Abstract: In recent days, the growing request of information and mobility has an unavoidable impact on efficient utilization of wireless systems and services with a consequent congestion of wireless medium. As a consequence, issues regarding an efficient and smart utilization of limited radio resource have been raised. To address these problems, a proposed method is the use of antenna systems that are able to first sense the external EM environment and then reconfigure the radiation characteristics of the generated field to guarantee a reliable communication by using time modulation in 4-D arrays. Harmonic radiations having different spatial distribution and shapes can be synthesized in order to receive signals arriving on the antenna from different directions. The capability to generate a field having different frequencies in spatial distribution implies that signal transmitted by time modulated 4-D arrays is direction dependent. Such a feature is exploited in this paper to implement a secure communication scheme directly at the physical layer.

Keywords: 4-D arrays, Cognitive radio, RF switches, Time Modulation, Harmonic Radiations.