Parabolic antennas, and circular slot arrays, for the generation of Non-Diffracting Beams of Microwaves

We propose in detail Antennas for generating Non-Diffracting Beams of Microwaves, for instance with frequencies of the order of 10 GHz, obtaining fair results even when having recourse to realistic apertures endowed with reasonable diameters. Our first proposal refers mainly to sets of suitable annular slits, having in mind various possible applications, including remote sensing. Our second proposal --which constitutes one of the main aims of this paper-- refers to the alternative, rather simple, use of a Parabolic Reflector, illuminated by a spherical wave source located on the paraboloid axis but slightly displaced with respect to the Focus of the Paraboloid. Such a parabolic reflector yields "extended focus" (non-diffracting) beams. [OCIS codes: 999.9999; 070.7545; 050.1120; 280.0280; 050.1755; 070.0070; 200.0200. Keywords: Non-Diffracting Waves; Microwaves; Remote sensing; Annular Arrays; Bessel beams; Extended focus; Reflecting paraboloids; Parabolic reflectors; Parabolic antennas].