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Present applications of microwave remote sensing systems cover a large variety. One utilisation of the frequency range
from 1 - 300 GHz is the domain of security and reconnaissance. Examples are the observation of critical infrastructures
or the performance of security checks on people in order to detect concealed weapons or explosives, both being frequent
threats in our world of growing international terrorism. The imaging capability of concealed objects is one of the main
advantages of microwave remote sensing, because of the penetration performance of electromagnetic waves through
dielectric materials in this frequency domain. The main physical effects used in passive microwave sensing rely on the
naturally generated thermal radiation and the physical properties of matter, the latter being surface characteristics,
chemical and physical composition, and the temperature of the material. As a consequence it is possible to discriminate
objects having different material characteristics like ceramic weapons or plastic explosives with respect to the human
body. Considering the use of microwave imaging with respect to people scanning systems in airports, railway stations, or
stadiums, it is advantageous that passively operating devices generate no exposure on the scanned objects like actively
operating devices do. For frequently used security gateways it is additionally important to have a high through-put rate in
order to minimize the queue time. Consequently fast imaging systems are necessary. In this regard the conceptual idea of
a fully-electronic microwave imaging radiometer system is introduced. The two-dimensional scanning mechanism is
divided into a frequency scan in one direction and the method of aperture synthesis in the other. The overall goal here is
to design a low-cost, fully-electronic imaging system with a frame rate of around one second at Ka band. This frequency
domain around a center frequency of 37 GHz offers a well-balanced compromise between the achievable spatial
resolution for a given size, and the penetration depth of the electromagnetic wave, which are conflictive requirements.
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