Surface waves on a grounded dielectric slab covered by a resistivesheet

Surface wave propagation in a grounded dielectric slab covered with a resistive sheet is examined. Transcendental equations are derived for each polarization and are solved using iterative techniques. Attenuation and phase velocity are shown for a representative geometry. The results are applicable to both a grounded slab covered with a resistive sheet and an ungrounded slab covered on each side with a resistive sheet     

Surface waves on a grounded anisotropic plasma slab

The dispersion relations of the plane surface waves supported by a grounded magnetoplasma slab immersed in free space are discussed for the case in which the magnetostatic field is parallel to both the direction of propagation and the vacuum-plasma interface. The dependence of the surface-wave characteristics on the thickness of the plasma slab and the strength of the magnetostatic field is also examined.     

Excitation of a grounded dielectric slab by a horizontal dipole

The structure consisting of a horizontal electric dipole above a grounded dielectric slab is examined, primarily from the standpoint of power distribution among the two power-carrying wave components, i.e., surface and space waves. It is shown that surface wave propagation is always in the form of two distinct modes characterized by the same cutoff properties. Also, surface wave excitation efficiency curves are given for a range of parameter variation.     

Surface wave diffraction by a truncated inhomogeneous dielectric slab recessed in a conducting surface

The study of surface wave diffraction by a truncated dielectric slab recessed in a perfectly conducting surface is of importance in designing flush-mounted dielectric covered antennas. The incident surface wave gives rise to waves diffracted and reflected by the junction at the termination of the dielectric. A strong reflected surface wave is undesirable in certain situations in that it may cause a problem in matching antenna impedances. One way to reduce the reflected surface wave is to use an inhomogeneous dielectric near the junction. If the inhomogeneous dielectric near the junction is lossy, a substantial reduction of the reflected surface wave can be achieved as demonstrated in the present study. Owing to the added complexity by including inhomogeneous dielectrics, this diffraction problem is solved using an integral equation numerical approach.     

Analytical, numerical, and experimental investigation of guided waves on a periodically strip-loaded dielectric slab

The electromagnetic waves guided by a periodically strip-loaded dielectric slab were investigated. The determinantal equation was obtained by assuming that the strips are narrow as compared to all other linear dimensions. Numerical results involving different combinations of the linear and dielectric parameters are presented in terms ofk-betadiagrams. The amplitudes of the space harmonics were computed and are discussed in connection with the characteristic phenomena such as radiation and coupling. In particular, the relations between the attenuation of the guided waves and the space-harmonic amplitudes are pointed out. As an interesting phenomenon, real solutions have been found to occur in the complex-wave region and this new result has been explained in the light of the space-harmonic amplitudes. The numerical results in the backward-radiation region have been verified experimentally by two different methods: by measuring the phase and amplitude variation in the near field and by calculation from radiation patterns. In both cases, good agreement with the theoretical results has been obtained.     

Electromagnetic scattering by a perfectly conducting patch array ona dielectric slab

The scattering characterization of an infinite and truncated periodic array of perfectly conducting patches on a dielectric slab is discussed. In particular, an approximate solution for the truncated array scattering that is based on the exact solution for the corresponding infinite array is presented. The latter is obtained numerically by solving for the patch currents using a conjugate-gradient fast Fourier transform (FFT) technique, eliminating the need to generate and store the usual square impedance matrix. The scattering pattern of the finite array is then computed approximately by integrating the infinite-period-array currents over the given finite array. Numerical results are presented for the infinite and finite arrays, and the accuracy of the approximate solution for the finite array is examined and discussed in relation to some available exact data. It is found that the approximate solution is of reasonable accuracy in predicting the scattering by the truncated array     

Reflection of millimeter waves by a corrugated dielectric slab waveguide

The TM wave propagation in a corrugated dielectric slab has been studied using a singular boundary perturbation procedure, which is supported subsequently by experiments in the millimeter-wave region.     

Analysis of electromagnetic scattering by periodic strip grating ona grounded dielectric/magnetic slab for arbitrary plane wave incidencecase

A new type of integral equation that is coupled with strip-electric and slot-magnetic currents is applied to the analysis of electromagnetic scattering by a periodic strip grating on a grounded dielectric/magnetic slab for an oblique incident plane wave with arbitrary polarization. In the analysis, the electric and magnetic currents are expanded into a product of a series of cosine functions and a function satisfying the edge condition. Coupled linear equations for the unknown electric and magnetic currents are obtained. From the coupled linear equations, explicit expressions for the reflection coefficients are derived by the use of a single edge-mode expansion. The validity of the method is examined by numerically calculated boundary conditions. A comparison between the calculated results from the present method and a previous method by measured ones shows that the accuracy of the method is excellent. Numerical calculations show that the method converges very rapidly with reasonable accuracy     

Surface waves on a lossy planar ferrite slab

The parallel-polarized surface waves which propagate on a planar ferrite slab are considered. The ferrite material is isotropic and homogeneous, the slab rests on a perfectly conducting ground plane, and the ambient medium is free space. Only one mode can propagate on a thin lossless slab, but more and more of the higher order modes begin to propagate when one increases the thickness or the loss tangent of the slab. As the thickness and the loss are increased, the lowest order mode takes on the properties of the Zenneck wave. At the same time, the higher order modes take on the properties of a homogeneous plane wave propagating in the grazing direction in the slab. Among the most interesting properties of a surface wave are the attenuation constant and the phase velocity. Contour maps are included to show how these quantities depend on the thickness, permittivity, permeability and loss tangents of the ferrite slab. Additional insight is provided by graphs showing the root trajectories, cutoff boundaries and field distributions of the four lowest order surface-wave modes.     

Radiation from a line source in a ground plane covered by a warm plasma slab

The problem of a magnetic line source in a ground plane coated with a warm plasma slab is investigated. Consideration is given to electromagnetic and plasma waves in the slab and to the coupling at the boundaries between these waves and the free-space fields. An integral expression for the radiation field is obtained and is evaluated by the method of steepest descent. The resulting radiation patterns display interesting effects due to electron pressure near the electron plasma frequency, and these are discussed with the help of the transmission line analog to the problem. The surface-wave poles are located and discussed using this same analog.     

On the location of leaky wave poles for a grounded dielectric slab

A simple numerical procedure for finding the loci of TE and TM leaky wave poles as the frequency or the thickness of the slab varies is presented. These loci provide important information when the integration path of the Sommerfeld integral for the grounded dielectric slab problem is deformed into the improper sheet of the Riemann surface. The accuracy of the loci has been checked extensively against contour plots of separate expressions for the electric flux density for the TE and TM cases     

Analysis of periodic arrays of waveguide apertures on conducting cylinders covered by dielectric

The analysis of infinite arrays of waveguide apertures on cylinders covered by a dielectric is approached by enforcing the continuity of the EM fields at the air-dielectric and at the dielectric-cylinder interfaces. The continuity of the EM fields at the first interface is enforced by representing the fields in the air and in the dielectric by an orthonormal set of modes LSE and LSM with respect to the radial direction. The matching of the fields at the second interface is performed by resorting to the "eigenexcitation" method [1]. The fields external to the cylinder are represented by a set of space harmonics matching the symmetry of the excitation of the array and the fields in the waveguides by a superposition of normal waveguide modes. The continuity of the fields is approximately enforced by using Galerkin's method. The rigorous analysis of these structures leads to rather involved expressions for the element driving point admittance and for the far fields. An approximate analysis is introduced to simplify the design of these structures for cylinders of large radius. Numerical examples illustrate the good approximation given by the simplified analysis. Numerical results are presented for the case of an array on a cylinder with radius approximately100lambda. The array element pattern shows the presence of resonance dips much more pronounced than the notches due to grating lobe phenomena.     

Quasi-optics of the waves guided by a slab of uniaxially anisotropic dielectric

A ray optical method is given for deducing the dispersion relation and the group velocity of the TM wave guided by a slab of uniaxially anisotropic dielectric with particular emphasis on confirming the correctness of the reverse lateral displacement of the ray on total reflection at an interface separating the dielectric from the free space.     

Complete location of poles for thick lossy grounded dielectric slab

In order to obtain accurate closed-form representations of the microstrip Green's functions, it is often necessary to find the locations of the proper and improper surface-wave poles. In this paper, we present an efficient and robust iterative algorithm based on contraction mapping, which can locate all the proper and improper solutions of the characteristic equations of the grounded dielectric slab. The dielectric may also be lossy     

Frequency-adjustable circularly polarised dielectric resonator antenna with slotted ground plane

Circularly polarised (CP) dielectric resonator antennas (DRAs) with a slotted ground plane are proposed. The proposed CP design is achieved by embedding two pairs of unequal slots in the finite ground plane of the feed substrate, which results in the excitation of two near-degenerate orthogonal modes and leads to CP radiation. For the proposed design, a large CP bandwidth, determined from 3 dB axial ratio, as high as 2.7% is also obtained. The resonant frequency can be tuned by changing the slot length. This proposed design is applicable to DR antennas where post-manufacturing trimming is required. Details of the proposed designs and experimental results of the constructed prototypes are presented.     

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     

Response of a grounded dielectric slab to an impulse line sourceusing leaky modes

Describes how expansions in leaky (or improper) modes may be used to represent the continuous spectrum in an open radiating waveguide. The technique requires a thorough knowledge of the life history of the improper modes as they migrate from improper to proper Riemann surfaces. The method is illustrated by finding the electric field resulting from an impulsively forced current located in the free space above a grounded dielectric slab     

Diffraction from a truncated grounded dielectric slab: acomparative full-wave/physical-optics analysis

The problem of diffraction at the edge of a semi-infinite grounded dielectric slab excited by a line source is investigated. This canonical problem may be used as a reference solution in the high-frequency regime for patch antennas radiating from a finite grounded slab. Both physical optics (PO) and integral equation (IE) approaches are used and compared. The PO formulation is cast in a convenient asymptotic form that neatly describes the diffraction processes associated with the various wave species. The IE, solved by the method of moments, is formulated by enforcing the continuity of the electric field on an infinite aperture orthogonal to the slab. This allows a drastic reduction of unknowns, provided that appropriate entire domain basis functions are used that are shaped to match the asymptotic behavior of the aperture field. Comparison between the PO and IE solutions is presented to determine the range of validity of PO     

Electromagnetic plane wave scattering by large and finite strip array on dielectric slab

Plane wave scattering from a large but finite strip array on dielectric substrate is analysed in the frequency domain via a decomposition into plane wave spectra by using the method of moments and a closed analytical form of the spectral Green’s function for the structure under examination. Closed form asymptotic expressions are developed for mutual coupling terms which lead to a highly efficient and accurate procedure. New results for radar cross section in the ultra-wideband frequency range of the finite strip array are shown. Influence of the resistivity of the strips in the variation of the radar cross section is noted and discussed. Variations of the radar cross section with the scattering angle are presented as well.     

Scattering from perfectly conducting and resistive strips on agrounded dielectric slab

The scattering properties of perfectly conducting and resistive strips are predicted for strips which are located on a dielectric slab backed by a perfectly conducting ground plane. The spectral domain Green's function is used to relate the currents and fields on the strip, and the resulting integral equation is solved using the method of moments. Both TE and TM strips are examined using piecewise linear and pulse subdomain basis functions, respectively, to model the current on the strip. Calculated results are compared with results measured at the NASA Langley Research Center