Showing papers on "Feed horn 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.

Radio frequency beam forming network

Abstract: A radio frequency beam forming network is disclosed wherein a plurality of antenna feed elements arranged in the focal plane of a radio frequency lens is coupled to corresponding input ports of a radio frequency energy distributing means. Output ports of such radio frequency energy distributing means are coupled to a receiver/transmitter through different paths. Disposed in the different paths are active elements, including variable phase shifters and attenuators. The active elements, in response to control signals, provide proper attenuation and phase shift to the signals passing therethrough thereby to form a desired antenna beam. Such antenna beam is comprised of one or more "spot" beams. With such arrangements failure of a single one of the active elements will only slightly degrade system performance without resulting in a complete loss of any one of the "spot" beams.

Broadband corrugated horn with double-ridged circular waveguide

Abstract: A broad band corrugated horn antenna with a double-ridged circular wavegu feed is disclosed in which the horn is driven by the wide band signal source having a bandwidth greater than 2:1. The bandwidth is accomplished by providing a ridge pattern with gaps therebetween in which the width of the gaps is greater than the width of the ridges.

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.

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.

Investigation of a 90° corrugated horn

Abstract: Wide-angle corrugated horns have found important practical applications as feeds for front-fed reflector antennas when low levels of crosspolarisation are required. A theoretical study has been carried out on the 90° corrugated horn for a structure possessing an 'arbitrary, but finite, number of corrugations. Computed and measured results are shown to be in good agreement for a horn possessing three annular slots.

High resolution side-looking airborne radar antenna

Abstract: A feed horn mounted within a streamlined enclosure upon the top surface of a wing of an aircraft at an outwardly-spaced location to direct electromagnetic wave energy toward the face surface of a dielectric slim lens having a metallic reflector between the lens and the fuselage of the aircraft to effect a double-traversal of the incident wave energy. The metallic reflector is planar or parabolic to trim the aerodynamic cross section. When the metal skin of the fuselage is used as the reflector, the dielectric constant of the lens is modified by varying its thickness to produce a very sharp beam by compensating for the curvature of the fuselage at the lens support site.

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.

Square horn antenna having improved ellipticity

Abstract: A multisided horn antenna such as a square horn is disclosed having an improved axial ratio circular polarization or ellipticity. Ellipticity of a square horn antenna is improved by placing a conical section or ring of conductive material at the aperture of a horn antenna. The conical ring causes a relatively directive beam having a low axial ratio to be produced throughout most of the pattern generated similar to that of a conical horn antenna. Yet, the square horn antenna provides increased power over a conical horn.

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.

Analysis and Synthesis of Corrugated Conical Horns

Abstract: The characteristics of corrugated conical horns, radiating the balanced hybrid mode HE11 have been summarized in a number of linear curves giving the beam width at different levels versus the horn flare angle (2?) and versus the radius of the horn aperture, normalized to the wavelength (? = r/?). Moreover the feed horn performance for single or double reflectors antennas, have been analysed and curves are presented for the antenna illumination efficiency (aperture efficiency by spillover efficiency) versus parameters d and a. All the curves reported are a useful basis for the antenna design and give a fast and accurate solution to the following problems: - synthesis of a corrugated conical horn with a specified amplitude radiation pattern - synthesis of a corrugated conical horn as a function of the antenna illumination efficiency.

Apparatus for testing metal detectors

Abstract: An apparatus and method for testing low-power, low-band radio frequency metal detectors of the type employing a radio transmitter alone or a transmitter and a receiver. The apparatus is characterized by a variable voltage power supply, a transmitter, an antenna, a voltmeter, a rectifier connected to the voltmeter, a switch for connecting the rectifier to either the antenna or the power supply and for selectively energizing the transmitter, and a surface placed in a fixed position relative to the antenna and defining the proper position for placement of the equipment under test.

Raising the crossover level of dual-beam parabolic antennas

Abstract: A method for raising the crossover level of dual-beam parabolic antennas is shown. Controlled coupling between the primary radiators, with the input ports almost decoupled simultaneously, can be applied to front-fed linearly polarised parabolic antennas of about 10° beamwidth. Mention is also made of a second method with lossy directional couplers.