  Circular aperture probes have been successfully used for high-resolution
near-field microwave imaging. It has been established that circular aperture
probes could conceivably provide higher image fidelity compared to rectangular
aperture probes used conventionally for near-field imaging. In this paper, it
is proposed to further enhance the near-field imaging resolution and
sensitivity by loading the circular aperture with a resonant iris. The proposed
probe herein operates in the X-band frequency range and exhibits very localized
near-field distribution at the opening of the iris. Consequently, its imaging
resolution and sensitivity are enhanced compared to the conventional aperture
probes operating over the same frequency band. The imaging capability of the
proposed probe is analyzed using 3D electromagnetic simulation, and its
performance is validated experimentally. The efficacy of the proposed probe for
high-resolution imaging is demonstrated by practical imaging dielectric and
metallic samples. Furthermore, the obtained images using the proposed probe are
compared to those acquired using conventional circular and rectangular aperture
probes. It will be demonstrated that the proposed probe provides higher
sensitivity and resolution compared to the conventional aperture probes.
