Detection of concealed threats is a key issue in public security. In short range applications, passive imagers operating at
millimeter wavelengths fulfill this task. However, for larger distances, they will suffer from limited spatial resolution.
We will describe the design and performance of 0.8-THz imaging radar that is capable to detect concealed objects at a
distance of more than 20 meter. The radar highlights the target with the built-in cw transmitter and analyses the returned
signal making use of a heterodyne receiver with a single superconducting hot-electron bolometric mixer. With an
integration time of 0.3 sec, the receiver distinguishes a temperature difference of 2 K at the 20 m distance. Both the
transmitter and the receiver use the same modified Gregorian telescope consisting from two offset elliptic mirrors. The
primary mirror defines limits the lateral resolution of the radar to 2 cm at 20 m distance. At this distance, the field of
view of the radar has the diameter 0.5 m. It is sampled with a high-speed conical scanner that allows for a frame time
less than 5 sec. The transmitter delivers to the target power with a density less than ten microwatt per squared centimeter,
which is harmless for human beings. The radar implements a sensor fusion technique that greatly improves the ability to
identify concealed objects.
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