Near-field phase modulation using a semicircular radially gradient metasurface for beam steering of an RF antenna

A semicircular radially gradient metasurface (SCRGM) structure is proposed to modulate the phase of the electric field of a radiofrequency (RF) antenna in the near field. The metasurface partially covers the antenna aperture, thus facilitating tilting of the beam in the elevation plane (E-plane). In the proposed configuration, the phase modulation capability of the radially gradient metasurface is utilized in combination with a semicircular superstrate made of low-dielectric-constant material, placed at a height of $$0.17 \lambda _0$$0.17ý0 above and parallel to the antenna aperture. Firstly, the broadside beam of the patch antenna is tilted away from the normal direction by the phase modulation of the electric field over the aperture of the antenna. Beam steering in the E-plane is achieved by in-plane translation of the SCRGM in front of a stationary primary feed antenna, further modulating the phase. The aperture area and weight of the proposed SCRGM are $$3.77\lambda _0^2$$3.77ý02 and 22.0 g, respectively. The compact antenna structure with integrated SCRGM offers $$-45^{\circ }$$-45ý to $$+45^{\circ }$$+45ý beam steering in the E-plane with reasonably constant gain in the range of 10---11 dBi (with scan loss better than 1 dB). The strategy of partially covering the antenna aperture and further translating the radially gradient metasurface enables a considerably wide beam scanning range using a compact configuration.