Radiation characteristics of a waveguide-excited short backfire-fedparabolic reflector operating in Q-band

Presents measured results at 31-38 GHz of the radiation characteristics of a 0.252 m diameter parabolic dish fed at the prime focus by a short backfire antenna. The feed consists of an experimentally optimised design of a short backfire antenna, having a conical main reflector of 15° slant angle. The measured radiation patterns of the reflector system generally agree quite well with the prediction based on aperture field integration     

Radiation characteristics of dielectric cones

Theoretical and experimental radiation patterns are favourably compared for a dielectric-cone feed made from polythene with a semiflare angle of 25°. The patterns are also shown to be very similar to those of a conical corrugated horn of the same flare angle. Theoretical results for other angles are also presented.     

Radiation characteristics of dielectric tube antennas

A study of the radiation characteristics of dielectric tube antennas is made with a possibility of its application in communications satellites. It has been shown through a systematic analysis that a multimoded dielectric tube shows a dip in the boresight region which is suitable for satellite antennas.     

Radiation characteristics of multilayer periodic dielectric structures

Radiation characteristics of multilayer periodic dielectric structures are investigated by the method which combines the building block approach of multimode network theory with the rigorous mode matching procedure. The multilayer periodic structure is composed of uniform dielectric layers and single periodic layers. Two examples are given in this paper; first, radiation property of the double dielectric grating antenna is analyzed. The results indicate that the double dielectric grating antenna has relatively smaller dimensions than that of the single one. It is undoubtly of great importance in the case that the limitation of the weight and the volume of the system is strictly required. Secondly, some curved profile grating antennas are analyzed by combining the present method with the staircase approximation. In such a way, the effects of groove profile on the performance of the grating antennas are systemetically studied and some useful guidelines for the design of the dielectric grating antennas are thereby suggested.     

Radiation characteristics of a dielectric disk-loaded circularcylindrical waveguide

The radiation pattern of a circular cylindrical waveguide that is loaded inside with periodically spaced dielectric disks is derived by considering the region between two disks as a medium with anisotropic permittivity and using Schelkunoff's equivalence principle. The far-field electric field components and their relationship to cross-polarization ratio are determined. The variation of the latter quantity with the size, spacing, and dielectric constant of the dielectric disks is studied     

Radiation characteristics of a dielectric sphere-loaded corrugated pipe

The fields radiated by a feed structure consisting of a dielectric sphere placed in front of, but displaced from, the open end of a corrugated pipe with quarter-wave teeth, carrying the HE11mode, are derived. It is shown that this feed system has near-circular far-field characteristics with increased on-axis gain. The feed also has a reduced input VSWR due to the aperture-sphere separation. Theoretical expressions are derived for the radiated far-field components, by treating the off-set sphere as a microwave lens. Experimental results obtained from a test feed confirm the theoretical calculations made.     

Radiation characteristics of wide-angle H-plane sectoral horn loaded with dielectric of multiangular shape

Radiation characteristics of H-plane sectoral horns can be improved or modified by inserting a proper dielectric loading. A study of the radiation of wide-angle sectoral horns with a multiangular dielectric insert that behaves as a lens is presented. Two types of loading are considered, the first in the waveguide feed, the second in the aperture. The method of analysis is the domain product technique utilizing Mathieu function expansions. Numerical investigation has shown that both configurations can provide improvements, but the first lens possesses certain advantages in comparison with the second one. Specifically, it has smaller dimensions and allows minimization of the reflected wave amplitude. Proper choice of the shape of the first insert and material of the dielectric can ensure reduction in the beamwidth, lowering the side lobe level and low return losses in a broad band of frequencies.     

Classical capacitance of few-electron dielectric spheres

The capacitance of few-electron dielectric spheres differs from the many-electron Gauss model of infinitesimally-divisible charge as a result of the electrostatic interaction of discrete electrons. Minimization of the total classical interaction energy for nanometer-size devices without quantum effects for up to 12 electrons is obtained. Unlike the Gauss model, capacitance is non-constant. The variation of capacitance with N, thus, with voltage, in a non-magnetic, classical domain, opens a new field of discrete charge nanometer-size devices and applies to the general chemistry of nanoparticles.     

Radiation characteristics of strip loaded hollow dielectric E-planesectoral horn antennas

The authors report the development of a novel E-plane sectoral horn. A metallic strip of optimum length loaded on the horn is capable of giving symmetric patterns both in the E and H-planes with low sidelobe levels     

Electromagnetic resonances of immersed dielectric spheres

The complex natural resonances (CNR) for lossless dielectric spheres in a lossless dielectric medium are investigated. Significant differences between the external and internal resonances are presented. The external resonances are related to the external creeping waves and the internal resonances to the internally reflected waves. The internal resonances are more important in practice because of their smaller damping factors. A simple physical interpretation for predicting the resonance behavior of a general dielectric sphere is obtained     

Waveguide excited dielectric spheres as feeds

The results of experiments with dielectric obstacles of various geometries placed directly upon the apertures of circular and rectangular waveguides are presented. It is found that dielectric spheres, and in some instances dielectric cubes, two to four wavelengths in dimension produce directive patterns with low sidelobe levels. For some cross sections, the measured gain of these antennas is greater (6 dB in some cases) than that produced by optimum horns having apertures of identical cross section. The linearity of the polarization of these antennas is essentially the same as that of an open-end waveguide antenna.     

Near-field centripetal scattering from dielectric spheres

The fields scattered from small dielectric spheres illuminated by a plane wave have been computed as part of a study of spherical dielectric antennas. Studies of scattering of 3 cm wavelength from a 6.6 cm diameter sphere of dielectric constant between 2 and 3 show large regions on the surface of the sphere where the Poynting vector is inwardly directed. These regions form sidelobes of inwardly directed power density between the sidelobes of outwardly directed power density in the principal planes. Away from the sphere the angular extent of the centripetal power flow is reduced until they disappear at 2-3 cm from the surface.     

Radiation characteristics of a dielectric sphere loaded corrugated E-plane sectoral horn

The experimental results of the radiation characteristics of a dielectric sphere in front of a corrugatedE-plane sectoral horn together with the design aspects of the horn are reported. The experiments were carried out with the test antenna system consisting of dielectric (paraffin wax) spheres kept offset at the minimum input VSWR position in front of the horn excited in the balanced HE11mode. The test results have shown that such a feed system produces radiation patterns with reduced sidelobe levels and increased on-axis gain with reduced 3-dB beamwidths as compared to the same horn radiating in free space. The feed system may also produce a low input VSWR and can be used as a variable beamwidth feed for praraboloidal reflectors.     

Radiation characteristics of the short dielectric rod antenna: A numerical solution

The problem of the dielectric rod antenna is studied numerically. The surface integral equation is used to simulate the problem in its actual form. From the surface currents induced on the antenna surface, the far-field radiation patterns are calculated. Different parameters are considered, such as the extension of the dielectric from the waveguide aperture, the waveguide and the dielectric diameter, the dielectric constant and finally the effect of shaping of the dielectric end. The performance of the antenna as a feed for the reflector antenna is also studied by calculating the gain factor, spillover efficiency and the phase center location of the feed. Some of the results are compared with the available experimental data of Dombek. The agreement is found to be excellent.     

Radiation and matching characteristics of a novel dual-band dielectric loaded coaxial horn

Copolar and crosspolar radiation as well as matching characteristics of a novel dual-band coaxial hybrid-mode feed horn with partial dielectric loading [1] for reflector antennas have been numerically and experimentally investigated. In comparison with dual-band corrugated horns this horn has higher crosspolar level, but provides larger band separation and rather good electrical performances over a wide frequency range (20% and more) within each operational frequency band. Furthermore, the main concept of the coaxial feed system can be easily extended for multi-band cost-effective applications in reflector antennas with polarization diversity.     

Whispering-gallery rays within dielectric circles and spheres

The attenuation of rays propagating at nearly grazing incidence within lossless dielectric circles and spheres is given. There are no trapped rays, no matter how great the refractive index of the structure; however, many rays are only very weakly attenuated. These are the `leaky rays? that are predicted, incorrectly, by Fresnel's laws to be trapped.     

The detection of dielectric spheres submerged in water

The basic theory is developed for the use of lateral electromagnetic waves to detect dielectric spheres submerged in fresh or salt water or human flesh. The source and receiver are, respectively, center-driven and center-loaded eccentrically insulated dipoles. A numerical example is computed to determine the magnitude of the scattered field that must be detected     

Radiation characteristics of a waveguide excited dielectric sphere backed by a metallic hemisphere

The experimental results of the radiation characteristics of waveguide excited dielectric spheres backed by metallic hemispheres are reported. The test antenna consists of a dielectric loaded hemispherical horn excited by a circular waveguide. The test data have shown that such a structure produces a radiation pattern with low sidelobe levels, increased on-axis gain, and reduced 3 dB beamwidth as compared to a waveguide excited dielectric sphere of same diameter and an optimum horn having an aperture of identical cross section area. Also, it presents a low VSWR over the waveguide band.     

Radiation characteristics of a source in a thin substrate mountedover a dielectric medium

The radiation pattern of a line source is calculated for the case in which the source is lying on the top or the bottom surface of a lossless dielectric substrate that is mounted on the top of semi-infinite dielectric medium. It is found that in both cases the pattern along the interfaces has a null; that the pattern in the upper semi-infinite medium has a single lobe; and that the pattern in the lower semi-infinite medium has many lobes, the number of which varies with the substrate thickness. In both cases, the power radiated into the lower medium is more than that radiated into the upper medium. Applications of this calculation to remote sensing, microstrip antenna technology, and antenna arrays are discussed