Free space near field focusing from an array of sinusoidally modulated half-mode LWAs

This work shows the capability to focus the radiated fields inside the near-field zone, by using a radial array of sinusoidally modulated half-mode leaky-wave antennas (HMLWAs). The proposed array is formed by 8 HMLWAs, which are simultaneously fed by a central coaxial line. Each LWA radiates into the backward direction with the n = -1 Floquet harmonic, which is excited by the periodical perturbation introduced with the sinusoidal modulation. Furthermore, the backward pointing angle and the leakage rate are properly tapered along the the antenna length, by controlling the width W of the microstrip line and the modulation index M of the sine function. In this manner, the radiated near fields can converge in a common focus spot located above the array center.