Concealed Weapon Detection with Active and Passive Millimeterwave Sensors, Two Approaches Helmut Essen 1 , Hans-Hellmuth Fuchs 1 , Manfred H¨ agelen 1 , Stephan Stanko 1 , Denis N¨ otel 1 , Sreenivas Erukulla 1 , Johann Huck 1 , Michael Schlechtweg 2 , Axel Tessmann 2 1 Research Institute for High Frequency Physics and Radar Techniques (FGAN-FHR), Neuenahrer Str. 20, D-53343 Wachtberg, Email: Essen@fgan.de 2 Fraunhofer Institut f¨ ur Angewandte Festk¨ orperphysik (IAF) Tullastr. 72, D-79108 Freiburg, Email: Michael.Schlechtweg@iaf.fraunhofer.de Abstract— The increasing interest in the security of public spaces leads to a demand for sensor technology beyond metal detectors. Two different approaches of concealed weapon detec- tion using millimeter wave systems are presented in this paper. The design of a passive radiometric sensor in the W-band is presented. On the active side, an FMCW radar system at 94 GHz is introduced for the scanning of persons. The resulting images are shown which enable a first comparison of both approaches. I. I NTRODUCTION Sensors used for security purposes have to cover the non- invasive control of humans, baggage and letters with the aim to detect weapons, explosives and chemical or biological threat material. Those sensors have to cope with different environmental conditions. Preferably, the control of people has to be done over a longer distance. In times of increasing threat by terrorist attacks the control of passengers at airports and stations is one of the major items. People carrying concealed weapons or explosives or those, who have other terroristic attacks in mind, have to be detected under all circumstances. Very similar requirements have to be met for all aspects of homeland security. Currently, emphasis is placed on system concepts and technology for this type of applications employ- ing millimeterwave, submillimeterwave and terahertz sensors. This is based on the capability of these frequency bands to look through textile material and the possibility to achieve a geometric resolution, which is sufficient to resolve critical items within the necessary range. II. MILLIMETERWAVE TECHNOLOGY FOR SECURITY APPLICATIONS Due to other applications, civilian and military, the fre- quency region around 94 GHz is best developed. Both, devices and components, have been designed and manufactured by Fraunhofer IAF, who have been involved with the demon- strators discussed below. Key components are low noise and medium power HEMT amplifiers [1] and a miniaturized single chip FMCW radar at 94 GHz [2]. Demonstrators have been set up using active and passive sensors. A single channel Dicke type radiometer was designed using three stacked LNAs and a PIN SPDT to switch between Fig. 1. Radiometric channel of the Dicke type (top), layout of an LNA (right) and LNA performance (left) [1]. Fig. 2. Functional diagram of single chip FMCW radar (left) and layout at 94 GHz (right)[2]. receiver and the matched second port, which serves as a ref- erence. While the bandwidth of the amplifier chain is 20 GHz, the total bandwidth is limited by the PIN switch to 4 GHz. The overall gain, in this case, is 60 dB. The general set-up and a photo of the LNA layout as well as typical performance curves are shown in Figure 1. To show the rapid improvements in LNA development, the system was then modified to work as a total power sensor. By definition, a total power setup is twice as sensitive as a Dicke type system and offers a lower system noise temperature as no PIN switch is necessary at its input. The second demonstrator, which was involved in the comparative test, is based on the single chip FMCW radar at 94 GHz sketched in Figure 2. It was combined with a linear scanning antenna [3] for the azimuth scan and mounted on a