Superdirective radiation from finite gratings of rectangular grooves

In this paper, the superdirective property of arrays comprising a finite number of rectangular grooves is studied by using the modal approach, which is a simple but powerful technique for analyzing these gratings. Numerical results show that when a specific characteristic mode of the structure referred to as the pi mode is excited, the intensity of the field scattered in the specular direction exhibits a maximum, which becomes sharper and narrower as the number of grooves is increased. The far field patterns exhibit superdirectivity at these resonant frequencies as evidenced by their beamwidths that are narrower than those expected from apertures of comparable size. The model-based parameter estimation (MBPE) technique has been employed to help locate extremely narrow resonances that are characteristic of superdirective arrays and its usefulness has been demonstrated.