Mutual admittance characteristics for two-element parallel prolate spheroidal antenna systems

Spheroidal dipole antenna systems consisting of two thin center-fed parallel prolate spheroids in various configurations (side-by-side and collinear) are considered, The resultant EM fields are represented as modal expansions in terms of spheroidal vector eigenfunctions. The translational addition theorems for spheroidal functions developed by the authors in a previous paper play the central role in the formulation of a system matrix [G] which transforms the primary. EM excitations of the fed dipoles into their scattered responses. From the knowledge of the [G] matrix, the mutual admittances of the dipole system are obtained and plotted against center-to-center separation of the dipoles for side-by-side and collinear dipole configurations. The major to minor axial ratios of 10:1 and 100:1 of the prolate spheroidal dipoles are considered for presenting various curves. However, for the side-by-side configuration, due to a radius of convergence of the translational relation for outgoing wave to incoming wave transformation, the separationdof the spheroids is restricted tod > {a_{1}, a_{2}}_{max}, whosea_{1}anda_{2}are the semimajor axial lengths of the two spheroids.     

Field distributions in a three-layer prolate spheroidal human body model for a loop antenna irradiation

Analysis of the field distributions in a three-layer prolate spheroidal human body model for a loop antenna irradiation is described. The loop radiator is assumed to be placed symmetrically with respect to the spheroid axis. Spheroidal wave functions are employed to expand the field components inside and outside of the prolate spheroid. The boundary conditions on the interface layers are satisfied by using a mode matching procedure. The loop radiator can be very close to the human body. Numerical results are given for the 13 MHz frequency.     

Electromagnetic radiation from a slotted-cylinder antenna with an inhomogeneous sheath

This letter deals with a perfectly conducting infinitely long circular cylinder coated with a radially stratified sheath. Radiation of electromagnetic waves from an infinitely long axial slot is considered. A certain profile of permittivity in the sheath is taken, leading to a particularly simple result.     

长椭球介质人头模型中的场分布

文中给出一长椭球介质人头模型中的电磁场全波解。运用并矢格林函数和散射叠加原理 ,求解的电磁场表示为椭球矢波函数。导出了在人头模型中的耦合系数 ,最后给出了数字结果的讨论。     

Complex source radiation in a cylindrical radome ofmetal-dielectric grating

The radiation fields of a line source enclosed in a circular dielectric radome with grating consisting of an array of thin lossy metal strips are analyzed. The variations of the directivity of the source beam with respect to the beam direction are studied. The possibility of damping these variations by an appropriate design of the radome is demonstrated     

Electromagnetic radiation from heterogeneous plasma

It was found that the electromagnetic radiation frequency, strength, and waveforms from a heterogeneous plasma were independent of the circuit but were influenced by the material of the electrodes. Using the same circuit for various electrodes, radiation ranging from 10 to 50 MHz, power from 0.5 to 200 mW, and sinusoidal to spiked waves were observed.     

Electromagnetic radiation from hot carriers in FET-devices

We report on the emission of light from si MOS and GaAs MES devices. Processes involving band-to-band transitions and a Bremsstrahlung-continuum below the band-gap are shown to exist. Spatially nonuniform emission from the MESFETs is observed. The GaAs results are compared with Monte Carlo simulations.     

Transient radiation from a linear antenna with nonreflecting resistive loading

The transient waveforms radiated by step voltage or Gaussian pulse excited resistively loaded linear antennas are investigated by numerical means. Current distributions on the harmonically excited antenna are obtained as functions of frequency and for different values of the loading. The transfer functions of the antenna and the spectral densities of the radiated waveforms are obtained as functions of frequency and the loading and for different directions in space. The time dependent radiated waveforms produced by the antenna are obtained by using the fast Fourier inversion technique. The effects of the various antenna parameters on the radiated waveforms are also investigated. Some of the results are compared with available approximate analytical results.     

Electromagnetic field due to a loop antenna in a borehole

The radiation of a loop antenna embedded in a borehole with complicated geometry is analyzed by perturbation method and an efficient fast multiple-integration technique. The perturbation method is not used directly because there is a drill-stem whose conductivity and magnetic permeability are very large in the borehole. The prolate ellipsoid equivalence of the metal drill-rod is made, then the drill-rod may be removed and the perturbation method is valid. Some numerical results indicate that the approach is efficient and stable at low frequencies     

Corrections for the effects of a radome on antenna surfacemeasurements made by microwave holography

Measurements of the surface deviations of a parabolic antenna by microwave holography have been corrected for the effects of an enclosing radome. The largest correction, which is due to diffraction from the metal space frame, is made by using a model computed from the radome structure. This model accounts for the changing diffraction as the antenna is scanned during the interferometric mapping of the complex beam pattern. Correction for reflections from the radome panels is made by simultaneously measuring the beam pattern at multiple frequencies to provide delay discrimination to reject antenna sidelobes generated by multiple reflections which arrive with delays different from that of the main beam     

Electromagnetic analysis of an antenna embedded in a compositeenvironment

This paper addresses the problem of an antenna embedded in a hole dug in the ground. The composite medium configuration consists of a half-space dielectric (representing the Earth-air interface) containing a cylindrical hole filled with a different dielectric medium. The wire antenna resides within this hole, on the axis. The solution strategy is based on decomposing the problem into simpler subproblems, which are treated sequentially. First we calculate a numerical dyadic Green's function for the composite medium by solving an integral equation formulated over a background consisting of the unperturbed dielectric half space (for which the Green's functions are known in a spectral integral form). This integral equation is solved via the fictitious currents method, which is a special case of the method of moments. We then solve the integral equation for the antenna currents using this numerical Green's function and determine the input impedance and radiation pattern     

Electromagnetic radiation from selected telecommunications systems

Because of the growing interest in potential health effects associated with exposure to electromagnetic (EM) radiation at microwave and radio frequencies (RF's), a study was initiated within the Bell System to document existing levels of EM energy associated with various radio transmission systems. To this end, power density and electric field strength measurements were made at selected facilities, particularly at locations judged to be representative of those frequently encountered by various crafts personnel. For the case of point-to-point microwave radio, measurements were made in the vicinity of various antenna towers in order to obtain information that could be compared with the corresponding levels predicted by analytical techniques. These data allow one to assess the environmental impact, with respect to EM radiation, of the microwave radio system as well as the impact of future standards and guidelines on the system. This paper describes the instrumentation and measurement techniques used for this study and provides a summary of the results obtained for several different types of radio systems including high frequency (HF) radio, tropospheric scatter, earth-satellite and ubiquitous microwave radio relay.     

Radiation of an aperture antenna covered by a spherical-shellchiral radome and fed by a circular waveguide

This paper presents a full-wave analysis of the radiation characteristics of an aperture antenna that is flush-mounted on a ground plane and fed by a circular waveguide supporting the dominant TE₁₁ mode. The antenna is covered by a dielectric hemispherical chiral radome. Huygen's equivalence principle and the image theory are utilized to simplify the problem. The magnetic dyadic Green's function for the three-layered geometry is formulated and applied to analyze the radiated electromagnetic fields outside the chiral radome. Both the exact and approximate expressions of electric fields valid for the Fresnel and Fraunhofer zones are obtained using the spherical vector wave functions and their approximations in the far zone. Various chiral materials are assumed and computations of antenna parameters are carried out. The effects of the dielectric chiral radome on the radiation power patterns, sidelobe levels, and 3-dB beamwidths are also discussed numerically     

Electromagnetic plane wave scattering by a system of two parallel conducting prolate spheroids

By means of modal series expansions of electromagnetic fields in terms of prolate spheroidal vector wave functions, as exact solution is obtained for the scattering by two perfectly conducting prolate spheroids in parallel configuration, the excitation being a monochromatic plane electromagnetic wave of arbitrary polarization and angle of incidence. Using the spheroidal translational addition theorems recently presented by the authors which are necessary for the two-body (or multibody) scattering solution, an efficient computational algorithm of the translational coefficients is given in terms of spherical translational coefficients. The field solution gives the column vector of the series coefficients of the scattered field in terms of the column vector of the series coefficients of the incident field by means of a matrix transformation in which the system matrix depends only on the scatterer ensemble. This eliminates the need for repeatedly solving a new set of simultaneous equations in order to obtain the scattered field for a new direction of incidence. Numerical results in the form of curves for the bistatic and monostatic radar cross sections are given for a variety of prolate spheroid pairs having resonant or near resonant lengths.     

Scattering of the electromagnetic wave by a phased antenna array with consideration for the radome

A model for calculating the field scattered by the antenna of an aircraft radar with consideration for the radome is described. Backscattering patterns of phased antenna arrays with and without a radome are presented. Substantial contribution of diffraction lobes into the radar visibility of the antenna is noted.     

Theory and experiments of the enhanced radiation from a plasma-coated antenna

The plasma sheath existing between an antenna ana a surrounding plasma layer plays an essential role. It is predicted that, for a given operating frequency, there exist certain plasma densities for which the system is resonant, and this very strongly enhanced radiation is fully confirmed by experiments.     

The optimum transient radiation from an arbitrary antenna

Bounds on the optimum transient radiation from an arbitrary antenna enclosed by a spherical surface of specified size are presented. The optimization criterion is either maximization of the radiated electric field amplitude at a specified time and far-zone position, or maximization of the radiated energy density in a specified time interval for a particular far-zone position. The latter optimization results in the prolate spheroidal wave functions. In both cases, the total energy radiated by the antenna is constrained to be 1 J, and the antenna excitation is assumed to be bandlimited. The performance of the optimum arbitrary antenna is compared to that of optimized practical antennas, such as dipoles and arrays of dipoles. The effect of a sidelobe constraint is also studied.     

Electromagnetic scattering and radiation from finite microstripstructures

Two techniques are presented for the analysis of electromagnetic radiation and scattering from finite microstrip structures. The two techniques are based on two different formulations, viz. the volume-surface and surface-surface formulations. In the volume-surface formulation the finite-sized dielectric is replaced by an equivalent volume polarization current whereas the conducting plates are replaced by equivalent surface currents. For the surface-surface formulation the surface covering the dielectric volume is replaced by equivalent electric and magnetic currents and the conducting plates by surface electric currents. Both techniques can be utilized for the analysis of arbitrarily shaped finite microstrip structures. The techniques are quite accurate, and they are utilized to validate each other. Typical numerical results are presented to demonstrate the agreement between these two solution techniques     

Electromagnetic plane wave scattering by a system of two uniformlylossy dielectric prolate spheroids in arbitrary orientation

By means of modal series expansions of electromagnetic fields in terms of prolate spheroidal vector wave functions, an exact solution is obtained for the scattering by two uniformly lossy dielectric prolate spheroids in arbitrary orientation embedded in free space, the excitation being a monochromatic plane electromagnetic wave of arbitrary polarization and angle of incidence. Rotational-translational addition theorems for spheroidal vector wave functions are employed to transform the outgoing wave from one spheroid into the incoming wave at the other spheroid. The field solution gives the column vector of the unknown coefficients of the series expansions of the scattered and transmitted fields expressed in terms of the column vector of the known coefficients of the series expansions of the incident field and the system matrix which is independent of the direction and polarization of the incident wave. Numerical results in the form of curves for normalized bistatic and monostatic radar cross sections are given for a variety of two-body system of uniformly lossy dielectric prolate spheroids in arbitrary orientation having resonant or near resonant lengths and different distances of separation     

Monopole antenna radiation into a parallel-plate waveguide

A rigorous solution of coaxially fed monopole antenna radiation into a parallel-plate waveguide is obtained. The Fourier transform/series representations are used to represent scattered fields and the boundary conditions are enforced to obtain the simultaneous equations for discrete modal coefficients. Fast convergent series of the reflection coefficient is obtained and compared with other existing results