Abstract
A transformation-optical method is presented to enhance the directivity of a cylindrical wire antenna by using an all-dielectric graded index medium. The strictly conformal mapping between two doubly connected virtual and physical domains is established numerically. Multiple directive beams are produced, providing directive emission. The state-of-the-art optical path rescaling method is employed to mitigate the superluminal regions. The resulting transformation medium is all-dielectric and nondispersive, which can provide broadband functionality and facilitate the realization of the device using available fabrication technologies. The realization of the device is demonstrated by dielectric perforation based on the effective medium theory. The device’s functionality is verified by carrying out both ray-tracing and full-wave simulations using finite-element-based software COMSOL Multiphysics.
Highlights
A transformation-optical method is presented to enhance the directivity of a cylindrical wire antenna by using an all-dielectric graded index medium
If the material in the virtual space is taken as vacuum, CTO implies that the refractive index of the graded index (GRIN) transformation medium in the physical space follows the below equation[2]: n(x, y) = df (z) = f ′(z) . dz
There is no way to remedy this defect fully, we can significantly reduce it by employing the optical path rescaling m ethod[9], bringing the refractive index to a very moderate range
Summary
A transformation-optical method is presented to enhance the directivity of a cylindrical wire antenna by using an all-dielectric graded index medium. Having such GRIN material opens up a wide range of fabrication methods to realize the device, including drilling sub-wavelength holes in a dielectric s ubstrate[5,39,40], using graded photonic crystals[41,42,43], dielectric layered shell deposition[39,44,45], electron-beam lithography[46,47,48], and 3D printing[49,50] Owing to their practicality, CTO and QCTO have drawn a great deal of attention. In contrary with the case of a point source where the transformation is established between two connected regions, for the case of a wire, the conformal mapping needs to be established between two doubly connected regions
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