Circularly Polarized Metasurfing Antenna G. Minatti 1 , F. Caminita 1 , P. De Vita 2 , M. Casaletti 1 , S. Maci 1 1 Department of Information Engineering, University of Siena, Via Roma 56, 53100, Siena, Italy, http://www.dii.unisi.it ; email: {Minatti, Caminita, Casaletti, Maci}@dii.unisi.it 2 Ingegneria dei Sistemi, IDS S.p.a., Via Enrica Calabresi 24, 56121 Pisa, Italy, http://www.idscompany.it ; email: p.devita@ids-spa.it Abstract In this paper we present a planar circularly polarized antenna based on transformation of a surface wave into a leaky wave. The antenna is designed by using the concept of modulation of surface re- actance. Such a modulation is obtained by printing a dense texture of square sub wavelength metal patches on a grounded dielectric slab. The final device is a planar thin antenna with a simple feeding constituted by single vertical monopole. Numerical results are presented and discussed. Experimental results are announced for the oral session. 1. Introduction The antenna we are going to illustrate is a planar circularly polarized leaky wave (LW) antenna ex- cited by a single-point feed. The basic structure we are dealing with is constituted by variable, spiral- shaped modulated surface impedance realized on a grounded dielectric slab with a small vertical di- pole used as a feeder. A cylindrical surface wave (SW) excites the surface which converts the SW into a circularly polarized LW. The design process is based on describing the local interaction between an elemental angular wave front of cylindrical SW and the corresponding elemental angular sector of the spiral. The interaction is faced by means of a 2D canonical problem of a sinusoidal reactance excited by a planar SW. The latter is treated by means of the Oliner-Hessel method described in [1]. This local interaction can also be interpreted as the holographic principle illustrated in [2]. This interpretation is given in [3]. This paper is structured as follow. In section II the local canonical problem is presented as a basis step for the design of antennas based on modulation of surface reactance. Also, the interaction of the excit- ing surface wave with a spiral impedance surface is introduced, providing an interpretation of the pro- duced circularly polarized radiation. Section III presents the procedure and the main design guidelines to reconstruct the modulated surface reactance by using printed patches on a grounded dielectric slab. Numerical results for a prototype that is going to be realized are also present and discussed. The final conclusions in Section IV discuss the main features of this class of antennas. 2. SW interaction with a spiral shaped sinusoidally modulated reactance. The canonical problem of a surface wave propagating on a modulated surface reactance is illustrated in [1]. The surface is assumed infinite and invariant along the y direction and is excited by a TM 0 sur- face wave (see Fig. 1a). In the canonical problem the surface wave is assumed to propagate along the x direction, impinging with normal incidence, thus allowing a TM-TE modal decomposition. The pres- ence of the periodic medium affects more or less quantitatively the wave number of the SW, depend- Metamaterials '2011: The Fifth International Congress on Advanced Electromagnetic Materials in Microwaves and Optics ISBN 978-952-67611-0-7 - 709 - © 2011 Metamorphose-VI