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The emerging field of transformation optics, with its powerful ability to manipulate and control electromagnetic waves, represents a promising new approach to tailor the radiation properties of antennas. However, previously reported source transformation designs have been severely limited by their narrow operating bandwidth, as well as the number and directions of radiated beams. In this paper, we design, fabricate, and characterize a new type of broadband transformation optics lens capable of converting the radiation from an embedded isotropic source into any desired number of highly directive beams pointing in arbitrary directions. We exploit the dispersive properties of the metamaterial building blocks to greatly enhance the impedance bandwidth of the embedded antenna. Moreover, the simple material parameters required by the demonstrated transformation make it amenable to the development of practical beam collimating devices that operate in both the microwave and the optical regimes.
Jiang et al. (Tue,) studied this question.