In this work, a systematic design of Fabry-Perot cavity antennas based on leaky waves is proposed in the THz range. The use of different topologies for the synthesis of homogenized metasurfaces shows that a specific fishnet-like unit-cell is particularly suitable for the design of efficient THz radiating devices. Accurate full-wave simulations highlight advantages and disadvantages of the proposed geometries, thoroughly considering the bounds dictated by technological constraints and the homogenization limit as well. The radiative performance of different designs for achieving theoretical directivities ranging from 15 dB to 30 dB is evaluated with reliable analytical and numerical methods, and completely validated with full-wave simulations. The relevant results corroborate the proposed systematic design, consolidating the validity and the usefulness of the leaky-wave approach, well-established at microwave frequencies, to the more challenging and still unexplored THz range.

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Terahertz frequencies are increasingly gaining attention due to the recent efforts made in narrowing the technological gap among microwave and optical components. Still the demand of efficient THz antennas is high, due to the difficulty in obtaining directive patterns and good radiation efficiencies with planar, low-cost, easy-to-fabricate designs. In this regard, leaky-wave antennas have recently been investigated in the THz range, showing very interesting radiating features. Specifically, the combination of the leakywave antenna design with the use of metamaterials and metasurfaces seems to offer a promising platform for the development of future THz antenna technologies. In this Chapter, we focus on three different classes of leaky-wave antennas, based on either metasurfaces or tunable materials, namely graphene and nematic liquid crystals. While THz leaky-wave antennas based on homogenized metasurfaces are shown to be able to produce directive patterns with particularly good efficiencies, those based on graphene or nematic liquid crystals are shown to be able to dynamically reconfigure their radiating features. The latter property, although being extremely interesting, is obtained at the expense of an increase of costs and fabrication complexity, as it will emerge from the results of the presented study.Transformation Optics in 2006 by Pendry [2], metasurfaces have represented a privileged platform for achieving a considerable control of electromagnetic waves propagation. Electromagnetic cloaking and metasurfing, i.e., controlling surface or guided waves through tunable metasurfaces [3], are one of the most known applications of metasurfaces. However, in this Chapter, we focus on the application of metasurfaces for the realization of reconfigurable leakywave antennas (LWAs) [4].In the microwave range, there exists numerous realizations of metasurfaces (see, e.g., [4] and refs. therein), but at terahertz (THz) frequencies (nominally comprised between 300 GHz and 3 THz [5]), very few designs are available. Nowadays, THz technology is recognized as one of the most promising and challenging area of research for a twofold reason: (i) on the one hand, the wide and interdisciplinary character of THz applications, spanning from molecular spectroscopy and astrophysics, to high data rate communications and high-resolution imaging, passing through security screening and drug detection [6]; (ii) on the other hand, the increasing availability of efficient THz sensors and sources [7] that have recently contributed to considerably narrow the so-called THz gap.Nevertheless, the demand of efficient THz antennas is still high [6]. Indeed, even though various solutions have been proposed (see, e.g., [8][9][10][11]), efficient realizations often require high fabrication costs and complexity [11]. To better handle the efficiency vs. cost/complexity tradeoff, leaky-wave antennas [12] have been proposed and experimentally demonstrated as valid alternatives for the design of efficient, low-cost, THz antennas [13,14]. Such prototypes...