Showing papers on "Cassegrain antenna published in 2004"

Secondary reflector for SHF antennae of the cassegrain type

Abstract: The invention concerns the secondary reflectors of SHF antennae of the Cassegrain type. It consists of providing the secondary basic reflector (103) of this antenna with a first circular ring (104) in the shape of a cylinder directed toward the main reflector, and a second ring (105) in the shape of a circular crown fixed to the end of the cylinder, and projecting outward from the latter. These rings are made from a conducting material. The length of the cylinder and the width of the crown are of the range of one quarter of the average wavelength for which the antenna is dimensioned. This enables the “overspill radiation” of the secondary reflector to be reduced considerably, and therefore allows the dimensions of the antenna to be reduced significantly for equivalent performance.

Deployable antenna with 10-m maximum diameter for space use

Abstract: This paper describes a large deployable antenna which is used at L-, C-, and Ka-bands on an artificial satellite in space. The main reflector with 10-m maximum diameter is formed using the tensioned truss concept which was proposed by one of the authors. The mechanical structure of the antenna is briefly explained and a more detailed description given of the electrical design of the antenna and the verification method of electrical characteristics. This antenna was successfully launched and deployed in space in 1997 and is used for a Space VLBI mission.

Particle swarm optimization (PSO) for reflector antenna shaping

Abstract: It has been shown that reflector antenna systems can benefit substantially from careful shaping of the main or sub-reflectors, or both, in order to maximize the antenna's performance (Duan, D.-W. and Rahmat-Samii, Y., 1995). Shaped reflectors can be used to achieve high efficiencies and gains, low side-lobe levels, and arbitrarily contoured beams. As the demands placed on satellite broadcasting and communications channels and the use of space-borne radar applications increase, so too do the requirements for the antennas on which these systems rely. The paper establishes particle swarm optimization as a candidate for solving difficult reflector synthesis problems. This is done by developing the tools required to perform the reflector synthesis and solving an example to serve as proof-of-concept. The example is to shape the main reflector of a reflector antenna with F/D=1.0, such that the scanning performance of the antenna. is improved.

Novel multiple phase centre reflector antenna for GMTI radar

Abstract: Adaptive cancellation of stationary clutter for a ground moving target indicator (GMTI) radar requires antenna sensing using multiple apertures. In essence, simultaneous independent observations of the target plus clutter are required. Conventionally, multiple antenna apertures can be achieved through the use of physically separated antennas, or antennas which can be controlled so that subsections are used to receive. Herein, the use of reflector antennas to effect multiple phase centres is described. Multiple feedhorns pointed laterally from the focal point of the reflector are first reviewed, with capabilities and limitations discussed. A new technique for achieving multiple phase centres with a reflector antenna is then introduced. This technique is based on the excitation and combination of TE and/or TM modes from a single antenna feedhorn. It is shown that, by proper combination of multiple TE modes from a single feedhorn, radiation patterns with separate phase centres can be produced from the same reflector. TE and TM modes can also be combined to effect the same, but this is omitted for brevity. The characteristics of the resulting radiation patterns are analysed with a view towards maximising the separation of the antenna phase centres while maintaining symmetry between the patterns and minimising the reduction in gain and constant phase beamwidth with respect to the reflector's conventional radiation pattern.

An omnidirectional ADE reflector antenna

Abstract: In this work, an axially-displaced-ellipse (ADE) dual-reflector antenna for the achievement of an omnidirectional coverage is proposed. Its geometry is briefly presented and some relevant features are compared against previously suggested reflector antennas, designed for the same purpose. The present ADE configuration is capable of yielding the desired aperture illumination with relatively smaller reflector dimensions, thus providing a compact arrangement suited for use at base stations of point-to-multi-point radio links. Numerical simulations are presented to illustrate the usefulness and advantages of the proposed reflector antenna. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 250–254, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11344

Feed assembly for multi-beam antenna with non-circular reflector, and such an assembly that is field-switchable between linear and circular polarization modes

Abstract: A feed assembly for an antenna having a non-circular reflector, in which the feed assembly includes a feed horn capable of correcting the distortions of circularly polarized signals caused by the non-circular reflector profile, and wherein the feed horn is coupled with a polarizer that is field-switchable between linear and circular polarization modes of operation. The feed assembly can include a second receive-only feed located in close proximity to the feed horn for communication with adjacent satellites.

Patch array feed for an automotive radar antenna

Abstract: An improved transceiver assembly for a vehicle for detecting potentially hazardous objects is disclosed. The transceiver assembly preferably comprises a patch array feed antenna having an array of a plurality of patches for generating a beam and for detecting the beam as reflected from the potential hazards. The antenna is formed in or on a housing which also contains a parabolic dish that moves to sweeps the beam of radiation towards the potential hazards outside of the vehicle. In a preferred embodiment, approximately 77 GHz radiation is generated from and detected by the antenna.

Single-aperture antenna system for producing multiple beams

Abstract: A novel single-aperture antenna system for producing multiple closely spaced or overlapping beams. The antenna system has multiple feeds for radiating energy, and a hyperboloidal or ellipsoidal main reflector responsive to the radiated energy for forming multiple beams. The main reflector is configured to form one beam for each of the multiple feeds in the antenna system.

Characteristics of the large deployable antenna on HALCA Satellite in orbit

Abstract: This paper describes measurements of the characteristics of a large deployable antenna using the tensioned cable truss scheme in orbit. From observations of celestial radio sources, the antenna gain degradation after launch was shown to be acceptable at L- and C-bands. At Ka-band, however, serious degradation of 24 dB was measured. From observations of the earth and moon, the degradation at Ka-band was shown to be attributed to the transmission line loss. The systematic and random errors of the main reflector surface are separated on the basis of these measurement results and theoretical analysis. Accordingly, the reflector status in orbit is estimated.

Design of a Vlasov antenna with reflector

Abstract: The Vlasov antenna, composed of a slant-cut radiator and a parabolic cylinder reflector, is designed by using vector diffraction theory. The experiential formulae on the antenna design are given. A C-band Vlasov antenna, composed of a cylindrical waveguide of 4.5 cm radius with 35° as the bevel-cut angle, and a reflector, was designed. The calculations and measurement results show that the antenna can work over a wide bandwidth (from 3.6 GHz to 5.6 GHz). The gain is about 21 dBi at 4 GHz and over 23 dBi at 5.6 GHz. The energy emission efficiency exceeds 90% at 4 GHz and the overall efficiency exceeds 88% in the range from 3.6 GHz to 5.6 GHz.

Differential switched oscillators and associated antennas. Part 2

Abstract: Building on previous results, switched oscillators and associated antennas are extended to new variations. Differential systems are considered with inline differential oscillators near the reflector focus for the purpose of increasing the voltage delivered to the antenna and thereby the far field. This leads to the concept of a separated reflector with two ground planes, two separated reflector foci, and a space between the ground planes for placing pulse-power equipment.

Compact antenna test range without reflector edge treatment and RF anechoic chamber

Abstract: There are several types of CATRs (compact antenna test ranges) used in antenna-pattern measurements. An offset reflector is generally used to generate the quiet zone of a CATR. Serrated edges, rolled edges, or R-cards are generally chosen along the reflector's edge to reduce the edge-diffraction field inside the quiet zone of the CATR. In order to reduce stray signals from the environment, a high-quality RF anechoic chamber is required for a CATR. In this paper, a new type of CATR, without either a reflector edge treatment or an RF anechoic chamber, is developed. A commercially available DBS (direct-broadcast satellite) reflector antenna, without edge treatment, is used as the reflector antenna of the CATR to generate the quiet zone of the antenna test range. In order to improve the quiet zone's performance, the fields due to feed spillover, edge diffractions, and other stray signals are gated out by the ITDAMS (impulse time-domain antenna measurement system). The RF interference in the environment can also be reduced by time synchronization and pulse integration of the impulse time-domain antenna measurement system. In order to verify the capabilities of the proposed CATR, three kinds of antennas (a low-directivity horn antenna, a high-directivity 60 cm direct-broadcast satellite reflector antenna, and a 25 cm Ka-band Cassegrain LMDS - local microwave distribution system - antenna) were measured by the proposed CATR. The antenna-pattern results agreed quite well with those of a near-field range and a far-field range.

94 GHz zonal ring reflector for helicopter collision avoidance

Abstract: A single-layer reflector antenna combining eight and four correcting Fresnel zones is presented. The progressive phase shift is achieved by circular and annular patches. The choice of a quarter-wavelength thickness substrate provides naturally 0 and 180° correcting zones that simplify the reflector design. A prototype of reflector antenna working at 94 GHz has been designed, built and measured. Measurement results show 70% improvement of antenna aperture efficiency compared to the half-wave Fresnel zone plate reflector .

AVTIS - a dual-mode imaging millimetre wave radar/radiometer for volcanological surveying

Abstract: We present the design and preliminary results for an advanced mm-wave remote sensing instrument. AVTIS (AH Weather Volcano Topography Imaging Sensor) is a dual-mode passive imager and active radar operating at 94 GHz, designed to yield topographic and thermal maps of volcanic lava domes. The mechanically scanned imager uses a 0.5m Cassegrain antenna mounted on a pan & tilt gimbal. The radiometer is of the total power heterodyne type, and the radar operates in an FMCW mode. When images are collected from multiple viewpoints, it will be possible to construct a thermo-spatial 3D map of the lava dome. The project volcanologists will use this data to enhance the modeling of the growth and collapse mechanisms in lava domes, which may ultimately lead to improved hazard warning.

Antenna with Rotatable Reflector

Abstract: A directional antenna formed by associating a stationary generally omni-directional antenna element with an RF reflector formed from, for example, a folded, parabolic or elliptical RF reflecting surface. Rotating the RF reflector about the stationary antenna element creates a directional characteristic in the resulting antenna over, for example, a 360 degree range of azimuth. Rotation of the RF reflector may be remotely driven by a motor coupled, for example, to a gear connected to the RF reflector. The direct connection of the antenna element and the enclosed lightweight rotating assembly provide a reliable, easy to install and cost effective antenna.

Effect of aperture feed and reflector configuration on the time- and frequency domain radiation patterns of reflector impulse radiating antennas

Abstract: The prompt off-boresight radiation from an arbitrary reflector impulse radiating antenna (IRA) is considered in both the time and frequency domains using a time-domain physical optics formalism. The theory is used to compare the performance between reflector IRAs with common transverse electromagnetic feed configurations that have been designed to maximize the boresight fields. It is found that moving the feed arms of reflector IRAs toward the vertical helps to reduce sidelobe levels, as reflector IRAs with their feed arms oriented at 60/spl deg/ from the horizontal have sidelobes that are 4-5 dB lower in the H plane and 1-2 dB lower in the E plane than more traditional reflector IRAs with feed arms oriented at 45/spl deg/. The lower sidelobes are accompanied by a higher peak gain, albeit with a wider beamwidth. There are corresponding significant differences in the time domain waveforms that result. The theory is verified by comparison with experimental data from a half IRA with feed arms at 45/spl deg/. The peak fields, pulse widths, and overall waveform shapes agree well between theory and experiment, though there are temporal asymmetries in the measured data that are not predicted by the theory.

Illumination module for automobile headlamp

Abstract: The module has one reflector (2) and another reflector (3) to produce one light beam. A third reflector (4) has a cut edge arranged near a focus of reflector (2) to form a cut in the beam. A fourth reflector (13) has a passive position in which it does not intercept light rays at end of the reflector (3) and an active position in which it produces another light beam by intercepting light rays at end of the reflector (3). An independent claim is also included for a lighting system with two types of beam having several modules.

Co-located multi-band antenna

Abstract: A multi-band reflector antenna having a main reflector, a sub reflector, a first feed and a second feed. The first feed, the sub reflector and the main reflector positioned in a Gregorian optic configuration wherein an output of the first feed is directed to the sub reflector, from the sub reflector to the main reflector and from the main reflector into a first beam. The sub reflector may be shaped to distribute the output of the first feed reflecting off the sub reflector onto the main reflector whereby a central area of the main reflector has a lower illumination than a surrounding outer area of the main reflector and or elongated vertically. The second feed projecting from a hole in the sub reflector is oriented whereby an output of the second feed is directed to the main reflector and from the main reflector into a second beam.

Multibeam reflector antenna with interlaced focal feeds by using a 1-d dielectric ebg resonator

Abstract: The use of a single reflector antenna with horns on the focal plane leads to excessive losses by spillover or by beam crossover. The 1-D dielectric resonator EBG (1) allows to generate directive and interlaced reflector feeds in order to obtain at the same time maximum reflector antenna efficiency and closely spaced beams. Consequently, it is not necessary with our passive system to use a complex, costly and heavy beam forming network behind the focal feeds.

Experimental Characteristics of a Printed Open-Slot Antenna with Reflector for PCS, DCS, and IMT-2000

Abstract: In this paper, we investigate a new rectangular-fed printed open-slot antenna (POSA) with reflector, which has the advantages of improved radiation-pattern properties along with broad-bandwidth characteristics. The measured bandwidth of the proposed POSA with reflector is approximately 47.6% (−10 dB ≥ S11), thus, it can be used for PCS, DCS, and IMT-2000. But the measured bandwidth of the PCSA with reflector is approximately 46% (with VSWR ≤ 2.0). The tilt angle at maximum gain is enhanced by using a modified POSA with reflector for practical applications. The radiation pattern null and distortion of the open-slot antenna exhibited better performances than those of the closed-slot antenna. The back-lobe level of the POSA with reflector also presented much better results than the PCSA with reflector. The proposed antenna obtained not only wider bandwidth but also better radiation patterns characteristics than the PCSA with reflector. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 348–350, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20138

Performance of multimode (TE 11 +TE 21 ) feed horn for offset reflector antenna providing multiphase centres

Abstract: The phase centre of a feed horn is a theoretical point along the axis of the horn which is the centre of curvature of the phase fronts of the spherical waves. In most feeds, there is a phase centre region rather than a single point because radiation is due to a summation of spherical waves, which seems to emanate from the aperture [1]. Determination of the feed phase centre helps, its location relative to the focal point of the reflector. Different techniques to compute and determine the phase centre location in single and dual reflector geometries are reported in [1-3]. However, when the feed horn has a multimode excitation, the amplitude and phase control of modes provide different constant phase centre locations, which in turn helps to conceptualize a virtual array on the reflector antenna aperture [4].

Planar antenna fitted with a reflector

Abstract: A planar antenna fitted with a reflector of small shape and small depth. A reflector 21 of planar shape is provided at the rear face of a radiator 20 of planar shape made of a triangular loop element. The side sections 21 b on both sides of the reflector 21 are bent towards the radiator 20 and the separation .alpha. 2 between the leading edges of the side sections 21 b and the side edges of the radiator 20 is thereby reduced. In this way, an excellent electrical characteristic of the planar antenna 2 fitted with a reflector and can be achieved by reducing the separation D 2 of the radiator 20 and reflector 21.

Contaminants in ATCA baselines with shadowing: a case study of cross-talk in short-spacing interferometers

Abstract: Interferometric telescopes made of close-packed antenna elements are an important tool for imaging extended radio sources, specifically structures that have angular sizes comparable to or even greater than the full width at half maximum of the beams of the antennas. They have proved useful in observations of cosmic microwave background anisotropies that require high brightness sensitivity. However, the visibilities measured in baselines formed between close antenna elements – in particular, between shadowed elements – of Fourier-synthesis arrays are often observed to be corrupted. We discuss the multiplicative and additive errors affecting such short-baseline interferometers. As a case study, we have examined the nature of the spurious correlations between the Cassegrain-type paraboloidal reflectors that are elements of the Australia Telescope Compact Array. In configurations with geometric shadowing, the cross-talk here appears as an additive component. Analysis of the characteristics of this cross-talk leads us to believe that when these reflector antennas are in a shadowed configuration, the receivers in the antenna pair pick up correlated emission from opposite sides of the main reflector surface of the front antenna. The slots between the panels that make up the main reflector surface provide the pathway for the coupling across the reflector surface. This mode of cross-talk may be avoided by constructing the main reflectors of short-spacing interferometers as continuous conducting surfaces.

Gravitational deformation of a reflector antenna measured with single-receiver holography

Abstract: Holographic measurements of deformations in a large antenna reflector are described. The deformations were brought about by changing elevation angle and gravitational loading. A phase-switching arrangement was used, which allowed a single, already installed and operating receiver to be shared by both the main antenna signal and a reference signal. Natural H/sub 2/O masers in our galaxy were used as signal sources, and a reference antenna was attached rigidly to the antenna under test so as to move with it. Observing techniques are described that accommodate changes in source elevation angles and antenna feed position while acquiring a data set.

Proposal of a shaped optical antenna realized as a lower‐order aspheric surface approximation

Abstract: Optical antennas used for point-to-point communication in optical intersatellite communication must have high aperture efficiency. By means of the reflector surface shaping method, it is possible to design an antenna with high aperture efficiency and low side lobes. However, the reflector surface becomes a nonspherical surface described by a higher-order polynomial and is very susceptible to errors in the manufacturing process. This paper proposes a shaped optical antenna whose shaped surface is described without a higher-order polynomial but with a nonspherical surface of the lowest order. The error characteristics are compared with those of the conventional shaped antenna. It is demonstrated that the proposed shaped optical antenna not only is more easily fabricated but also possesses almost identical error robustness to a nonshaped antenna. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(5): 62–74, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10145

Synthesis of curved fan‐beams by generalized theory of doubly curved reflectors

Abstract: Although a reflector antenna with a single reflecting surface called a doubly curved reflector, based on a reflector shaping technology that uses geometrical optics approximation, was effective in synthesizing a fan-beam, there was ambiguity in the reflector design technique. This paper shows that an exact and unique solution in the sense of geometrical optics is obtainable as a solution of an ordinary differential equation. It then generalizes the doubly curved reflector design method, extending it to the synthesis of a curved fan-beam whose beam footprint has curvature. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(12): 39–48, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10219

Results of reflection loss measurements of sample material for radio astronomy telescope antenna for Planck Project

Abstract: Advanced radio telescope antennas for space applications are realised by the use of stable composite materials, which are lighter in general than various metal realisations. Reflectivity measurements have been carried out on high technology samples for the Planck radio telescope. Highly accurate results have been obtained at the Applied Physics Institute in Nizhny Novgorod, and an independent measurement with a totally different setup at the University of Stuttgart confirmed that one of the samples showed a strange behaviour. Moreover, it confirmed the high accuracy of the testing method.

A broadband rolled edged cavity antenna

Abstract: A cavity antenna has been developed to feed a small reflector antenna efficiently over a relatively wide bandwidth. Efficient antenna feeds for reflector antennas generally require rotationally symmetric, low sidelobe patterns. The novel cavity antenna has a broadband crossed dipole and a rolled edge cavity termination to reduce illumination loss resulting from feed backlobes. The design is motivated by a future GPS monitoring application covering the L5 (1186 MHz) to L1 (1575 MHz) frequencies. The compact feed reduces blockage in a relatively small (4 ft) reflector. Analyses and validating measurements are presented.

An efficient dual frequency antenna feed

Abstract: Terminals for weather satellite readout require a compact feed for small reflector antennas and operate at L-band (1670-1710 MHz) and S-band (2200-2300 MHz). Both bands require right hand circular polarization and L-band requires linear polarization as well. The analysis and measurement of a novel dual frequency antenna feed is described. Stacked microwave patches for operation at the two separated frequency bands are surrounded by a corrugated surface to improve illumination efficiency. The feed is configured for orthogonal linear polarization, has filtering and modest preamplification with amplitude and phase matched LNAs for each linearly polarized feed terminal, and uses a quadrature hybrid to combine the two outputs for circular polarization. Linear polarization is obtained by turning off one of the preamplifiers.

Evaluation of degradation of shaped radiation pattern caused by excitation coefficient error for onboard array-fed reflector antenna

Abstract: We evaluated the degradation of the radiation pattern caused by the excitation coefficient error of the phased array-fed reflector antenna. In the case of the excitation coefficient quantized and with the error added in accordance with the manufacturing specifications, for example, 99.9 % of the gain of the nationwide beams is more than 40 dBi and 99.99 % of the gain of the nationwide beams is more than 39.5 dBi. The calculation method with power restriction is thus not only efficient, but the performance is nearly equal to the calculation method without power restriction.