Dielectric Hemisphere Research Articles

Whispering-gallery modes in a barrel-shaped dielectric resonator

We experimentally study a new type of resonator, namely, a barrel-shaped dielectric resonator with whispering-gallery modes which is formed by the cutting dielectric hemisphere. Compared with a hemispherical dielectric resonator, the E type oscillation spectrum of such a resonator is rarefied with respect to the azimuthal index. Comparative analysis of the electromagnetic characteristics of the barrel-shaped dielectric resonator and half-disk dielectric resonators shows that the radiation losses of the mode energy from the spherical surface are smaller than those from the cylindrical surface. This fact stimulates the high values of the internal Q-factor of modes of the barrel-shaped dielectric resonator.

Optical antenna design for indoor optical wireless communication systems

AbstractIn the present paper, the design of the non‐imaging totally internally reflecting concentrator family denominated optical antennas (OAs) is discussed, and its use for indoor optical wireless communication systems is explained. The lenses presented here can be designed to provide a prescribed angular response in order to limit the central wavelength shift in thin‐film optical filters. They can also be designed for any specific field‐of‐view (FOV), which allows greater rejection of unwanted background radiation and higher gains. The use of a variety of optical filters to achieve a high signal‐to‐noise ratio at the receiver is described. Design methods and properties of different Optical Antennas are explained. Comparisons of size and performance of total internal reflection based concentrators with those based on dielectric hemispheres and compound parabolic concentrators (CPCs) are carried out. Finally different experimental results are presented. Copyright © 2005 John Wiley & Sons, Ltd.

A comparison of performance of three orthogonal polynomials in extraction of wide-band response using early time and low frequency data

The objective of this paper is to generate a wideband and temporal response of three-dimensional composite structures by using a hybrid method that involves generation of early time and low-frequency information. The data in these two separate time and frequency domains are mutually complementary and contain all the necessary information for a sufficient record length. Utilizing a set of orthogonal polynomials, the time domain signal (be it the electric or the magnetic currents or the near/far scattered electromagnetic field) could be expressed in an efficient way as well as the corresponding frequency domain responses. The available data is simultaneously extrapolated in both domains. Computational load for electromagnetic analysis in either domain, time or frequency, can be thus significantly reduced. Three orthogonal polynomial representations including Hermite polynomial, Laguerre function and Bessel function are used in this approach. However, the performance of this new method is sensitive to two important parameters-the scaling factor l/sub 1/ and the expansion order N. It is therefore important to find the optimal parameters to achieve the best performance. A comparison is presented to illustrate that for the classes of problems dealt with, the choice of the Laguerre polynomials has the best performance as illustrated by a typical scattering example from a dielectric hemisphere.

Excitation of Oscillations in a Hemispherical Dielectric Resonator by a Radial Magnetic Dipole

Forced oscillations excited by a radial magnetic dipole in a dielectric hemisphere (resonator) placed on a perfectly conducting plane are studied. It is shown that the dipole excites H modes. When the dipole radiation frequency equals the eigenfrequency of the resonator, an amplitude resonance is observed in the spectrum. The excitation efficiency is high when the magnetic dipole is placed at the maximum of the radial field component of the resonator’s eigenmode.

Analysis of waveguide-fed dielectric resonator antenna using a hybrid finite element method∕moment method

A hybrid finite-element method/moment method (FEM/MM) is used to analyse a waveguide-fed dielectric resonator antenna with a dielectric constant /spl epsiv//sub ra/. Green's function for the dielectric hemisphere, rather than the free-space Green's function used in conventional hybrid FEM/MM, is employed to establish the integral equation. To simplify the analysis, two different kinds of basis function are used to discretise the slot field in the FEM and MM, respectively. The accuracy of the hybrid FEM/MM is confirmed by measured data for the special case of one waveguide-fed slot radiator, i.e., /spl epsiv//sub ra/=1. The numerical results demonstrate that the energy coupling can be greatly improved by placing a dielectric resonator inside the waveguide.

Whispering-gallery modes in shielded hemispherical dielectric resonators

The results of the numerical and experimental investigations of whispering-gallery (WG) modes in shielded hemispherical dielectric resonators are presented in this paper. It is shown that the Q factor of WG modes in the shielded resonator can be ten times much higher than the Q factor of the similar open hemispherical dielectric-resonator modes. Shielding the resonator can decrease the dimensions of both the dielectric hemisphere and resonator as a whole, saving the high-Q factor of WG modes. The usage of a cylindrical shield and local flat reflectors in the experiment provides the investigation of the high-Q factor of WG modes in the resonator.

Superconductors and cryogenics for future communication systems

In the framework of a German research program on superconductors and ceramics for future communication technology, efforts are undertaken to demonstrate the feasibility of cryogenic and high-temperature superconductor technology for applications in communication satellites and base transceiver stations (BTS's) for terrestrial mobile communication. For the receiver front end of C-band satellites, noise reduction filters as well as input-multiplexer channel filters have been developed. A three-channel output multiplexer was composed of dielectric hemisphere filters with elliptic response. Associated encapsulation and cooling issues for spaceborne systems were investigated and an in-orbit demonstration of the complete setup will be performed on the International Space Station. Activities toward applications in terrestrial mobile communication are focused on BTS cryogenic front ends with single preselect filters of superior selectivity, and on reconfigurable front ends allowing some electronically controlled change in the preselection frequency response. A first version of a demonstrator for a cryogenic BTS front end was developed.

Analysis of a Rectangular Slot Antenna Loaded By a Dielectric Hemisphere With Double Dielectric Coatings

A rigorous analysis method is provided for a rectangular slot antenna loaded by a dielectric hemisphere with double dielectric coatings. The method is an integral equation approach and the moment method solution is sought. The antenna input impedance and radiation patterns are obtained and compared with the case with a single dielectric coating layer. The bandwidth of the antenna is found to be significantly improved with a second dielectric coating layer. The thickness of the second dielectric coating layer is found to be able to control the bandwidth, the impedance and the resonant frequency of the antenna. The low-profile radiation patterns and the enhanced bandwidth characteristic of the antenna is suggested to have a potential application in mobile base-station communications.

General solution of a monopole loaded by a dielectric hemisphere for efficient computation

A simple result for the general solution of a monopole loaded by a dielectric hemisphere is presented. The result can be calculated without the need for any numerical integration and, thus, it is computationally very efficient. In addition, the result is very easy to implement and should be useful to the design engineer.

Loaded TEM cell versus free space: comparison of the E-fields inside dielectric spherical objects

A Crawford (1974) cell is a convenient tool for generating transverse electromagnetic fields. In this work, a dielectric hemisphere is assumed to be placed on the central septum of a Crawford cell; the field inside the hemisphere is numerically evaluated and then compared with that inside the corresponding sphere in free-space (illuminated by a plane wave) for which the analytical solution is known.

Compound parabolic concentrators for narrowband wireless infrared receivers

We discuss the design of optical concentrators based on dielectric and hollow compound parabolic concentrators (CPCs), for use in free-space infrared communication receivers. In order to acheive a high signal-to-noise ratio in a direct-detection receiver, it is desirable to use an optical bandpass filter that passes the signal but attenuates ambient radiation. Placement of a planar bandpass filter at the entrance aperture of a CPC results in a receiver having a narrow passband and high gain, but a narrow acceptance angle. The addition of a second, angle-transforming CPC at the entrance aperture allows the receiver to achieve simultaneously a narrow passband and an acceptance angle approaching 90 deg. We have employed a Monte Carlo ray tracing method to calculate the optical gains of several optical concentrator designs. We find that the optical gains of single and double CPCs are, respectively, about 94% and 93% those of ideal optical concentrators, while addition of planar bandpass filters decreases these gains to about 88% and 86%, respectively. We compare the performance and size of CPC-based concentrators with those based on dielectric hemispheres fitted with hemispherical bandpass filters.

Hemispherical concentrators and spectral filters for planar sensors in diffuse radiation fields

A dielectric hemisphere of refractive index N can act as an N(2) concentrator of isotropic diffuse radiation under appropriate conditions. We give an analytic expression for the gain of a concentrator of arbitrary radius, neglecting surface reflections, and numerical methods for calculating the gain when the surface transmissivity is an arbitrary function of incidence angle. The theory is applied to the design of multilayer spectral filters for hemispherical concentrators. When an appropriate wavelength shift is incorporated into the design process, an 11-layer, coupled-cavity spectral filter on the surface of a hemisphere of index 1.5 shows excellent bandpass performance with a concentrator radius as small as 3 times the sensor radius. This concentrator-filter combination shows a peak response of 97% of the ideal N(2) response at 950 nm, together with a FWHM of 55 nm.

Analysis of hemispherical dielectric resonator antenna

This paper describes the analysis of a hemispherical dielectric resonator antenna fed by a coaxial probe. The electric field Green's function of a vertical point current located inside the dielectric hemisphere is derived by mode matching technique. Delta gap source excitation model is employed. The input impedance of the antenna is calculated using a variational formula. Both the broadside TE111 mode (the lowest‐order transverse electric mode) and the end‐fire TM101 mode (the lowest‐order transverse magnetic mode) are considered. Numerical calculations and experimental results validating the theory are shown. The variation of input resistance with dielectric constant of the antenna is studied.

Retroreflective properties of a hemispherical surface

A dielectric hemisphere and a reflective hemisphere are presented as a new type of retroreflector. The conditions that create this property and potential applications are discussed.

Erratum: Reflection and transmission properties of annular slot covered by dielectric hemisphere

Erratum: Reflection and transmission properties of annular slot covered by dielectric hemisphere

Reflection and transmission properties of annular slot covered by dielectric hemisphere

A coaxial line flush mounted on an infinite perfectly conducting ground plane and covered by a dielectric hemisphere is investigated. Green's functions for the region above the ground plane are derived with separated homogeneous and particular solution parts so as to be compatible with numerical analysis techniques. A magnetic field integral equation is obtained in terms of the unknown annular aperture tangential electric field and is solved by the method of moments. A comparison between the present case and that of a flush-mounted coaxial line with an infinite homogeneous region above the ground plane is presented in terms of the tangential aperture electric field, the coaxial line apparent input impedance and the far radiated field.

Resonant hemispherical dielectric antenna

An antenna consisting of a resonant dielectric hemisphere on top of a ground plane is investigated. Calculations of the internal and external fields are made with emphasis on the lowest-order mode that results in efficient radiation in the direction perpendicular to the ground plane. Measured input impedance data are also presented for a practical radiator.

Dielectric Hemisphere-Loaded Scalar Horn as a Gaussian-Beam Launcher for Microwave Exposure Studies

A new type of Gaussian-beam luncher for producing a focused-microwave exposure field in biological experiments for selective partial-body irradiation is studied. The proposed launcher consists of a scalar horn (corrugated cylindrical open-ended waveguide) excited with a balanced hybrid (HE/sub 11/) mode and the aperture of the horn is loaded with a dielectric hemisphere. This Iauncher is similar to the structure described by one of the authors elsewhere, except that a dielectric hemisphere instead of a full sphere is used, with the result that the spherical aberration is considerably reduced, as well as that the weight and the size are, to a certain extent, reduced. It is shown that the present structure also produces in the image space of hemispherical lens, a near-circular Gaussian beam with a high-focusing factor. Design details, theoretical calculations, and experimental results conceming a practical X-band launcher are presented.

Dielectric hemisphere on cone antenna excited in the unsymmetric hybrid mode at microwave frequencies

Approximate expressions for the radiation field and the gain of the dielectric hemisphere on cone antenna excited in the un-symmetric hybrid mode have been derived. The radiation pattern and gain of a number of antennas of different dimensions have been calculated and measured aver a band of frequencies from 8.5 GHz to 11.0 GHz. rhe input impedance of these antennas measured over Ihis range of frequencies is also reported.