Detection of moving objects around corners, with no direct line-of-sight to the objects, is demonstrated in experiments using
a coherent test-range radar. A setting was built up on the test-range ground consisting of two perpendicular wall sections
forming a corner, with an opposite wall, intended to mimic a street scenario on a reduced scale. Two different wall materials
were used, viz. light concrete and metallic walls. The latter choice served as reference, with elimination of transmission
through the walls, e.g. facilitating comparison with theoretical calculations. Standard radar reflectors were used as one kind
of target objects, in horizontal, circular movement, produced by a turntable. A human formed a second target, both walking
and at standstill with micro-Doppler movements of body parts. The radar signal was produced by frequency stepping of a
gated CW (Continuous Wave) waveform over a bandwidth of 2 or 4 GHz, between 8.5 and 12.5 GHz. Standard Doppler
signal processing has been applied, consisting of a double FFT. The first of these produced "range profiles", on which the
second FFT was applied for specific range gates, which resulted in Doppler frequency spectra, used for the detection. The
reference reflectors as well as the human could be detected in this scenario. The target detections were achieved both in the
wave component having undergone specular reflection in the opposite wall (strongest) as well as the diffracted component
around the corner. Time-frequency analysis using Short Time Fourier Transform technique brought out micro-Doppler
components in the signature of a walking human.
These experiments have been complemented with theoretical field calculations and separate reflection measurements of
common building materials.
This paper describes the research efforts made at the Swedish Defence Research Agency (FOI) concerning through-the-wall imaging radar, as well as fundamental characterization of various wall materials. These activities are a part of two FOI-projects concerning security sensors in the aspects of Military Operations in Urban Terrain (MOUT) and Homeland Defence.
Through-the-wall high resolution imaging of a human between 28-40 GHz has been performed at FOI. The UWB radar that was used is normally a member of the instrumentation of the FOI outdoor RCS test range Lilla Gåra. The armed test person was standing behind different kinds of walls. The radar images were generated by stepping the turntable in azimuth and elevation. The angular resolution in the near-field was improved by refocusing the parabolic antennas, which in combination with the large bandwidth (12 GHz) gave extremely high resolution radar images. A 3D visualization of the person even exposed the handgun tucked into one hip pocket. A qualitative comparison between the experimental results and simulation results (physical optics-based method) will also be presented.
The second part of this paper describes results from activities at FOI concerning material characterization in the 2-110 GHz region. The transmission of building, packing and clothing materials has been experimentally determined. The wide-band measurements in free space were carried out with a scalar network analyzer. In this paper results from these characterizations will be presented. Furthermore, an experimental investigation will be reported of how the transmission properties for some moisted materials change as a function of water content and frequency. We will also show experimental results of how the transmission properties of a pine panel are affected when the surface is coated with a thin surface layer of water.
A study of the microwave absorbing properties of polymer (epoxy) based nanocomposites is presented. The ferrite
nanoparticles employed as filler materials were produced by a co-precipitation method, which was designed for
production of large amounts at low cost. The absorbing properties of different kinds of ferrite nanoparticles, soft
(manganese) and hard (cobalt) magnetic nanoparticles, are compared. In addition, the impact of high and low densities of
the respective ferrite type has been investigated. Our analysis of the microwave absorbing properties is made over a wide
frequency band including both MHz and GHz regions, which is of high interest for a number of different applications
both military and civilian.
This paper describes the experimental research efforts performed at the Swedish Defence Research Agency (FOI) concerning fundamental characterization of different wall and clothing materials as well as through-the-wall imaging.
Results from on-going activities at FOI concerning material characterization in the millimeter wave range are presented. Wide-band measurements of five building materials have been carried out in two different ways. In the frequency range 0.04-40 GHz a vector network analyzer was used and the samples were positioned in waveguides. In the 2-120 GHz region a scalar network analyzer was used and transmission measurements of the materials were performed in free space. Transmission measurements in free space of two clothing materials were also performed.
Results from measurements of a human target standing behind an inner wall are presented.
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