Design of dual-reflector antennas with arbitrary phase and amplitude distributions
01 Jul 1963-Vol. 12, Iss: 4, pp 403-408
TL;DR: In this paper, a generalization of the optical design is presented which allows the synthesis of reflector shapes for arbitrary phase and amplitude distributions in the aperture of the larger reflector with an arbitrary primary feed.
Abstract: Conventional dual reflector antenna systems have been based largely on the Cassegrain parabola-hyperbola design or the Gregorian parabola-ellipse design[1]. The designs are based on the principles of geometrical optics with consequent limitations. A generalization of the optical design is presented here which allows the synthesis of reflector shapes for arbitrary phase and amplitude distributions in the aperture of the larger reflector with an arbitrary primary feed. In contrast, a single reflector design permits either phase or amplitude control in the aperture. The analysis will be made for a surface of revolution and results presented for a uniform phase and amplitude case.
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TL;DR: The Arcminute Microkelvin Imager as discussed by the authors is a pair of interferometer arrays operating with six frequency channels spanning 13.9-18.2 GHz for observations on angular scales of 30 arcsec-10 arcmin and for declinations greater than 15°.
Abstract: The Arcminute Microkelvin Imager is a pair of interferometer arrays operating with six frequency channels spanning 13.9–18.2 GHz, for observations on angular scales of 30 arcsec–10 arcmin and for declinations greater than ?15°; the Small Array has a sensitivity of 30 mJy s?1/2 and the Large Array has a sensitivity of 3 mJy s?1/2. The telescope is aimed principally at Sunyaev–Zel'dovich imaging of clusters of galaxies. We discuss the design of the telescope and describe and explain its electronic and mechanical systems
241 citations
01 Dec 1973
TL;DR: In this paper, the aperture phase and amplitude distributions are sampled by a scanning field probe, and then the measured distributions are transformed to the far field by a plane wave that is created by a feed and large reflector in the immediate vicinity of the test antenna.
Abstract: In many cases, it is impractical or impossible to make antenna pattern measurements on a conventional far-field range; the distance to the radiating far field may be too long, it may be impractical to move the antenna from its operating environment to an antenna range, or the desired amount of pattern data may require too much time on a far-field range. For these and other reasons, it is often desirable or necessary to determine far-field antenna patterns from measurements made in the radiating near-field region; three basic techniques for accomplishing this have proven to be successful. In the first technique, the aperture phase and amplitude distributions are sampled by a scanning field probe, and then the measured distributions are transformed to the far field. In the second technique, a plane wave that is approximately uniform in amplitude is created by a feed and large reflector in the immediate vicinity of the test antenna. And in the third technique, the test antenna is focused within the radiating near-field region, patterns are measured at the reduced range, and then the antenna is refocused to infinity. Each of these techniques is discussed, and the various advantages and limitations of each technique are presented.
232 citations
TL;DR: In this article, a generalized diffraction synthesis technique for single and dual-reflector antennas fed by either a single feed or an array feed is presented, which combines optimization procedures and diffraction analysis such as physical optics (PO) and physical theory of diffraction (PTD).
Abstract: Stringent requirements on reflector antenna performances in modern applications such as direct broadcast satellite (DBS) communications, radar systems, and radio astronomy have demanded the development of sophisticated synthesis techniques. Presented in the paper is a generalized diffraction synthesis technique for single- and dual-reflector antennas fed by either a single feed or an array feed. High versatility and accuracy are achieved by combining optimization procedures and diffraction analysis such as physical optics (PO) and physical theory of diffraction (PTD). With this technique, one may simultaneously shape the reflector surfaces and adjust the positions, orientations, and excitations of an arbitrarily configured array feed to produce the specified radiation characteristics such as high directivity, contoured patterns, and low sidelobe levels, etc. The shaped reflectors are represented by a set of orthogonal global expansion functions (the Jacobi-Fourier expansion), and are characterized by smooth surfaces, well-defined (superquadric) circumferences, and continuous surface derivatives. The sample applications of contoured beam antenna designs and reflector surface distortion compensation are given to illustrate the effectiveness of this diffraction synthesis technique. >
181 citations
TL;DR: In this article, a technique for synthesizing reflector surfaces that transform a known input ray-field (e.g., the radiation field of a feed) to a desired output ray-fraction distribution is presented.
Abstract: A technique for synthesizing reflector surfaces that transform a known input ray-field (e.g., the radiation field of a feed) to a desired output ray-field (e.g. an aperture distribution) is presented. The synthesis problem is reduced to solving linear equations by local biparabolic expansions of the reflector surfaces. Because the solution is easier to control, this is advantageous compared to existing techniques based on solving nonlinear differential equations. The condition to obtain low cross polarization can therefore be readily included, and the requirements for an exact solution to exist can be found clearly. The latter has been the subject of discussion in the literature for several years. The synthesis technique is applied to a shaped-offset dual-reflector antenna and to the proposed dual-reflector feed of the spherical reflector antenna in Arecibo. In both cases circular and elliptical apertures are considered. >
86 citations
TL;DR: In this article, a solution of the inverse problem consisting of reconstructing the reflector R from the following data: the position of the source O, its radiation intensity I, the object T, and prespecified energy pattern to be achieved on T was presented.
Abstract: Consider a reflector system consisting of a reflecting surface R, a point light source O and some object T. Suppose that the source O, reflector R and object T are positioned so that the rays reflected off R are incident on T. Depending on the geometry of R, the energy, radiated by O and redirected by R, is distributed on T producing a certain illumination pattern. We present here a solution of the inverse problem consisting of reconstructing the reflector R from the following data: the position of the source O, its radiation intensity I, the object T, and prespecified energy pattern to be achieved on T. It is shown that under assumptions of geometric optics theory the problem admits a solution, provided the total input and output energies are equal, and some other geometric conditions are satisfied. In analytic formulation, the problem leads to an equation of Monge - Ampere type in a domain on a unit sphere. In this paper we formulate the problem in terms of certain associated measures and establish the existence of weak solutions.
85 citations
References
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TL;DR: In this paper, the fundamental performance of a Cassegrain double-reflector system was analyzed by means of the equivalent-parabola single reflector concept, and a set of polarization-operative surfaces was developed for these twisting antennas.
Abstract: A microwave antenna can be designed in the form of two reflecting dishes and a feed, based on the principle of the Cassegrain optical telescope. There are a variety of shapes and sizes available, all described by the same set of equations. The essential performance of a Cassegrain double-reflector system may be easily analyzed by means of the equivalent-parabola single-reflector concept. Techniques are available for reducing the aperture blocking by the sub dish of the Cassegraln system: one method minimizes the blocking by optimizing the geometry of the feed and sub dish; other methods avoid the blocking by means of polarization-twisting schemes. The former method yields good performance in a simple Cassegrain antenna when the beamwidth is about 1\deg or less. The latter methods are available for any application not requiring polarization diversity, and an optimized set of polarization-operative surfaces has been developed for these twisting Cassegrain antennas. Experimental results, presented for practical antennas of both types, illustrate the feasibility of these principles. A number of unusual benefits have been obtained in the various Cassegrain antenna designs, and additional interesting features remain to be exploited.
192 citations
01 Oct 1948
TL;DR: In this paper, a method based on conservation of energy and the simple laws of geometrical optics is described for the calculation of double-curvature surfaces to produce from a point source a shaped beam of arbitrary shape in one plane and uniformly narrow in the perpendicular planes.
Abstract: A method based upon conservation of energy and the simple laws of geometrical optics is described for the calculation of double-curvature surfaces to produce from a point source a shaped beam of arbitrary shape in one plane and uniformly narrow in the perpendicular planes. A specific application of the shaped-beam antenna is in connection with radar antennas for airborne navigational systems, for which the optimum elevation pattern is found empirically to be G(0) = Kcsc20 cos 0. A reflector to produce from a given primary source the required pattern is the envelope of a family of paraboloids determined by a central-section curve which is adjusted to give the necessary distribution of energy for the shaped beam. A test for the single-valuedness of a computed surface is described. Patterns are shown for experimental antennas whose reflectors were computed by this method. It is demonstrated that some control of the antenna pattern can be achieved by proper motion of the antenna feed. A discussion of errors is included in an Appendix.
48 citations