Detection of objects in sandy ground by an FM-CW radar

An FM-CW radar system for the detection of objects buried in sandy ground is explored and applied to field measurement. The key factors for underground radar performance are the center frequency and the bandwidth determining the depth at which the radar can detect targets and the resolution in the range direction, respectively. To realize a practical underground radar, two ridged horn antennas are employed in the system, which are operative in the frequency range of 250-1000 MHz. The impedance matching to the ground is optimized by measuring the echo strength from a fixed target as a function of the spacing between the antenna aperture and the ground surface. It is shown that the radar with an output power of 18 dBm could detect a metallic plate (30×100 cm) and a pipe (10 cmφ) buried at a depth of 1.2 m. Also the synthetic aperture technique together with an averaging and subtracting method produced a fine image in a shallow region up to 100 cm in the sandy ground