Analysis and realization of a wideband mantle cloak with improved cloaking performance

An approach for improving the invisibility performance of mantle cloak is proposed. It is based on an interesting observation that the cloaking performance of mantle cloak can be significantly enhanced if the cloak is operated under tilted conditions with respect to the incident radiation (such that the wave is incident obliquely onto the cloak). The mantle cloak is thus designed by judiciously choosing the value of surface impedance corresponding to the tilt angle. It is because the optimum value of surface impedance changes with the tilt angle. An analytical method is devised for the calculation of optimum surface impedance under tilted conditions and subsequently verified with Ansys HFSS simulations. It is also shown that by deliberately tilting the mantle cloak, numerous advantages over normal incidence scenario, are obtained, such as (a) significant reduction in total scattering width, (b) considerable enhancement in bandwidth, and (c) increase in performance robustness with respect to the dispersion of surface impedance. These advantages of operating under tilted conditions are well elucidated by comparing it with that for normal incidence scenario previously presented in various literatures. The metasurface cloak is subsequently realized using I-shaped unit cell structure and varactor diodes, and cloaking performance is analyzed using HFSS simulations.