Design Methods for Dual Polarized Metasurface Antennas: Three Simple Approaches

Metasurface (MTS) antennas are based on the transformation of a cylindrical-wavefront surface wave (SW) into a general wavefront leaky wave (LW). The MTS aperture is constituted by a grounded dielectric slab printed with an electrically dense distribution of subwavelength patches realizing space-variable, homogenized tensor impedance boundary conditions (IBCs). One of the challenges in this type of antenna is related to obtaining dual polarization operations by using the same impedance modulation. In this article, we explore and compare three simple approaches to obtain two beams with orthogonal polarizations by feeding two ports. A first known method is based on exciting both a transverse electric (TE) and a transverse magnetic (TM) SW mode on the same modulated impedance. A second method exploits the concept of impedance modulation sharing, according to which two distinct modulations, designed to radiate different polarizations when properly illuminated by distinct offset feeding points, are superimposed on the same aperture. A third method consists in duplexing an outward (radially diverging) and an inward (converging to the center) SW. Simple analytical formulas are presented for the synthesis of the impedance that allows for the control of the inward/outward waves to ensure balanced radiation performances in terms of aperture efficiency for the two polarizations. A comparison in terms of performances between the latter two approaches is presented.