Chapter 3: Vehicle-Mounted GPR System for Landmine Detection

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34 3. Vehicle-Mounted GPR System for Landmine Detection Power [dB] Power [dB] 0 −10 −20 −30 −40 −50 −60 −70 0 −10 −20 −30 −40 −50 −60 −70 1000 2000 3000 4000 Frequency [MHz] (a) 1000 2000 3000 4000 Power [dB] 0 −10 −20 −30 −40 −50 −60 −70 1000 2000 3000 4000 Frequency [MHz] (b) Frequency [MHz] (c) Fig. 3.7: Power spectra of 100 ground reflections measured by VNA #1 (a), VNA #2 (b), and VNA #3 (c) with offset frequency of 300 kHz for VNA #2 and 1.25 MHz for VNA #3, and an IF bandwidth of 3 kHz. 3.2.3 Antennas Vivaldi antennas are employed in this system. It is a kind of microstrip antenna, which possesses a wide bandwidth and a high cross-polarization ratio (Guillanton et al., 1998). Since it can be made on a thin and lightweight circuit board, it has advantages, for example easy to be manufactured and to be configured as an array. For SAR-GPR, the antenna shown in Fig. 3.8(a) has been designed and manufactured. The size is 19×20 cm, and the antennas are aligned with a spacing of 6 cm as shown in Fig. 3.8(b). Return loss of the antennas with the array configuration is shown in Fig. 3.9.
3.2 Development of the System 35 (a) 60 200 Rx #3 Rx #2 Rx #1 Tx #1 Tx #2 Tx #3 190 (b) Fig. 3.8: Antenna array used in SAR-GPR. Picture of the single Vivaldi antenna (a), and Vivaldi antennas aligned as the array (b). Return loss [dB] 0 −10 −20 −30 −40 −50 1 2 3 4 Frequency [GHz] Fig. 3.9: Return loss in antennas arrayed. The solid, broken, and dotted-broken lines show that of antenna #1 (inner pair), #2 (middle pair), and #3 (outer pair), respectively.
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Page 11 and 12: 3.3 Image Reconstruction 37 N 1 Q()
Page 13 and 14: 3.4 Quick Detection Algorithm 39 1
Page 15 and 16: 3.5 Experimental Results 41 could d
Page 17 and 18: 3.5 Experimental Results 43 Fig. 3.
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Chapter 3: Vehicle-Mounted GPR System for Landmine Detection

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