Recent advances in millimeter-wave (MMW) radar technologies provide new applications for law enforcement use over-and-above the venerable speed timing radar. These applications include the potential to detect weapons under clothing and t o conduct surveillance through walls. Concealed Weapon Detection (CWD) and covert surveillance are ofhigh interest to both the Department of Defense in support of Small Unit Operations (SUO) and the Justice Department for civilian law enforcement applications. MMW sensors are under development which should provide the needed capabilities including radiometric sensors at 95 GHz, active 95 GHz real aperture radars, active focal plane array (FPA) radars, and holographic radars. Radiometric sensors include 2-D FPA systems, 1-D FPA, scanned systems, and single element scanned sensors. Active FPA radars include illuminated radiometric systems and coherent radar systems. Real aperture MMW radar systems include raster scanned and conical scanned sensors. Holographic systems ruse mechanical scanners.to collect coherent data over a significant solid angular sector.Keywords: concealed weapon detection, through-the-wall surveillance, millimeter wave radar MILLIMETER WAVE PHENOMENOLOGYRecently, Millimeter wave (MMW) radar has been explored concerning potential law enforcement application for concealed weapon detection (CWD) and through-the-wall surveillance (TWS). MMW lies between microwaves and infrared in the frequency spectrum. Microwaves are used for many conventional radar applications because atmospheric propagation is good, high powers can be generated, and many types ofnon-metallic materials can be penetrated. However, microwaves generally yield poor resolutions because ofthe relatively large wavelengths. Infrared (IR) lies below conventional visible light in the spectrum but retains much of the high resolution imaging properties of light due to the short wavelengths. On the other hand, propagation through rain and fog is significantly curtailed and little or no penetration though solid materials can be achieved. MMW's lie between the above frequency bands and retain some the properties of each. MMW can achieve relatively good imagery while penetrating many types of materials. Figure 1 gives the total attenuation though various objects and materials measured by Hughes Advanced Electromagnetic Technology Center. At 95 GHz (3 mm wavelength) the attenuation though paper, fiberglass, plastic, glass, wood, and drywall is relatively low while the attenuation through brick and concrete is high. Thus, 95 GHz is an excellent candidate for through the wall surveillance as long as the walls are not brick or concrete.On the other hand, the production of high quality imagery such as is desired for CWD requires high resolution. The one-way cross range resolution (3 dB) in azimuth or elevation for a focused MMW antenna can be approximated by:* Robert McMillan is currently serving as a visiting research scientist at Rome Laboratory under the Intergovernmental personnel act. 2 SPIE Vol. 3066 • 0277-78...
The need for through-the-wall surveillance sensors has existed for many years. Recent advances in microwave and millimeter-wave (MMW) technologies provide new applications for law enforcement use. These applications include the potential to conduct surveillance through walls and the ability to detect the presence of living persons behind doors or other barriers. Covert surveillance and personnel detection are of high interest to both the Department ofDefense in support ofSmall Unit Operations (SUO) and the Justice Department for civilian law enforcementapplications. Microwave sensors are under development that can detect the presence of persons (and even weapons) behind walls and track moving persons behind walls. MMW sensors are under development which can provide pseudo-images ofpersons behind walls including radiometric sensors at 95 GHz, active 95 GHz real aperture radars, and heartbeat detection radars. Radiometric sensors include 2-D FPA systems, 1 -D FPA, scanned systems, and single element scanned sensors. Active FPA radars include illuminated radiometric systems and coherent radar systems. Real aperture MMW radar systems include raster scanned and non-scanned (hand-held) sensors.Keywords: through-the-wall surveillance, millimeter wave radar, millimeter wave radiometry, microwave radar 1. MICROWAVE-MILLIMETERWAVE PHENOMENOLOGY Microwaves are used for many conventional radar applications because atmospheric propagation is good, high powers can be generated, and many types of non-metallic materials can be penetrated. However, microwaves generally yield poor resolutions because ofthe relatively large wavelengths. Infrared(IR) lies below conventional visible light in the spectrum but retains much of the high resolution imaging properties of light due to the short wavelengths. On the other hand, propagation through rain and fog is significantly curtailed and little or no penetration though solid materials can be achieved. MMW's lie between the above frequency bands and retain some the properties ofeach. MMW can achieve relatively good imagery while penetrating many types of materials. Figure 1 gives the total attenuation though various objects and materials measured by Hughes Advanced Electromagnetic Technology Center1 .At low frequencies of a few tenths to a few GHz (3 to 0.3 m wavelength) , attenuation is very low even through block walls. At 95 GHz (3 mm wavelength) the attenuation though paper, fiberglass, plastic, glass, wood, and drywall is relatively low while the attenuation through brick and concrete is high. Thus, a few GHz is suited for through the wall surveillance (TWS) though outer walls while 95 GHz is an excellent TWS candidate for thinner walls that are not composed ofbrick or concrete.On the other hand, the production of high quality imagery of scenes requires high resolution. (The rule of thumb is for good recognition ability, a resolution of 10 times the objects maximum dimension is needed by the sensor2.) The one-way cross range resolution (3 dB) in azimuth or elevation for a focused RF an...
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