Leaky wave lenses for spoof plasmon collimation

We theoretically demonstrate the feasibility of collimating radiating spoof plasmons using a leaky wave lens approach. Spoof plasmons are surface waves excited along reactance surfaces realized through metallic corrugations. By employing a periodic perturbation to the geometric profile of this type of reactance surface, it becomes feasible to convert the excited spoof plasmons into free-space radiating leaky wave modes. It is demonstrated that by structurally modifying such a corrugated surface through the introduction of a non-uniform sinusoidally modulated reactance profile, then a tapered wavenumber, with a real part less than that of free space, can be established along the surface. In this way the radiating properties of the structure (amplitude and phase) can be locally controlled thereby creating a radiating effect similar to that of a non-uniform current distribution. By properly engineering the space dependent wavenumber along the corrugated surface, different regions of the structure will emit spoof plasmon energy at different angles with varying intensity. The combined effect is the emission of an electromagnetic wave exhibiting a converging wave-front that eventually collimates spoof plasmon energy at some desired focal point.