The Electromagnetic Field of an Insulated Antenna in a Conducting Or Dielectric Medium

Insulated antennas are useful for localized heating as in the hyperthermia treatment of tumors and the extraction of shale oil. The distribution of current in and the admittance of a center-driven dipole embedded in a general medium are reviewed. Formulas for the electric field generated by the currents in the dipole are derived for all points outside the antenna. Near the antenna, the field is elliptically polarized. Formulas for the polarization ellipses are derived and evaluated for antennas with electrical half-lengths Beta/sub L/h = pi/4, pi/2, pi, and 3pi/2, where k/sub L/ =beta/sub L/ + i alpha/sub L/ is the wavenumber of the current, and this is different from the wavenumber of the ambient medium.     

有耗介质中单极天线的场分布和SAR图

用一段刚性同轴线制作的微细单极天线在医疗上已得到广泛应用。本文给出了单极天线在有耗介质中的近场分布的数值解，进而在有耗介质中测定了温度分布和ＳＡＲ图，利用近场分布计算的ＳＡＲ图和测定的ＳＡＲ图基本相符。     

Propagation on a Sheath Helix in a Coaxially Layered Lossy Dielectric Medium (Short Paper)

Radial and axial dependence of the azimuthally symmetric fields in each coaxial layer may be expressed in terms of modified Bessel functions and complex exponentials, respectively.     

Microwave Radiation from a Magnetic Dipole in an Azimuthally Magnetized Ferrite Cylinder (Short Paper)

The electromagnetic radiation pattern from a ferrite coated dipole antenna is a torus with a point center. By deriving an expression for the far-field electric field and defining a form factor F(Theta), the dilations and contractions of the radiation pattern were evaluated and demonstrated graphically.     

Irradiation of Prolate Spheroidal Models of Humans in the Near Field of a Short Electric Dipole

Analysis of the near-field irradiation of prolate spheroidal models of humans and animals by a short electrical dipole is described. The method of solution involves an integral equation formulation of the problem in terms of the transverse dyadic Green's function and expanding the fields irradiated by a short dipole in terms of the vector spherical harmonics. The extended boundary condition method (EBCM) is employed to solve the integral equations. The power distribution and the average specific absorption rate (SAR) are calculated and plotted as a function of the separation distance. It is shown that for a dipole placed along the major axis of the spheroidal (k-polarization), and for a very short separation distance, d= 0.15 lambda, the relative power values at both ends of the spheroid are about 40 compared with the ratio of 15 in the planewave exposure case. Furthermore, the calculated average SAR values as a function of the separation distance were found to oscillate around the constant value obtained from the planewave irradiation case. Differences between the near-and far-field exposure cases occurred only at separation distances shorter than 0.5 lambda where the magnitudes of the electric and magnetic energy densities are higher than the time-average radiation power density.     

Broadside-Coupled Slot-Line Field Components (Short Paper)

This paper presents expressions for the odd- and even-mode electric field components and also the magnetic field components in the air, overlay, and dielectric regions of the broadside-coupled slot-line structure. These expressions are numerically computed, and the fields in the cross section and the Iongitudinal section are illustrated. The surface current distribution on the metal surfaces are also illustrated.     

Experimental Simulation of Plasma Using Strip Medium (Short Paper)

A technique for the plasma simulation using a two-dimensional strip medium is developed. The experimental results for, X-band rectangular waveguide and cavity filled with the strip simulated plasma are in good agreement witi the theoretical results and thus validate the simulation.     

Parametric Equations for Surface Waves In Dielectric Slab (Short Paper)

For the dielectric slab it is shown that 1) the dispersion curve for the nth surface wave can be found using parametric equations in which the normalized inside wavenumber K/sub xl/ and the mode number are the parameters, 2) the dispersion curve for the nth surface wave mode can also be found by using parametric equations in which the mode number and a modified wavenumber x' with common domain [0, pi/2] are the parameters, and 3) an TE or all TM dispersion curves for surface waves are related to each other by a simple algebraic equation using the mode numbers and the normalized propagation constants K/sub 0/ and Beta as the variables.     

One-Root Intervals of Dispersion Relations for a Resonator with Dielectric Sample (Short Paper)

A method is developed yielding intervals with analytically expressed bounds that contain only one root of the dispersion relation corresponding to any chosen mode of a cylindrical resonator with a dielectric sample, filling its cross section along part of the length of the resonator. A method for finding both the eigenfrequency and the sample permittivity is given.     

A Transition from Rectangular to Nonradiating Dielectric Waveguide (Short Paper)

A transition between standard X-band waveguide and non-radiating dielectric (NRD) waveguide is described. It consists of a transition from air-filled rectangular waveguide to reduced-width dielectric-filled waveguide, cascaded with a transition to NRD. Both transitions are theoretically designed to provide both mode matching as well as a low reflection coefficient. The composite transition can be used for measurements in NRD while making use of conventional waveguide test equipment.     

Microstrip Transmission Line with Finite-Width Dielectric and Ground Plane (Short Paper)

Design data for microstrip transmission lines with finite-width dielectric and ground plane are presented. The characteristic impedance and velocity of propagation are tabulated from results of a moment-method solution of a quasi-TEM transmission-line model of this microstrip structure.     

Dielectric Losses in an H-Plane-Loaded Rectangular Waveguide (Short Papers)

The attenuation constant due to dielectric losses in a rectangular waveguide loaded with a dielectric slab in the H-plane is calculated. Results for the dominant LSM/sub 11/ mode are presented graphically.     

Field Propagation in an Open-Beam Waveguide (Short Papers)

A new method is described for the investigation of the open-beam waveguides, which may be applied even when the optical elements are not inserted in absorbing screens.     

The Annular Slot Antenna in a Lossy Biological Medium (Short Papers)

An integral equation is formulated for a coaxially fed annular aperture antenna. The integral equation in terms of the unknown tangential aperture electric field is solved numerically by the Method of Moments. The coaxial feed line is air filled while the exterior region consists of i) air, ii) fat or bone, and iii) muscle. Results are given for the aperture electric field, apparent input admittance, and contours of constant power absorption when the excitation frequency is 2.45 GHz.     

Scattering at an N-Furcated Parallel-Plate Waveguide Junction (Short Paper)

Using the conservation of complex power technique (CCPT), this paper presents a solution to the problem of EM scattering at the junction of a parallel-plate waveguide and an N-furcated parallel-plate waveguide with arbitrarily spaced thick septa. Although this junction can be regarded as an (N + 1)-port configuration, the problem is formulated so that it is viewed mathematically as a generalized 2-port. This leads to very simple expressions for the scattering parameters of the junction. Convergent numerical results are presented for bifurcated, trifurcated, and 4-furcated structures, and the effects of varying the thickness of the septa are investigated. The formulation is directly applicable to N-furcated rectangular waveguide junctions having TE/sub n0/ excitation, with application in the design of E-plane filters.     

Slant Dielectric Interface Discontinuity in a Waveguide (Short Papers)

The reflection and transmission of electromagnetic waves by a slant interface between two dielectric media is investigated. By using suitable Green's functions and a geometrical optics approximation for the field on the dielectric interface, expressions for the transmitted and reflected fields are derived. The approximate results obtained in this manner are compared with the available numerical data and are shown to be fairly accurate for a number of cases of interest.     

电偶极子在无限大各向异性媒质中的辐射场

分析电偶极子在无限大各向异性媒质中的辐射场，得出了近区场地级数表达式。分析计算了电偶极子平行天于地磁场时在无限大均匀各向异性电离层中的远区场。     

A Novel Low-Noise Downconverter System Using A Microstrip Coupled Transmission-Mode Dielectric Resonator (Short Paper)

A low-noise downconverter system for microwave downlink applications is presented. Although most downconverters with an internally generated local oscillator have been designed utilizing MESFET's and DGFET's, the circuit described herein uses a silicon bipolar Darlington pair as its active device and a dielectric resonator for feedback. Downconverters of the latter type have been realized with noise figures as low as 4.57 dB and conversion gains of 7 dB over an intermediate frequency range from 0.6 to 1.8 GHz.     

Excitation of an Enclosed Lossy Cylinder by an Aperture Source (Short Paper)

We present a formulation for an aperture-excited cylindrical structure of circular cross section and of finite length. The solution method is straightforward but it is sufficiently general to permit quantitative estimates of the internal heating. When the axial dependency of the fields is ignored, the solution reduces to one employed earlier in confection with hyperthermic heating of human torsos and limbs.