Chapter 3: Vehicle-Mounted GPR System for Landmine Detection

3.2 Development of the System 31
3.2.2 Use of three VNAs
In this system, three pairs of antennas are used to acquire multi-offset data. In
general GPR measurements of geological surveys, the data acquisition is done over
and over again with changing the separation of antennas or with switching the signal
using array antennas. However, the acquisition must be done three times for one
position and the goal cannot be accomplished by using these methods. Our solution
is simultaneous usage of three vector network analyzers. This manner can ideally
reduce the acquisition time by 1/3 compared to the case of using only one VNA.
There are two problems in the use of three VNAs simultaneously. One is the size
and weight. In general, a VNA is a huge and heavy instrument, e.g. 35×22×46 cm
and 25 kg (Anritsu MS4622). It is too large and heavy to carry three of them on a
robot arm or even on a vehicle. Thus, the team of Tohoku University developed a
new VNA shown in Fig. 3.4 together with Anritsu, Japan and USA under support of
JST. It is very small, 20×30×5 cm, and very light weight, less than 1 kg without
case, but it has almost the same performance as the general one, especially for the
sweep speed and accuracy. The specifications are listed in Table 3.1.
Fig. 3.4: Vector network analyzer employed in SAR-GPR.