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Are airport body scanners dangerous?

05 Jul 2013  | Steve Taranovich

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The VCO approach in comparison with an up-converter, which is another design approach, has the advantage of much lower spurious frequencies. To enable bidirectional operation of a single transmit-receive antenna a combination of a Wilkinson divider and a Lange coupler can be integrated. The circuit usually features coplanar technology and cascode High Electron Mobility Transistors (HEMTs) for compact size and low cost. These techniques can result in a small over-all chipsise of only 2x3 mm2 . The modules can have an output power of 2 mW at 94GHz and bandwidth of 4.5GHz, resulting in a theoretical range resolution of about 3 cm.

Figure 4: The ATOM W band FMCW radar module was developed at Fraunhofer IAF (Image courtesy of Fraunhofer Institute for High Frequency Physics and Radar Techniques2).


ATOM design
The paper in reference 2 describes the ATOM design: A small part of the transmit chirp is coupled by a directional coupler. This signal feeds a W band receiver module and is distributed by an internal power divider to the mixers. Because all receive signals are mixed with the same chirp signal which is derived by the mother oscillator, a coherent reception is realised. The receiver output yields the intermediate frequency (IF) signals which are digitized by the data acquisition board.


Figure 5: The ATOM data acquisition board digitizes the IF from the receiver output (Image courtesy of Fraunhofer Institute for High Frequency Physics and Radar Techniques2).


The antennas used are rectangular horn antennas with 20 dB gain. They have the advantage of being directly connected to the W band waveguides without waveguide transitions which could probably cause reflections. Sounds like a solid system design to me.

I think that this program sounds like a very effective way to eliminate security checkpoints and make things more difficult for the "bad guys" since they will not be able to identify where sensors are placed and cheat the system. I like the idea, but the compromise for safety from the "bad guys" still give is more RF radiation that will bombard us along with all the rest of the RF spectrum in the air today.


References
1. "94GHz Person Scanner with Circular Aperture as Part of a New Sensor Concept on Airports", Sebastian Hantscher, Stefan Lang, Manfred Hägelen, Helmut Essen, Fraunhofer Institute for High Frequency Physics and Radar Techniques, Department for Millimetre Wave Radar and High Frequency Sensors, Wachtberg, Germany

2. "Localisation of Concealed Worn Items Using a Millimeter Wave FMCW Radar", Sebastian Hantscher, Stefan Lang, Manfred Hägelen, Helmut Essen, Beverly Schenther, Fraunhofer Institute for High Frequency Physics and Radar Techniques, Department for Millimetre Wave Radar and High Frequency Sensors, Wachtberg, Germany, 2011


About the author
Steve Taranovich is a senior editor at EDN.


To download the PDF version of this article, click here.


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