The Propagation of Electromagnetic Video Pulses with Application to Subsurface Radar for Tunnel Detection

摘要

Pulse propagation in lossy media is considered over a seven decade frequency band to 1 GHz with a view to determining the design principles of video pulse subsurface radar systems. Two different radars may be required depending upon whether signal propagation is within the Low Frequency Window (LFW) or the High Frequency Window (HFW) as defined by Gabillard et al. (1971). The antenna type chosen is a finite length dipole. In the LFW it is essential that the dipole be maintained in conducting contact with the ground whereas in the HFW the antenna may be insulated. An LFW radar operates in a frequency range which is too low to excite resonances of subsurface targets whose characteristic dimensions are of the order of 1-2 meters (tunnels): consequently LFW radars are potential detectors of such targets. An HFW radar can operate in frequency bands that includes target resonances for the 1-2 meter radius tunnels. Consequently HFW radars are potential identifiers of targets, although LFW radars can be operated in a mapping mode for identification purposes. The choice of an LFW or an HFW rdar depends upon the depth of operation and the constitutive parameters of the ground. A design chart is presented for the appropriate selection of the radar type. Attenuation curves describing the signal loss for both LFW and HFW radars are also presented.