Showing papers on "Cassegrain antenna published in 2001"

Novel Gaussian beam method for the rapid analysis of large reflector antennas

Abstract: A relatively fast and simple method utilizing Gaussian beams (GBs) is developed which requires only a few seconds on a workstation to compute the near/far fields of electrically large reflector antennas when they are illuminated by a feed with a known radiation pattern. This GB technique is fast, because it completely avoids any numerical integration on the large reflector surface which is required in the conventional physical optics (PO) analysis of such antennas and which could take several hours on a workstation. Specifically, the known feed radiation field is represented by a set of relatively few, rotationally symmetric GBs that are launched radially out from the feed plane and with almost identical interbeam angular spacing. These GBs strike the reflector surface from where they are reflected, and also diffracted by the reflector edge; the expressions for the fields reflected and diffracted by the reflector illuminated with a general astigmatic incident GB from an arbitrary direction (but not close to grazing on the reflector) have been developed in Chou and Pathak (1997) and utilized in this work. Numerical results are presented to illustrate the versatility, accuracy, and efficiency of this GB method when it is used for analyzing general offset parabolic reflectors with a single feed or an array feed, as well as for analyzing nonparabolic reflectors such as those described by ellipsoidal and even general shaped surfaces.

Variable beamwidth and zoom contour beam antenna systems

Abstract: Variable beamwidth antenna systems for use on spacecraft that is capable of changing their beamwidths while the spacecraft in on orbit. The variable beamwidth antenna systems include a main reflector, a subreflector, a feed horn, a main reflector displacement mechanism and a feed horn (or subreflector) displacement mechanism. For broaden the beamwidth, the RF feed horn and the subreflector are moved close together by proper distance. The main reflector is moved away from the subreflector along a line through centers of their respective surface by a distance given by a predetermined equation. Another embodiment of the present invention provides for a zoom contour beam antenna system that radiates a contour beam and whose beam is variable or zoomable.

Phase-only reconfigurable multi-feed reflector antenna for shaped beams

Abstract: A method and apparatus for reconfigurably transmitting shaped beam satellite signals via reflector array antennas are disclosed. The apparatus comprises a reflector (406) for reflecting signals having a reflector focal plane (104) and a feed array (402) comprising a plurality of feed elements (414) wherein said feed array (402) is defocused from said reflector focal plane (104), yet produces an wavefront (312) substantially similar to a wavefront that would be produced by a feed array located at the reflector focal plane (104). The method of transmitting a signal in accordance with the present invention comprises forming a wavefront (312) with a feed array (402), wherein said feed array (402) is defocused from a reflector focal plane (104), yet produces a wavefront (312) substantially similar to a wavefront that would be produced by a feed array located at the reflector focal plane (104) and reflecting said wavefront (312) to a coverage area (408).

Designing classical Dragonian offset dual-reflector antennas from combinations of prescribed geometric parameters

Abstract: This paper proposes a simple procedure for the design of classical offset-Dragonian dual-reflector antennas from combinations of prescribed geometric parameters. This procedure has already been applied to classical Cassegrain and Gregorian antennas, and to classical displaced-axis Cassegrain and Gregorian antennas. We provide a list of 20 parameters from which the antenna system is fully characterized, but only five of these parameters need to be provided by the antenna designer, as the remaining 15 parameters can be derived in closed-form using the procedure described. We consider that the main reflector (MR) has a circular aperture, while the subreflector (SR) has an elliptical aperture.

A shaped reflector antenna for 60-GHz radio access points

Abstract: A shaped reflector antenna for a prototype 60-GHz wireless LAN access point has been designed and constructed. Its performance has been verified through measurements of the antenna far-field radiation patterns in the compact antenna test range. Near-field patterns have been reconstructed from the measured far-field data by using the Hankel transform. The results show that the amplitude across the footprint area remains within 6 dB of uniformity.

Triple reflector antenna deployment and storage systems

Abstract: An antenna deployment system for use in storing and deploying three antennas that are located on the same side of a spacecraft or other fixed body. The three antennas are nested and are stacked in a stowed condition and are individually and sequentially deployed to their respective deployed positions. One or more feed horns are attached to the spacecraft or fixed body that illuminate the respective antennas. A dual axis deployment mechanism is used to deploy each antenna. The dual axis deployment mechanism is also used to steer the beam produced by the antenna. The dual axis deployment mechanism comprises a dual-axis rotatable hinge structure affixed to the spacecraft or fixed body that is coupled to the antenna by way of a substantially rigid reflector support structure. The dual axis deployment mechanism is actuated and controlled to deploy the antenna and steer the antenna beam.

Reflector antenna having varying reflectivity surface that provides selective sidelobe reduction

Abstract: A composite antenna reflector architecture for improving beam-to-beam isolation in a multi-spot illuminated reflector antenna employs a plurality of annular rings surrounding a central reflective dish and having respectively different controlled reflectivity profiles. The reflectivity-tailored reflector rings alter illumination taper and reduce selected sidelobe energy, and minimize degradation in coverage performance and gain slope in the radiation profile of the antenna. A respective ring employs a frequency selective surface laminate of layers containing different elements that resonate at different frequencies spectrally spaced to provide at least one composite frequency response characteristic.

A 5-frequency millimeter wave antenna for a spaceborne limb sounding instrument

Abstract: Several spaceborne Earth observation missions such as the European Space Agency's (ESA) atmospheric chemistry instruments Millimeter wave Acquisitions for Stratosphere/Troposphere Exchange Research (MASTER), Soprano or Piramhyd require the development of complex millimeter and submillimeter wave range spectroradiometers. These instruments place stringent requirements on antenna electrical performance due to the low-noise signal levels and the high-vertical resolution involved. This paper focuses on the electromagnetic (EM) design and analysis of a 2.2-m diameter Cassegrain antenna operating in 5-frequency bands between 200 and 500 GHz. The primary feed network is an essential part. It has to provide not only the low-loss frequency separation of the bands but also the antenna illumination with nearly perfect amplitude and phase patterns for high-beam efficiency. Quasi-optical techniques are extensively used for the overall antenna design and focal plane demultiplexer breadboarding and testing.

Reflector antennas for microwaves

Abstract: A dual-reflector microwave antenna includes a main reflector having a shape that is a portion of a paraboloid generated by revolution of a parabola around having a single, common axis of rotation and symmetry. A primary feed extends along the axis of the main reflector on the concave side of the main reflector, and a subreflector located beyond the end of said primary feed has an image-inverting surface configuration that has a ring focus located between the main reflector and the subreflector and extending around the axis of the main reflector. In either a single or dual-reflector antenna, the main reflector has a shield with a band of dielectric or conductive material extending around at least a portion of the inner surface of the shield for reducing the return loss of the antenna. Patterns may be improved by providing a shield of absorber material extending around the outer periphery of at least an end portion of the primary feed. In the case of a dual-reflector antenna, return loss may be reduced by providing a dielectric or electrically conductive element between the primary feed and the subreflector, and/or by providing an annulus of absorber material on the surface of the subreflector.

Dual-band equal-beam reflector antenna system

Abstract: A satellite antenna system employing a dual-band feed horn and dual-band beam forming network. The feed horn provides a common aperture for both satellite uplink and downlink communications signal. The feed horn includes corrugations on an inside surface defining two sets of alternating channels having different depths to create circularly symmetric beams for the uplink and downlink signals. The antenna system includes at least one reflector, where the reflector shape, position, and the configuration of the feed horn, is determined so that the mainlobe of the lower frequency downlink feed signal illuminates the entire reflector, and the mainlobe of the higher frequency uplink feed signal illuminates an inner portion of the reflector. The first sidelobes of the higher frequency feed signal illuminate the outer portion of the reflector so that the uplink and downlink antenna signals have the same beamwidth, and thus cover the same cell size on the Earth.

Surveillance radar scanning antenna requiring no rotary joint

Abstract: A wave-scanning antenna is disclosed that does not require a rotary joint. The antenna produces a collimated beam that can be scanned through 360 degrees. The beam is directed perpendicular to the antenna's axis of rotation to form a disc-like surveillance volume, or at an angle above or below the perpendicular to form a cone-shaped surveillance volume. The radar's structure contains a transmitter and receiver coupled to a horn protruding through open centers of the support bearing and driven gear into the antenna housing. Energy emitted by the horn proceeds upward until deflected through an angle of 90 degrees by an angled reflector located on the axis of rotation. The energy is collected by a dielectric lens and focused into a collimated beam. Reflected energy is collected by the lens and directed by the reflector to the horn, where it is fed to a waveguide coupled to the receiver.

The new submillimeter-wave solar telescope

Abstract: A new and unique solar submillimeter telescope (SST) was installed in the El Leoncito site, Argentina Andes. It has a 1.5 m radome-enclosed cassegrain antenna, and arrays of four 212 GHz and two 405 GHz radiometers placed in the focal plane. We present a brief technical description of the system, preliminary results on its performance, the atmospheric opacity measured at the site, and the first detection of solar flare submm-wave emissions.

Analysis of circular reflector antenna covered by concentric dielectric radome

Abstract: The radiation from a two-dimensional cylindrical reflector antenna with a concentric dielectric radome is analyzed in an accurate manner for both H and E polarization cases. The problem is first formulated in terms of the dual series equations, and then it is regularized by using Riemann-Hilbert problem technique. The resulting matrix equation is solved numerically, with a guaranteed accuracy, and sufficiently little CPU time is needed. The feed directivity is included in the analysis by the complex source point method. Various characteristic patterns are obtained for the front-fed reflector antenna geometries in this study.

Common aperture reflector antenna with improved feed design

Abstract: A common aperture reflector antenna and feed are provided for use in common aperture sensor systems. The feed includes an array of individual elements. The array elements are configured to increase the overall efficiency of a reflector antenna by flattening the aperture illumination, and also by nullifying the illumination within the centrally-blocked-portion of the reflector antenna surface. More specifically, the array elements are carefully configured with respect to spacing and excitation, for example, such that the array illuminates only the non-blocked portion of the main reflector. In addition, the array pattern is optimized such that the non-blocked portion of the reflector antenna is quasi-uniformly illuminated.

A dual polarised antenna

Abstract: A dual polarised antenna comprising a reflector (101); one or more radiating element (102-104); and a plurality of directors (107-116) extending from the reflector dimensioned and positioned to emphasise one polarisation of the beam of the antenna at angles away from the main beam direction. The directors are in the form of fingers which act as resonant monopoles so as to produce beam equalising currents.

Full wave analysis and experimental verification of a broadband ridged horn antenna system with parabolic reflector

Abstract: In this paper we investigate the radiation pattern of a complete 1-18 GHz antenna system featuring a 1.8 in parabolic reflector and a double ridged broadband feed horn with coaxial input using a combination of the method of moments (MoM) and a physical optics (PO) approach. It was found that in the lower frequency range the horn antenna system exhibits a single main lobe in the direction of the center horn axis as expected. However, contrary to common belief, at frequencies greater than 12 GHz, the main lobe starts to split into four main lobes pointing into off-center-axis directions with a broadside gain reduction. This effect was observed both theoretically and experimentally. Although this type of antenna has existed for over four decades, up to now there is no explanation for this unwanted behavior in the open literature. In the past, several electromagnetic simulations of ridged horn antennas were made, but not over such a broad operational frequency range and neither including the coaxial feed nor the complete parabolic reflector system. The purpose of this investigation is to close this gap and to contribute to a better understanding of broadband ridged horn antennas.

Multimedia aircraft antenna

Abstract: An antenna system consisting of parabolic rectangular reflectors disposed contiguously in a linear array. The use of parabolic rectangular reflectors permits the reflectors to form a larger common rectangular aperture without gaps in illumination. The contiguous array of parabolic rectangular reflectors permits a lower profile which is ideal for use on an aircraft. Each parabolic rectangular reflector has its own feed system and each of the feeds are excited in phase. The combined radiation patterns of the parabolic reflectors produces a beam with a narrow width. This narrow beamwidth permits the system to communicate with one source while filtering out signals coming from other sources. In one embodiment, the antenna system may be mechanically steered in order to communicate with a transmitter and/or receiver whose relative position is continuously varying with respect to the antenna system.

Antenna structure for fixed wireless system

Abstract: The invention involves a novel mechanical assembly incorporating, in a preferred embodiment, a technically advanced Cassegrain antenna design The antenna achieves, in experiments, near theoretical performance with the minimum size The Cassegrain antenna incorporates an intergrated DR array feed

Side-fed offset cassegrain antenna with main reflector gimbal

Abstract: A steerable antenna comprises a steerable main reflector and a stationary feed assembly and subreflector assembly configured in a side-fed configuration where the feed assembly is to a side of both the main reflector and the subreflector. The main reflector, subreflector and feed assembly together produce an antenna beam which is directed in a preselected direction by the main reflector. A gimbal is coupled to the main reflector for positioning the main reflector and scanning the antenna beam over a preselected coverage area while the feed assembly and subreflector remain substantially stationary.

High efficiency low sidelobe dual reflector antenna

Abstract: A dual reflector antenna system includes a subreflector and a main reflector with optimized shapes defined from a desired field distribution pattern and a feed pattern The reflector shapes capture maximum energy from the feed and allow sidelobes to closely track a predetermined sidelobe envelope for optimal overall antenna efficiency

Feed-reflector design for large adaptive reflector antenna (LAR)

Abstract: A novel feed-reflector system for large Cassegrain antennas of radio astronomy and deep-space communication applications is investigated. This feed-reflector is used to illuminate a hyperboloid subreflector with a 5-10 m diameter located 500 m above the ground. Because the subreflector is located in the near field of the feed-reflector antenna, a theory based on the near field focusing properties of paraboloid reflectors is established. The focusing at near distance is formed by moving the feed horn away from the focal point of the feed-reflector. In this theory, the properties of axial defocused paraboloid reflectors at near distance are investigated in more detail. By using equivalence path law, the subreflector shape is obtained. It is found that the hyperbola can approximate the subreflector well. A detailed ray tracing is performed on the entire system which reveals that the feed system uses some part of the subreflector three times. The gain, side lobe level, cross polarization, and aperture distribution are calculated for different feed horn locations and taper at the edge of the feed-reflector and also for different sizes and eccentricities of the subreflector. Peak efficiency in excess of 74.8% and side lobe level around -20 dB are obtained for an unshaped system. The performance of the system over the operating band (1-22 GHz) is also studied and shown that the lower-frequency limit is dependent on subreflector and feed-reflector sizes.

Reflector shape optimization for FB ratio of dipole antenna

Abstract: This paper presents the enhancement of FB ratio by optimizing several types of reflector shape which are placed on the back of a dipole antenna for the sector antenna. By optimizing the size of each reflector shape, the FB ratio of dipole antenna is increased by more than 20dB. Comparing each shape for the same width of reflector, a dual box reflector has the best FB ratio of more than 30dB.

Enhancement of FB ratio for cellular base station antenna by optimizing reflector shape

Abstract: We presented the characteristics of the front-to-back (FB) ratio by using a dipole antenna backed by several types of reflector shapes. We simulated the radiation pattern and FB ratio of a dipole antenna by changing the size of rectangular reflector, dual reflector, and boxing reflector. There is an optimum size for each shape of reflector, and FB ratio of the dipole antenna is increased by more than 20 dB. Comparing each shape of the reflector when the width is constant, using a boxing reflector has the best FB ratio of a dipole antenna of about 29 dB.

Sub-reflector for dual-reflector antenna system

Abstract: An antenna includes a feed generating a communication signal. A sub-reflector is positioned to reflect the communication's signal to form a sub-reflective signal. A main reflector is positioned to reflect the sub-reflective signal. The sub-reflector has an elliptical rim.

Integrated dual beam reflector antenna

Abstract: The present invention discloses a method for generating multiple antenna beams and a system for generating multiple antenna beams. The system comprises a first reflector surface that has a primary and at least a first auxiliary surface, and a second reflector surface, and also comprises first, second, and third feed horns. The first feed horn illuminates the primary surface with radio frequency (RF) energy, the second feed horn illuminates the auxiliary surface with RF energy, and the third feed horn illuminates the second reflector surface with RF energy. The first feed horn and third feed horn are removed from an axis of symmetry of the first auxiliary surface. The method comprises illuminating a primary portion of a first reflector surface with radio frequency (RF) energy from a first feed horn, illuminating an auxiliary portion of the first reflector surface with RF energy from a second feed horn, illuminating a second reflector surface with RF energy from a third feed horn, wherein the first feed horn and third feed horn are removed from an axis of symmetry of the auxiliary portion of the first reflector surface.

Transient far-fields of offset reflector antenna

Abstract: Simple analytical expressions have been found for the transient far-fields of offset reflector antennas. It was shown that the time interval for non-zero values of the transient far-field transforms essentially as compared with symmetrical parabolic reflectors, and the cross component appears in the main section which is perpendicular to the direction of displacement of aperture center from paraboloid center.

Comparison of two flat reflector-type designs for dual-polarization, dual-band operation

Abstract: The parabolic reflector remains an essential antenna for high-gain applications This is a result of its desirable characteristics based on geometric optics These include relative frequency independence for sufficiently large apertures and high aperture efficiency However, the parabolic reflector occupies a large volume This may be aesthetically unappealing on the sides of buildings and structures Also, from a mobile user perspective, a desirable characteristic is having a large aperture during operation while having a small volume when packed away and not in use The parabolic reflector is typically constructed of multiple petals for mobile uses, but it does not pack into as small a volume as a flat, thin antenna would due to the curvature of the paraboloid Therefore, the primary goal of the antennas studied in this work is developing flat reflector antennas to utilize the advantages of large reflector apertures while remaining capable of packing into a small volume In addition, system requirements dictated dual-band, dual-polarized operation Two flat reflectors are compared: a reflectarray and a zoned reflector While each design is inherently narrow-band, methods of achieving dual-band operation were employed

Reflector for road vehicles

Abstract: A reflector is provided, which advantageously combines the functions of an optical reflector and a radar reflector, enabling objects with a low inherent radar cross-section to be reliably detected by automotive navigation systems.