Multi-beam Antenna Based On Artificially Controlling Electromagnetic Field

Multi-beam antenna has been applied in satellite communication, radar,electronic countermeasures since it was created in the1960s. Recently, it has beenwidely used in high-speed data communication, passive millimeter wave imagingand millimeter-wave radar system. However, conventional multi-beamantenna—reflector antenna has fatal disadvantages of heavy weight and bulkyvolume. Phased-array antenna not only requires complicated feeding ports andphase-shift network, but also has high cost. Lens multi-beam antenna basedartificially electromagnetic (EM) controlling requires low cost and shows a goodbeam shape. Transform optics (TO) is one main method. It has been employed todesign variety of novel microwave and optical devices combining with the emergingof metamaterials, such as invisibility cloaking and illusion optical device, etc. Oneimportant application of TO is to design multi-beam antenna.In this paper, a general design of N-beam antenna by thin, homogenous anduniaxially anisotropic media is proposed. A linear transformation mapping is used toachieve the homogeneous characterization of the transform optical lens, which istherefore easy to be fabricated compared with previously transformation designslimited by inhomogeneity. In the near field, the transformed space converts thespherical wave into quasi-plane waves in the desired directions. In the far field,omnidirectional radiation pattern becomes directed radiation pattern. Multi-beamsformed and there is almost no difference between beam shapes own to the symmetryof the transformation optics. In addition, only one embedded dipole is needed as thefeed. This tremendously overcomes the complexity of feed network of traditionalmulti-beam antenna formed by multiple horns. Also corresponding volume andweight have been decreased to a great extent.To verify the theoretical design, a four-beam transformation optics lens antennais designed, fabricated and tested. In the case of simplified TE mode, only onez-component of the permittivity of the transformed space is needed. And thispermittivity was fabricated by printed metallic strap lines on the substrate. It hasbeen measured that the realized gain of the four-beam antenna has increased6dBcompared with the single dipole while reflection coefficient and relative bandwidthare kept unchanged due to the impedance mismatching little. It works in the WLANband (5.3GHz–5.7GHz) and can be applied in the multiple-input-multiple-output(MIMO) systerm. For the impedance mismatch induced by simplification, we alsoresearch EM controlling based huygens’ surface whose impedance is matched. Anda plane wave focusing simulation experiment has been done. The proposed novel transformation which only requires one layer uniaxially anisotropic metamaterialsmakes it simple and realizable to design multi-beam antenna and other microwavedevices. This research provides important application value for domestic state-of-artsatellite communication and radar system.