Showing papers on "Fresnel zone antenna published in 1977"
TL;DR: In this article, it is shown that the separation of the co-and cross-polar components of the primary field does not depend on the symmetry of the antenna, and that it holds even for off-set fed reflectors.
Abstract: It is well known that focussed, axial symmetrical reflector antennas collimate the co- and cross-polar components of the primary field separately, i.e., the reflector does not create a contribution to the cross polarization of the far-field. By a simple extension of a classical physical argument it is demonstrated that this separability does not depend on the symmetry of the antenna, and that it, therefore, holds even for off-set fed reflectors. A new mathematical formulation of the collimation is derived in which this is shown. Yet the separability does depend on how the co- and cross-polar fields are defined, and the cross polarization of feeds for asymmetric reflectors is discussed in detail in the light of this. It is further suggested how to design low cross polarization feeds for off-set fed antennas. As a consequence of the separate collimation such feeds will lead to low cross-polarization of the secondary fields. Two simple examples are treated. The only limitations of the results are those due to the application of the aperture field version of the physical optics approximation.
23 citations
TL;DR: In this article, a method for removing the wavefront error caused by an Optically recorded Fresnel zone plate for laser beam scanning is discussed, and the feasibility of the method is demonstrated.
Abstract: Optically recorded Fresnel zone plates have proper spatial frequency characteristics for use as a laser scanner. Such grating scanners can easily be made and can scan over large cone angles with, however, severe aberrations of the diffracted laser beam at large deflection angles. Optically recorded Fresnel zone plates for laser beam scanning are investigated, and their aberration properties are analyzed. A method for removing the wavefront error caused by this type of zone plate is discussed, and the feasibility of the method is demonstrated.
19 citations
TL;DR: In this paper, an analytical model of a class of electrically small multiturn loop antennas has been formulated and compared with experimental measurements over a frequency range of 3 to 86 MHz.
Abstract: An analytical model of a class of electrically small multiturn loop antennas has been formulated and compared with experimental measurements over a frequency range of 3 to 86 MHz. Both air core and magnetically loaded eases were examined. Transmitted signal enhancement as high as 10 dB was predicted and observed by magnetic loading. Several interesting properties of the transmitting antenna were investigated experimentally and by analysis based upon the model. It is concluded that transmitted signals can be enhanced in the 2-30 MHz range, at reasonable power levels, as much as 10 dB with state-of-art ferrite materials. Secondly, the analytical model described in this paper should prove an effective design aid for a volumetrically constrained antenna of the class.
18 citations
TL;DR: Tilting the antennas up to obtain 2 dB loss (for each antenna) over maximum gain during steady signal conditions is shown to reduce fading over this particular path as mentioned in this paper, and the technique should also work on other paths where sufficient angular separation between the direct and reflected rays exists, and where antennas with sufficiently "sharp" main beams are used.
Abstract: Tilting the antennas up to obtain 2 dB loss (for each antenna) over maximum gain during steady signal conditions is shown to reduce fading over this particular path. The technique should also work on other paths where sufficient angular separation between the direct and reflected rays exists, and where antennas with sufficiently "sharp" main beams are used.
15 citations
01 Mar 1977
TL;DR: In this paper, the authors show that axially symmetric reflector antennas can be reduced, theoretically, to zero by use of special feeds like the Huygens' source.
Abstract: Cross-plarization in axially symmetric reflector antennas can be reduced, theoretically, to zero by use of special feeds like the Huygens' source. Alternatively, paraboloidal reflectors with large f/D ratio do not deteriorate further the cross polarization level relative to the value due to the feed itself. The Cassegrainian optics is equivalent to a large f/D paraboloid. The reflector of linearly polarized off set fed antennas contribute more cross-polarization than symmetrical reflectors fed by the same feed. With symmetrical reflectors the cross-polarized component generated by the reflector vanishes in the principal planes and is confined to four main lobes that have peak values in planes at 45° to the principal planes. In the case of offset fed reflectors cross-polarization vanishes in the plane of symmetry and has its peak in the plane of asymmetry. The reflector generated cross-polarization with offset fed antennas may be reduced by use of small offset angles and large f/D ratios. Feed offsetting has but little effect on the peak level of cross-polarization. This is usually accompanied with an asymmetry in the cross-polarization radiation pattern. Feed offsetting also results in spatial tilt in the copolarized and cross-polarized lobes with the cross-polar minimum always coinciding with the main beam peak. The effect of surface errors on the antenna cross-polarization is to partly fill the cross-polar along boresight. The peak cross-polarization, however, changes but slightly.
10 citations
TL;DR: Analysis of data shows that gain antennas have significantly less gain in areas where multipath propagation predominates and that the increased aperture of the gain antennas provides no significant smoothing of the received signals in the multipath environment.
Abstract: A program has been completed that investigated the effect of the urban multipath environment on mobile antennas at 900 MHz. The program involved the construction of several mobile antennas, careful measurement of these antennas on an antenna range to determine their characteristics in a controlled environment, and measurement of their characteristics in the multipath environment of cities. Measured results were compared to computed results and pattern range results were compared to field data to permit generalized conclusions to be reached. The results of the second phase of the program, measurements made in the mobile multipath environment, are presented. Analysis of this data shows that gain antennas have significantly less gain in areas where multipath propagation predominates and that the increased aperture of the gain antennas provides no significant smoothing of the received signals in the multipath environment.
10 citations
TL;DR: In this article, a simplified analytical method to predict the field distribution in the focal region of dual reflector antennas having circular symmetry is presented, which is used to analyze the ability of the antenna in focusing the incident wave.
Abstract: A simplified analytical method to predict the field distribution in the focal region of dual reflector antennas having circular symmetry is presented. The method is used to study the field distribution at the subdish and in the focal plane, and hence the ability of the antenna in focusing the incident wave. Experimental results obtained on a 2.6-m spherical Gregorian reflector operating at 9.0 GHz agree well with theoretical ones.
5 citations
TL;DR: In typical experiments with narrow field objects, it is shown that the zone plate behaves like a diffraction-limited lens, the gain in resolution is noticeable as the wavelength decreases, the use of the third-order focus improves the resolution of the system, and under certain conditions the depth of field can be increased without loss of resolution.
Abstract: The feasibility of optical systems for short wavelength radiations ranging from the near uv to soft x rays is supported by theoretical and experimental arguments. The major problem of absorption of these radiations by materials has been overcome in the near and middle uv by using the lens properties of a Fresnel zone plate generated on a thin self-supporting film. In typical experiments with narrow field objects, it is shown that the zone plate behaves like a diffraction-limited lens, the gain in resolution is noticeable as the wavelength decreases, the use of the third-order focus improves the resolution of the system, and under certain conditions the depth of field can be increased without loss of resolution. The chromatic aberrations of the zone plate are not restrictive for a large number of applications.
5 citations
TL;DR: In this paper, the admittance and current distribution of two parallel insulated monopoles in lake water were measured with three thicknesses of the insulation and the antennas were driven both in phase and in phase opposition.
Abstract: Measurements are reported of the admittances and distributions of current for two parallel insulated monopoles in lake water. Graphs of the admittance and impedance in the complex plane are displayed with the electrical distance between the elements as the parameter. These show significant coupling over electrically large separations. All data were obtained with the antennas driven both in phase and in phase opposition. Three thicknesses of the insulation were used.
4 citations
20 Jun 1977
4 citations
01 Jan 1977
TL;DR: In this article, an analysis of the solar concentration performance of a line-focusing flat-base Fresnel lens in the presence of small transverse tracking errors is presented, where simple optics and ray-tracing techniques are used to evaluate the lens solar transmittance and focal-plane imaging characteristics.
Abstract: Real sun-tracking solar concentrators imperfectly follow the solar disk, operationally sustaining both transverse and axial misalignments. This paper describes an analysis of the solar concentration performance of a line-focusing flat-base Fresnel lens in the presence of small transverse tracking errors. Simple optics and ray-tracing techniques are used to evaluate the lens solar transmittance and focal-plane imaging characteristics. Computer-generated example data for an f/1.0 lens indicate that less than a 1% transmittance degradation occurs for transverse errors up to 2.5 deg. In this range, solar-image profiles shift laterally in the focal plane, the peak concentration ratio drops, and profile asymmetry increases with tracking error. With profile shift as the primary factor, the ninety-percent target-intercept width increases rapidly for small misalignments, e.g., almost threefold for a 1-deg error. The analytical model and computational results provide a design base for tracking and absorber systems for the linear-Fresnel-lens solar concentrator.
20 Jun 1977
TL;DR: In this paper, the use of field matching techniques was used to design high-efficiency corrugated feeds for a 9-ft spherical dish with both single and dual-reflector antennas.
Abstract: With spherical antennas, the basic problem is to eliminate the effect of spherical aberration. Although various methods are available, this paper discusses the use of field matching techniques to design high-efficiency corrugated feeds for a 9-ft spherical dish. Both single and dual-reflector antennas are considered, but the emphasis is on the single-reflector system.
TL;DR: In this paper, a theoretical study of the variation of relative field amplitude with axial distance has been made for a plane and a spherical microwave zone plate with an incident plane wave front having non-uniform aperture excitation distribution.
Abstract: A theoretical study of the variation of relative field amplitude with axial distance has been made for a plane and a spherical microwave zone plate with an incident plane wave front having non-uniform aperture excitation distribution. The results show a sharper focussing property for the non-uniform excitation.
TL;DR: In this paper, a design procedure based on the principles of geometrical optics for antennas employing dielectric-cone feeds is described for any arbitrary amplitude and phase distributions, and can be used for dual-reflector antennas, reflector antennas with a subreflector supported with dielguides and reflector antenna with a shaped reflecting surface of the cone material.
Abstract: A design procedure based on the principles of geometrical optics, for any arbitrary amplitude and phase distributions, is described for antennas employing dielectric-cone feeds. The procedure can be used for dual-reflector antennas, reflector antennas with a subreflector supported with dielguides and reflector antennas using dielectric-cone feeds with a shaped reflecting surface of the cone material.