Simulation Analysis of Electromagnetic Surface Wave Suppression by Soft Surfaces, Including Effects of Resistive and Active Elements

The soft surface is defined by its anisotropic surface impedance, and it has the property of suppressing surface wave propagation for any polarization of the electric field. It can be used as a general design element for reducing scattering or controlling coupling between nearby antennas. In this paper, the suppression capabilities and bandwidth limitations of soft surfaces are analyzed using simulations to draw the following conclusions: (1) a soft surface is as good as an ideal perfect magnetic conductor for suppressing vertically polarized surface currents; (2) adding loss to the soft surface actually increases coupling between nearby antennas; (3) the bandwidth of soft surfaces can be extended using active loading; and (4) a soft surface boundary condition can suppress coupling below even the expected free-space wave coupling. Several simple examples are illustrated using simulations, including the effect of lossy substrates, designs for active loading, and the effects of soft surfaces on the contributions to coupling between nearby planar antennas.