Multimode Bragg diffractions in an ion-exchanged optical waveguide with a sputter-etched periodic surface corrugation

An optical diffraction phenomenon in an ion-exchanged planar optical waveguide with a sputter-etched periodic surface corrugation was experimentally investigated in detail. A single-mode incident beam simultaneously gave rise to several diffracted beams of different mode indices in different directions. This phenomenon was interpreted on the basis of the phase-matching diagram for the multimode Bragg diffraction by using measured wave vectors of the propagation modes and of the surface corrugation.     

Analysis of an anisotropic dielectric radome

A grooved-dielectric flat radome panel is analyzed in terms of an arbitrary direction of incidence onNplanar slabs each of which is dielectrically anisotropic, homogeneous, and lossless. Using this model for the grooved panel, transmission coefficients of 90 percent or greater over a 10:1 frequency band and over0degto60degincidence angle are predicted and demonstrated experimentally. Measurements are presented on two panels from 3 to 35 GHz.     

Eigenoscillations in waveguide junctions filled with an anisotropic dielectric

An electrodynamic model for calculation of the characteristics of waveguide junctions with an anisotropic filling is developed. Several dependences reflecting the relation between the resonance wavelengths of different oscillations and the geometric dimensions of the junction and the components of the filling permittivity tensor are found. These dependences can be used for measurements of the electric characteristics of anisotropic materials. The physics of resonance phenomena is studied.     

Scattering from an anisotropic cylindrical dielectric shell

The electromagnetic scattering from an anisotropic cylindrical dielectric shell is formulated by using the wave functions for anisotropic media and the boundary-value method. The cylindrical shell is assumed to be infinite in length, and it is illuminated by a plane wave or a cylindrical wave from a line source. The problem is two-dimensional and the solutions to both types of polarization (TE and TM) are presented. Numerical results for the effects of various geometrical and electrical parameters on the bistatic radar cross section are presented.     

Representation of imperfect dielectric materials by an equivalent circuit

A simple equivalent two-terminal electrical network that represents, over a wide frequency range and with sufficient accuracy, the dielectric properties of imperfect dielectric materials is given. The use of this network is illustrated with one of its applications in the mining industry, namely the determination of the concentration of metal in metallic ores.     

Diffraction by an anisotropic dielectric half-plane: a uniformasymptotic PO solution

A uniform solution is proposed to, describe the diffraction by a penetrable anisotropic dielectric halfplane illuminated at normal incidence by an electromagnetic plane wave. Resorting to second-order boundary conditions on a sheet simulating a special type of anisotropic dielectric thin layer, a physical optics (PO) approximation for the induced electric and magnetic surface currents is derived. Then, a uniform asymptotic evaluation of the corresponding radiation integral provides the diffracted field in terms of the standard transition function relevant to the uniform theory of diffraction. The effectiveness of the solution is proved by many numerical tests     

Analysis of an anisotropic plate Faraday rotator coated with multilayer dielectric plates

The analysis of an anisotropic plate Faraday rotator coated with multilayer dielectric plates is presented by means of the matrix methods in conjunction with Fourier transformation technigues. It provides a closed-form representation of the electromagnetic field over the whole multilayer regions. The treatment does not limit the direction of the biased magnetic field and the numbers of the coated dielectric plates. Numerical results are presented and compared with that calculated with the method in ref.[1], and full-waveguide-band bandwidth for 47.5°±1.5° rotation angle is obtained for transmission type rotator in W band. Calculation for reflection type rotator is also presented and compared with the experiments.     

Scattering of plane waves by an anisotropic dielectric half-plane

Scattering of plane waves by a semi-infinite anisotropic thin dielectric layer is investigated, which can be considered as an example for electromagnetic energy absorbing materials. A pair of second-order boundary conditions is used to simulate an anisotropic thin dielectric layer as an infinitesimally thin sheet. Formulation is based on the Fourier integral transform technique, which reduces the scattering problem to two decoupled scalar Wiener-Hopf equations. Diffracted, reflected, and transmitted field terms are evaluated by using the Wiener-Hopf solutions that is obtained by the standard method. The uniqueness of the solution is satisfied by imposing an edge constraint in addition to the classical edge condition     

An X-ray free-electron laser loaded with a periodic dielectric

When a periodic medium is inserted along the axis of a free-electron laser (FEL), the synchronism condition between the electron beam and the electromagnetic wave is changed. This alteration permits a wider parameter selection than the conventional FEL, and provides for the possibility of X-ray operation. The device is a hybridization of the FEL and the stimulated-transition-radiation laser. Photon absorption by the periodic medium and scattering of the electrons limit the interaction length, but calculated gains are still high enough for oscillation. The analysis shows that ultrarelativistic electron beams and low-density foil materials give the most physically realizable parameters. Higher order resonant transition modes (r>1) should be used to maximize gain     

Multilayered open dielectric waveguide with a gyrotropic layer

Open dielectric waveguides with a gyrotropic layer have been studied with a view to find structures in which the nonreciprocity in the propagation constant is maximized. A prediction based on a qualitative analysis and numerical studies for confirming the theory are included.     

On waves in an anisotropic plasma imbedded in a moving dielectric medium

The governing equations for electromagnetic fields in an anisotropic plasma imbedded in a moving dielectric medium are obtained. Examination of the wave and dispersion equations yields information on the elliptically or linearly polarized waves which may exist when the external magnetic field is parallel or perpendicular to the direction of motion, respectively.     

Electromagnetic field radiated by a point source in an anisotropic layer

The field of a point electromagnetic source localized in a homogeneous anisotropic coating of a perfect conductor is constructed by the Fourier method. The field in the anisotropic layer can be interpreted as a sum of ordinary and extraordinary waves (Felsen and Marcuvitz, 1973). The asymptotics of the electromagnetic field in the far zone is studied. Far from the surface, the main contribution is due to the outgoing spherical wave and near the coating the field is represented as the sum of waveguide modes contributions. Specific asymptotics appear in a vicinity of critical directions across which the number of waveguide modes changes.     

Analysis of microstrip structures with an inhomogeneous dielectric layer in an unbounded region

The method of lines (MoL) is used to compute the frequency dependent propagation characteristics of planar waveguides with an inhomogeneous dielectric layer. To simulate unbounded regions, absorbing boundary conditions (ABC) are used. It is shown that in this case excellent results are achieved even if the boundaries are placed very close to the dielectric edge of the structure.<>     

Design of microstrip antennas covered with a dielectric layer

The design of a microstrip antenna covered with a dielectric layer is presented. Due to loading, the resonant frequency of the antenna changes. The absolute value of the change increases with the operating frequency, the relative permittivity (except plasma), and the thickness of the dielectric layer. This change may cause degradation in performance due to the inherent narrow bandwidth of microstrip antennas if the effect of loading is not considered in the design. The curves presented here may be used to design microstrip antennas that may be subjected to icing or a plasma environment or coated with protective layers. Numerical and experimental results for the fractional change in the resonant frequency are round to be in good agreement.     

Scattering by an infinite periodic array of thin conductors on a dielectric sheet

The solution to the problem of scattering of a plane wave by an infinite periodic array of thin conductors on a dielectric slab is formulated in this paper. Numerical results are given as well as a comparison of this theory with experimental data.     

On the equivalent circuit representation of the slittedparallel-plate waveguide filled with a dielectric

An investigation of the equivalent π circuit representation for the transverse slit in the wall of a transverse electromagnetic (TEM) parallel-plate waveguide is presented. For the narrow slit, approximate analytic expressions for the equivalent circuit parameters are given in terms of the centerline representation and, for the arbitrarily width slit, the equivalent circuit parameters are considered by the method of moments in terms of both the centerline representation and edge representation, and various characteristics of the equivalent π admittance circuit representation are discussed. A critical look is taken at the validity of the previous model of th E-plane gap coupling between two rectangular microstrip patch antennas, and the improved model is considered for the narrow slit (gap) width case     

The RCS of a cylindrical array antenna coated with a dielectric layer

The scattering properties of dielectric coated waveguide aperture antennas mounted on circular cylinders are investigated. Both the single element antenna and the array case are treated. The array antenna consists of 4 /spl times/ 32 rectangular apertures placed in a rectangular grid on the surface of an infinitely long circular cylinder. The problem is formulated in terms of an integral equation for the aperture fields which is solved with the method of moments using rectangular waveguide modes as basis and test functions. An efficient uniform asymptotic technique is used to calculate the excitation vector and the backscattered far-field. The asymptotic solution is valid for large cylinders coated with thin dielectric layers away from the paraxial (i.e. near axial) region. A similar asymptotic solution is used to calculate the mutual coupling in the nonparaxial region. For the self coupling terms and for the mutual coupling in the paraxial region a planar approximation is used with a corresponding spectral domain technique. Numerical results are presented as a function of frequency, angle of incidence, cylinder radius, and electrical thickness of the coating.     

Wave propagation through a hollow rectangular anisotropic dielectric guide

Wave propagation through a hollow rectangular dielectric guide with anisotropic surrounding is studied here. It has been shown that anisotropy can be utilized to reduce the loss in resonating structure of the gas laser system.     

Modeling lossy anisotropic dielectric waveguides with the method oflines

This paper presents a new formulation useful for modeling waveguides constructed from lossy inhomogeneous anisotropic media. Our approach is based on a pair of Sturm-Liouville type wave equations that have been derived to handle inhomogeneous, diagonalized complex permittivity and permeability tensors. The method of lines is then applied to these wave equations, and related field equations, creating an indirect eigenvalue problem that correctly models this class of structure. Some refinements to the method of lines are also proposed, particularly, regarding the construction of the modal matrices found in the eigenvalue problem. Using our approach, modal dispersion curves have been computed for millimeter-wave and optical structures. Comparisons made with results available from the literature validate our approach     

Reflection and transmission coefficients of a periodic dielectric slab

The plane-wave reflection and transmission coefficients of a dielectric slab having a sinusoidal variation of its permittivity are deduced from the solution of the full electromagnetic boundary-value problem and compared with the results of the approximate procedure based on the coupled-mode equations for the slowly varying amplitudes.