This paper proposes the concept, analysis and design of a sinusoidally-modulated graphene leakywave antenna with beam scanning capabilities at a fixed frequency. The antenna operates at terahertz frequencies and is composed of a graphene sheet transferred onto a back-metallized substrate and a set of polysilicon DC gating pads located beneath it. In order to create a leaky-mode, the graphene surface reactance is sinusoidallymodulated via graphene's field effect by applying adequate DC bias voltages to the different gating pads. The pointing angle and leakage rate can be dynamically controlled by adjusting the applied voltages, providing versatile beamscanning capabilities. The proposed concept and achieved performance, computed using realistic material parameters, are extremely promising for beamscanning at THz frequencies, and could pave the way to graphenebased reconfigurable transceivers and sensors.

Abstract-The substrate integrated waveguide (SIW) technology allows to construct several types of commonly used antennas in a planar way. However, frequency limitations associated to commercial substrates appear in the implementation of certain types of antennas, e.g., SIW horn antennas are not well matched when the substrate thickness is much smaller than the wavelength. A printed transition is proposed to overcome this problem. Differently from current solutions, no bulky elements are required allowing to maintain the most important features of this technology namely its compactness and ease of manufacturing. In order to quickly analyze and design the transition, both a coupled resonator and a transmission line models are developed, together with design guidelines. The proposed transition is designed to match a H-plane SIW horn antenna built in a thin substrate at different frequency bands at the Ku-band. Experimental results for 3 different transitions show that the matching characteristics are efficiently improved compared with the conventional SIW horn antenna and validates the proposed models.

An approach to couple free-space waves and non-resonant plasmons propagating along graphene strips is proposed based on the periodic modulation of the graphene strip width. The solution is technologically very simple, scalable in frequency, and provides customized coupling angle and intensity. Moreover, the coupling properties can be dynamically controlled at a fixed frequency via the graphene electrical field effect, enabling advanced and flexible plasmon excitation-detection strategies. We combine a previously derived scaling law for graphene strips with leaky-wave theory borrowed from microwaves to achieve rigorous and efficient modeling and design of the structure. In particular we analytically derive its dispersion, predict its coupling efficiency and radiated field structure, and design strip configurations able to fulfill specific coupling requirements. The proposed approach and developed methods are essential to the recent and fundamental problem of the excitation-detection of non-resonant plasmons propagating along a continuous graphene strip, and could pave the way to smart all-graphene sensors and transceivers.

Abstract-The substrate integrated waveguide (SIW) technology allows to construct several types of commonly used antennas in a planar way. However, some practical constraints limit their performances when frequencies below 20 GHz are considered. In the case of SIW horn antennas, the available substrates are much thinner than the wavelength yielding to poor matching and undesired back radiation. In this paper, an innovative structure to overcome these limitations is presented. It consists of a transition printed on the same SIW substrate, which improves both the radiation and the matching performances of conventional SIW horns. The horn shape is also further optimized by reducing its dimensions required for a given directivity. This is obtained by modifying the horn profile in order to effectively combine different TE modes. Guidelines are provided to design this type of thin and compact SIW horn antenna. They were applied to manufacture a prototype in the Ku-band with a substrate thinner than . Measurement results validate the proposed concepts showing excellent performances.Index Terms-End-fire, front-to-back ratio, horn antenna, horn taper, low profile, printed transition, size reduction, substrate integrated waveguide, vertical polarization.

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