In this paper, using quasi-conformal mapping, a bi-functional coating layer is designed with the intention of both cloaking and directivity enhancement of an omnidirectional antenna. For TM external waves coming from a certain direction, the proposed coating layer conceals the inner objects. In addition to the cloaking performance, the designed coating layer plays the role of a metamaterial-based lens that dramatically enhances the directivity level of inner omnidirectional loop-family antennas. To reach this goal, a proper coordinate transformation is elaborately utilized to transform the cylindrical wavefronts radiated from the antenna into semi-pure plane waves. With appropriate simplifications, the proposed coating layer turns into an isotropic meta-device, which is more suitable to be fabricated. To prove the feasibility of the implementation, an SRR-meander line meta-atom is designed to locally realize the required permittivity and permeability distribution of the bi-functional layer. Full-wave simulations are performed via COMSOL finite element solver to validate the cloaking effect and directivity enhancement of the proposed coating layer, at the same time.
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