Anisotropic Artificial Impedance Surfaces /

Anisotropic artificial impedance surfaces are a group of planar materials that can be modeled by the tensor impedance boundary condition. This boundary condition relates the electric and magnetic field components on a surface using a 2x2 tensor. The advantage of using the tensor impedance boundary condition, and by extension anisotropic artificial impedance surfaces, is that the method allows large and complex structures to be modeled quickly and accurately using a planar boundary condition. This thesis presents the theory of anisotropic impedance surfaces and multiple applications. Anisotropic impedance surfaces are a generalization of scalar impedance surfaces. Unlike the scalar version, anisotropic impedance surfaces have material properties that are dependent on the polarization and wave vector of electromagnetic radiation that interacts with the surface. This allows anisotropic impedance surfaces to be used for applications that scalar surfaces cannot achieve. Three of these applications are presented in this thesis. The first is an anisotropic surface wave waveguide which allows propagation in one direction, but passes radiation in the orthogonal direction without reflection. The second application is a surface wave beam shifter which splits a surface wave beam in two directions and reduces the scattering from an object placed on the surface. The third application is a patterned surface which can alter the scattered radiation pattern of a rectangular shape. For each application, anisotropic impedance surfaces are constructed using periodic unit cells. These unit cells are designed to give the desired surface impedance characteristics by modifying a patterned metallic patch on a grounded dielectric substrate. Multiple unit cell geometries are analyzed in order to find the setup with the best performance in terms of impedance characteristics and frequency bandwidt

Metasurface antennas

International audienceThis chapter reports design and analysis methods for planar antennas based on modulated metasurfaces (MTSs). These antennas transform a surface wave (SW) into a leaky wave by means of the interaction with a MTS having a spatially modulated equivalent impedance. The basic concept is that the MTS imposes the impedance boundary conditions (BCs) seen by the SW, and therefore the MTS controls amplitude, phase, and polarization of the aperture field. Thus, MTS antennas are highly customizable in terms of their performances, by simply changing the MTS and without affecting the overall structure. Several technological solutions can be adopted to implement the MTS, from sub-wavelength patches printed on a grounded slab at microwave frequencies, to a bed of nails structure in the millimetre and sub-millimetre wave range in any case, the resulting device has light weight and a low profile. The design of the MTS is based on a generalized form of the Floquet wave theorem adiabatically applied to curvilinear locally periodic BCs. The design defines the continuous BCs required for reproducing a desired aperture field, and it is verified by a fast full-wave solver for impedance BCs. Next, the continuous BCs are discretized and implemented by a distribution of electrically small printed metallic elements in a regular lattice, like pixels in an image. The final layout is composed of tens of thousands of pixels and it is analyzed by a full-wave solver which makes use of entire domain basis functions combined with a fast-multipole algorithm. Examples of design and realizations of MTS antennas are shown, proving the effectiveness of the concept. © Springer International Publishing AG 2018