectric properties and provided on each side with electromagnetically transparent highly resistive films ( 24, 34 ) each fed by means of a pair of parallel highly conducive edge wires ( 22, 23 and 32, 33 ). By applying a controllable voltage across each pair wires the lobe of the continuous aperture scanning reflector antenna can be controlled in a plane X-Z by a voltage U x and in a plane Y-Z by a voltage U y .