Shadowing Efiect Analysis at Multiple Moving Persons Tracking by UWB Radar

Ultra wideband (UWB) radars appear as the suitable technology for detection and tracking of moving people in critical situations and hazardous environments. Our experiences with such applications of UWB radar systems have shown that for the multiple moving person detection and tracking, a single radar with a small antenna array is capable to detect very often the person moving closest to the radar antennas only, whereas the other target (persons) are usually not detected. This is a serious and unsolved problem of UWB radar applications for detection and tracking of multiple moving persons. In this paper, we will outline the results of the series of measurements with short range UWB radar which were dedicated for examination and quantitative description of this negative efiect. The short range UWB radar appears to be an attractive and perspective solution for the detection and localization purposes. The UWB radar system is the special type of noise radar and can be used to detect and track moving targets in critical environments with an advantage. One of the possibilities of the UWB radar systems is their use for the various security, rescue and surveillance applications (e.g., through wall and through flre detection and tracking of moving targets during police or military operations, protection of facilities with high industrial or flnancial importance etc.) Their primary advantage comes from the large bandwidth of the transmitted stimulation signals of up to several GHz (typically between 100MHz and 5GHz). The large bandwidth results in an excellent localization precision of such UWB devices and to the ability to penetrate many common materials (e.g., walls, rubble, non-metallic obstacles). Then, such devices are able to detect moving person by measuring changes in the impulse response of the environments (1). For detection and tracking applications outlined above, the short range UWB devices (range up to 20{25m) are usually applied. Our experiences with such applications of UWB radar systems have shown that at multiple moving person scenarios, that a single radar with a small antenna array is able to detect very often the person moving closest to the radar antennas only. The other target (persons) are also detected but usually with a small reliability or none at all. This degradation of radar performance can be explained in such a way that the person located in front of the radar antenna array acts as an obstacle and creates an area with high attenuation of the energy of the electromagnetic waves behind his/her (so-called shadowing person). The area with the additional attenuation is referred to as the shadow zone. The shadowing person absorbs and re∞ects the energy of electromagnetic waves transmitted by the radar transmitting antenna and/or re∞ected by the other targets and hence, only a negligible part of the energy of the electromagnetic waves re∞ected by the other targets can be received by the radar. The presence of such shadowing persons and hence the shadow zones cause that the radar eventually cannot detect and track any of the persons which are located within these zones. This efiect is referred to as shadowing efiect. The outlined problem of due to shadowing efiect has been addressed for the flrst time in (2), where a qualitative analysis of shadowing efiect has been described. The main contribution of this paper is the quantitative analyses of attenuation within the shadow zone due to the person localized in front of the radar transmitting antenna. 2. ANALYSIS OF SHADOWING EFFECT