Low-mass low-profile metasurface antennas based on anisotropic surface impedance

Leaky-wave antennas are a class of antennas that use a non-completely confined traveling wave as the main radiating mechanism The possibility of transforming a surface wave into a leaky wave by using a periodically varying isotropic impedance plane has been demonstrated by Oliner and Hessel [1]. An example of antenna designed by using this concept is reported in [2]. In the last years, metasurfaces (MTS) have revealed to be a powerful tools to realize a variable impedance sheet. In the microwave range, impenetrable MTS are obtained by printing a periodic arrangement of electrically small elements on a grounded slab; due to the small periodicity compared with the wavelength, MTS can be characterized in terms of a surface impedance which imposes boundary conditions on the ratio between the average tangential components of the electric and magnetic fields A modulation of the MTS equivalent surface impedance may be obtained by gradually varying the geometry of the elements in contiguous cells [3]. The effective impedance is obtained by considering each constituent element of the metasurface as embedded in a locally uniform periodic structure and identifying the local value of reactance with that of a periodic texture which matches the local geometry [summary form only given].