  In this paper, the design, realization, and demonstration of a broadband
millimeter-wave imaging system based on the synthetic aperture radar technique
(SAR) are discussed. The proposed system, operating within the frequency range
of 25.3-30.8 GHz, consists of a tapered slot antenna as the transmitter and two
half-circle antennas as the receivers. The size of the antenna is 19.5 * 8 mm
with a maximum gain of 8.5 dB. The transmitter and the receiver antennas are
printed on the same board. This feature leads to a highly compact and flexible
configuration, enabling the applicability of the proposed imaging system in the
handheld devices. Furthermore, it significantly reduces the fabrication cost of
the system. The proposed broadband imaging system, being capable of performing
3D real-time imaging with high resolutions, can be easily calibrated for each
frequency within the desired range. By performing 3D imaging from metallic
objects with different shapes, we experimentally demonstrate the high
performance of the proposed system, which offers great potentialities for a
broad range of applications such as security, medical diagnostic, concealed
object detection, to name a few.
