Multi-layered coating metasurfaces enabling frequency reconfigurability in wire antenna

In this work, we introduce a conceptually new approach for designing frequency reconfigurable wire antennas based on the use of multi-layered wrapping metasurfaces. Specifically, we demonstrate that the complex-valued input impedance of a wire antenna can be tailored by engineering the electromagnetic characteristics of a coating metasurface and we discuss how this effect can be exploited for achieving wide-band frequency reconfigurability. We report the advantages and limitations of this approach – especially compared to conventional impedance matching techniques - and, as a relevant example, we discuss the design of a reconfigurable half-wavelength dipole. For this example, the coating metasurface consists of a three-layer capacitive structure loaded with varactor diodes. It is shown that the operative frequency band of the antenna can be dynamically and continuously shifted in a quite broad range of frequencies (2/3 octave bandwidth) while preserving the current distribution of the fundamental mode and the omnidirectional shape of its radiation pattern on the horizontal plane. The possibility to allocate the antenna service within continuous sub-bands of operation makes this solution particularly suited for cognitive radio systems.