Showing papers on "Cassegrain antenna published in 1976"

Microwave holographic metrology of large reflector antennas

Abstract: A microwave holographic technique for the determination of amplitude and phase of the principal and cross-polarized aperture fields of large reflector antennas is described. The hologram formation process utilizes the elevation over azimuth scanning system normally associated with these antennas, and, in this respect, appears to be unique among other proposed methods of field probing. The present work describes the means used to obtain vital information on the antenna structure such as E - and H -plane phase centers of the feed, and rms values of the reflector surface profile errors. Accurate prediction of E - and H -plane radiation patterns in the near- and far-field is also demonstrated.

Some highlights in reflector antenna development

Abstract: Reflector antennas have been used since the radio pioneering era of Lodge, Hertz, and Marconi, but it took the exigent demands of radar in World War II to stimulate a real development in the reflector art. Subsequent interest in the science of radio astronomy and the inception of microwave ground communication links were responsible for a burgeoning growth in the field, so that in the 1940s and 1950s the design principles and requirements for prime focus fed systems were well established. Cassegrain, or secondary focus systems, and horn reflectors came into prominence in the early 1960s with the advent of satellite tracking and communication networks. The desire to maximize the gain, or the gain-temperature ratio, then led to development of sophisticated techniques for properly shaping the illumination over the reflector aperture in order to maximize efficiency and minimize spillover, among them being the shaping of the sub-reflector in Cassegrain systems and the use of multimode and hybrid mode feed horns. Not all reflector antennas utilize paraboloidal surfaces. Some recent developments in line source feeds make the spherical reflector attractive for scanning applications and the conical reflector for deployable, space-borne antennas. The large 1000-foot diameter reflector at Arecibo is a well known example of the former. Although some extremely large spaceborne reflector antennas have been proposed and studied, the largest now in use appears to be the unfurlable 30-foot reflector carried by ATS-6. Finally, some gain comparisons are given for a few of the (electrically) largest reflectors that have been built both for radio astronomy and for space communications. If some milestones in reflector development have been overlooked it is due to the limitations inherent in a review paper.

Analysis of the radiation patterns of reflector antennas

Abstract: The development and application of a numerical technique for the rapid calculation of the far-field radiation patterns of a reflector antenna from either a measured or computed feed pattern are reported. The reflector is defined by the intersection of a cone with any surface of revolution or an offset sector of any surface of revolution. The feed is assumed to be linearly polarized and can have an arbitrary location. Both the copolarized and the cross polarized reflector radiation patterns are computed. Calculations using the technique compare closely with measured radiation patterns of a waveguide-fed offset parabolic reflector. The unique features of this technique are the freedom from restrictive feed assumptions and the numerical methods used in preparing the aperture plane electric field data for integration.

The design of correcting secondary reflectors

Abstract: A computer program called DERIVE is described for the design of the reflecting surfaces of two-mirror radio telescopes. It calculates the shape of a secondary reflector to any given primary by use of geometrical optics, yielding zero path length errors for all paraxial rays. The only condition to be fulfilled is (for Cassegrain types) that incoming rays, after reflection at the primary, do not cross each other before reaching the secondary. Equations for this condition are given. This method can be used to improve existing telescopes at short wavelengths by correcting for the surface deviations of the primary reflector with a specially shaped secondary. The results of 17 calculated examples are described, for various types of deviations

L-band radar antenna array

Abstract: A stripline horizontally polarized dipole and passive director antenna ar, operative at L-band (1220-1280MHz), mounted in a 90° corner reflector constructed of a grid of cylindrical rods which are hinged along its apex permitting folding of the reflector over the antenna array to protect the elements of the array, for example, during transport.

Wide angle scanning antenna assembly

Abstract: An antenna assembly wherein the direction of a beam of radio frequency energy may be changed by combining the effects of a mechanically movable reflector and an electromagnetic lens is disclosed. In the preferred embodiment the antenna arrangement includes a corporate monopulse feed arranged to produce a linearly polarized divergent beam which is first reflected from a linearly polarized paraboloid to direct a convergent beam toward a mechanically rotatable polarization-twisting reflector. A selected portion of a spherical electromagnetic lens arrangement is illuminated by the still convergent beam from the latter reflector, such lens then determining the direction of the beam finally propagated in free space. The relative positions of the corporate monopulse feed, the linearly polarized paraboloid, the mechanically rotatable polarization-twisting reflector and the characteristics of the spherical electromagnetic lens arrangement are selected so that, for a given antenna assembly for electromagnetic energy of a given frequency, the linearly polarized divergent beam from the corporate monopulse feed is converted to a substantially collimated beam in free space.

On the front to back ratio of a parabolic dish antenna

Abstract: Adopting the earlier work of Kouyoumjian's Ohio State group, as recently reviewed and extended by Rusch, an explicit expression for the radiation field in the back zone of a typical parabolic dish antenna is obtained. Evaluation of this expression directly in the back for both the ideal 100 percent aperture efficiency feed and for an arbitrary, feed gives (in conjunction with the known front field for the 100 percent case) the front to back ( f/b ) ratio for the arbitrary feed case of (f/b) = G + T + K - G horn . Here G is the gain of the dish with the arbitrary feed, G horn is the on axis gain of the feed, T is the feed's average pattern edge taper relative to on axis, K = 20 \log_{10}{\sqrt{1 + 16(F/D)^{2}}/4(F/D)} (all being in decibels), and F/D is the ratio of the focal length to the dish diameter. Comparison of this result with measured values for dishes ranging from 6 to 15 ft in diameter operating over a 920 MHz to 14 GHz range gives an agreement within several decibels in most cases.

Satellite tracking cassegrainian antenna

Abstract: An antenna apparatus comprising a primary radiator having an axially symmetric field pattern, and a main reflector and a subreflector coupled to the primary radiator through a beam wave-guide path. The antenna rotating axis is aligned with the axis of the primary radiator but a little deviated from the polar axis or the earth. At least one movable beam waveguide reflector or electromagnetic lens is provided in a radio wave path between the primary radiator and the subreflector. The antenna rotating axis is adapted to be rotatable only within a small angular range. The beam wave-guide reflector or electromagnetic lens is moved to thereby deflect the antenna beam.

Fields in the focal region of offset parabolic antennas

Abstract: An analysis which provides the electric field distribution in the focal region of an offset parabolic reflector as a function of small scan angle has been performed. Formulae which predict both the principal and cross polarized fields have been obtained. These formulae are relatively simple and compact, provide a useful design tool, and allow efficient computer calculation. The results obtained from these formulae compare favorably with results obtained by other authors.

Matched-Feeds for Offset Parabolic Reflector Antennas

Abstract: In many practical applications the performance of offset parabolic reflector antennas are limited by the reflectors' depolarising and beam-squinting properties. The paper describes progress in the development of a new class of primary-feed antennas which overcome these major limitations. Computed data based upon analytical models of the antennas and experimental results obtained from antennas constructed for operation at 30 GHz are presented for applications which include both communications and tracking radars.

Switching subreflector for millimeter wave radio astronomy

Abstract: A method of beam switching a Cassegrain antenna used for radio astronomy by tilting the hyperbolic secondary reflector is described. The system described has been in use for over a year at the 11‐m millimeter wave antenna operated by the National Radio Astronomy Observatory at Kitt Peak, Arizona.

Reflector with frequency selective ring of absorptive material for aperture control

Abstract: An antenna is made operative for two frequency bands, ΔFB and ΔFH, the latter higher than the former, by means of a frequency selective absorber, covering, in its edge region, a reflector of the antenna in order to reduce the diameter of the reflecting surface of the reflector and therefore the gain of the antenna for frequency band ΔFH.

Improvement of TE 11 mode coaxial waveguide and horn radiation patterns by incorporation of a radial aperture reactance

Abstract: The TE_{11} mode coaxial waveguide or horn radiator provides a natural geometry for multiple frequency confocal feeding of a paraboloid reflector antenna system. Its radiation patterns, however, are generally characterized by unequal E - and H -plane beamwidths and high E -plane sidelobe amplitudes. These characteristics become increasingly more obvious for coaxial radiators designed to illuminate reflector systems requiring feeds with reduced fields of view, such as the symmetrical paraboloid reflector antenna with large focal-length-to-diameter ratio or the offset paraboloid reflector antenna. Left uncorrected, these feed characteristics severely limit the available antenna performance. Incorporation of a radial reactive iris in the aperture plane of a TE_{11} mode coaxial radiator has been found to produce rotationally symmetric pattern characteristics with reduced sidelobe levels. This paper describes an approximate technique for determining the radiation patterns of a TE_{11} mode coaxial radiator with a radial aperture reactance. Experimental results are shown that reveal the pattern improvements predicted by the analysis. A multiple frequency coaxial feed that employs radial aperture reactances is capable of providing the aforementioned reflector systems with a high performance capability.

Frequency scanned corner reflector antenna

Abstract: The frequency scanned corner reflector antenna is a modified corner refler antenna that incorporates a feeding technique to achieve monopulse or sequential lobing radiation patterns in one principal plane and one or more frequency-scanned beams in the other principal plane. Scanning of the beam of the corner reflector antenna for direction finding and tracking applications is accomplished without destroying the unique monopulse and sequential lobing capabilities of the antenna.

Line scan radar antenna using a single motor

Abstract: According to the present invention, radar rays are reflected off a rotatingecondary reflector which is both tilted with respect to and synchronously translated, in simple harmonic motion, in a direction transverse to the axis of rotation of the secondary reflector. The combined effect of the tilting and translating of the secondary reflector is to produce a line scan when the rays from the secondary reflector are reflected off a primary reflector.

Dual scan corner reflector antenna

Abstract: The dual scan corner reflector antenna is a frequency scanned antenna for dar, direction finding, or guidance systems which provides increased information gathering capacity over that of prior art systems. The antenna utilizes a helix frequency scanning feed to drive a dipole antenna array. Each output port of the feed is connected to a power divider or combiner to form a common line to the antenna element. At each end of the helix frequency scanning feed are hybrid terminals used to simultaneously form two receive or transmit radiation patterns. The respective helix feed couplers have symmetrical values about the center of the helix feed, allowing the two radiation patterns to be mirror images of each other at the same frequencies. These two radiation patterns can be scanned simultaneously and independently.

Beam squint in a linearly polarised offset reflector antenna

Abstract: A beam squint has been found to occur in the field radiated by an offset paraboloid antenna illuminated by a feed with linear polarisation in the plane of offset The squint, whose existence has been confirmed by computed and measured radiation patterns, occurs in the offset plane, and is typically 003 of a beamwidth for a reflector of 6-wavelengths diameter An assessment is given of the likely effect of the squint on the performance of an offset reflector radiating a circularly polarised field

Optimum Design of Corrugated Feeds for Low Cross-Polar Radiation

Abstract: The paper describes the prediction and measurement of the cross-polar radiation from corrugated feeds. The influence of the flange, periodicity of the corrugations and corrugation depth is identified and design recommendations are made. Satisfactory agreement between experimental measurements and theoretical predictions are demonstrated for feeds which are suitable for use at the prime focus or secondary focus of a reflector antenna.

Dish antenna with impedance matched splash plate feed

Abstract: A directional microwave antenna system comprising a concave reflector fed by a wave guide and splash plate assembly. Two rectangular apertures in the wave guide at the focus of the reflector admit energy to and from the splash plate. Impedance matching tabs protrude into the rectangular apertures to match the antenna system. Rectangular tabs provide improved VSWR, high side-lobe reduction with the reflector on-axis. Circular tabs provide improved VSWR and good side-lobe reduction with the reflector on or off axis.

Parametric study of the crosspolarisation efficiency of parabolic reflectors

Abstract: The crosspolarisation efficiency of a reflector antenna is the ratio between the peak crosspolarisation from the complete antenna to that from the feed. The results of a parametric study into this factor for parabolic reflectors fed by a mathematical model of a common class of feeds are presented, and it is concluded that the efficiency is typically −4 to −6 dB.

1.2. Types of Astronomical Antennas

Abstract: Publisher Summary This chapter discusses different types of astronomical antennas. The pattern of the pencil-beam antenna has one main lobe or maximum with a single-output terminal pair or a few main lobes each with its own separate output. The output at a single terminal pair corresponds to one main lobe for only one sense of polarization: linear, circular, or elliptical. The most common antenna used for radio astronomy is the parabolic reflector with the feed horn or dipole located at the parabolic focus. One principal advantage of this antenna is the ease with which the receiver may be coupled to it. The input terminals are at the feed horn or dipole. Operation over a wide range of wavelengths is simple; changing from one band of wavelengths to another requires only the change of the feed. The multi-element interferometer consists of a number of two-element interferometers operating simultaneously. The outputs of all the antenna elements are combined in pairs and recorded at the same time. The result is a system that can complete the aperture synthesis for a given region of the sky in a time shorter than that required by a simple two-element telescope.

A modular off-set Cassegrain antenna operating simultaneously in four frequency bands

Abstract: The increasing in capacity on Radio Links and the limitation in places on the tower lead to group on the same antenna, as much as possible, a maximum of frequency plans. The principal frequency bands are : 1.7-2.3 GHz for 960 telephone channels (T. C) equipment, 3.6-4.2 GHz for 1800 T. C, 5.925-6.425 GHz for 1800 T.C, 6.43-7.11 GHz for 2700 T. C and 10.7-11.7 GHz for 1800 T. C. The antenna, which is, object for this paper, can operate simultaneously with four, three or two of these four frequency bands. This antenna consists of : a radiating part and a microwave multiplexer part.

Filtering secondary mirror for a dual-band Cassegrain reflector antenna

Abstract: A dual-frequency Cassegrain reflector antenna has been investigated in which the secondary mirror is constructed from a stack of waveguides. The secondary mirror behaves as a highpass filter, giving access to the prime-focus feed position at the higher-frequency band. The copolar and crosspolar radiation patterns are discussed.

Symmetric reflectors with zero depolarisation

Abstract: The polarisation performance of a symmetric reflector antenna illuminated by an ideal feed is limited by depolarisation introduced by the reflector, even if other sources of cross-polarisation are negligible. It is shown that depolarisation can theoretically be eliminated by the use of anisotropic reflectors.

A Four-Step-Ladder-Type Loop Antenna with a Plane Reflector

Abstract: UHF, VHF帯のテレビ送信用アンテナとして正方形の1波長ループを4個はしご状に配列し, その後部に反射板を付加したアンテナを提案し, 電流分布と指向性について, 実験および近似理論計算の結果を示した.このアンテナは簡単な構造ではあるが, 指向性の周波数に対する変化が少なく, 垂直面内にヌル点が存在しない特徴があり, 比較的高利得なアンテナである.