  We study the characteristics and radiation mechanism of antenna superstrates
based on closely located periodical grids of loaded wires. An explicit
analytical method based on the local field approach is used to study the
reflection and transmission properties of such superstrates. It is shown that
as a result of proper impedance loading there exists a rather wide frequency
band over which currents induced to the grids cancel each other, leading to a
wide transmission maximum. In this regime radiation is produced by the magnetic
dipole moments created by circulating out-of-phase currents flowing in the
grids. An impedance matrix representation is derived for the superstrates, and
the analytical results are validated using full-wave simulations. As a
practical application example we study numerically the radiation
characteristics of dipole antennas illuminating finite-size superstrates.

Classical Physics