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.