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Anisotropic MM Multibeam Antenna Lens

In the previous two sub-sections, anisotropic MM slabs were used to generate a single highly directive beam. In this sub-section, we extend the idea to embed an isotropic source inside an AZIM lens with multiple lens segments for generating multiple highly directive beams over a wide operational bandwidth. Moreover, such an AZIM multibeam lens is experimentally demonstrated at microwave frequencies.

Two-dimensional/three-dimensional AZIM lens concept and numerical results

Two- and three-dimensional full-wave numerical simulations were performed to validate the concept of multiple highly directive beam generation via AZIM lenses. For the two-dimensional lens examples, only TMz polarization with a z-directed i'-field was used in the simulations for simplicity. The first example is a square lens with four collimated beams uniformly distributed in the x-y plane pointing at f = {0°, 90°, 180°, 270°}, as shown in Fig. 1.15a, while the second example is a hexagonal lens with six beams uniformly distributed in the x-y plane pointing at f = {30°, 90°, 150°, 210°, 270°, 330°}, as shown in Fig. 1.15b. To demonstrate the flexibility of controlling the radiated beams, a third lens is displayed in Fig. 1.15c having five customized collimated beams, each radiating at the desired angles of f = {30°, 90°, 165°, 247.5°, 322.5°}. All three lenses have a low value for the mT' parameter with a magnitude of 0.01 in each of the segments. From the electric field distribution, it is observed that the waves radiated from the central isotropic source are well-collimated, even in close proximity to the source.

For the three-dimensional example, we surrounded a previously reported quasi-isotropic radiator [60], shown in Fig. 1.16 (left part), with six lens segments, each having low-value permittivity and permeability tensor parameters with a magnitude of 0.01 in the direction of the radiated beam. Figure 1.16 (right part) shows the three-dimensional radiation patterns with and without the presence of the transformation optics lens simulated by HFSS. It can be observed that the antenna alone has a near-isotropic radiation pattern, whereas with the lens present, the radiation pattern exhibits six highly directive beams. It should be noted that not all of the six directive beams have the same linear polarization, which is due to the quasi-isotropic source antenna employed here and not the AZIM lens since its response is polarization independent.

Snapshots of the z-directed near- and far-zone electric field determined via a two-dimensional COMSOL simulation of the transformation optics lens at 3 GHz with

Figure 1.15 Snapshots of the z-directed near- and far-zone electric field determined via a two-dimensional COMSOL simulation of the transformation optics lens at 3 GHz with (a) four radiated beams uniformly distributed, (b) six radiated beams uniformly distributed, (c) five radiated beams non-uniformly distributed in the x-y plane.

Three-dimensional coordinate transformation lens applied to a quasi-isotropic antenna proposed in Ref

Figure 1.16 Three-dimensional coordinate transformation lens applied to a quasi-isotropic antenna proposed in Ref. 69. (a) The three-dimensional directive emission lens and the embedded quasi-isotropic antenna. The lens is designed to produce six highly directive beams: one normal to each face of the lens as indicated by the labels. (b) The simulated radiation pattern of the quasi-isotropic antenna without (left) and with (right) the lens. Reprinted, with permission, from Ref. 62, Copyright 2012, IEEE.

 
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