Showing papers on "Cassegrain antenna published in 1999"

Multiple frequency reflector antenna with multiple feeds

Abstract: A reflector antenna system with multiple feeds each operating in a separate frequency band. The antenna system includes a main parabolic reflector and an ellipsoidal subreflector configured in a Gregorian arrangement. Mutual blockage between the multiple feeds is reduced by their orientation and arrangement. The system includes a transversely positioned feed and an axial feed located in the focal region of the main reflector. The transverse feed may be integral with the subreflector. The system also includes a third feed placed at the virtual focal point of the subreflector.

Multibeam satellite communication antenna

Abstract: A low-cost spherical reflector and a mechanically scanned antenna system utilizing such reflectors. The system employs one or more (substantially similar) primary spherical reflectors (each a truncated spherical surface), each having an associated moveable feed driven by a two-axis positioner mechanism that has few moving parts. The feed structure may preferably comprise a point source waveguide feed in combination with a shaped concave secondary reflector used in a Gregorian-like configuration to correct for spherical phase error. The positioner mechanism moves Gregorian-like congiguration to correct for spherical phase error. The positioner mechanism move the waveguide feed and secondary reflector in tandem to shift the position of the far field beam direction in the sky. After phase correction by the secondary reflector, the resultant signal reflected from the primary aperture can simultaneously transmit and receive at two or more independent frequencies. With an assembly of multiple such spherical reflectors, each having a moveable feed driven by its own positioner mechanism, a compact arrangement is achieved. The assembly is mounted on a circular baseplate and preferably is covered by a radome.

A compact offset gregorian antenna system for providing adjacent, high gain antenna beams

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.

Unfurlable sparse array reflector system

Abstract: An unfurlable reflector antenna system having one or more unfurlable arms that are each shaped in the form of a parabolic right cylinder when it is unfurled. Each arm comprises an RF reflecting membrane or a thin shell as the reflector structure. Each arm is coupled by way of a line feed to a receiver. The system is specifically designed for use on a spacecraft. Each arm may be stowed by flattening the parabolic membrane or shell, and then rolling up the arm, which is accomplished without stretching. The sparse reflector antenna array system is thus stowable in a compact configuration, yet easily unfurls to provide a very large diameter lightweight reflector.

Apparatus and method for reconfiguring antenna contoured beams by switching between shaped-surface subreflectors

Abstract: A configurable antenna (100) includes a main reflector (102) and at least two subreflectors (104). Each of the subreflectors (104) is configurably disposed relative to the main reflector (102) to provide an active subreflector (106) for reflecting radiation between the main reflector and a point off of the main reflector in a desired beam pattern. Each subreflector typically has a different shape and may be moved into the active subreflector position to produce a desired beam pattern during operation of the antenna. The antenna (100) further includes a horn (110) disposed at a point off of the main reflector for feeding signals to the reflectors and for receiving signals from the reflectors. The configurable antenna is typically mounted on a satellite system which itself, or in response to instructions or commands from a ground station, reconfigures the antenna to provide the desired beam shape.

A compact front-fed dual reflector antenna system for providing adjacent, high gain antenna beams

Abstract: An antenna system comprising a feed array, a subreflector and a main reflector which are oriented to define a front-fed dual reflector antenna geometry. The feed array is comprised of a plurality of separate feeds which are aligned in 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 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.

Resistive taper for dense packed feeds for cellular spot beam satellite coverage

Abstract: Providing a tapered surface reflectivity to the reflecting surface of the parabolic reflector in a parabolic antenna using resistive material reduces side lobes and produces steeper roll off in the principal lobe, permitting use in the antenna of a smaller diameter microwave feed than required by an antenna without that tapered surface resistivity and, effectively, emulates the latter antenna. As a consequence of the smaller feed diameter, multiple feeds may be positioned contiguously to form multi-beam antennas that produce contiguous beam patterns. A satellite cellular communications multi-beam antenna incorporating the invention achieves greater regional coverage of the Earth.

Switched parasitic feeds for parabolic antenna angle diversity

Abstract: The radiation direction from a parabolic dish antenna can be electronically controlled through the use of a switched parasitic element closely coupled to a dipole feed. Through the application of a dc voltage, the half-wavelength-long parasitic element is switched between open and short circuit using a p-i-n diode at its center. With a parasitic element vertically offset from the horizontal dipole, the performance of the antenna in both switch positions has been optimized. At 1.5 GHz, using a 2.4 m diameter reflector, beam skewing on the order of 1.5° at the −6 dB point can be achieved for a feed element spacing of 0.6 wavelengths. At a parasitic element spacing of 0.5 wavelengths, the main lobe is better than 15 dB above the unshifted null. The analysis of such a structure requires the calculation of the current in both the driven element and the parasitic element and the summation of their fields on the surface of the reflector independently. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 200–203, 1999.

One dimensional interleaved multi-beam antenna

Abstract: An efficient multi-beam antenna system (10) for use with a high capacity communications satellite or spacecraft (11) that maximizes frequency re-use of the allocated frequency spectrum. The antenna system (10) has first and second offset reflectors (13e, 13w) disposed adjacent first and second sides of the spacecraft. A first plurality of the feed horns (14e) feed the first reflector (13e), and a second plurality of the feed horns (14w) feed the second reflector (13w). The feed horns and offset reflectors cooperate to produce a predetermined number of beams. Even numbered beams use a set of frequencies and polarizations that are orthogonal to a set of frequencies and polarizations used by odd numbered beams. The antenna beams (15) are contiguous in one dimension.

The characterization of a 34-meter beam-waveguide antenna at Ka band (32.0 GHz) and X band (8.4 GHz)

Abstract: New antennas for the NASA Deep Space Network (DSN) have been built to replace the aging antennas of older designs for deep-space communications. These new antennas incorporate a new dual-shape design as well as a beam waveguide (BWG), which utilize a series of additional secondary mirrors to relocate the focal point into a stationary room below the main reflector. The advantages of using such a design include increased isolation of the feed package from outside environmental factors, such as moisture, wind, and temperature changes; and ease of access to the equipment for maintenance, troubleshooting and repair purposes. This article reports on the performance of a beam waveguide antenna at X-band and Ka-band microwave frequencies. The Ka-band antenna performance experiment (KaAP) antenna-efficiency measurements presented in this article were acquired at the Goldstone DSS-13 research and development (R&D) beam-waveguide antenna between December, 1993, and November, 1995. The measured antenna efficiency and ground-station figure-of-merit (gain divided by operating system noise temperature) as a function of elevation angle and their uncertainties are presented. Also described are the station configuration, the measurement technique, the modeling used in the analysis processing, and the historical evolution of the DSS-13 Ka-band antenna-efficiency measurements as progressive improvements and configuration changes were implemented.

A C/X/Ku-band dual polarized Cassegrain antenna system

Abstract: There is an increasing demand for multiple frequency band capability in satellite Earth station antenna systems. This paper describes an 18.3 m shaped Cassegrain antenna with a single aperture, tri-band, six-port receive-only, feed system. The frequencies of operation are 3.4-4.2 GHz, 7.25-7.75 GHz, and 10.9-12.75 GHz. The C- and X-band feed ports offer dual circular polarization, and the Ku-band ports offer dual linear polarization with an internal polarization vector angle adjustment mechanism. Frequency and polarization multiplexing is performed by a novel OMJ structure.

Antenna reflector having a configured surface with separated focuses for covering identical surface areas and method for ascertaining the configured surface

Abstract: A reflector for reflecting electromagnetic waves has a configured surface for these waves whereby localized deformations or configurations such as bumps (B) and dents (D) of the reflector ( 1 ) are so constructed that the reflector cooperates with several focuses ( 10 A, 10 B; 110 A, 110 B) which are spatially separated from the reflector proper. These focuses are so arranged that the electromagnetic beams emanating from the respective radiators ( 4 A, 4 B; 40 A, 40 B) and are directed onto the reflector can be directed through the reflector onto a common region ( 3 A, 3 B) to be illuminated, whereby particularly the beams may be tuned to different frequencies or for operation in different frequency bands. Such reflectors are particularly useful in antenna systems for communications such as satellite communications.

Antenna system with plural reflectors

Abstract: An antenna system having a front reflector and a rear reflector arranged in tandem, a front feed for illuminating the front reflector, and a rear feed for illuminating the rear reflector. Each of the reflectors has a generally dish-shaped configuration, and the feeds are located in positions offset from axes of the respective reflectors. The front reflector is reflective to a first radiation, while being substantially transparent to a second radiation except for a fraction of the power of the second radiation. The fractional part of the second radiation is reflected from the first reflector as an interfering beam, the interfering beam being scanned away from a coverage region of a beam of the first radiation by an offset between the feeds. The radiations may differ in polarization or in frequency. There may be a complete shading of the rear reflector by the front reflector from the radiation of the rear feed to produce uniform illumination of the rear reflector for greater accuracy in a formation of a beam from the rear reflector. Six degrees of freedom in positioning and orientation of the reflectors and their feeds provides maximum design flexibility for obtaining a compact antenna.

Multi-pattern antenna having frequency selective or polarization sensitive zones

Abstract: A multi-pattern antenna for providing a plurality of antenna patterns at different frequencies or polarizations from a single reflector body eliminates the need for multiple reflector antennas on a single spacecraft. The reflector antenna comprises a reflector body and an illumination source. The illumination source illuminates the reflector with a plurality of RF signals each of a preselected frequency or polarization. The reflector comprises a plurality of zones with each zone reflecting preselected RF signals. A plurality of antenna patterns are generated from the reflected RF signals. Each zone is sized to a preselected shape such that the antenna patterns have a desired shape or beamwidth characteristic.

Sectoral antenna with changeable sector beamwidth capability

Abstract: A modular antenna has a primary radiating aperture which can either be an array of radiating elements or a passive reflector. In regards to the array of radiating elements, a feed network interfaces with the radiating elements to form the modular antenna array. The feed network has a number of output ports wherein each output port of the feed network is adapted to interface with each feed port of the radiating elements. The feed network can be placed at various locations along the antenna array to change to radiation characteristics of the antenna array. When passive reflector is used, a modular feed interfaces with the waveguide. The feed module controls the sector radiation pattern. The vertical reflector surface controls the elevation radiation pattern. The feed module can consist either of an antenna array or a single element utilizing beam shaping.

Elastically deformable antenna reflector for a spacecraft, and spacecraft including such a reflector

Abstract: An antenna reflector for a spacecraft includes a radial slot which facilitates stowage of the reflector in the spacecraft. When the reflector is in a folded position, opposing edges of the radial slot overlap in such a way that the reflector assumes an at least approximately conical shape, thereby allowing the reflector to be housed in a casing so as to be oriented vertically in line with the spacecraft.

Satellite terminal antenna installation

Abstract: A method for configuring a satellite antenna (20) to receive a downlink signal from a geosychronous orbiting satellite (12) in a satellite communication system (10), comprising the steps of: (a) providing a satellite antenna (20) with a feed positioner mechanism (40) for adjusting the position of a feed device (42), such that the feed device (42) is selectively movably between a focus position (46) and a defocus position (44); (b) defocusing a beam of the satellite antenna (20) by using the feed positioner mechanism (40) to adjust the feed device (42) in relation to a dish component of the satellite antenna (20); (c) pointing the satellite antenna (20) towards the satellite (12), such that the downlink signal from the satellite (12) is received by the satellite antenna (20); (d) optimizing the beam of the satellite antenna (20) in relation to a near center of the downlink signal from the satellite (12); and (e) focusing the beam of the satellite antenna (20) using the feed positioner mechanism (40), thereby configuring the satellite antenna (20) to receive the downlink signal from the satellite (12).

A compact folded optics antenna system for providing adjacent, high gain antenna beams

Abstract: An antenna system comprising a feed array, a subreflector and a main reflector which are oriented to define a folded optics antenna geometry The feed array is comprised of a plurality of separate feeds which are aligned on a predetermined contour Each feed is coupled to a feed network which acts to combine the illumination beams 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 illumination beams 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 adjacent, antenna beams over a full Earth field of view coverage area where each antenna beam is approximately symmetrically shaped

Dual gridded reflector antenna

Abstract: An improved dual gridded reflector antenna configuration which allows cross-polarization radiation to be scanned in any given direction. The dual-gridded reflector assembly includes a front parabolic reflector illuminated by a first source, and a second parabolic reflector illuminated by a second source. The second reflector is positioned adjacent to and behind the front reflector such that the center points of the reflectors align to define a center axis. Additionally, the first and second sources are positioned at different offsets with respect to the reflectors and have a respective rotated offset angle with respect to the center axis such that the sources define an antenna feed separation. By modifying the offsets and the rotated offset angles, the feed separation can be designed to have an inclination with respect to the north-south or east-west feed separation direction.

Antenna for reception of satellite broadcast

Abstract: An antenna for receiving a satellite broadcast can adjust orientation at higher precision than a method based on a compass and a level, without being influenced by environmental magnetic field generated by magnetic body or electromagnetic sources, can perform adjustment of orientation even before a radio wave from the satellite is not catched, can monitor the deviation during the fixation of the antenna orientation to improve the workability in adjustment of antenna orientation. The antenna for receiving a satellite broadcast has a reflector for reflecting a radio wave from a satellite on a reflecting surface for convergence and a receiving portion for receiving the radio wave reflected by the reflector. The antenna further includes a light blocking portion forming a shadow by the sun light, a scale determining a direction of the sun by the shadow formed by the light blocking portion. The light blocking portion and the scale are provided at an upper end portion of the reflector.

Reflective antenna system with increased focal length

Abstract: A multiple beam antenna system including an offset parabolic reflector has an increased focal length (FL) and/or an increased FL/D (where D is a diameter of the reflector) in order to improve off-axis performance of the system. In certain embodiments, the system can simultaneously receive different signals from different satellites that are orbitally spaced.

A shaped reflector antenna for mobile communications

Abstract: The characteristics of a shaped reflector antenna with omnidirectional radiation pattern are presented with a view towards its possible application in radio base stations for cellular communications at microwave frequencies and above. It comprises a single circularly symmetrical shaped reflector surface fed by an axial horn and synthesized for a cosecant squared secondary antenna pattern in the vertical plane while complying with omnidirectional specifications in the azimuthal plane. Numerical results for a physical optics (PO) reflector surface synthesis considering a rigorous feed model highlight the main features of the proposed design.

An antenna device

Abstract: An antenna arrangement includes an antenna reflector (10), a transceiver element (11) and a signal detection unit (12) having a signal converter (121-122) and a computing unit (123) for generating in response to incoming signals control signals for controlling the alignment of the antenna reflector (10) with a target object. The signal converter (121-122) is adapted to reduce its bandwidth automatically and incrementally from a requisite maximum frequency range to a narrow band frequency range. Changes in the direction of the antenna reflector are detected through the medium of a movement detection unit (13) that includes 3d-sensors (131, 132, 133). Mechanical control of the alignment direction of the antenna reflector (10) is effected with the aid of a drive unit (15).

Dual-frequency window for a reflector and reflector antenna equipped with said window

Abstract: The bi spectral window is made of dielectric material with a low loss factor and high dielectric constant. The window has rotation symmetrical, aspherical front and rear surfaces. The front surface is arranged on the side of the reflector on which the millimeter wave radiation is incident, and is optimally matched to the reflector surface. The rear surface is designed for optimal millimeter wave reflectivity. An Independent claim is also included for a reflector antenna.

Electronically scanned cassegrain antenna with full aperture subreflector/radome

Abstract: A Cassegrain antenna system (50) includes a flat dielectric plate radome (52) having a thickness of one-half wavelength at a frequency of operation. The plate has an electrically conductive grid (54) disposed on an inside surface thereof to permit perpendicularly polarized energy rays to pass therethrough. A parabolic twist reflector (70) is spaced from the radome, and includes a dielectric substrate (74) having a thickness equivalent to one-quarter wavelength at a frequency of operation and having formed on an interior surface thereof an array (72) of conductive strips oriented by 45 degrees relative to the incident ray polarization. An RF housing (60) including a plurality of RF feed elements (62A-62I) is located at the focal region and the elements spaced by a single beamwidth.

Low Profile Dielectric Resonator Antenna Arrays for Reflector Feeds

Abstract: Arrays of dielectric resonator antennas (DRAs) are investigated as replacements for conventional corrugated feed antennas in a reflector system. These arrays are low profile, offer relatively wide bandwidth (15%), and are amenable to device integration. Prototype passive arrays of four and eight elements have been designed and tested at X-band. Arrays at Ka-Band are currently being designed.

Design and Practice of Reflector Antennas and Feed Systems in the 1990s

Abstract: This chapter contains sections titled: Introduction Reflector Design Feed System Design Reflector Systems Conclusion Acknowledgment References ]]>

A comparison between coverage performances of usual antenna arrays for radio base stations and a proposed shaped reflector design

Abstract: The radiation properties of antenna arrays usually employed in radio base stations for mobile communications, as well as the main features of a recently proposed shaped reflector design for that application, are reviewed. Numerical results highlight the comparison of corresponding main coverage performances.

Properties of a large scale multibeam antenna using a phased array fed reflector with radially aligned elements

Abstract: Communication satellites achieve global communication coverage by using high-gain multibeam satellite antennas. These antennas fall into two types: direct radiating phased arrays for low Earth orbit (LEO) satellites and large reflector antennas fed by cluster feeds for geostationary orbit (GEO) satellites. This paper provides an analytical study of the phased array fed single reflector antenna that can cover wide regions like Asia by 127 beams based on our design techniques. To confirm the feasibility of the designed phased array fed reflector antenna a partial model of the array feed was manufactured and its electrical properties tested. Evaluation of the measured properties proves the feasibility of the phased array fed single reflector antenna as a large scale multibeam antenna.