Mitigation of RF interference in air-launched 2 GHz GPR antennas

Air-launched ground penetrating radar (GPR) antennas are useful for analyzing roadway, bridge, and rail-bed construction at very high speeds. The disadvantage of these antennas versus ground-coupled antennas is an increased susceptibility to radio and broadcast interference, predominantly from FM and TV broadcasting as well as cellular telephone base stations. A novel hardware/software interference removal technique has been developed that allows 2 GHz air-launched antennas to operate in the presence of most broadcast interference sources while maintaining data integrity and measurement capability of the interference-free scenario. The performance of the conventional 2 GHz air-launched antenna is compared to the new interference-rejecting system along a 182 km (113 mile) route traversing through the harshest interference-prone highways in the Greater Boston Metropolitan area. It was found that for this data collection route, the amount of unacceptable data was reduced from 18% to 7% with the new technology. It was further found that when only unpredictable interference sources are considered, namely cellular telephones, only 2% of the measurement data is impacted. Finally, a comparison of measurement results during different times of day and antenna polarizations is made, where no improvement was observed in either case.