Showing papers on "Cassegrain antenna published in 1985"

Adjustable antenna mount for parabolic antennas

Abstract: An antenna mount for aiming a parabolic antenna towards a geosynchronous satellite characterized by four, pivotal sub-assemblies, each of which is rotatable around its own axis. The mount can be quickly adjusted to point the antenna at a particular geosynchronous satellite, or may be caused to sweep across the satellite belt in a scanning manner. The antenna mount can be attached to a support post of virtually any orientation ranging from vertical to horizontal.

Factorization of the feed efficiency of paraboloids and Cassegrain antennas

Abstract: The first approximation to the aperture efficiency of a paraboloidal reflector antenna is called the feed efficiency. The factorization of the feed efficiency into subefficiencies which account for losses due to spillover, cross polarization, nonuniform aperture illumination, and phase errors is considered. The relations between the radiation patterns of circularly and linearly polarized feeds are also derived.

Phase retrieval in the radio holography of reflector antennas and radio telescopes

Abstract: Methods of phase retrieval from simulated intensity information have been tested for use in the radio holography of reflector antennas In numerical simulations the Misell algorithm has been used successfully to retrieve the aperture phase distribution from two numerically simulated power polar diagrams, one in focus and the second defocused The technique uses no auxilliary reference antenna However, it does need a high signal to noise ratio, typically 50 dB if a 60 \times 60 array is to be measured to a precision such that the gain is within 1 percent of ideal It should be most useful where no direct phase measurements are possible and ground-based or satellite transmitters can be used as sources The use of astronomical maser sources (22 GHz) can give information on large scale deformations

Dual reflector folding antenna

Abstract: A folding antenna for use in a satellite communication system comprises a box having a base (1) which forms the supporting structure for the antenna. A main reflector (16) is mounted on a platform (11) to which it is pivotted about a first axis (14). A sub-reflector (26) is pivotted to the main reflector about a second axis (21). By pivotting the sub-reflector and the main reflector downwardly they can be stowed into a position close to the base (1) and the lids (8) of the box closed to protect the system during transportation.

Dual offset reflector multibeam antenna for international communications satellite applications

Abstract: Dual offset reflector antenna systems offer exciting possibilities for achieving both low scan losses and low cross polarization in geosynchronous communications satellite antennas providing narrow ( 100 \leq D/\lambda \leq 400 ) and multiple beam frequency reuse coverages over an 18\deg conical field of view. Novel geometrical configurations for the reflectors are characterized by simultaneously achieving: 1) blockage free apertures for all element beams within the 18\deg conical field of view, 2) compatibility with large planar feed arrays, 3) additional degrees of design freedom by orientation and shaping of reflector surfaces for depolarization and scan loss optimization, and 4) large effective f/D ratio achieved in compact and foldable geometries. A comparison of new front-fed offset Cassegrain (FFOC) and side-fed offset Cassegrain (SFOC) systems is made.

A small dipole-fed resonant reflector antenna with high efficiency, low cross polarization, and low sidelobes

Abstract: The computer-aided optimization of a small five-wavelength diameter reflector antenna with a center-supported dipole-disk feed is described. The primary radiation is controlled by using a patented beamforming ring to give low cross polarization and low sidelobes due to spillover. The efficiency is maximized by controlling and taking advantage of the multiple reflections between the feed and the reflector. This has inspired the name "resonant reflector antenna." The gain from the feed reflector resonances is so large that it compensates almost completely for the about 1 dB loss due to center blockage of the aperture.

Surface accuracy of Cassegrain antennas

Abstract: For a Cassegrain antenna system, a simple and general procedure is presented for computing the effective surface root mean square (rms) and beam deviations considering primary surface distortions and relative translations and rotations of the antenna components It is shown that certain primary reflector distortions can be compensated for by an appropriate adjustment of the subreflector position Different methods in use for calculating surface rms are reviewed It is shown that the method in which the deformed configuration of the primary reflector is best fitted with another paraboloid yields a surface rms almost equal to that obtained by the optimal positioning of the antenna components The actual deformation patterns of several large Cassegrain antenna systems with different structural concepts are reviewed It is shown that for a class of antenna structures, the gain can be significantly improved by an optimal positioning of the subreflector

Electronic Tracking Systems for Satellite Ground Stations

Abstract: A new tracking technique for reflector antenna configurations is described. Using simple waveguide components in the primary feed chain, mode conversion is employed to induce a beam squint in the secondary pattern of the antenna. The principle of operation is described and various salient features identified. A prototype antenna system incorporating electronic beam steering has been field evaluated successfully under operational conditions and results are described. The technique can be used with conventional receivers and a variety of system configurations.

A simple derivation of the basic design equation for offset dual reflector antennas with rotational symmetry and zero cross polarization

Abstract: A simple geometric derivation is given of the equation for designing an offset dual reflector antenna with perfect rotational symmetry and zero cross polarization.

Horn reflector antenna with absorber lined conical feed

Abstract: A conical horn microwave antenna has a reflector positioned at the large end of a conical feed horn which has the side walls of the horn wider than the projected effective area of the reflector such that microwave absorber material lining the feed horn does not obstruct wave propagation between the feed horn and the effective reflector area.

Antenna dish reflector with integral azimuth track

Abstract: An antenna for receiving satellite broadcast television reception only (TVRO) programming, includes a main reflector dish, a pivot tube for pivotally mounting the reflector dish from a support, and an integrally formed azimuth track and drive comprising an arcuate track bolted to the back of the reflector dish with a trolley drive which engages the pivotal mount to drive the reflector dish along the azimuth to move the dish from satellite to satellite. The integral track and drive rides freely in the vertical direction on the pivotal mount to permit adjustment of the declination and elevation of the main reflector dish without disassembly or removal of the azimuth track and drive.

Reflector antenna for operation in more than one frequency band

Abstract: A reflector antenna is constructed for operation in at least two frequency ranges. For this purpose the concave surface of the antenna reflector body, which preferably has a paraboloid configuration, is provided with surface zones arranged in regular arrays or patterns. These surface zones provide antenna or reflector elements which are reflecting or transparent with regard to a particular frequency range or band width, while other surface zones of the antenna reflector surface are transparent or reflecting in another given frequency range or band widths. Thus, depending on the configurations and dimensions of these different surface zones one and the same antenna is capable of handling frequencies in a plurality of different band widths and different apertures.

Crossed polarization same-zone two-frequency antenna for telecommunications satellites

Abstract: The antenna comprises a parabolic reflector (1) and a primary source (2). The reflector (1) comprises a first grating of conductor wires (7) and a second grating of conductor wires (8) which are orthogonal to the wires of the first grating, and with both gratings constituting elliptical reflective surfaces. The sizes of the major and minor axes of the ellipses are determined in such a manner that both operating frequencies of the antenna have identical coverge zones on the surface of the globe.

Mirror antenna dual-band lightweight mirror design

Abstract: The mirror antenna, sometimes called an inverse Cassegrain antenna, is used in modern radar systems where efficient wide angle scan is required in combination with light weight and small size. Although previous applications have been single band, an additional advantage of the mirror antenna is that it is practical to implement dual-band configurations which can greatly enhance the capability of radar or other radiating systems. The most difficult part of a dual-band mirror antenna design is the 90\deg polarization rotating mirror (half-wave plate). The challenge is to achieve effective performance at two bands and maintain that performance over a wide range of aspect angle. Basic mirror antenna operation and design and fabrication techniques for a dual-band half-wave plate mirror are described. The solution for design parameters is derived for perfect 90\deg polarization rotation at a given aspect angle for each of the two bands. The design approach includes a process for optimizing the design for the full desired range of aspect angles. Practical fabrication considerations are discussed along with inclusion of the effects of capacitive susceptance of a protective mirror coating in the design theory. Theoretical performance is compared with measurements of mirror samples.

Front fed offset cassegrain type multibeam antenna

Abstract: Introduction Large high capacity communication satellites with multibeam antennas are being developed in Japan(l), Ilnited States(2) and so on. The merits of multibeam antenna are ( 1 ) high EW, (2) reuse of frequencies. But in the design of multibeam antenna, one of the most difficult problems to be solved is to obtain the high beam-to-beam isolation. In conventional antennas, for instance Offset Gregorian, the increase of scan angle causes the increase of sidelobe level and scan loss on account of aberration and increase of cross polarization level, so beam-to-beam isolation becomes lower.

Optimum beam scanning in offset single and dual reflector antennas

Abstract: Optimum beam scanning in offset single reflector (paraboloid) and dual reflector (Cassegrain and Gregorian) antennas is considered. Analytical, computationally efficient solutions and results are presented for the optimum feed position, the constant beam direction feed loci, and the optimum feed position locus. Examples are presented to verify that the analysis technique yields the optimum feed position, which exhibits better gain, pattern symmetry, and sidelobe levels when compared with other feed positions producing beams scanned to the same direction. The solutions described were obtained under the ray optics approximation and a "receive mode" analysis. Although the developed method was applied to the antennas listed above, it can be easily extended to other n -reflector systems, shaped reflector antennas, lenses, and other similar systems.

Shaped offset-fed dual reflector antenna

Abstract: OF THE DISCLOSUREA shaped offset-fed dual reflector antenna having a main reflector, a sub-reflector and a primary radiator which do not block the wave-path of said main reflector is improved by using a primary radiator inclined from a boresight axis of the antenna, and shaped non-quadratic surfaces in the main reflector and/or the sub-reflector, to provide the desired aperture field distribution, improved cross-polarization characteristics, and improved side-lobe characteristics. The incline angle of the primary radiator is in the range between 10 degrees and 40 degrees. When a gregorian type antenna is used, and the aperture field distribution is Tailor's-40 dB distribution, the incline angle is preferably 16 degrees.

Multi-mode feed horn

Abstract: A linearally polarized multiport multimode feed for a reflector type antenna generates a plurality of beams, each in a different pointing direction, from a single radiating aperture. Each beam possesses a distinct phase center determined by the waveguide modes establishing the aperture distribution for that beam. The feed is linear and bilateral, therefore may be utilized in a receiving or transmitting antenna.

Planar-parabolic reflector antenna with recessed feed horn

Abstract: An axisymmetrical planar-parabolic reflector antenna has a paraboloidal reflector dish (10) and a planar reflector (13) into which the feed horn (11) illuminating the dish (10) is recessed so as to reduce (and preferably minimise) aperture blocking caused by the feed horn (11). In its upper frequency band, the feed horn (11) has a vanishing electric field at the edge of its aperture which suppresses edge currents at the mouth of the feed horn (11) and along the planar reflector surface (13), thereby preventing the flow of ground-plane currents in the planar reflector (13) which would degrade the antenna's performance. In its lower frequency band, the feed horn's choke surrounding the mouth of the feed horn (11) effectively accomplishes the edge current suppression. At a given frequency band, the feed horn (11) produces virtually equal E and H-plane radiation patterns.

Crosspolarisation due to radial field components in reflector antennas

Abstract: The letter stresses the importance of including the radial component of the transmit field of the feed horn when analysing reflector antennas. Omission of this component leads to errors in the prediction of crosspolar patterns similar in magnitude to those produced by diffraction effects within a dual reflector antenna.

Satellite radio ground station antenna arrangement operating on the Cassegrain principle

Abstract: Satellite radio ground station antenna arrangement operating on the Cassegrain principle. In the case of a Cassegrain antenna, which is supplied by a beam waveguide and can be pivoted about an azimuth and an elevation rotation axis (11, 10), and whose supply input/output is located in a fixed-position operating space (12), the supply system consists of an excitation horn radiator (5), whose supply side projects into an operating space projection (15), in the azimuth rotation axis (11), a deflection mirror (8) in the azimuth rotation axis and two deflection mirrors (6, 7) in the elevation rotation axis (11). The three deflection mirrors (6, 7, 8) and the catchment and main reflector (3, 1) are supported by means of a holding device (17, 18) as an entity, such that they can rotate about the azimuth rotation axis. The main reflector, the catchment reflector and the deflection mirror (6), which is located behind a central main reflector opening (4) and, in radiation terms, follows the catchment reflector, are jointly articulated on the holding device in order to rotate about the elevation rotation axis. The design measures according to the invention allow satellite tracking of the antenna in relatively large spatial angle ranges. The antenna arrangement according to the invention is suitable for satellite radio ground stations having antenna reflectors with a relatively large diameter.

Shifted focus cassegrain antenna with low gain feed

Abstract: A new type Cassegrain antenna provides a shifted or ring focus by use of a subreflector having a reflecting surface in the shape of an ellipsoid of revolution or a shape similar to two foci arrangements in combination with a low gain radiating element having a phase center which is relatively-insensitive to frequency The result is an extremely-compact, axially-symmetrical Cassegrain antenna construction for less than sixty wavelength antenna diameters, maintaining approximately a 10 per cent subreflecter to main reflector diameter ratio

An offset reflector antenna with low sidelobes

Abstract: The corrugated conical horn is considered to be an ideal feed for low sidelobe reflector antennas because of its unique characteristics. Analysis is carried out to show that low flare horns are preferred over high flare horns to give rise to low sidelobe performance for a given offset reflector antenna system.

A figure of merit for signal processing reflector antennas

Abstract: In recent years a new class of reflector antennas utilizing array feeds has been receiving attention. An example of this type of antenna is a reflector utilizing a moveable array feed for beam steering. Due to the circuitry required to adjust the weights for the various feed array elements, an appreciable amount of loss can be introduced into the antenna system. One technique to overcome this possible deficiency is to place low noise amplifiers with sufficient gain to overcome the weighting function losses just after each of the feed elements. In the evaluation of signal processing antennas that employ amplifiers the standard antenna gain measurement will not be indicative of the antenna system's performance. In fact, by making only a signal measurement, the antenna gain can be made any arbitrary value by changing the gains of the amplifiers used. In addition, the IEEE Standard Test Procedures for Antennas does not cover the class of antennas where the amplifier becomes part of the antenna system. There exists a need to establish a standard of merit or worth for multi-element antenna systems that involve the use of amplifiers. A proposed figure of merit for evaluating such antenna systems is presented.

Offset Spherical Reflector Earth-Station Antennas

Abstract: The Paper describes theoretical and experimental results for a novel low cost earth-station antenna. The antenna deploys a spherical reflector in an offset configuration. It yields a very low sidelobe envelope with albeit a slightly lower efficiency than conventional offset reflector antennas.

Microwave technique for reflector antenna profile measurement

Abstract: A method for microwave measurement of the reflector antenna surface profile is described. The technique uses a focused monostatic secondary reflector located on axis at approximately two focal lenths from the reflector under test. Measurement of the two-ways phase change provides profile error information over a set of annular sections. Practical results are provided to illustrate the spatial resolution and sensitivity of the technique.

Automatic tracking correction device

Abstract: PURPOSE:To simplify the circuit constitution by performing secant correction, coordinate conversion, and phase difference correction collectively in one place in an azimuth elevation mount four-converging reflective mirror beam feeding Cassegrain antenna. CONSTITUTION:Azimuth and elevation angle error signals are read through error signal input circuits 3 and 4, and an azimuth thetaAZ and an actual elevation angle thetaEL of the antenna are read from input circuits 5 and 6, and they are operated by a microprocessor 9. Azimuth and elevation angle error signals which are detected with new rotated azimuth-elevation coordinates are subjected to coordinate rotation by DELTAtheta=thetaAZ+thetaEL to convert them to azimuth and elevation angle error signals on reference azimuth-elevation coordinates, and cosecthetaEL is multiplied by the azimuth angle error signal to perform secant correction. Coordinate rotation is performed by DELTAthetaS, which is a phase difference between the sum signal and the error signal generated by route switching of a low noise amplifier or frequency switching of a beacon signal, thus compensating the phase error.

Secondary pattern computation of an offset reflector antenna

Abstract: Reflector antennas are widely used in communications satellite systems because they provide high gain at low cost. In analyzing reflector antennas the computation of the secondary pattern is the main concern. A computer program for calculating the secondary pattern of an offset reflector has been developed and implemented at the NASA Lewis Research Center. The theoretical foundation for this program is based on the use of geometrical optics to describe the fields from the feed to the reflector surface and to the aperture plane. The resulting aperture field distribution is then transformed to the far-field zone by the fast Fourier transform algorithm. Comparing this technique with other well-known techniques (the geometrical theory of diffraction, physical optics (Jacobi-Bessel), etc.) shows good agreement for large (diameter of 100 lambda or greater) reflector antennas.