Ricerc@Sapienza

A planar antenna radiating twisted beams with different azimuthal order and a consistent beam angle is designed by employing a single uniform circular array embedded in a Fabry–Perot cavity. Circular phased arrays placed in free space are commonly employed to radiate conical beams carrying orbital angular momentum. However, the beam angle depends on both the array radius and the azimuthal order of the beam, thus requiring the use of multiple concentric circular arrays in order to produce beams with different azimuthal order and a common beam angle.

The generation of higher-order cylindrical leaky waves (HOCLWs) by means of canonical electric or magnetic ring sources was discussed in Part I, where radiation formulas for such waves were also presented. In the second part of this sequence, the practical excitation of HOCLWs in a Fabry–Perot cavity antenna is discussed considering the use of ring sources in a discrete form, i.e., circular phased arrays of vertical electric or horizontal magnetic dipoles.

The possibility of generating a higher-order non-diffracting Bessel beam by means of a fast backward spatial harmonic is discussed in this work. The focusing features of the radiated near field are achieved by the excitation of a higher-xorder cylindrical leaky wave supported by an annular metal-strip grating placed on a grounded dielectric slab, which is excited by a circular arrangement of elementary sources.