Ultra-wideband Ground Penetrating Radar System Research Articles

Comparison of antenna dispersion and digital signal processing effects in ultrawideband Ground Penetrating Radar systems

Abstract In Ground Penetrating Radar it is of great interest to have a pulse width as narrow as possible to achieve best resolution capability. However, ultrawideband antennas may cause distortion to the radar signal due to dispersion, which is dependent on the frequency and bandwidth, as well as the direction of radiation. As dispersion causes an increase of the peak's width, the resolution capability is degraded. When frequency-based radar systems are utilized, such as stepped-frequency radar, a transformation of the recorded frequency-domain data to time domain is often required. There are different means of transformation at hand, the most popular being inverse Fourier Transform. Generally, such a transformation involves certain degrees of freedom in the processing of the data, which affect the appearance or even distort the resulting signal in time domain. In the same way, distortion may also be introduced to signals obtained by pulse radar, which is operating in time domain, when digital signal processing filters are applied to the time-domain data, modifying their frequency content. In contrast to dispersion these effects can be controlled — but not avoided. As an example, the typical sinc-shaped distortion of the time-domain signal after inverse Fourier Transform may be avoided by windowing of the frequency-domain data, a well-known basic technique in the digital signal processing domain. As dispersion, also windowing causes a broadening of the peak's width. However, this leads to the important question, to which degree both, dispersion and windowing, affect the time domain signal and which of them has more severe impact. In this paper we investigate both effects. We compare dispersion of different ultrawideband Vivaldi, Bowtie and Loaded Bowtie antennas with the ideal (theoretical) non-dispersive one. And we compare these results with the distortion effects introduced to the radar signal by windowing frequency-domain data prior to inverse Fourier Transform.

Mine-Detection Test Facilities at TNO-FEL Site “Waalsdorp”: Some Examples of Results Obtained with an Array Based GPR System

At the TNO Physics and Electronics Laboratory (TNO-FEL), one of the recent research programs explores the use of ultra-wide-band (UWB) electro-magnetic fields in a bi-static ground-penetrating radar (GPR) system for the detection, location and identification of buried items of unexploded ordnance (e.g., land mines). An experimental UWB ground-penetrating radar system was designed to operate in the frequency band from 200 MHz to 3 GHz and uses impulse radiating antennas (IRAs) as transponders to radiate and receive very short electro-magnetic pulses from a short distance above the soil. Part of the development of this UWB GPR system involved the erection of an outdoor tent covered UWB GPR testing facility. In another program an outdoor multi-sensor humanitarian de-mining test facility was constructed. This facility enables semi-automated measurements, with several different sensor on lanes with different soil types. This article highlights the development of the above mentioned system and facilities and presents some results obtained with one of the commercial systems that is present at the site.