Near-field Focusing through Higher-order Cylindrical Leaky Waves

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. By properly phasing the array elements, the azimuth order of the radiated beam is controlled, offering the possibility of generating a focused beam of arbitrary order carrying a nonzero orbital angular momentum. Full-wave simulations of a prototype are developed using a commercial code and the field profiles are compared with the ideal beam supported by an infinite aperture.