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 ofte n 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 b e able to design new structures which avoid these drawbacks, the problem of plane mace scattering from an infinite axially periodic cylinder of arbitr ary geometric and material parameters is analyzed in this paper by a hybrid finite element/boundary element method. Covariant-projection edge elements are employed in the inhomogeneous region of the unit cell and the scattere d field is expanded in terms of cylindrical Floquet harmonics. The resultin g practical numerical procedure has been tested to ensure that power conser vation rules are obeyed and checked satisfactorily against both analytical results and measurements on periodically loaded struts.