An array of antenna elements (20) can be used to detect subwavelength sized anomalies on a surface below the array. An array (20) is illuminated at optical frequencies by a coherent optical energy source (26). The change in reactance and radiated power of the antenna elements that results from the proximity of the anomaly to the near field of the antenna element's open-circuited is detected and holographically filtered to eliminate the radiation caused by the antenna array itself. Image processing is performed on the detected scattered radiation (100) to determine whether an anomaly is present and to locate the anomaly and its characteristics.