Highly directive antennas based on a slim Luneburg lens

Optics Express, 2011

Luneburg lens is a marvellous optical lens but is extremely difficult to be applied in any practical antenna system due to its large spherical shape. In this paper, we propose a transformation that reduces the profile of the original Luneburg lens without affecting its unique properties. The new transformed slim lens is then discretized and simplified for a practical antenna application, where its properties were examined numerically. It is found that the transformed lens can be used to replace conventional antenna systems (i.e. Fabry-Perot resonant antennas) producing a high-directivity beam with low side-lobes. In addition, it provides excellent steering capabilities for wide angles, maintaining the directivity and side-lobes at high and low values respectively.

Microwave and Optical Technology Letters, 2018

We demonstrate a new method for realizing modified Luneburg lens antennas with nearly continuously graded permittivity profiles in three-dimensions. The method used a quasi-conformal transformation optics (QCTO) approach to modify the geometry and permittivity of a spherical Luneburg lens to have a flat surface for convenient integration of antenna feeds. The modified lens was then fabricated using Fused Deposition Modeling (FDM) printing with an effective media approach that employs space-filling curves. The method was validated by designing and fabricating a modified Luneburg lens antenna designed to operate in the Ka-band. The antenna performance of the sample was measured experimentally and shown to compare well to predicted results using full wave simulations. The device was able to achieve a reasonably high degree of beam steering (ie, −55 to +55) over the entire Ka-band. We believe this new approach provides a cost-effective and scalable means of realizing practical passive beam steering lenses that operate over a broad range of frequencies.

Photonics and Nanostructures - Fundamentals and Applications, 2012

A high gain lens antenna is designed by using a new transformation different from the discrete optical transformation. The antenna is composed of two blocks. Each block is made of homogenous and anisotropic materials, and thus can be easily achieved by metamaterial. The numerical results based on full wave simulation indicate that the antenna can be used to realize highly directive radiation beam, and the direction of radiation beam can be controlled artificially by changing the geometry parameters of the device. The electromagnetic field in the transformation region can be either stretched or compressed along both transverse and longitudinal directions by varying the geometry parameters in the virtual space while the distribution of electromagnetic field outside the antenna is little influenced. Moreover, effective medium theory is applied to realize such an antenna with isotropic materials. Also, the multi-beams antenna is investigated. It is indicated that this antenna can generate multi-collimated beams radiating at the desired angles.

Journal of Applied Physics, 2009

Spatial coordinate transformation is used as a reliable tool to control electromagnetic fields. In this paper, we derive the permeability and permittivity tensors of a metamaterial able to transform an isotropically radiating source into a compact ultradirective antenna in the microwave domain. We show that the directivity of this antenna is competitive with regard to conventional directive antennas ͑horn and reflector antennas͒, besides its dimensions are smaller. Numerical simulations using finite element method are performed to illustrate these properties. A reduction in the electromagnetic material parameters is also proposed for an easy fabrication of this antenna from existing materials. Following that, the design of the proposed antenna using a layered metamaterial is presented. The different layers are all composed of homogeneous and uniaxial anisotropic metamaterials, which can be obtained from simple metal-dielectric structures. When the radiating source is embedded in the layered metamaterial, a highly directive beam is radiated from the antenna.

2012

Using the idea of wave manipulation via coordinate transformation, we demonstrate the design of novel antenna concepts. The manipulation is enabled by composite metamaterials that realize the space coordinate transformation. We present the design, realization and characterization of three types of antennas: a directive, a steered beam and a quasi-isotropic one. Numerical simulations together with experimental measurements are performed in order to validate the concept. Near-field cartography and far-field pattern measurements performed on a fabricated prototype agree qualitatively with Finite Element Method (FEM) simulations. It is shown that a particular radiation can be transformed at ease into a desired one by modifying the electromagnetic properties of the space around it. This idea can find various applications in novel antenna design techniques for aeronautical, telecommunication and transport domains.

IEEE Transactions on Antennas and Propagation, 2019

A new lens antenna for wide-angle beam-steering application is presented. The 2D lens permittivity profile according to Luneburg is modified using transformation optics to obtain a planar focal surface, allowing for a simple, cost-effective planar feed technology. A slice of the lens is confined between two metallic surfaces forming a parallel-plate transmission line, enabling beam-steering in the plane containing the slice. Stacking up such slices results in a more focused beam and beam-steering capabilities in the perpendicular plane. As a result, full two-dimensional beam-steering becomes possible, with a very wide steering range of ±60°i n one plane and a smaller steering range of ±15°in the orthogonal plane. The inhomogeneous dielectric slice is made of four dielectric materials with different permittivity, with a pattern of drilled holes of different diameters realizing a smooth gradient of the effective permittivity. The measured performance of the antenna prototype, operating at about 10 GHz includes 17.2 dB maximum directivity, a scan loss better than 0.8 dB, a side-lobe level better than 11 dB and an aperture efficiency of 74 %, outperforming any other reported beam steering antenna with planar focal surface.

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

Current designs of electromagnetic cloaks are largely based on the use of metamaterials and a technique called "transformation optics/electromagnetics". Free space cloaks require materials with extreme properties and, hence, they are difficult to implement in practice. However, the theory of "transformation optics/electromagnetics" offers a useful design tool for antenna engineers, and enables them to develop novel antennas. In this paper, we will review some research activities at Queen Mary, University of London, regarding applications of transformation electromagnetics in the antenna and microwave engineering. Design examples such as flat reflectors, lenses and sub-wavelength antennas will be introduced. Novel FDTD techniques to deal with the design of gradient index metamaterials will be also demonstrated and used to evaluate the performance of transformation-based antennas. In particular, the tradeoff in antenna performance whether or not metamaterials are required in the design will be discussed.

IEEE iWEM2011, 2011

We present two different points of approaches to a class of antenna designs, based on two variations of the Transformation Electromagnetics (T-EM) approach, both of which have been introduced recently in the literature. The first of these addresses the antenna and absorber design problems from the Transformation Optics viewpoint, while the second looks at the same problem from a Field Transformation approach. Illustrative examples based on the application of both of these approaches will be included in the presentation. Antenna design is very well established field, and it is commonly practiced by engineers who rely on years of experience when developing new antenna configurations that can better meet the desired performance specifications than can the legacy designs. Recently, new concepts for antenna design have been introduced via the use of "Transformation Electromagnetics,"or TEM, in which Maxwell's Equations are transformed from one coordinate system to another in order to design material parameters of the medium in which an antenna is embedded, with a view to realizing a desirable antenna performance that may be difficult to achieve by using conventional approaches and/or with conventional media. Transformation EM, or more specifically on Transformation Optics (TO), evolved from an original concept which was based on the use of materials that could bend or route the propagation of light around an object to conceal it electromagnetically, as though it were a magic cloak. The process involved a mapping of the initial configuration of the electromagnetic fields onto a Cartesian mesh (see Fig.1), in a way such that a 'bump' on a flat surface became totally flat in the new system, though the material in the new system became modified in this process in a way that was dictated by the transformation equations. Ideally, light could travel in the new system in an undistorted manner, though this would require placing a blanket comprised of inhomogeneous media over the bump in the original system such that light would bend around it and behave as though the bump did not exist (see Fig.2). The basic concepts of TO are relatively simple. It relies on the notion that, in principle, it is possible to manipulate the propagation of electromagnetic waves in any fashion, for the desired application, by capitalizing on the fact that Maxwell's equations are form-invariant to a coordinate transformation. As pointed out before, this is only true provided we concurrently transform the material parameters as well, as we go from one coordinate system to another, in a manner dictated by the Transformation Optics paradigm. It was recognized even during the early stages of development of TO that these materials for the blanket or the cloak often fall in the category of Metamaterials (MTMs), because the requisite materials are not available in nature and, hence, must be artificially synthesized. We show in this paper how the concepts of Transformation Optics are applicable to the problem of designing a class of antennas as well, and they can lead to new antenna design paradigms not considered hitherto. The coordinate transformation approach can be employed to designs flat lenses, for instance, whose material parameters are derived via an application of the TO. As an example, let us consider the problem of designing a flat lens type of antenna whose properties are similar to those of a spherical version of the same. We transform the surfaces of the spherical lens into flat surfaces by using a suitable coordinate transformation, recognizing, of course, that the medium properties in the new coordinates system would be modified in the process from those in the original spherical system. At this point, it becomes necessary to synthesize electric and magnetic media that closely approximate the medium properties dictated by the transformation we have used so that the flat lens can mimic the properties of a spherical one that we are trying to replace. Although, to the best of our knowledge, there is no systematic procedure currently available for synthesizing such media, and issues pertaining to feasibility as well as realizablity remain open questions at present, considerable recent progress has been made toward fabricating devices made of MTMs that are very good approximations of the ideal media specified by the TO to realize the desired performance. We also note that the bandwidth typically associated with the media synthesized on the basis of the