Showing papers on "Feed horn published in 1974"

Cassegrain antenna with improved subreflector for terrestrial communication systems

Abstract: A Cassegrain antenna for use in terrestrial communication systems. The antenna has the conventional subreflector including a central area which provides tapered illumination of the entire main reflector, and a peripheral area which directs spillover from the central area onto the peripheral portion of the main reflector to improve the uniformity of illumination of the main reflector, thereby improving illumination efficiency and reducing gain loss due to spillover. The central and peripheral areas of the subreflector are preferably both surfaces of revolution of conic sections of the same kind, such as hyperboloids, ellipsoids or paraboloids, although the peripheral area may be a frustoconical surface if desired. The virtual focal points of the two conic sections of the subreflector are both coincident with the phase center of the feed horn.

Large lateral feed displacements in a parabolic reflector

Abstract: The radiation patterns of a parabolic reflector with large lateral-feed displacements are computed utilizing both the vector current method and scalar aperture theory, and compared to experimental results. The theory is general enough to include asymmetric primary pattern illumination. The scalar and vector solutions are derived from the same initial equation so that the approximations used in obtaining the scalar solution are clearly displayed. Results from the vector and scalar theories are compared and the range of validity of the approximate analysis is indicated.

Highly efficient antenna system using a corrugated horn and scanning hyperbolic reflector

Abstract: In a horn-reflector antenna system for producing a spherical aperture phase front, a corrugated conical horn illuminates a section of a hyperbolic reflector to produce a spherical aperture phase front which produces a far-field beam with low sidelobes and high beam efficiency. The system is insensitive to frequency and polarization changes, and is also insensitive to orientation about the axis of the conical horn for beam scanning.

Cross-polarized parabolic antenna

Abstract: A cross-polarized parabolic antenna employs a horn fed by two rectangular waveguides having their longer transverse dimension in a common plane, with a 90 DEG polarization rotator in the feed between the connection points of the waveguide.

A new class of medium-size high-efficiency reflector antennas

Abstract: The new class of reflector antennas that is described in this communication yields a higher directive gain than obtained with conventional reflector antennas of the same area. An antenna of this new design consists of a reflecting surface, a peripheral rim, and a feed system in the reflector center. It is analyzed as a combination of two radiating sources whose radiation maxima and mutual phase relations can be simply adjusted for highest directive gain in the axis normal to the reflector. The marked directive gain increase is explained on the basis that there is a virtual extension of the radiating aperture beyond the physical dimensions of the reflector. The two antenna models that are described develop directive gains of almost 3 dB above those of conventional reflector antennas of equal size and comparable pattern characteristics. Optimized for a given frequency, the new design covers a pattern bandwidth of approximately 4:1.

Dual frequency feed horn using notched fins for phase and amplitude control

Abstract: A dual frequency band horn-type antenna feed is described which has primary application to optimally illuminate a parabolic cylindrical reflector operating simultaneously at high power in both of the two bands. The principle of the invention is applicable to any two frequency bands regardless of their frequency separation including coincidence as a limiting case. The basic requirement of such a feed is that it must be as directive as possible within constraint of the feed aperture size in the plane of the cylinder axis because the cylindrical reflector does not collimate the beam in this plane and it must be relatively nondirective in the plane of the parabola for efficient illumination of the reflector. This requirement requires the phase front in the directive plane to be controlled within a small fraction of a wavelength at both frequencies.

Method of forming a feed horn

Abstract: A method of forming a plastic microwave feed horn by first forming a mandrel which is thereafter incorporated into a mold apparatus.

Large reflector antenna pattern computation using moment methods

Abstract: A technique, whereby the radiation patterns of large size reflector antennas can be approximated by computers using a moment method without excessive computer time or memory, is described. Computational time increases only linearly with antenna size. There is no limit on the minimum reflector size (a single wire reflector can be analyzed). An example is discussed showing the radiation patterns of a truncated parabolic reflector excited by feeds displaced from the parabola focus.

Pattern shaping with hybrid mode corrugated horns

Abstract: Hybrid modes in a square corrugated waveguide are investigated, and a technique of combining several modes for pattern shaping is described The mode amplitudes are calculated from a known throat excitation and used to compute radiation patterns One horn was designed, constructed, and tested The theoretical patterns were in good agreement with experimental data

Optimum designs of broad and narrow band parabolic reflector antennas fed with log-periodic dipole arrays

Abstract: The Log-Periodic Dipole Antenna (LPDA) is attractive as a broadband feed for paraboloid reflectors despite its tendency to cause defocusing owing to axial phase-center movement with frequency. The gain loss due to defocusing in a parabolic reflector is only a function of the defocusing in terms of wavelengths and not dependent on the diameter of the reflector. Hence, antennas such as the LPDA which have a frequency independent phase center location in terms of wavelengths from some geometrical point (virtual apex) will experience a frequency independent defocusing loss over its bandwidth if the virtual apex is placed at the focal point. The optimum feed design for maximum gain will change with varying reflector f/D (reflector focal length to diameter ratio) since spillover, aperture illumination, and defocusing loss are functions of f/D, while primary pattern beamwidth and symmetry, gain and VSWR are functions of the feed parameters.

Vertical plane pattern calculations for shaped beam reflectors with multiple feeds

Abstract: The calculation of approximating vertical plane radiation patterns for doubly curved shaped beam antenna reflectors illuminated by a multiple feed is discussed. Separability of the vertical and horizontal plane patterns is assumed. A calculated example for a two-element feed is compared with measured pattern data. Farfield pattern shaping behavior with multiple feed excitation is described in terms of vector superposition of the patterns due to the individual feed elements.

Optimum design of horn feeds for reflector antennas

Abstract: A method of determining the optimum dimensions of a horn feed for a parabolic reflector using the power transferred to the feed as a criterion is described. To reduce the computation time, the focal plane and feed-horn aperture field distributions were expanded into finite power series whose coefficients were determined using collocation techniques. The paper extends previous work to include horns with flare angles greater than 10\deg and contains useful design curves.

Wide-angle sectoral horns using leaky-wave wall structures

Abstract: A lensless method of phase correction for wide-angle sectoral horns is presented. It consists of supplying the narrow walls of the horn with a leaky-wave interface corresponding to a fast phase velocity. An analytical expression of the radiated field is derived by operating the Fourier transform of the theoretical distribution, and a set of theoretical radiation patterns are presented. The limitations of this type of correction, as far as bandwidth is concerned, are also examined theoretically. Two horn antennas illustrating this method of correction are described: an E -plane sectoral horn and an H -plane sectoral horn. Both have a flare angle of 120\deg and an aperture of 6\lambda . The H -plane horn uses a longitudinal U -shaped section, and the E -plane horn a transversely slotted rectangular waveguide. Both of them are measured with and without correction, and the experimental results are compared with the theoretical predictions.

One-Hybrid-Mode Feed with High Aperture Efficiency and Low Spill-Over

Abstract: A new class of one-hybrid-mode primary focus feed with high aperture efficiency and low spill-over is described These antennas are suitable for use in deep parabolic reflectors (F/D<035) The propagation characteristics in the horn and far field radiation pattern are derived The antenna efficiency and spill-over are computed Finally, the comparison between the theoretical and experimental radiation pattern and possible applications are discussed

Coupling between crossed-dipole feeds

Abstract: Various effects of coupling between crossed-dipole antennas are analyzed and by using an arbitrary feeding network some generality is preserved With one cross excited and another cross acting as a parasitic loaded antenna, coupling losses and gain and polarization losses are presented as a function of orientation and feeding network properties The antennas are used as feeds for a parabolic reflector, and the effect of coupling on the secondary fields is analyzed Especially significant is the polarization loss and it may, to some extent, be reduced by a proper choice of feeding network

Time domain aperture antenna study, volume 2

Abstract: : This research employs a direct time domain model applicable to aperture antennas of any shape excited by fields of any form in space and time to study theoretically the electromagnetic far fields of a paraboloid reflector when fed by a transverse electromagnetic (TEM) horn antenna. First, the TEM horn antenna is considered as an aperture antenna with an arbitrary excitation V(t) applied to its apex. The time domain model is then applied to determine the electric far fields of the TEM horn, and the theoretical results are compared with published experimental data on a relative basis. Reasonable agreement is obtained. Approximate closed form solutions for the electric far fields of the TEM horn in the azimuth plane are also found. Secondly, the TEM horn is studied in terms of current sheets using the vector potential formulation in order to confirm the approximate closed form solutions found in the azimuth plane using the aperture model.