Superdirective radiation from finite groove gratings

The feasibility of generating superdirective radiation from antenna arrays comprising a finite number of active elements has been previously established in theoretical research, and has also been verified experimentally. In an earlier paper the authors have demonstrated that the scattered field of a structure formed by a finite array of coupled slotted cylinders exhibits superdirective characteristics at the resonance frequencies of the system. It is interesting to examine the question whether this property is a common attribute of scatterers formed by coupled resonant elements. This prompts us to investigate, in this paper, a corrugated structure formed by a finite array of rectangular grooves in a conducting surface. We find that the scattered field from such gratings also exhibits superdirective properties and that the superdirective scattering is associated with a high Q resonance that can only be excited in finite gratings. At these resonances, the magnitude of the electromagnetic field excited in the grooves is very high and the phase alternates between 0 and /spl pi/.