Focusing through cylindrical leaky waves

Bessel-beam launchers with wideband features are required to generate focused pulses in the near field. In this work, we demonstrate the capabilities of backward cylindrical leaky waves, supported by a planar wideband device, of generating nondiffracting beams and pulses at microwave frequencies. The structure consists of a metallic radial waveguide whose upper plate is replaced by an annular metal strip grating. The period of the strips is designed so that the structure supports a fast backward spatial harmonic, as required to focus a Bessel beam in the near field. Experimental results confirm the wideband focusing features of this class of devices, as well as the unprecedented capability of generating X-waves in the microwave range