Dynamic phase control by rigid spiralized Fresnel zone plates

Spiral antennas for the generation of bessel beams with tunable nondiffractive range

“…In [31,32], the controllable transmission and focusing of an in-line propagating optical wave through a spiral lens with a circle-involute profile are discussed. Here, we aim to take advantage of a similar structure working at microwaves and featuring subwavelength mutual distances between filaments, whose rotation around a central joint will induce the formation of an envelope figure presenting circular density bands.…”

“…where Λ is the effective period in rotated spiralized filaments, given by Λ = d 0 N S [32]. We remind that the actual n Eff does not remain constant after introducing scattering elements, but it rather experiences slight changes while moving the filaments, so the emission angle is subject to slight yet unavoidable perturbations.…”

“…The solution presented here is based on an LWA made of spiral filaments with subwavelength spacings which, under proper displacements, assume a variable envelope configuration with a given density function equivalent to a concentric arrangement of solid metal rings (see figure 1). Such displacements mainly consist of simple rigid translations and rotations, as shown for optical lensing [31,32], but they can also involve elastic deformations. We shall also consider this latter case by pushing the filament rotation beyond the first-contact angle, to provide the overall structure with a sharper density pattern and so with a further perturbation of the surface current distribution or, equivalently, a higher leakage constant.…”