Multilayer active metasurface for beam scanning antenna applications

Metasurfaces are layered microwave structures allowing unconventional manipulation of wave propagation in free space. A considerably portion of the metasurface research is inspired by the idea of generalized Snell´s Law (N. Yu et al., Science 334, 2011), which utilizes the gradient of the abrupt phase shift along the metasurface to control the beam propagation. Works have been conducted in both microwave and optics regime (S. Sun et al., Nature Mat. 3292, 2012, Z. Wei et al., Opt. Exp. 21, 2013), and an application outlook of the methodology on beam scanning antenna is expected. However, these proposed structures mostly implemented fixed element arrays along the metasurface. To realize an actively tunable beam scanning antenna, active elements must be used to control the phase gradient, thus the scanning angle, and the scanning range is largely limited by the tunable range of the elements. In common designs, the scanning range is limited to a few to ten degrees.