Showing papers on "Cassegrain antenna published in 1996"

Small volume dual offset reflector antenna

Abstract: The problem of reducing the size of a dual offset Cassegrain reflector type microwave antenna without adversely affecting performance while retaining the simplicity of the main reflector's (1) and subreflector's (3) traditional simple surface curvatures is solved by having the paraboloidal shaped main reflector's focal length, fm, and diameter, D, fulfil the criteria that the ratio of fm to D is less than 1.0; and in which the hyperboloidal shaped subreflector (3) is oriented so that its left foci, at which the microwave feed (5) aperture is placed, lies above the main reflector's focal axis. It's subreflector subtends an angular arc about the focal point that is slightly larger than the corresponding arc subtended by the main reflector. The elegance of the compact antenna is demonstrated by improved performance, attaining efficiencies in excess of seventy three percent.

Spherical lens antenna having an electronically steerable beam

Abstract: The invention relates to an antenna system which is capable of producing multiple, high-gain, independently steerable antenna beams from a single antenna aperture. The system accomplishes this, in part, by utilizing a separate phased array antenna as the feed element of a spherical lens for each desired beam. In this fashion, the beam(s) produced by the antenna system can each be electronically steered (independently of the other beams, if any) and physical movement of the feed element(s) is not required. The invention may also use multiple spherical lenses, wherein each lens includes at least one phased array feed.

Orientable antenna with conservation of polarization axes

Abstract: An antenna is orientable, directional and capable of use as a transmit and/or receive antenna. It includes at least one reflector, at least one source of electromagnetic radiation including means for exciting the source with two orthogonal linear polarizations and a mechanical system for positioning and holding the source and the reflector. The orientation of the antenna is made up of depointing and rotation about a preferred direction of propagation of the radiation and the mechanical system enables such rotation while keeping the source fixed, so conserving the orientation of the orthogonal linear polarization. A preferred embodiment of the antenna includes a parabolic main reflector and a hyperbolic auxiliary reflector in a Cassegrain geometry, and the mechanical system enables rotation of both reflectors about the preferred direction of radiation and holds the source fixed to conserve the orthogonal linear polarization axes of the beam. Applications include radar, direct broadcast satellites and telecommunications employing frequency re-use by polarization diversity, especially advantageous in space and airborne applications.

Synthesis technique for scanning and/or reconfigurable beam reflector antennas with phase-only control

Abstract: Scanning and/or reconfigurable reflector antennas can be conveniently set up by using a hybrid antenna consisting of a reflector illuminated by a small phase-only controlled array feed. However, no general synthesis procedure performing the optimum design of such antennas seems to exist. In the paper a new general and flexible formulation of this synthesis problem is presented together with an iterative solution scheme, which make it possible to determine simultaneously the reflector geometry, the amplitude of the excitation coefficients common to all radiated beams and the phases of such excitations corresponding to each beam. The technique handles general and flexible requirements on the radiated beams (expressed by masks) as well as general constraints on the excitations of the feed array elements (the phase-only control is one of these). Furthermore, it exploits a new choice for the quantity to which the design specifications concerning the radiated field are applied, in order to alleviate the trapping problems encountered in power synthesis. A numerical analysis is performed in order to demonstrate the effectiveness of the approach as well as the possibilities offered by the hybrid reflector antenna configuration.

Communication and tracking antenna systems for satellites

Abstract: A communication and tracking antenna is formed by embedding a tracking patch array in a shaped dual gridded reflector. The reflector includes first and second reflector grids that have orthogonally arranged grid lines and are respectively fed by feed horns. The patch array is positioned so that the first reflector grid is between the patch array and the first feed horn. The first reflector grid thus serves as a filter to remove unwanted polarization components and enhance the quality of both the tracking radiation and the radiation that is reflected from the second reflector grid. In other embodiments, a tracking array is positioned adjacent a reflector's perimeter.

Surface error measurements of large reflector antennas by phase retrieval holography—an application of extrapolation algorithm

Abstract: This paper investigates the phase retrieval holography (PRH) method using the Misell algorithm for measuring the surface error of a large reflector antenna. PRH is a technique that does not require phase measurement. The algorithm is investigated experimentally and the estimation errors are evaluated quantitatively using measurement simulation. First, it is shown that estimation errors can be reduced using an initial aperture distribution calculated by ray-tracing. The measurement resolution is improved by applying an extrapolation algorithm to the Misell algorithm. Finally, the surface error of a Cassegrain antenna with an aperture of 64 m to resolution of about 4.1 m in the aperture plane was measured by receiving a test signal from a geostationary satellite (frequency: 1.545 GHz). As a result of the experiment, the surface error of 1.57 mm RMS and measurement reproducibility of 0.54 mm RMS were obtained and it was confirmed that this method is effective as a simple surface measurement method.

Different methods of PO analysis in a dual reflector antenna with a shaped main reflector

Abstract: The shaped reflector has emerged as a vital technology in the field of satellite antennas. The dual offset Gregorian geometry considered, using an ellipsoidal subreflector fed by a spherical source feed, is shown. In a Cassegrainian system, a hyperboloid is used as the subreflector. By choosing an optimum tilt angle between the main reflector and the subreflector axes, the cross-polarization in a dual offset reflector can be minimized. Thus, by shaping the main reflector a shaped beam with superior cross-polar performance can be realized. The surface profile of the shaped reflector is synthesized using an accurate analysis embedded inside an optimization. This accurate analysis is usually based on physical optics (PO). Ideally a dual reflector analysis using PO on both the subreflector and the main reflector is necessary to synthesize the main reflector shape. This can be very time consuming and unnecessary especially if only the main reflector shape is synthesized. Two other simplified techniques which can be used more efficiently during the main reflector synthesis, are presented. A brief overview of the different analysis techniques are also presented.

Compact antenna test range reflector edge treatment

Abstract: The physical optics technique is used to compare the performance of single offset compact antenna test ranges with different reflector edge treatments and rim shapes. A comparison between reflector edge taper and rim serrations in controlling edge diffraction is demonstrated.

End-fire array antennas with divergent reflector

Abstract: An end-fire array antenna achieves improved performance with an array of radiative members that are arranged collinearly between an array first end and an array second end and a divergent reflector which is arranged collinearly with the radiative members. The radiative members are spaced to facilitate radiation and reception of electromagnetic signals in an antenna direction which extends from the array second end and the divergent reflector is spaced from the array first end to enhance this radiation and reception. A wall of the reflector preferably diverges from an antenna axis by an angle in the region of 24 to 48 degrees. The divergent reflector terminates in an open end which has a transverse width that preferably exceeds 1.4 λ dsgn wherein λ dsgn is the design wavelength of the antenna. In-service antennas are modified with a divergent reflector that is configured for coupling to an existing antenna back wall or antenna cup.

A folded lens antenna with triple use of the lens

Abstract: A novel type of folded lens antenna is presented in this contribution. In addition to known concepts of folding reflector or lens antennas, the lens of the antenna described here is used threefold, resulting in a further reduction of antenna depth. Furthermore, a novel type of twist reflector printed on a planar dielectric substrate of given thickness is included. As an example, a test antenna in the 20 GHz range was designed, fabricated and tested, showing good results and giving the basis for compact antennas, especially in the mm-wave frequency range.

Mobile phone set with antenna reflector

Abstract: With all mobile phone sets (1) such as Natel C, Nadel D etc. equipped with an integrated antenna or directly mounted antenna (3) th antenna is held very close to the head of the user by the nature of the application. As a result, the signal emitted from the antenna (3) becomes more or less dumb and attenuated, depending on the shape of the user's head, with a great deal of the emitted power being absorbed by the said head. By fitting an antenna reflector with a large surface area (2) such drawbacks are eliminated, in particular the radiation impact on the user of the phone, which is reduced by a ratio of 1:20.

Design of an asymmetric parabolic cylinder antenna with high aperture efficiency

Abstract: With respect to the asymmetric cylindrical parabola antenna constructed for radio astronomical observation at 327 MHz, the design method and the verification of the design values are reported. The present antenna placed emphasis on the improvement of the receiving sensitivity and is designed to increase the aperture efficiency as much as possible. To carry out an optimum design of the primary feed made of a dipole array with a corner reflector, the structural parameters of the primary feed have been studied. It was found that there exist optimum values. The reduction of the efficiency due to the transmission loss and the phase error loss of the reflector surface made of stainless wires was derived. The overall aperture efficiency was estimated to be 75.9 percent. In an actually constructed antenna, the aperture efficiency measured with a celestial radio source as the standard radio source was 71 ± 5 percent. It was confirmed that the aperture efficiency derived from the computation and the optimum design values are reasonable.

Development of antenna system for S-band mobile satellite communications and broadcasting

Abstract: Advanced Space Communications Research Laboratory is studying an antenna system for future S-band mobile satellite communication and broadcasting. This system uses a GEO satellite and is composed of a large deployable satellite antenna with a 10 m diameter mesh reflector and a mobile antenna for vehicles and hand-held terminals. In this paper, we present our deployable satellite antenna program and discuss the radiation characteristics of the antenna. These characteristics include a shaped multibeam synthesis for communications, and a shaped beam synthesis for broadcasting. We also describe a switching plane array antenna for vehicles.

Offset-paraboloid geometry: relations for practical use

Abstract: Offset-paraboloidal reflector antennas are used for satellite-communication systems, because they provide low sidelobes and high eficiency. The analysis of the radiation characteristics for the reflector antenna have been studied, with the geometric parameters related to focal length. But we sometimes need to convert the geometrical parameters of the offset-paraboloidal reflector to dimensions relative to the plane of the rim, especially during manufacture. The focal length and geometric parameters are also formulated from the easily measured parameters of the reflector, such as length, width, and depth.

Triple corner reflector antenna and its performance in H-plane

Abstract: An experimental investigation of a novel corner reflector antenna with improved performance is reported. The corner reflector antenna has been structurally modified by attaching two more reflector elements. The parameters such as the primary corner angle, position, width and angle of the secondary elements have significant effects on the H-plane radiation characteristics of the antenna. Certain symmetric configurations of this triple corner reflector (TCR) antenna provide sharp beams with a gain of the order of 3 dB over that of the conventional corner reflector (CR) antenna.

Antenna system parabolic reflector, flat plate shroud and radome

Abstract: In a parabolic reflector system for directing or receiving radiation from or to a radiation feed, having a parabolic reflector surface defining a parabolic reflector axis, a parabolic reflector focus and a radiation aperture, wherein the parabolic reflector has a flat plate shroud attached thereto at the aperture thereof and a radome covering the shroud aperture.

Multi-Factor Optimisation of Large Reflector Antenna Structures

Abstract: A novel multi-parameter overall situation optimisation method has been developed for use on antenna reflector structures. Various structural performances arc included as objective functions. The design variables involve geometric and size variables of structures. Various working environments and loading cases which affect antenna performances could be combined in the optimisation mathematical model. An important aspect to the work is the establishment of evaluation criteria to optimise the design of a system. Such an optimisation procedure would satisfy extremely high design requirements. An 8m antenna structure is significantly optimised and the results are given.

Double reflector type small aperture parabolic antenna system

Abstract: PROBLEM TO BE SOLVED: To allow a general home to use suitably the antenna system for receiving a satellite broadcast and a satellite communication by selecting a small aperture for a main reflector and for a sub-reflector and ensuring a required efficiency. SOLUTION: The antenna system is provided with a small sized main reflector 11, a small sized sub-reflector 12, a circular waveguide feeder 13, and a converter 14 connecting to the feeder 13. When the diameter of the main reflector 11 is called D, the diameter of the sub-reflector 12 (d), the focal distance of the main reflector 11 F, the distance between the center of the main reflector 11 and the focus of the sub-reflector 12 F', the distance between the focus of the main reflector 11 and the focus of the sub-reflector 12 be F-F', and a wavelength of an electromagnetic wave λ, then relations 0.25<=F/D<=0.30, 18λ<=D<=22λ, 2λ<=d<=3λ, and 1.0λ<=F-F'<=1.5λ are required to be satisfied.

Dual-band offset gimballed reflector antenna

Abstract: There are two ways to scan a reflector antenna using a gimbal. One is to gimbal the whole antenna assembly, called gimballed antenna assembly. The other is to gimbal the reflector only while the feed and support structure are stationary, called gimballed reflector. The pros and cons for the two approaches are listed. In summary, the gimballed reflector has more advantages than the gimballed antenna assembly such as a simple mechanical structure, light weight, and low manufacturing cost. However, the only disadvantage of the gimballed reflector is the scan loss associated with the feed displacement due to the reflector focal point change. The antenna consists of a front-fed offset gimballed reflector and a circularly polarized dual-frequency band feed. The gimballed reflector allows scanning the beam within any Earth coverage area. The antenna is capable of providing simultaneous EHF reception and SHF transmission for the MILSTAR payload.

Design and Development of VSAT Antenna Feed .

Abstract: The paper deals with the design and development of a dual polarised corrugated conical horn employed as a feed for parabolic reflector antennas used in very small aperture terminal applications. The VSAT antenna feed is designed, fabricated and tested to operate over a band from 3.7 GHz to 6.5GHz with good pattern symmetry, low side lobes and low cross-polarisation.

Synthesis of the multibeams reflector antenna directivity patterns on the given magnitude

Abstract: The problem of synthesis of the given shape contoured directivity pattern of a spacecraft hybrid antenna with the purpose of uniform "illumination" of the some territorial zone is considered. The variational formulation of the synthesis problem according to the given magnitude pattern is used. The mean-square deviation of given and synthesized magnitudes is chosen as an optimization criterion. It permits one to improve the approximation quality of the magnitudes, to influence the polarized properties of synthesized directivity patterns, and also to satisfy set additional requirements. Examples of synthesis of the contoured directivity patterns, which cover the given territory uniformly are presented. In these examples, the hybrid antenna consisting of a rectangular cutting from a parabolic reflector and a feed array is used.

Investigation of the Planar Near-Field Measurement of a Reflector Antenna and a Reflector-plus-Splash Plate Antenna System at X-band.

Abstract: : This investigation is motivated by the difficulty of measuring certain multiple reflector antenna systems in a typical near field range configuration. The three primary objectives of this investigation are: (1) to investigate alternative planar near field measurement configurations, (2) to support computational simulation studies and (3) to investigate the performance of a particular dish plus splash plate antenna system.

Moment method design of a large S/X band corrugated horn

Abstract: The design of a dual frequency corrugated horn, working at S- and X-band simultaneously, is presented. The horn was designed to feed the 20 m radio telescope at the Onsala Space Observatory (a classical Cassegrain), via two feed reflectors. The feed system is intended for geodetic measurements using very long baseline interferometry (VLBI). Large corrugated horns are mainly designed by using software based on mode matching. The moment method (MM) for bodies of revolution (BOR) has successfully been used to design small corrugated horns. The design of large horn antennas using MM for BOR is difficult because of the large memory requirements. Internal resonances may also occur and give incorrect results. These resonances are difficult to distinguish from actual performance problems. However, the paper shows that it is possible to identify the internal resonances by scanning the frequency and thereby it is possible to design even large horns, using the MM for BOR.

Synthesis of the surface of reflector antenna for a given power pattern

Abstract: Several problems of synthesis of reflector antennas for a given power pattern are considered. The antenna consists of a cylindrical reflector and radiation source. The problems are solved in the approximation of induced currents. Falling on the reflector, a nonuniform plane wave is supposed to be known in the first problem. The reflector surface is synthesized here. It produces an electromagnetic field with directivity, which is approximate to the given power pattern. The second problem consists in synthesis of the surface of a reflector antenna, where the falling cylindrical wave is formed by a certain excitation source with given directional characteristics. In the third problem, one more degree of freedom is added, i.e. both the shape of the reflector and directivity pattern of the antenna feed (radiation array) are synthesized. The variational statements of the problems are considered. Minimization of the corresponding functionals leads to a solution of the nonlinear integro-differential Euler equations. The methods of solution of the obtained equations are presented. Numerical results of synthesis are considered.

Analysis of quasiperiodic reflector antenna

Abstract: A procedure for the design of a planar reflector antenna comprising a quasiperiodic metallic echelette grating is described. The reflector is designed so that the power radiated by the feed is deflected by the various portions of the reflector towards a desired direction. The possibility of steering the main beam by shifting the frequency with nearly no loss in gain is demonstrated. The sensitivity to cell fabrication errors and to improper feed location, which is essential information for the antenna designer, is examined.

Antenna system design and optimization for a fixed imposed geometry and environment

Abstract: This paper describes the design and the optimization performed for the elements of the MWR antenna system, a microwave radiometer embarked on the ENVISAT-1 platform of the European Space Agency. This instrument provides, through the Earth atmosphere analysis, a scientific support to the radar altimeter RA-2 positioned on the same spacecraft. The MWR radiometer antenna system is composed by a parabolic offset reflector antenna called the "measurement antenna" pointed toward the Earth and by a corrugated feed called the "sky horn" pointed toward the cold sky for calibration purposes. The parabola is illuminated by two feedhorns, FH-24 and FH-37, to provide an analysis capability in two frequency bands from 23.6 to 24.0 GHz and from 36.3 to 36.7 GHz and the sky horn supports simultaneously these two bands. An analogous radiometer was embarked on the ERS-1 and ERS-2 satellites and the MWR instrument for the ENVISAT-I platform must be similar to the precedent versions. For this reason the parabolic antenna optic is a fixed and the inherited parameter which can not be changed but must be taken into account for the design and optimization activity. Starting from the electrical requirements that the antenna system must satisfy, a description of the design and optimization activity are given for all the elements and parameters which do not affect the antenna optic but are "degrees of freedom" useful to reach the required electrical performance.

Minimise pattern degradation when subreflector vertex shaping is used to improve feed match

Abstract: A knob placed at the vertex of a subreflector to reduce subreflector mismatch in a shaped Cassegrain antenna can significantly degrade the radiation pattern and reduce efficiency. A practical procedure is described to lessen these effects. Best results are obtained using a cosine-squared-shaped knob, keeping a low knob height and knob base within the feed blockage region. The importance of simultaneously optimising for return loss, antenna efficiency and sidelobe level is emphasised.

Space antennas: design, analysis and measurement challenges

Abstract: Modern technological demands necessitates utilization of sophisticated antenna configurations as an integral part of future satellite communications and scientific payloads. A typical configuration consists of multi offset reflector antennas illuminated by feed arrays operating at various frequency bands. Additionally, it is desired to use large reflector antennas providing improved link performances and high resolutions for various applications. An overview of representative recent advances in large antenna design, analysis and measurements are presented. Examples of recent developments of mesh deployable and inflatable reflector antennas are given.