Contrarily to classic Right-Handed Materials (RHMs), the role of losses is crucial for composite materials called
metamaterials such as Ultra-refractive Right-Handed Materials (URHMs) and Left-Handed Materials (LHMs). As the
loss-free case for a metamaterial is not stable, a small variation of losses can drastically modify the expected properties
of such a material. Thus, it is important to understand how the input of lossy term affects URHM and LHM aspects, and
also to define, for each of them, the tolerance level for which the interesting metamaterial properties are still valid. The
role of losses is investigated analytically and numerically, a full study about the action of the losses on all the properties
is done. It is shown that those properties almost completely disappear for an LHM slab with loss tangent over 0.01,
which at optical frequencies corresponds to a good material.
This paper presents a theoretical, numerical and experimental study for the design of a three-dimensional directive
antenna for microwave telecommunications (KU-band: 12-18 GHz) applications. The presented structure consists of a
stack of 6 metallic crossed grids above a ground plane, which is potentially capable to replace parabolic antennas,
because it is much more compact than classical solutions and uses a single patch as feeding device. Such structure acts as
a metallic photonic crystal at the band edge or as an ultra-refractive metamaterial. A numerical 3D code computing the
diffraction by metallic bi-periodic gratings, and a fast layer-by-layer approach, allows to model and to optimize this kind
of antennas. Especially, it is reported how both directivity and frequency bandwidth can be improved simultaneously.
Numerical results are confirmed by experiments in an anechoic chamber.