Experimental verification of two-dimensional subwavelength resolution using a near-field probe

The subwavelength resolution capability of a near-field antenna-array probe is experimentally verified. The probe is an end-fire monopole array designed with a high degree of rotational symmetry to support two-dimensional imaging. Small field perturbations due to the presence of short dipole objects can be detected by scanning with the probe and monitoring the input reflection coefficient. In simulations, the minimum resolvable separation between two objects placed λ/4 away from the probe was reduced from 0.519λ for a single monopole probe to 0.256λ for the array probe. The experimentally measured full-width half-maximum beam width for the detection of a single object by the array probe was 0.217λ with a minimum resolvable separation of 0.259λ for two objects.