See-around-corner with X-band measurements - Lilla Gåra August 2007
Publish date: 2008-01-07
Report number: FOI-R--2369--SE
Pages: 52
Written in: Swedish
Keywords:
- radar
- see-around-corner
- doppler
- X-band
- urban scenario
- multiple
- reflections
- diffraction
Abstract
Radar measurements have been made on the FOI test range at Lilla Gåra, near Linköping, to study the possibility to detect moving objects around corners without direct sight, in an urban scenario. For this purpose, a simple model corner with a facing wall was arranged to mimic a street crossing or a corridor corner, using metallic wall sections. The objects to be detected consisted of radar reflectors with well-known properties, viz a sphere and a cubic corner reflector, with square sides. Horn-type antennas of two sizes were used. The targets were moved in a circular orbit on a turntable around its axis. The radar measurements were made by determination of the frequency spectrum of the radar return from the target by frequency stepping between 9 and 11 GHz, in 2 MHz steps. The signal processing has consisted of a double Fourier transform of the received frequency spectrum. The first of these inverts the frequency spectrum into a time or range profile of high resolution (7.5 cm), whereupon the second one produces a Doppler spectrum of the signal in each resolution cell of this profile. The measurements indicated that the return from an object behind the corner was detectable. Both target returns from diffraction (bending) around the corner and from multiple reflections in the opposite wall could be detected. As expected, the diffraction signals were considerably weaker than the returns from the multiple reflections. The detections are made possible by using the Doppler effect, by integration of the radar return from a number of pulses (the second Fourier transform mentioned above). A coherent system is needed for this, with phase control, like the one used. As a rule, a single pulse return without this integration gave no reliable detection. Knowledge of the target position and its movement was another condition for the detection result, since it makes optimal integration possible, which will not be the case, as a rule, in an operative situation, with unknown measurement parameters. A suitable task for a continuation of this work is the study of how to perform automatic Doppler processing for detection in an efficient way. An equally important point is the use of more realistic walls and target objects, both with respect to material and geometry. The experiment has shown that the Lilla Gåra test range facility is well suited for controlled, accurate Doppler measurements.