Airframe Effects on Loran H-field Antenna Performance

The 2001 Volpe National Transportation Systems Center report on GPS vulnerabilities identified Loran-C as one possible backup system for GPS. The Federal Aviation Administration FAA observed in its recently completed Navigation and Landing Transition Study that Loran-C, as an independent radio navigation system, is theoretically the best backup for GPS however, this study also observed that Loran-Cs potential benefits hinge upon the level of position accuracy actually realized as measured by the 2 drms error radius. For aviation applications this is the ability to support non-precision approach NPA at a Required Navigation Performance RNP of 0.3 which equates to a 2 drms error of 309 meters. The recently released report of the DOT Radionavigation Task Force recommended to complete the evaluation of enhanced Loran to validate the expectation that it will provide the performance to support aviation NPA and maritime HEA operations. To meet this need, the FAA is currently leading a team consisting of members from industry government, and academia to provide guidance to the policy makers in their evaluation of the future of enhanced Loran eLoran in the United States. Through FAA sponsoring, the U.S. Coast Guard Academy USCGA is responsible for conducting some of the tests and evaluations to help determine whether eLoran can provide the accuracy, availability, integrity, and continuity to meet these requirements. One area of importance that has been under investigation has been the use of H-field antennas to receive the Loran signal the times of arrivals of the signals, or TOAs, are used in the navigation position solution. H-field antennas provide better performance than E-field antennas the usual maritime antenna in the presence of precipitation static, which is a common problem on aircraft.