High-resolution 96-GHz (3 mm) passive millimeter-wave imaging system and the effect of scanning resolution on images

Abstract

A high-resolution 96-GHz (3 mm) passive millimeter-wave imaging system is constructed. The system has a 96-GHz radiometric receiver, which is placed on the focal point of a 50-cm diameter parabolic reflector designed and created. A specially written program for the system controls the antenna via control hardware in desired steps by a 2-axis positioner motor. A balance weight has been calculated and mounted to the rear of this parabolic reflector antenna to prevent possible damage to the rotor of the positioner motor due to the antenna’s weight. The maximum field of view of the system is 120 deg in azimuth and 90 deg in elevation. The angular scan step can be varied from 0.1 deg to 1 deg. Although the system can shoot 1190 × 890 samples (pixels) images, which is close to the HD quality (1280 × 720 pixels) in the full field of view, the actual resolution of the image is limited by the antenna’s beamwidth (BW). Some measurements were performed to investigate the effect of scanning steps on PMMW image quality for different angular scan steps. It is observed that the PMMW image scan with the smallest step gives a detailed image that is the closest to the scene’s optical image as expected. Even though the angular scan step angle is less than half of the antenna’s BW at Nyquist sampling, it is observed that the image quality still improves due to averaging effect of the received signals giving a better estimated S/N. The resolution and scan step values of our system are compared with that of some systems found in the literature and it is shown that ours has the highest value among them. This system can be used to obtain high-resolution images in remote sensing and other applications.