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.