Showing papers on "Cassegrain antenna published in 1998"

Designing axially symmetric Cassegrain or Gregorian dual-reflector antennas from combinations of prescribed geometric parameters

Abstract: A procedure to design axially symmetric Cassegrain or Gregorian dual-reflector antennas from various combinations of prescribed geometric parameters is presented. From these input parameters, the overall geometry of the antenna is derived in closed form. This procedure can be used as the starting point of a synthesis procedure, where both main reflector and subreflector are shaped to create the desired aperture field distribution.

A retrodirective microstrip antenna array

Abstract: A Van Atta retrodirective reflector was designed and developed, using an aperture-coupled microstrip antenna array. This reflector possesses the advantage of reflecting high fields to the source point over a wide range of incidence angles and, owing to the low cost and conformability of the structure, is suitable for applications in intelligent vehicle highway systems (IVHS). An approximate theory associated with the reradiation and scattering principles of the reflector is presented for the purpose of understanding and designing the reflector. The utility of the retrodirective reflector was demonstrated by comparison with a plate reflector and a microstrip antenna array without a feed structure. Finally, a reflector with switches in the middle of the microstrip feed lines was investigated for possible applications in communications and remote identification.

Analysis and characterization of multilayered reflector antennas: rain/snow accumulation and deployable membrane

Abstract: There are important engineering issues in designing reflector antennas that cannot be addressed by simply assuming a perfect electric conductor (PEC) reflector surface For example, coatings may exist on antenna surfaces for protection, rain or snow can accumulate on outdoor reflectors, and the deployable mesh or inflatable membrane antennas usually do not have solid PEC reflector surfaces Physical optics (PO) analysis remains the most popular method of reflector analysis owing to its inherent simplicity, accuracy, and efficiency The conventional PO analysis is performed under the assumption of perfectly conducting reflector surface To generalize the PO analysis to arbitrary reflector surfaces, a modified PO analysis is presented Under the assumptions of locally planar reflector surface and locally planewave characteristic of the waves incident upon the reflector surface, the reflection and transmission coefficients at every point of the reflector surface are determined by the transmission-line analogy to the multilayered surface structure The modified PO currents, taking into account by the finite transmissions of the incident waves, are derived from the reflection and transmission coefficients Applications on the analyses of the rain and snow accumulation effects on the direct-broadcast TV antennas and the effects of finite thickness and finite conductivity of the metal coating on a 15-m inflatable antenna are described and results are presented

Low earth orbit earth station antenna

Abstract: An improved very small antenna terminal (VSAT) dual-beam antenna system for use with user subscriber terminals that communicate with low-earth orbiting and other satellites. In one embodiment, the dual-beam antenna system has two offset Gregorian dual-reflector antennas that each has an ellipsoidal subreflector and a rotatable paraboloidal reflector having a focus in common with a focus of the ellipsoidal subreflector. The rotatable paraboloidal reflector couples energy to and from the ellipsoidal subreflector. An RF feed system couples RF energy to and from the ellipsoidal subreflector. Rotating apparatus rotates the paraboloidal reflector and ellipsoidal subreflector together around an azimuth axis of the antenna. The rotating apparatus independently and simultaneously rotates the paraboloidal reflector about an axis between the paraboloidal reflector and ellipsoidal subreflector which points the antenna at an orbiting satellite. A controller is coupled to the rotating apparatus that controls rotation of the paraboloidal reflector and the antenna to point the antenna toward the orbiting satellite. The two antennas are preferably mounted side-by side and the one antenna is pointed at a first satellite while the second antenna tracks a rising satellite. A VSAT radio is automatically handed-off to the rising LEO satellite by switching it from the one antenna to the second antenna. Another embodiment may be used to track a inclined-orbit satellite having a figure-eight orbit, wherein the actuators move the antenna more slowly to track the satellite. Another embodiment employs a single antenna that is fixed relative to an orbiting satellite.

Reflector antenna with improved return loss

Abstract: An improved reflector antenna with far improved return loss than prior art subreflector antennas is disclosed herein. The invention uses a circular waveguide antenna feed (1) employing a non-planar subreflector (5) having a radial cavity which reflects the energy from the waveguide onto a rotationally symmetrical main reflector (1). The dimensions of the feed tube, the subflector, and the connection (3) between them are chosen to make the total reflection back into the feed tube very close to zero. The dimensions of the antenna feed are also chosen such that its radiation pattern has an amplitude null along the antenna feed axis. This further improves return loss by minimizing the amount of energy from the main reflector that gets directed back into the feed tube. An alternate embodiment features a feed radiation pattern with an asymmetric amplitude taper for improvement of the sidelobe envelope in a preferred plane.

Satellite dish antenna targeting device and method for operation thereof

Abstract: A satellite dish antenna targeting device which corrects for incline and parabolic offset angle. The satellite dish antenna is connected to a base by a support member so that the satellite dish antenna is able to move through an elevation. An inclinometer is mounted to move in unison with the satellite dish antenna for sensing when the base is oriented at an inclination angle with respect to a tangent to the earth at a location where the satellite dish antenna is being targeted. The inclinometer further senses the elevation the satellite dish antenna moves through. The inclinometer thereby provides a dish elevation corrected for the incline and elevation of the satellite dish antenna to a microprocessor. The microprocessor corrects the dish elevation for the parabolic offset angle of the satellite dish antenna. A display device connected to the microprocessor displays a corrected dish elevation of the satellite dish antenna. The satellite dish antenna is thus rapidly and accurately positioned within one degree to receive the satellite signal by moving the satellite dish antenna until the display device displays a predetermined target elevation compensated for by the incline and/or parabolic offset angle of the satellite dish antenna.

Designing axially symmetric Cassegrain or Gregorian dual-reflector antennas from combinations of prescribed geometric parameters. 2. Minimum blockage condition while taking into account the phase-center of the feed

Abstract: For pt.1 see ibid., vol.40, no.2, p.76-82 (1998). An easy procedure to design classical Cassegrain or Gregorian dual-reflector antennas has been presented in Granet (1998). This procedure allows the antenna designer to fully define the antenna geometry with different sets of input parameters, depending on the requirements of the antenna size and its performance. In this paper the conditions derived in Granet are extended to take into account the phase-center position of the feed, to achieve the minimum-blockage condition. This procedure can be used as the starting point of a synthesis procedure, where both main reflector and subreflector are shaped to create the desired aperture-field distribution.

Low-windload satellite antenna

Abstract: A satellite communications antenna includes a low-windload reflector so that the antenna may be used on high windload locations, such as on a ship. The reflector has a support structure which includes a grid-like structure having relatively large apertures therein to allow wind to pass therethrough. The reflector further includes reflective radiators, such as dipoles, mounted to the support structure for focusing at least one desired frequency of operation. The reflector is also formed in component parts for easy assembly/disassembly should it be necessary to deploy the system elsewhere.

Inflatable space antennas-a brief overview

Abstract: The use of inflatable structures in space has both fascinated and challenged many in the space community for forty years or more. The authors present some history on the evolution of precision inflatable reflector design from simpler inflatable structures that have flown in space. Examples of reflectors that have been ground tested are presented and discussed, followed by a description of the Inflatable Antenna Experiment off the Shuttle in 1996. Results from the surface accuracy measurements of some of these reflectors are also presented, along with measured and calculated RF gain and beam patterns of the 3-meter L'Garde Demonstrator Program (LDP) reflector. Finally, the authors comment on the current status of space inflatable reflector technology at L'Garde.

Multifunction impulse radiating antennas: theory and experiment

Abstract: A Multifunction IRA is an extension of a standard Impulse Radiating Antenna that has the additional flexibility of an adjustable beamwidth. This adjustability is implemented by defocusing the feed, in order to select between a narrow or broad beam. We provide here the theory of operation of the antenna, for both in-focus and out-of-focus situations. Furthermore, we built and tested a design with a 46 cm diameter. We found good agreement of the experiment with theory.

RF characterization of an inflatable parabolic torus reflector antenna for space-borne applications

Abstract: Space-borne satellite applications provide a vast array of services extending from global connectivity to Earth observation systems. The soil moisture radiation mission is a proposed space-borne passive microwave system complementary to the existing Earth observing system operating at low microwave frequencies and requiring an antenna with multibeam, high-beam efficiency, and dual polarization capabilities. To achieve both the large reflector size and the multibeam pattern at the operational frequencies an innovative multibeam reflector antenna design was needed. The advances in inflatable antenna technology has been proposed to overcome the launch vehicle size and weight restrictions. This paper describes a novel offset parabolic torus reflector antenna design that produces the desired multibeam pattern and is compatible with the inflatable antenna technology. Using the system requirements of this mission as an example, the design process for an inflatable parabolic torus reflector antenna is outlined, the development of suitable distortion models is given, and representative RF characteristics are presented. These RF characteristics include far-field patterns, beam contour patterns, beam efficiency, and other key performance parameters. The development of an advanced analytical modeling/numerical tool in support of the design effort is also detailed.

Improved reflector antenna with a self-supported feed

Abstract: The invention consists of improvements of reflector antennas with self-supported feeds. The feed consists of a waveguide tube, a dielectric joint and a sub-reflector. The tube is attached to the center of the rotationally symmetric reflector and extends to the focal region of it. The sub-reflector is located in front of the tube, and the surface of this sub-reflector is provided with rotationally symmetric grooves also called corrugations. The improvements of the present invention are (1) a ring focus reflector to improve the gain of the antenna, (2) an elevated central region of the reflector to reduce the return loss, (3) metal screws or cylinders to strongly fasten the sub-reflector to the tube, (4) corrugations or other similar means around the rim or the reflector in order to reduce far-out sidelobes, (5) dual-band operation by means of a coaxial waveguide outside the circular waveguide in the tube, and (6) dielectric filling or covering of the corrugations or of the region between the corrugations and the waveguide tubeend, both in order to avoid the gathering of water, dust or other undesired material in this area which could destroy the performance of the antenna.

Aperture-coupled microstrip antennas using reflector elements for wireless communications

Abstract: The design advantages provided by aperture-coupled microstrip patches can be very useful in wireless communications applications. A way to improve the front-to-back ratio is to place a microstrip antenna element behind the aperture as a reflector. Proximity coupling between the feed line and the reflecting element is negligible due to the thick foam substrate used, allowing use of the reciprocity method of analysis. Also, the directive patch elements are shielded from the reflector by the ground plane. Therefore, only interactions between the reflector and the aperture need to be modeled, resulting in a simple analysis. For aperture-coupled patch designs with a front-to-back ratio of 10 dB or greater, the introduction of a reflecting element has a negligible effect on the input impedance of the antenna. Therefore, a reflector element can readily be incorporated into existing designs.

Variable beamwidth corner reflector antenna

Abstract: A simple and successful design for a variable beamwidth corner reflector antenna is presented. The gain and the -3 dB beamwidth of the antenna are predicted using the finite difference time domain (FDTD) method. The predicted results are compared with measured data and good agreement is reported.

Multiple beam by shaped reflector antenna

Abstract: An antenna system has a reflector illuminated by a primary feed for producing a primary beam. The reflector is illuminated further by a secondary feed formed of an array of secondary feed elements of which the respective electromagnetic signals are adjustable in terms of their relative amplitudes and phases to produce a secondary beam with sidelobes oriented in directions away from the directions of the primary beam. Spacing among feed elements of the secondary feed array is selected for further control of orientation of sidelobes of the secondary beam. Highest efficiency is attained for signals of the primary feed by configuring the reflector for forming the primary beam, while the secondary beam is produced with lower efficiency but with isolation from the primary beam. The surface of the reflector is contoured to provide maximum primary-beam efficiency and minimal primary-beam sidelobes in the direction of the secondary beam.

Micromachined monolithic reflector antenna system

Abstract: A micromachined reflector antenna system is integrated onto a substrate by firstly etching a reflector aperture surface defining a dish cavity in an oxide layer and secondly rotating a hinge over the reflector aperture surface with the hinge being used as the reflector central feed. The micromachined reflector antenna system can be made with an array of reflector antennas and integrated onto a single substrate with front end receiver circuits operating as a high frequency receiver on a chip with reduced size and cost and operating at hundreds of GHz.

Adaptive beamforming with a multiple beam antenna

Abstract: Adaptive array processing is seen as one possible solution to the severe bandwidth and power restrictions in a communications system between a geostationary satellite and a mobile terminal. This paper considers the use of an offset parabolic reflector with an array feed, referred to as a multiple beam antenna (MBA), as a way of combining the high gain of the reflector with the spatial filtering ability of the antenna array. A signal model is developed in which the key quantity is the steering vector which represents the response of the antenna array to a plane wave arriving from a given angle. The steering vector for the MBA is found numerically by finding the secondary field of each of the antenna elements, and then using the principle of reciprocity to relate this field to the received amplitude. Statistically optimum beamforming on the MBA is demonstrated followed by a simulation of the direct matrix inversion (DMI) algorithm.

Broadband omnidirectional microwave parabolic dish--shaped cone antenna

Abstract: An omnidirectional microwave antenna comprises a paraboloidal reflector disposed above the ground and facing downwardly with a substantially horizontal aperture and a substantially vertical axis. A vertically oriented feed horn is located below the paraboloidal reflector on the axis of the paraboloidal reflector and has a phase center located near the focal point of the paraboloidal reflector. A conical reflector having a shaped reflecting surface defined by the parameters of a mathematical equation extends downwardly away from the periphery of the feed horn for reflecting radiation received vertically from the paraboloidal reflector in a horizontal direction away from the conical reflector, and for reflecting horizontally received radiation vertically to the paraboloidal reflector. A radome extends downwardly from the outer periphery of the paraboloidal reflector and includes an absorber material for absorbing radiation propagated laterally from the feed horn and the conical reflector above the aperture of the feed horn.

Electronically scanned cassegrain antenna with full aperture secondary/radome

Abstract: A Cassegrain antenna system includes a flat dielectric plate radome having a thickness of one-half wavelength at a frequency of operation. The plate has an electrically conductive grid disposed on an inside surface thereof to permit perpendicularly polarized energy rays to pass there-through. A parabolic twist reflector is spaced from the radome, and includes a dielectric substrate having a thickness equivalent to one-quarter wavelength at a frequency of operation and having formed on an interior surface thereof an array of conductive strips oriented by 45 degrees relative to the incident ray polarization. A conductive ground layer is formed on an exterior surface of the substrate, wherein radiation reflected by the ground layer and passing through the dielectric substrate is shifted by 180 degrees in phase and is rotated in polarization when combined with energy reflected from the conductive strip array by 90 degrees relative to radiation incident on the twist reflector. The reflected energy from the polarization twist reflector is again reflected, this time by the grid formed on the radome surface, to a focal region. An RF housing with a plurality of RF feed elements is located at the focal region and are respectively spaced by a single beamwidth.

Calculation of phase centers of feeds for reflectors when the phase variations are large

Abstract: The aperture efficiencies of classical symmetrical front-fed or Cassegrain reflector antennas can be factorized in different sub-efficiencies. Of these, the phase efficiency is the only one which depends on the location of the feed relative to the focal point of the reflector, provided the reflector is in the far-field of the feed. We present an improved formula for calculating the location of the phase center which is valid also when the radiation field of the feed has large phase variations. The new formula is applied to two different versions of the hat feed.

Modification of Cassegrain Earth station antenna for dual band operation

Abstract: The modification of a C-band Earth station antenna for efficient reception at both C- and Ku-bands is discussed. The original antenna was a 9-meter Cassegrain type, which employed shaped reflectors to receive signals in the 3.7 to 4.2 GHz frequency range. By replacing the original aluminum subreflector with an identically shaped composite incorporating a Frequency Selective Surface (FSS), and placing a feed at the best focal point of the main reflector, the antenna becomes a high gain prime focus type over the Ku-band range of 10.95 to 12.75 GHz. At C-band, Cassegrain operation is maintained with very little loss. This paper details the design procedure which led to the successful frequency selective subreflector, provides measured transmission data on several FSS candidates and subreflector samples, and compares the radiation patterns of the original and revised antenna. Emphasis is placed on the design of the frequency selective composite, particularly those practical aspects of the composite construction, which are not readily available in the literature.

Method and apparatus for an unfurlable isometric antenna reflector

Abstract: An antenna reflector comprising a single membrane antenna reflector surface and means for supporting said antenna reflector surface are disclosed wherein a shape of said antenna reflector is reconfigured to assume a stowed position. The shape of the stowed reflector allowing a large, single piece antenna reflector to be stowed efficiently inside a minimum payload area of the space vehicle. The method and apparatus of this invention ensure that both the deployed and stowed surfaces of the membrane antenna reflector are isometric, or length preserving, mappings of one another. The circumferential dimension of the antenna reflector is decreased having the effect of rolling up the paraboloid so that its surface is similar to a cone. Additionally, the method and apparatus are employed such that when the antenna reflector surface is deployed the antenna reflector membrane unrolls without stretching.

Planar retrodirective array reflector using dual-slot antennas

Abstract: An X-band planar reflector with a broad responding beam was developed using the Van Atta retrodirective antenna array. The reflector contained four antenna sub-arrays, each with six dual-slot antennas appropriately fed and paired by microstrip lines on the backside of the substrate. Good agreement has been achieved between theoretical and measured results.

Reflector antenna for analog or digital mobile telephone

Abstract: A rod or dipole antenna (2) has a metallic reflector for receiving and emitting radio waves. A planar or convex radio wave reflector (1) is arranged inside or on the rear side of the telephone, and screens the radio waves emitted from the antenna in a certain angular range alpha, while having a directionality in the remaining angular region of 360 degrees minus alpha for transmitting and receiving. The reflector may by made by metalising the rear of the telephone housing.

Micromachined reflector antenna method

Abstract: A method of manufacturing a micromachined reflector antenna onto a substrate firstly etches a reflector aperture surface defining a dish cavity in an oxide layer and secondly rotates a hinge over the reflector aperture surface with the hinge being used as the reflector central feed. The micromachined reflector can be made into an array of reflector antennas and integrated onto a single substrate with front end receiver circuits operating as a high frequency receiver on a chip reduced in size and cost and operating at hundreds of GHz.

Phased array feed for communication satellite antennas

Abstract: Phased array antennas are attractive for geostationary satellites because of their many advantages. This paper provides an analytical study of a single reflector antenna fed by an array feed composed of radially aligned elements. The antenna is compared with other phased array antennas such as a direct radiating array and a dual reflector antenna. Given the same environments for feeds and subreflectors, the comparison shows that a phased-array-fed single reflector antenna is superior to a dual reflector in wide angle beam scan capability. A manufactured array feed is described and measured radiation properties are shown. Secondary radiation patterns of the array fed reflector antenna calculated using measured array feed radiation patterns are presented. The agreement with original prediction proves the feasibility of the phased-array-fed single reflector antenna and the usefulness of radially aligned feed array elements.

Anomalous results from PO applied to reflector antennas: the importance of near field computations

Abstract: In the design of reflector antennas the physical optics (PO) analysis technique is the most popular numerical technique. Powerful computer codes are available for the analysis of single or multi reflector antenna systems. Additionally, ever-increasingly demand on the antenna performance necessitates the computation of antenna far field patterns under various situations. For example, in using multi-reflector antennas such as Gregorian or Cassegrain, it may become necessary to determine the total fields including the feed radiation pattern, subreflector scattered pattern and the main reflector scattered pattern. In these situations, the common practice is to sum up various scattered fields and the incident field contributions to obtain the desired total field. It is the purpose of this paper to demonstrate that the typical approach based on the far field pattern of the feed would result in an erroneous result and special care must be exercised to obtain the correct result. This is demonstrated through a detailed investigation of a representative test case.

Gaussian beam analysis of multiple beam reflector antennas

Abstract: The design and performance analysis of multiple beam antennas (MBAs) is quite tedious requiring several iterations of first computing the radiation patterns of reflector antennas for all the beams using the physical optics method and then performing minimum coverage area directivity and copolar isolation evaluations for each beam. The whole process typically takes a few weeks to arrive at an optimal MBA design. The objective of this paper is to present a simplified analysis such that the complete design and performance analysis can be performed very efficiently using hand calculators. The analysis is based on approximating both the primary and secondary patterns as Gaussian beams and deriving simplified equations for the MBA design and performance evaluations. The results of the analysis presented agree well with the computations using the rigorous physical optics analysis of reflector antennas.

Development of dual gridded reflector antenna for superbird-c

Abstract: Satellite communication antenna is required high EOC (Edge of Coverage) gain and XPD ( Cross polarization discrimination ) performance. Dual gridded reflector antenna is suitable to achieve these requirements because gridded reflector antenna has excellent cross polarization supperssion characteristics.[1][2] This antennaconsists of two single reflectors and two feed horns, which are one for transmit and another for receive, horn support structure and feed waveguides. MELCO developped the dual gridded reflector antenna for communication satellites in Ku-band. This paper describes the design concept, design method and measurement result.