A Near-Field Probe for Subwavelength-Focused Imaging

A near-field antenna array probe is presented that can perform subwavelength-focused imaging at a distance of 0.25¿ . The array is composed of a centrally fed dipole with open-circuited secondary dipoles placed less than half a wavelength away on each side. Together, they produce a subwavelength focal spot that can be used to detect the presence of small wire loops with subwavelength resolution. This is done by raster scanning the array over the focal plane and monitoring the probe return loss for perturbations. An experiment was conducted that verified the 1-D subwavelength imaging of two loops placed in the focal plane. The minimum resolvable loop separation was 0.31¿ for the array probe compared to 0.72¿ for the single-dipole probe. The array probe had a 13% resolution bandwidth for two loops spaced at 0.4¿.