Chapter 3: Vehicle-Mounted GPR System for Landmine Detection

More documents

Recommendations

Info

32 3. Vehicle-Mounted GPR System for Landmine Detection The second problem is interference of the signals. Use of some VNAs simultaneously means the same signals are emitted and measured by each VNA, yielding a signal radiated by the transmitter #1 may be received by not only the receiver #1 but also the receiver #2 and #3, for instance. To fix this problem, slightly different frequency ranges are used in each of the VNA as shown in Fig. 3.5. The offset frequencies are defined by trial and error. Fig. 3.6 shows the power spectra of 100 ground surface reflections measured by the system with offset frequencies of 100 kHz and 300 kHz and an IF bandwidth 1 of 30 kHz. The obvious fluctuations can be observed, and those for VNA #2 are more than 10 dB. Fig. 3.7 shows the spectra with offsets of 500 kHz and 1.25 MHz and an IF bandwidth of 3 kHz. They have almost no fluctuations. From the trials, it is found that an offset frequency must not be a multiple of the other offset, because the harmonics may be radiated by the transmitter and it can be measured by a receiver of another pair. Moreover, a sweep of a VNA can catch up with another sweep since each VNA has its own individual characteristics. In SAR-GPR, the offset frequencies of 500 kHz and 1.25 MHz are used. Table 3.1: Specification of the VNA, Anritsu MS6223 (commercial) 2 . Measurement mode Frequency sweep range Amplitude accuracy Frequncy accuracy Output level Dynamic range S21 100 MHz to 4 GHz ± 1 dB (at -20 dB) ± 5 kHz (at 2GHz) -5 dBm to +10 dBm 70 dB Number of frequencies 69/137/275/551 Sweep Speed Frequency resolution Weight Size 0.86 s (551 points) < 100 kHz < 3.5 kg (with case, battery) 313× 211× 77 mm (with case) Operating temperature -10 to +50 ºC 1 IF (intermediate frequency) bandwidth is the filter bandwidth for an input signal of a VNA. 2 Actual installed VNA is modified for the system.
3.2 Development of the System 33 Frequency Offset 2 Offset 1 VNA #1 VNA #2 VNA #3 Time Fig. 3.5: Frequency sweeps of VNAs. Three VNAs use slightly different frequency ranges with two offset frequencies. 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. 3.6: Power spectra of 100 ground reflections measured by VNA #1 (a), VNA #2 (b), and VNA #3 (c) with offset frequency of 100 kHz for VNA #2 and 300 kHz for VNA #3, and an IF bandwidth of 30 kHz.
Page 1 and 2: 3. VEHICLE-MOUNTED GPR SYSTEM FOR L
Page 3 and 4: 3.2 Development of the System 29 fo
Page 5: 3.2 Development of the System 31 3.
Page 9 and 10: 3.2 Development of the System 35 (a
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.
Page 19 and 20: 3.5 Experimental Results 45 10 Ampl

Chapter 3: Vehicle-Mounted GPR System for Landmine Detection

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?