Microwave techniques for NDE: antenna and front end design

The antennas used in surface penetrating radar systems are, for reasons of portability, usually electrically small and consequently exhibit low gain. This has a profound effect on the performance of the overall system and is probably the only example of a radar system when antenna gain is, in general, so low. However, the bandwidth of the antennas is very much greater than that normally used in conventional radar systems, and surface penetrating radar generally demonstrate very high range resolution. The choice of antenna is generally straightforward. The resistively loaded dipole, bow-tie and TEM travelling wave antenna have been primarily used for the impulse based radar. Where matched filtering can be incorporated in impulse radar then either horn or frequency independent antennas can also be considered. All the classes of antenna discussed can be used in synthesised, FMCW or noise modulated radar. The front end design of ground probing radar is generally complicated by wide bandwidth and wide dynamic range. In the case of time domain radar the effect of mismatches within the radar front end can cause clutter which causes contamination of the data