  In this paper a planar electromagnetic absorber is introduced whose
performance is maintained over a wide change of the incidence angle for both TE
and TM polarization. The absorber comprises an array of patches over a grounded
dielectric slab, with clear advantage in terms of manufacturability. It is
shown that a high value of the relative permittivity of the substrate is
essential for the operation of the absorber. The main contribution of the paper
is to demonstrate and practically use the presence of an additional resonance
of high-impedance surfaces when the plasma frequency of the wire medium
comprising metallic vias in the dielectric substrate is close to the original
resonance of the high-impedance surface. The presence of the vias between FSS
and the ground plane is discussed both for the case of a high-permittivity
absorber and for a low permittivity one. The radius of the vias influences the
oblique incidence TM absorption, and when properly designed, the insertion of
the vias result in bandwidth enlargement and higher absorption.
