Antenna terminals based on ultra-compact retrodirective antenna arrays

A novel physical effect of angular super-resolution based on the direction-of-arrival information sampling using highly oscillatory evanescent harmonics in dense antenna array environment is demonstrated theoretically and experimentally. This phenomenon enables realisation of novel, ultra-compact antenna terminals (ATs) with superdirective radiation patterns and spatial auto-focusing characteristics for any direction of arrival of the excitation waveform. The use of these ATs should enhance the signal-to-noise ratio at the receiver, increase overall energy efficiency of the wireless communication or power transmission systems and lead to substantially lower interference and EM pollution across the wireless network area. Special attention is given to the antenna array operating in the presence of a flat metal ground plane or a ground plane with EM band-gap structure. Near-field scattering phenomena arising as a result of the antenna array coupling to the ground planes of both types and their effects on the far-field radiation patterns are analysed in detail. The results of the study should be important for the development of the electrically compact ATs to be employed in the energy-efficient wireless communication systems including the Internet-of-Things, wireless sensor networks and wireless powering systems.