Longitudinal coupling impedance of a circular iris

IEEE Transactions on Antennas and Propagation, 2017

Closed-form analytical expressions for the on-axis scattered fields by a subwavelength circular aperture in an infinite perfectly conducting plane were derived using a vector potential formulation and the equivalence principle. The final expressions are valid for the nearfield, intermediate-field, and far-field zones. The underlined formulation is based on the equivalent quasi-static magnetic current distributions in the aperture, which were derived by Bethe and Bouwkamp in the mid 40's and early 50's. The resulting scattered-field integrals, which involve the free-space Green's function, were evaluated analytically after introducing Taylor series expansion and using transformations. The final closed-form expressions of the scattered fields are given in terms of a recursion formula. Obtained results based on these closed-form expressions are in excellent agreement with data generated by a numerical integration scheme.

1973 Antennas and Propagation Society International Symposium

Radio Science, 2003

1] An asymptotic Green s function technique is presented for the calculation of the surface fields on a perfect electric conductor circular cylinder covered with a dielectric layer. The sources are apertures located on the perfect electric conductor surface. This method is very efficient and valid for large cylinders in terms of wavelengths. The new representation is obtained via Watson s transformation and integral contour deformations. The efficiency of the method results from the circumferentially propagating representation of the Green s function as well as the efficient numerical evaluation of various integrals. Numerical results are presented showing good agreement when compared to other solutions as well as measurements.

IEEE Transactions on Electromagnetic Compatibility, 1998

Electromagnetic (EM) coupling through apertures of arbitrary shape in a perfectly conducting infinite screen of negligible thickness, is considered. In particular, general configurations that include the presence of wires are analyzed. These latter may be asymmetrically located on both sides of the aperture, with some element passing through the aperture. The problem is formulated in terms of an integral equation involving (as unknowns) the equivalent magnetic current at the aperture and the electric current distribution on the wires, which is, therefore, solved by the method of moments (MoM). A set of measurements has been conducted to verify the accuracy of the technique.

IEEE Transactions on Microwave Theory and Techniques, 1995

A formally exact solution is described for the problems of scattering at a junction between two circular waveguides with their axes offset and at a thick off-centered iris in circular waveguide. The analysis method uses Graf's addition theorem for cylindrical functions and the conservation of complex power technique (CCPT). Sample numerical results are presented and compared with available data in the literature.

IET Microwaves, Antennas & Propagation, 2013

The authors investigate extraordinary electromagnetic transmission through a circular aperture surrounded by surface corrugations. An electromagnetic boundary-value problem of a circular aperture surrounded by surface corrugations in a conducting plane is solved based on the mode matching method. The eigenfunction expansion and Hankel transform are used to represent the scattered fields in terms of the discrete and continuous modes, respectively. The boundary conditions are enforced to obtain a set of simultaneous equations. The transmission coefficient and the radiated fields are represented in a fast-convergent series. Computation is performed to illustrate the behaviours of transmission and radiation against the corrugation geometries. The effects of the corrugation geometries on the extraordinary electromagnetic transmission are discussed.

Wave propagation is an important phenomenon in the context of mobile systems. From basic diffraction one can develop methods for objects that are used as models for obstacles in the path of propagation. In order to combine a number of objects, the method known as Physical Optics can be used. This method is mostly used for perfectly conducting surfaces but can be extended to surfaces described by means of an impedance boundary condition. It will be shown that targets that have impedance surfaces yield RCS results that are lower than the results of perfectly conducting surfaces. The results obtained are compared with exact methods and other approximation methods and they are in good agreement. Application of these results to stealth technology and wave propagation is discussed.

IEEE Transactions on Microwave Theory and Techniques, 1997

Progress In Electromagnetics Research C

The problem of electromagnetic (EM) wave scattering on small particles is reduced to solving the Fredholm integral equation of the second kind. Integral representation of solution to the scattering problem leads to necessity to determine some unknown function contained in integrand of this equation. The respective linear algebraic system (LAS) for the components of this unknown vector function is derived and solved by the successive approximation method. The region of convergence of the proposed method is substantiated. The numerical results show rapid convergence of the method in the wide region of the physical and geometrical parameters of problem. Comparison of the obtained results with Mie type and asymptotic solutions demonstrates high degree of accuracy of the proposed method. The numerical results of scattering on particles of several forms and sizes are presented.

30th European Microwave Conference, 2000, 2000

International Journal of Numerical Modelling: Electronic Networks, Devices and Fields, 1991

Calculation of the electromagnetic field diffracted by an aperture situated in a perfectly conducting ground plane can be made through the well-known theory of polarizabilities. However, simple expressions are only obtained under conditions which are not often fulfilled in electromagnetic compatibility problems since, for example, the disturbing field incident on the aperture must be considered as a uniform one. Furthermore, if the aperture is loaded by a low conducting material, available approximate formulas are only valid for a small circular hole. In this paper, we present a numerical approach based on the determination of the equivalent magnetic current distributed on the surface of the aperture. This distribution is the solution of an integral equation solved by the method of moments. This formulation allows us to take the surface impedance of a loading material and the contact resistance between this material and the rim into account. The validation of the computer code is shown by comparing computed and analytical results on some typical examples. Few applications are also described.

Progress In Electromagnetics Research C

In this paper, we use magnetic vector potential formulation, along with equivalence principle and image theory, to solve the electromagnetic scattering of a polarized incident plane wave by a subwavelength circular aperture in a conducting screen. The underlined analytical formulation yields a closed-form solution that is accurate for any angle of incidence or polarization and valid for the near-, intermediate-and far-field regions of observation. The formulation is based on Bouwkamp's diffraction model that uses dominant quasi-static magnetic current modes to represent the governing magnetic current distribution in the circular aperture for any incident wave. Taylor series expansion was implemented on the free-space Green's function, and the individual Taylor terms were integrated analytically to produce closed-form expressions for the scattered fields in all regions. In doing so, the Gegenbauer polynomial expansion was applied in order to allow evaluation of the resulting integrals for any observation point in the lower half space. The results obtained from the proposed analytical approach were compared with data generated through a direct application of a numerical integration technique. The comparison illustrates the validity and accuracy of the proposed analytical formulation.

Radio Science, 1969

The existence and character of modal fields on a two-dimensional structure comprising an infinite periodic series of slotted metal planes is considered. The problem is two-dimensional, since no variation in one transverse coordinate is assumed. Integral equations involving the unknown field in one iris and the propagation constant are formulated for both types of field polarization with the aid of appropriate Green's functions. The integral equations are reduced to infinite matrix equations by a novel procedure that involves the application of Galerkin's method in the Fourier transform domain. It is shown that radial Mathieu functions provide a rapidly convergent series representation for the iris field. For a given polarization, the first two modal propagation constants and iris field distributions are computed for even field symmetry. The real or attenuating part of the propagation constant is found to oscillate between a maximum and minimum value as a function of the distance beween adjacent planes when this distance is large compared with the iris width. The field distribution in the iris is also found to be very insensitive to plane spacing but becomes more peaked as the iris width is increased. ß ß ß ß ß IA• A z I I II (y,z) POINT OF OBSERVATI ON and then verify by numerical means if a convergent solution to the eigenvalue problem can be generated by progressively truncating the infinite matrices. MODAL FORMULATION Let F represent either the electric (E) or magnetic (FI) field vector. The solution of the vector wave equation v• + ko• = o with appropriate boundary conditions may be found by solving the equation

Mathematical Modelling of Natural Phenomena, 2014

Scattering of electromagnetic (EM) waves by small (ka ≪ 1) impedance particle D of an arbitrary shape, embedded in a homogeneous medium, is studied. Analytic, closed form, formula for the scattered field is derived. The scattered field is of the order O(a 2−κ), where κ ∈ [0, 1) is a number. This field is much larger than in the case of Rayleigh-type scattering. The numerical results demonstrate a wide range of applicability of the analytic formula for the scattered field. Comparison with Mie-type solution is carried out for various boundary impedances and radii of the particle.