The article presents the method of finding the complete equivalent circuit of two waveguides with coplanar axes coupled through a centered inclined slot in the common broad wall. The variational method based on dyadic Green's function is used for finding the parameters of the equivalent circuit. A cosinusoidal aperture field distribution is assumed. Considerable mathematical simplification is resulted from replacing the centered inclined slot by an equivalent magnetic dipole. Coupling slot characteristics are deduced, including resonant length, dominant mode scattering in both the waveguides. Numerical and experimental results for resonant lengths and scattering parameters are presented over a range of tilt angles, frequencies, and waveguide dimensions. These results have significant applications in linear waveguide arrays and coupler design. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.

Abstract This article presents a method to evaluate the cutoff wave-numbers of higher-order modes of eccentric circular waveguides employing the method of conformal transformation combined with the method of finite difference. Bilinear conformal transformation has been used to transform eccentric cylinders into concentric cylinders. The cutoff frequencies are evaluated from the eigenvalues by solving the characteristic equation expressed in terms of matrices obtained from a set of simultaneous equations satisfying the boundary conditions. A comparison of numerical data with that available in the literature is presented.

Lightning is typically an atmospheric phenomenon and is a threat to human life, houses, historical monuments, electronic and electrical systems. Through a good will of research the scientific community has come to some conclusion about the cause of lightning and its hazards to system. In this paper the generation process of Cloud to ground lightning is described in brief and the most harmful one, the return stroke has been modeled. The reason behind taking return stroke in all formulation related to lightning is it's continuous nature. Other forms are branched and therefore discontinuous.

The paper presents a study of the voltage induced on an overhead line due to lightning discharge. Lightning discharge releases energy over a large frequency band, generally from few hundreds of hertz to megahertz. The bulk of the radiated electromagnetic energy within VLF and ELF band, which is horizontally polarized, is picked up by the electrical power lines, and the interfering signal appears in the form of a surge on these lines. This surge propagates along the transmission line, and affects all equipment and appliances connected to the mains supply. Any lightning strike induces voltage in an open wire overhead line, communication line and other similar structures. The current that flows from cloud to ground is of transient nature and is expressed as superposition of two decaying exponentials with rise and fall time constants as parameters and peak current amplitudes. The nature of the return stroke current waveform is used in accordance with the one considered in. From the expression of current in time domain, the frequency spectrum covered by the lightning discharge can be estimated using Fourier Integral transform. Several studies, both theoretical and practical have been carried out by many researchers to provide insight of the lightning induced voltages. The induced voltage on an overhead line is related to the field produced by the transient current resulting from the lightning discharge. The transient voltage induced on the overhead line as well as communication line produces over-voltage effect to the system connected to the line. The field induced on the overhead lines can be estimated from knowledge of per unit length (PUL) parameters of the line and its geometrical structure and alignment. The PUL parameters are considered for a two conductor line with dielectric coating and having separation between them and the parameters are obtained following the method in reference.

The electrically conducting region of the upper atmosphere of earth's surface, the ionosphere, plays a major role in all sorts of radio communication. In 1901 when Marconi was carrying out the experiment, surprisingly the signal was found to be received on the area behind the Atlantic Ocean. The presence of signal could not be justified considering only ground wave propagation. Ground reflection and diffraction effect would be insufficient to permit such a long distance transmission and reception of signal around the earth's curvature. This finally led to the discovery of ionosphere which surrounds the earth. Later details study of ionosphere leads to the discovery of different layers (D, E, F1 and F2) and variation of characteristics from day to night and vice-versa. Lightning is considered to be the strongest natural source on the ground so far. Lightning discharges radiate the bulk of their electromagnetic energy in the very low frequency and extremely low frequency ranges. Radio wave in ELF and VLF are either penetrate through or reflected back from these ionized layers. If the lightning burst takes place not far from ionosphere it will modify the electronion density of ionosphere thereby modifying its characteristics.

The paper presents the method of finding the complete equivalent circuit of crossed rectangular waveguides coupled through a centered inclined slot in the common broad wall. The centered slot is replaced by an equivalent magnetic elliptic cylindrical dipole and the method of finding the length of their principal axes as well as their angle of inclination θ, looking from the top and bottom guides are discussed. Using conformal transformation, the elliptic cylinder is transformed into circular cylinder, whose radii are different but depend on θ looking from the top and bottom guides. The variational method based on waveguide dyadic Green's function is used for finding the parameters of the equivalent circuit. Numerical data are presented.

The variational method is used in the present paper to derive the expressions for the complete equivalent circuit of a central transverse slot in the broad wall of a rectangular waveguide. The magnetic field is found from the vector potential involving waveguide (internal) dyadic Green's function. The expression for the self-reaction between the magnetic field and the magnetic current appears in the form of infinite double summation. The double summation appearing in the expression for the self-reaction is simplified to a series, which converges very rapidly. Numerical data evaluated using a complete equivalent circuit is presented.

The capacitance of dielectric coated metallic cylinder and truncated cone are evaluated using the method of moments based on the pulse function and point matching. The analysis is based on the boundary condition for the potential on the conductor surface and the normal component of the displacement density at the dielectric-free space interface. The total free charge on the conductor surface is found from the inversion of a matrix partitioned into submatrices. Numerical data on the capacitance and charge distribution are presented.

The paper presents the method of derivations of the elements of the capacitance matrix of a dielectric coated twin cylinder transmission line with two semiinfinite grounded-plates with a gap, located at the plane of symmetry between the cylinders. The cotangent hyperbolic transformation transforms the cylinders to parallel plates and the grounded semiinfinite plates with a gap to a grounded strip between the plates. The transformation of the dielectric boundaries coincident with equipotential contours and concentric with individual conductors are obtained as straight and curved contours respectively in the transformed plane. The characteristic parameters of the eigenmodes are found from the solution of the eigenvalue equation. It is shown that for a symmetrical structure the eigenvalues are identical when the dielectric boundaries coincide with equipotential contour but are different when they are concentric with conductor boundaries. Numerical data are presented.

The paper presents a method of evaluation of the variation of capacitance of an insulated wire above a dielectric substrate as a function of substrate and dielectric thickness for a wide range of values of dielectric constant. Application of cotangent hyperbolic transformation transforms conductor boundaries to parallel plates and dielectric boundaries to curved contours, which are divided into a number of subsections. Considering the series combination of all capacitances of the subsections and their parallel combinations, the expression for the total capacitance is obtained in the form of an integral. Numerical data on capacitance reveal, that for dielectric constant above a certain value, increase in separation between the conductor and ground plane due to increase in thickness of the dielectric substrate and width of the dielectric coating on the conductors does not always lead to decrease in the value of capacitance.

The paper presents a simplified method of evaluation of capacitance per unit length of an insulated wire above a ground plane. Hyperbolic cotangent Transformation is used for the derivation of expression for the capacitance of the wire for any arbitrary angular and radial width of the dielectric insulation. Numerical data on the variation of capacitance with angular and radial widths of the insulating material are presented for a wide range of values of the dielectric constant. A comparison with data available in the literature is presented.

This paper presents the method of derivation of the formula for the capacitance of a metal sphere in the presence of a number of concentric dielectric layers. Analysis is based on boundary condition for the potential on the surface of the conductor due to combined action of the bound plus free charges on the conductor surface and bound charges an all the dielectric interfaces and normal components of displacement densities at dielectric to dielectric to free space interfaces. The agreement of general formula with those for all the limiting cases justifies the validity of the analysis.

Surface photoconductance of sintered titanium dioxide (TiO2) pellet has been studied at room temperature (306 K) and above (upto 475 K). Within the temperature range studied, the conduction in dark has been found purely extrinsic with the activation energies of 0.07 and 0.24 eV. Moderately slow growth of photocurrent at all temperatures indicated the presence of traps. Photosensitivity of the sample was found to increase continuously with the rise of sample temperature. Analysis of the photoconductive decay of the sample has revealed the existence of carriers with two different relaxation times (τ1 and τ2) which varied with the sample temperature in a peculiar fashion.

This paper presents a formulation for evaluation of the capacitance of a pair of cylinders of unequal radii with variable and different width of dielectric on the cylinders, Conformal transformation using co-tangent hyperbolic function transforms the conductor boundaries to parallel plates and dielectric boundaries to curved contours. The expression for the capacitance is derived taking into account the changes in signs of the functions representing the curved contours. Numerical data on capacitance are presented.

This paper presents a rigorous analysis of a slot-coupled T-junction between a primary circular cylindrical waveguide and rectangular waveguide, forming the coupled T-arm. The analysis is based on moment-method formulation using full-wave basis functions and Galerkin's technique for testing. Expression for the coupling and reflection coefficients are found, taking into account the effect of finite wall thickness of the circular waveguide in which the coupling slot is milled. A comparison between the theoretical and experimental results on coupling and return loss are presented.

The surface photoconductance of the sintered Bi2O3 pellets have been studied at room temperature (305K) and above (upto 474 K). Within the temperature range studied, the conduction in dark has been found purely extrinsic with the activation energies of 0.16 and 0.34 eV. Moderately slow growth of photocurrent at all temperatures indicated the presence of traps. Photosensitivity of the sample was very low in magnitude and has been found to increase continuously with the rise of sample temperature. Analysis of the photoconductive decay of the sample has revealed the existence of carriers with two different relaxation times (tau(1) and tau(2)) which varied with the sample temperature in a peculiar fashion.

The paper presents a method for the evaluation of capacitance and charge distribution of metallic truncated cone of finite length with top and bottom circular hat plates and isolated in free space. The integral equations relating the potential and unknown charge distribution on the surfaces are solved using moment method employing pulse and delta functions as basis function and testing functions, respectively, The elements of the matrix to be inverted are found by dividing the surfaces into subsections which are combination of curvilinear rectangles and triangles. Capacitance and charge distribution are evaluated as function of the geometrical parameters of the structure. Numerical results on capacitance and charge distribution are presented.

The authors present a method of finding the effect of fringing on capacitance and charge distribution of conducting structures consisting of coaxial cylinders or of parallel cylinders of identical diameter, each of finite and equal length. The moment method, employing pulse and delta functions as the basis and testing functions, respectively, is used for the analysis. Numerical data on charge distribution and capacitance per unit length, normalised to the same quantity for similar structure of infinite length, are presented

A method is presented of finding the characteristic impedance of twin-cylinder transmission line, each of which is covered by multilayer dielectric based on conformal transformation. Cotangent hyperbolic transformation is used to transform the cross-sections of the metallic boundaries to parallel plates and dielectric boundaries to curved contours. The curved contours are replaced by a large number of discrete steps and the capacitance per unit length of the structure is found from a series and parallel combination of infinitesimal capacitances. The characteristic impedance is found from the capacitance per unit length. Numerical results on capacitance per unit length and characteristic impedance are presented.

The paper presents a method of the evaluation of capacitance of paraboloidal and spherical bowls using the method of moments based on the pulse function as the basis function and point matching for testing. The analysis is carried out by dividing the surface into curvilinear rectangular and triangular subsections. Numerical data on capacitance are presented.