Ronald L. Ferrari

Hybrid finite-element analysis of electromagnetic plane wave scattering from axially periodic cylindrical structures

In many antenna systems the primary feed or the subreflector will most often be supported by struts which obstruct the aperture and therefore cause a reduction in the directivity and an increase in sidelobe levels. So as to be able to design new structures which avoid these drawbacks, the problem of plane wave scattering from an infinite axially periodic cylinder of arbitrary geometric and material parameters is analyzed by a hybrid finite element/boundary element method. Covariant-projection edge elements are employed in the inhomogeneous region of the unit cell and the scattered field is expanded in terms of cylindrical Floquet harmonics. The resulting practical numerical procedure has been tested to ensure that power conservation rules are obeyed and checked satisfactorily against both analytical results and measurements on periodically loaded struts.

Finite element analysis of electromagnetic wave scattering by a cylinder moving along its axis surrounded by a longitudinal corrugated structure

A hybrid finite element/boundary element technique (FEM/BEM) is presented for the analysis of plane wave scattering from an axially corrugated cylinder of arbitrary geometric and material parameters. Inside the periodic structure a cylinder of infinite length composed of a piecewise uniform isotropic medium moving uniformly in the axial direction is also considered. Covariant-projection edge elements are employed in the inhomogeneous region of the unit cell to solve the Maxwell-Minkowski equations, whilst the scattered field is expanded in terms of cylindrical Floquet harmonics. Numerical results, for both TE/sub z/ and TM/sub z/ polarised incident fields, are presented and validated as far as was possible.

The Finite-Element Method, Part 2: P. P. Silvester, an Innovator in Electromagnetic Numerical Modeling

The work of P. P. Silvester - mainly on the Finite-Element Method applied to problems in electrical engineering and as recorded by his writings - is reviewed, with particular reference to the innovations he introduced. A complete bibliography of Silvesters work is appended.

Finite element analysis of electromagnetic plane wave scattering from axially periodic cylindrical structures

In antenna systems there are many situations where EM waves are obstructed by some mechanical structures that cause an increase in the sidelobes and gain reduction. These mechanical structures often consist of one or more rods that are shaped and loaded in such a way that the blockage is minimised. The blockage effect of simple uniform cylindrical struts and masts of different cross section was widely analysed in the past. However, new structures have been designed in order to minimize this negative effect. Due to the complexity of the problem, only a few simple cases of corrugated axial-symmetric cylinders have been studied. In this communication, a hybrid technique that utilises a finite element/boundary element method (FEM-BEM) is presented to analyse the scattering of an electromagnetic plane wave obliquely incident on an axially periodic cylinder of arbitrary geometric and material parameters. This provides a useful tool for the study of new struts and masts. In particular, the complex structure is analysed by using a simple Galerkin weighted residual finite element method (FEM) employing three-dimensional covariant projection elements. The periodicity of the structure has been properly taken into account using periodic weighted functions whilst the radiation condition has been imposed by expanding the field in the free space surrounding the structure in terms of cylindrical Floquet harmonics.

Finite-element analysis of high-frequency axisymmetric device problems

A finite-element scheme for solving wave propagation problems in devices with complete azimuthal symmetry both in their material properties and in their geometry is presented. The phi -coordinate variation is restricted to sin(n phi + xi ), thus requiring only a two-dimensional space for the complete finite-element analysis. The open radiating boundaries inherent in many propagation problems are tackled through simulated absorption of the radiation by lossy materials. Also proposed for these kinds of boundaries is a hybrid FEM-BEM (finite-element-method-boundary-element-method) formulation, based on the vector Greens function for the Helmholtz equation. This method has been tested by application to an open-ended circular waveguide and by a comparison with the simulated-absorption results. >