Near-field microwave imaging radiometers for security applications

Abstract:
Microwaves in the range of 1-300 GHz are used in many respects for remote sensing applications. The imaging of persons and critical infrastructures for security purposes is of increasing interest particularly for transportation services or public events. Personnel inspection with respect to weapons and explosives becomes an important mean concerning terrorist attacks. Microwaves can penetrate clothing and a multitude of other materials and allow the detection of hidden objects by monitoring dielectric anomalies. Passive microwave remote sensing allows a daytime independent non-destructive observation and examination of the objects of interest under nearly all weather conditions without artificial exposure of persons or areas. Some imaging results of passive experimental equipment are shown. The first system is a millimetre-wave near-field scanner used for personnel screening in order to detect hidden objects. The second system presently under final construction operates as an imaging spectrometer at the lower microwaves. Since a hybrid technology between a scanner and the principle of aperture synthesis is used, both near and far-field operation is applicable by adequate data processing. First test images using most of the system electronics are shown.