Showing papers on "Cassegrain antenna published in 1989"
TL;DR: In this article, the authors proposed to use a single shaped reflector with a single feed element for a prescribed contour beam and feed, an optimization method for designing the reflector shape is given.
Abstract: Eliminating the corporate feed network in shaped contour beam antennas will reduce the expense, weight, and RF loss of the antenna system. One way of producing a shaped contour beam without using a feed network is to use a single shaped reflector with a single feed element. For a prescribed contour beam and feed, an optimization method for designing the reflector shape is given. As a design example, a shaped reflector is designed to produce a continental-United-States (CONUS) coverage beam. The RF performance of the shaped reflector is then verified by physical optics. >
78 citations
TL;DR: In this article, a 15 meter diameter Hoop-Column antenna was analyzed and tested to study shape adjustment of the reflector surface, which consisted of finite element and least squares error analyses to minimize the surface distortions.
Abstract: A 15 meter diameter Hoop-Column antenna has been analyzed and tested to study shape adjustment of the reflector surface. The Hoop-Column antenna concept employs pretensioned cables and mesh to produce a paraboloidal reflector surface. Fabrication errors and thermal distortions may significantly reduce surface accuracy and consequently degrade electromagnetic performance. Thus, the ability to adjust the surface shape is desirable. The shape adjustment algorithm consisted of finite element and least squares error analyses to minimize the surface distortions. Experimental results verified the analysis. Application of the procedure resulted in a reduction of surface error by 38 percent. Quasi-static shape adjustment has the potential for on-orbit compensation for a variety of surface shape distortions.
37 citations
TL;DR: In this paper, simple design procedures for use when a Gaussian beam is used to illuminate a classical reflector antenna are presented for the case of electrically small antennas where the aperture is in the near field of the feed.
Abstract: Simple design procedures are presented for use when a Gaussian beam is used to illuminate a classical reflector antenna. Displacement of the location of the beamwaist toward the focusing element in the case of electrically small antennas where the aperture is in the near field of the feed was calculated together with modification of the required beamwaist radius. Dual reflector antennas were discussed and design procedures appropriate for systems with large and small focal length to diameter ratio developed. Cases where a reflector or subreflector is electrically small, or in the near field of a feed, are readily treated. For elliptical beam antennas, a simple illumination system using only a scalar horn and a single cylindrical lens can generally be found; this has no ray optics analogue. A configuration of this type is discussed, with a practical case study of a 28-by-80- lambda elliptical Cassegrain antenna operating at a wavelength of 3 mm. The design process for designing the feed system is discussed in detail. Despite the small size and relatively large aperture blockage, an aperture efficiency of 0.48 was measured, which compared quite well with the expected efficiency of 0.53, thus verifying the validity of the Gaussian beam design approach. >
26 citations
TL;DR: In this article, the radiation characteristics of a circular microstrip antenna were studied numerically and an analytic method was used to design a microstrip feed and to achieve symmetric radiation patterns with low cross polarization and backlobe levels.
Abstract: The radiation characteristics of a circular microstrip antenna are studied numerically. Surface integral equations are used to formulate the problem from the boundary conditions and moment methods are used to reduce the integral equations to a matrix equation. An analytic method is used to design a microstrip feed and to achieve symmetric radiation patterns with low cross polarization and backlobe levels. The backlobe level is reduced by adding a quarter-wavelength choke to the side wall or the ground plane of the antenna and the bandwidth is improved by stacking two layers. The performance of the feed with the reflector antenna is also considered. One of the feeds was fabricated and tested. Satisfactory agreement between the computed results and the measurement data was obtained. The microstrip feed has a very small size which should reduce its blockage of the reflector aperture. >
26 citations
01 Oct 1989
TL;DR: In this paper, a reconfigurable mesh reflector antenna is demonstrated with the antenna surface adjusted while mounted on the Antenna Range, and the replacement of hand-adjusted actuators by motorised actuators is described.
Abstract: Preliminary measurements are reported on a novel reconfigurable mesh reflector antenna. Reconfiguration from a spot-beam to an elliptical-beam is demonstrated with the antenna surface adjusted while mounted on the Antenna Range. The replacement of hand-adjusted actuators by motorised actuators is described.
17 citations
Patent•
NEC1
TL;DR: An omnidirectional antenna assembly for use with a satellite and others includes a four-element whip antenna, a first and a second reflector which are positioned to face each other, and a third reflector connecting the first and second reflectors to each other as mentioned in this paper.
Abstract: An omnidirectional antenna assembly for use with a satellite and others includes a four-element whip antenna, a first and a second reflector which are positioned to face each other, and a third reflector connecting the first and second reflectors to each other. The third reflector is provided with a frustoconical configuration and is highly conductive, whereby the range of antenna gain is broadened.
13 citations
04 Apr 1989
TL;DR: In this article, an offset mesh reflector is proposed with reconfiguration achieved by means of adjustment to forces applied at control points on the reflector surface, which is demonstrated for typical regional coverage patterns.
Abstract: Describes a novel method for controlling the coverage pattern of a spacecraft antenna. An offset mesh reflector is proposed with reconfiguration achieved by means of adjustment to forces applied at control points on the reflector surface. Synthesis software has been developed and this is demonstrated for typical regional coverage patterns. A model of the mesh based on a network of springs is used and this has been successfully verified following precision mechanical measurements using an 85 cm diameter reflector. Gold-plated molybdenum mesh has been chosen so that the antenna can be tested electrically at a frequency of 10 GHz.
12 citations
26 Jun 1989
TL;DR: In this article, the authors compared the ability of six single and dual reflector designs to scan up to 300 beamwidths in order to determine the feasibility of wide-angle scans using reflector antennas.
Abstract: The authors compare the ability of six single- and dual-reflector designs to scan up to 300 beamwidths in order to determine the feasibility of wide-angle scans using reflector antennas. The single reflectors are either parabolic symmetric dishes with f/D=2 or f/D=1 or an offset reflector with f/D=2. Scanning is accomplished for the first two designs by tilting the reflector dish. The third design is scanned electronically. The dual reflectors are Cassegrain designs. All designs have a circular diameter of 1000 wavelengths. Results obtained are presented and discussed. >
9 citations
Patent•
09 May 1989
TL;DR: In this article, the size and apex angle of the conical reflector were optimized to yield the desired feed pattern, the optimization parameters depending on the reflector size and focal length and being obtained numerically or experimentally to maximize reflector gain.
Abstract: A dipole feed for a paraboloidal reflector antenna uses a conical reflector to direct the radiation of the dipole towards the concave reflecting surface of the parabola. The size and apex angle of the conical reflector are optimized to yield the desired feed pattern, the optimization parameters depending on the reflector size and focal length and being obtained numerically or experimentally to maximize reflector gain.
9 citations
Patent•
18 Aug 1989
TL;DR: In this paper, a parabolic-type reflector antenna for radar was proposed, where the horizontal and vertical axes and the axis XX' of the reflector pass through the centre of phase 21 of the primary source, which centre is coincident with the focus of the reflectionor, in such a way that the system is constantly focused.
Abstract: The invention relates to a reflector antenna for radar. This antenna includes a fixed primary source 2 and a parabolic-type reflector 1 which is movable in rotation around a vertical axis GG' for pointing in azimuth, and around a horizontal axis SS' for pointing in elevation. The horizontal and vertical axes and the axis XX' of the reflector pass through the centre of phase 21 of the primary source, which centre is coincident with the focus of the reflector, in such a way that the system is constantly focused. The invention applies especially to very high power radiation with very short pulses.
8 citations
TL;DR: In this article, the computer analysis of dual-offset reflector antennas fed by a circular corrugated horn, using an accurate feed model, is described, where near-field, thermal-paint, and carbon-fiber-reinforced plastic (CFRP)-structure effects are included to simulate a realistic design scenario and predict their impact on the radiation characteristics.
Abstract: The computer analysis of dual-offset reflector antennas fed by a circular corrugated horn, using an accurate feed model, is described. Near-field, thermal-paint, and carbon-fiber-reinforced plastic (CFRP)-structure effects are included in order to simulate a realistic design scenario and predict their impact on the radiation characteristics. The theoretical results have been verified by experiment for a near-field illuminated offset Gregory antenna. >
04 Apr 1989
TL;DR: In this article, the outer surface of the axial waveguide is used as a desired radiating element, and thereby it does not cause an undesired blocking of the aperture like in other self-supported feeds.
Abstract: The hat feed is a new axially self-supported feed for a single-reflector antenna. The advantage of it is that the outer surface of the axial waveguide is used as a desired radiating element, and thereby it does not cause an undesired blocking of the aperture like in other self-supported feeds. The authors present a hat feed at 15 GHz in a deep reflector with 43 cm diameter. The reflector is so deep that a plane radome can be mounted across the aperture. The antenna efficiency including mismatch is larger than 60% over a 6% bandwidth, and the sidelobes are extremely low.
TL;DR: In this paper, the authors present an analysis based on geometrical optical computations. And they show that the shaping to match feed horn illumination leads inevitably to severe coma and curvature of the field.
Abstract: Antennas which have been shaped for optimal aperture efficiency will not give sharp off-axis images. This is true for even quite small fields of view. The shaping to match feed horn illumination is at fault here; it leads inevitably to severe coma and curvature of the field. The analysis presented here is based upon geometrical optical computations.
04 Apr 1989
TL;DR: In this paper, a new form of microwave diagnostic imaging that enables sources of IMP on a reflector antenna to be located has been reported, using a paraboloid reflector.
Abstract: Reports on a new form of microwave diagnostic imaging that enables sources of IMP on a reflector antenna to be located. The problem of IMP generation by reflector antennas has been reported by a number of workers including Higa who observed IMP generation due to the metal-oxide-metal (MOM) junctions present on a large aluminium reflector antenna, and Ghione and Orefice who have reported on IMP produced by a carbon fibre reflector. Microwave holographic imaging is now a well established method of antenna diagnostics. By adapting these techniques it is possible to scan a reflector to locate sources of IMP on its surface. Initial obtained by these methods have already been reported, but the authors present further developments including results obtained from a paraboloid reflector.
26 Jun 1989
TL;DR: In this paper, a 5.5-in. diameter EHF/SHF dual-band reflector antenna was developed as an earth terminal for satellite communication, with minimal changes from an old design, demonstrating significantly higher antenna efficiencies at both hands.
Abstract: A new 5.5-in. diameter EHF/SHF dual-band reflector antenna was developed as an earth terminal for satellite communication. With minimal changes from an old design, this new design demonstrates significantly higher antenna efficiencies at both hands. The original design was a 5.5-in. diameter parabolic main reflector with a 1.87-in. focal length. One of the criteria for the new design is that the main reflector must stay the same. The single-shaped configuration with a parabolic main reflector and shaped subreflector turned out to be an excellent choice for this case. A test model was built and tested. Antenna gains of 27.0 dB at 20.7 GHz and 33.3 dB at 44.5 GHz, which are at least 0.5 dB higher than the antenna gain requirements, were obtained. >
26 Jun 1989
TL;DR: In this article, a closed-loop adaptive feed array system for compensating reflector surface deformations is investigated, which uses the concept of conjugate field matching to adjust the feed array complex excitation coefficients.
Abstract: The feasibility of a closed-loop adaptive feed array system for compensating reflector surface deformations is investigated. The performance characteristics (gain, sidelobe, level, pointing, etc.) of large communication antenna systems degrade as the reflector surface distorts mainly due to thermal effects from a varying solar flux. The compensating systems described here can be used to maintain the design performance characteristics independent of thermal effects on the reflector surface. The proposed compensating system uses the concept of conjugate field matching to adjust the feed array complex excitation coefficients. To demonstrate the concept a simulated distorted reflector case is presented with several element patterns. >
TL;DR: In this paper, two signal processing techniques are discussed that improve the accuracy of a microwave holographic measurement by removing unwanted signals from the aperture distribution: pattern simulation and subtraction, and time domain filtering.
Abstract: Two signal processing techniques are discussed that improve the accuracy of a microwave holographic measurement by removing unwanted signals from the aperture distribution: pattern simulation and subtraction, and time domain filtering. Pattern simulation and subtraction involves modeling unwanted scattering mechanisms and then removing them from the measured far-field data. Measurements taken on a focal point geometry and a Cassegrain geometry at 11 GHz were processed by the holographic analysis system. Pattern simulation and subtraction was applied to both geometries. Surface deformation profiles generated for the Cassegrain antenna by this system were compared to an optical measurement of the main reflector surface.
26 Jun 1989
TL;DR: In this paper, the reflector shape and the far field of the feed system are synthesized starting from the knowledge of only the dimensions and positions of the reflectors and feed region.
Abstract: Starting from the analytical properties of the scattered fields, a complete and simple operational relationship is established between the primary field and the secondary one. On this basis the reflector shape and the far field of the feed system are synthesized starting from the knowledge of only the dimensions and positions of the reflector and feed region. The technique makes it possible to synthesize essentially the same pattern with different reflector-feed couples, thus allowing the effects of the reflector shaping and the primary source extension to be balanced at the designer's convenience. The technique turns out to be numerically effective, as it is based on the use of fast Fourier transforms. >
04 Apr 1989
TL;DR: The authors discuss a proposed 12/14 GHz subsystem design which makes appropriate use of both a dual shaped reflector and a dual gridded reflector system within one subsystem.
Abstract: Satellite antennas are usually required to provide radiation patterns which match an irregularly shaped coverage zone. The two main techniques for achieving this shaping are multiple feeds or shaped reflectors. The authors discuss a proposed 12/14 GHz subsystem design which makes appropriate use of both a dual shaped reflector and a dual gridded reflector system. The application of the two technologies within one subsystem provides an opportunity to compare their performance and to examine the component technologies used by each.
26 Jun 1989
TL;DR: In this paper, an array-fed dual imaging reflector antenna at 36 GHz is described, which consists of a large parabolic main reflector fed from a small linear phased array via a confocal Gregorian subreflector.
Abstract: The author describes an array-fed dual imaging reflector antenna at 36 GHz. The antenna system comprises a large parabolic main reflector fed from a small linear phased array via a confocal Gregorian subreflector. The phased array is magnified by the two reflectors and an image of the near field of the phased array is formed on the aperture of the reflector. The scanning capability of the antenna system is demonstrated. Typical antenna patterns computed for a 100- lambda diameter main reflector operating at 36 GHz are shown. >
01 Feb 1989
TL;DR: In this article, a simple procedure is described for determining the excitation coefficients of an array feed which compensates for the surface distortion of a reflector antenna to improve the radiation pattern in such a way as to approximate the performance of the undistorted antenna.
Abstract: A simple procedure is described for determining the excitation coefficients of an array feed which compensates for the surface distortion of a reflector antenna to improve the radiation pattern in such a way as to approximate the performance of the undistorted antenna. A computer simulation for a practical feed array is presented as an example of compensation for the distortion of an actual antenna.
04 Apr 1989
TL;DR: In this article, Gaussian beam theory is applied to reflector antenna design and a suggested method for generalising inverse square law factors in a mixed Gaussian-ray geometry is illustrated.
Abstract: Procedures for applying Gaussian beam theory to reflector antenna design are discussed, and a suggested method for generalising inverse square law factors in a mixed Gaussian-ray geometry illustrated. These methods allow practical designs to be generated with almost negligible computation, in unusual geometries. In the practical elliptical antennas described, Gaussian beam concepts have led to a single-lens configuration, involving a real imaged waist in one plane. >
04 Apr 1989
TL;DR: In this paper, the authors discuss MM-wave compact antenna test range design (CATR) and describe the construction of a high precision reflecting surface and an MM-Wave CATR, and the performance of a CATR is evaluated both theoretically and experimentally.
Abstract: The authors discuss MM-wave compact antenna test range design (CATR), and describe the construction of a high precision reflecting surface and the construction of an MM-wave CATR. Reflector surface alignment is explained, and the performance of a CATR is evaluated both theoretically and experimentally.
Patent•
14 Nov 1989
TL;DR: In this article, a parabolic reflector with support means for mounting the antenna feed and/or receiver offset relative to the aperture of the reflector is designed for use in both C band and Ku band communications (3.65 GHz to 14.5 GHz).
Abstract: An antenna for use in both C band and Ku band communications (3.65 GHz to 14.5 GHz) comprises a parabolic reflector (10) with support means (14) for mounting the antenna feed and/or receiver (13) offset relative to the aperture of the reflector. The antenna is designed such that F/D is in the range 1 to 1.12 and d/D is in the range 0.052 to 0.11, where F is the focal length, D is the diameter of the projected beam of the reflector, and d is the displacement of the projected beam edge from the focal axis of the axisymmetric parent paraboloid of the reflector. The antenna is suitably fed by a low flare angle corrugated feed horn.
TL;DR: In this paper, the authors describe a method for providing phase shifts suitable for high-power applications, where the reflectors are closely spaced to form a dense array, and the array beam can be steered (within the beamwidth of a single reflector) by connecting the reflections through appropriate time delays or through phasers (phase shifters).
Abstract: Very large antenna apertures, for radioastronomy and other purposes, can be achieved through the use of an array of reflector antennas. When the reflectors are closely spaced to form a dense array, the array beam can be steered (within the beamwidth of a single reflector) by connecting the reflectors through appropriate time delays or through phasers (phase shifters). The letter describes a method for providing phase shifts suitable for high-power applications.
01 May 1989
TL;DR: A corrugated horn was designed and fabricated for use as a feed for the half-scale accurate antenna reflector as mentioned in this paper, which allows the reflector to be used in a compact range configuration as part of a microwave reflectance measuring system.
Abstract: A corrugated horn was designed and fabricated for use as a feed for the half-scale accurate antenna reflector This feed allows the reflector to be used in a compact range configuration as part of a microwave reflectance measuring system The horn design is described, and the measured farfield patterns of the horn are presented The horn was installed at the focus of the reflector, and the nearfield of the antenna was measured The results of these measurements are presented and discussed with respect to the compact range application
TL;DR: In this paper, a numerical approach to solving these equations is discussed which circumvents some of the difficulties encountered by Galindo-Israel et al., particularly for small values of theta.
Abstract: Synthesis of dual-shaped offset reflector antennas to control the exit aperture distribution of amplitude and phase has received considerable attention in recent years. For a given feed illumination and desired aperture field distribution, an exact formulation of the problem of simultaneously synthesizing the shapes of the sub and main reflectors was presented recently by Galindo-Israel et al. (1987) in terms of a set of nonlinear first-order differential equations. In this paper, a numerical approach to solving these equations is discussed which circumvents some of the difficulties encountered by Galindo-Israel et al., particularly for small values of theta.
TL;DR: A quasi-optical antenna with one elliptical reflector and one parabolic reflector has been built for millimeter wave scattering measurements on the TORTUS tokamak plasma at the University of Sydney as mentioned in this paper.
Abstract: A quasi‐optical antenna having one elliptical reflector and one parabolic reflector has been built for millimeter wave scattering measurements on the TORTUS tokamak plasma at the University of Sydney. This letter reports the first demonstration of the properties of such an antenna using a gyrotron millimeter wave source. Its advantages are (1) good two‐dimensional focusing (along the major radius and the toroidal directions) and (2) easy movement of the focus across the diameter of the plasma by changing the orientation of the parabolic reflector.