No abstract

This paper presents new designs, implementation and experiments of metasurface (MTS) antennas constituted by subwavelength elements printed on a grounded dielectric slab. These antennas exploit the interaction between a cylindrical surface wave (SW) wavefront and an anisotropic impedance boundary condition (BC) to produce an almost arbitrary aperture field. They are extremely thin and excited by a simple in-plane monopole. By tailoring the BC through the shaping of the printed elements, these antennas can be largely customized in terms of beam shape, bandwidth and polarization. In this paper, we describe new designs and their implementation and measurements. It is experimentally shown for the first time that these antennas can have aperture efficiency up to 70%, a bandwidth up to 30%, they can produce two different direction beams of high-gain and similar beams at two different frequencies, showing performances never reached before.

Modulated metasurface (MTS) antennas with broadside beam rely on the interaction between a radially modulated equivalent impedance and a surface wave (SW) with cylindrical wave-front, launched by a point source. At the frequency where the SW wavelength matches the period of the impedance modulation, the-1 indexed (leaky) mode of the Floquet-mode expansion in cylindrical-coordinates provides a broadside beam. The mismatch between the SW wavelength and the period of the modulation imposes a limitation on the product bandwidth-gain. Here, we overcome this limitation by exponentially stretching the radial period of the impedance modulation. Doing so, an annular active region is generated on the antenna aperture, which moves from the antenna center to the circular rim as the frequency decreases. This mechanism enables a broadside beam over an extreme large bandwidth. We therefore extend significantly the applicability of these antennas, e.g., to requirements of 30 1.5 dB  gain over 30% bandwidths. Here, an analytical formulation is proposed to treat the active region migration and edge outgoing by a Fresnel-type transition function. This function predicts in closed form the antenna bandwidth and average gain. A more accurate gain versus frequency response is also introduced by an integral formula that accounts for the frequency dependent amplitude distribution of the aperture fields. The theory is validated by full-wave simulations and by measurements of a prototype realized by subwavelength elliptical patches. The presented results show that these antennas can provide a performance difficult to reach by any other flat antennas based on printed technology.