Airframe effects on Loran H-field antenna performance
Date of Original Version
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-C's 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. However, in the past, our research has shown that H-field antennas suffered from loop coupling and other effects that led to variations, or errors, in the received TOAs as a function of bearing to the Loran station. New antennas are improved over older models; however, the installation of the antenna on the airframe changes the performance from that of the antenna alone. A necessary task to certify Loran for NPA is bounding the effects of those error sources that cannot be eliminated. The USCG Academy and Alion in partnership with the FAA Technical Center have been conducting tests on H-field antennas both on and off the Convair 580 in order to characterize the impact the aircraft has on the antenna performance. This paper presents the results of this testing and makes an assessment as to the error bounds required for H-field antennas on aircraft.
Proceedings of the Annual Meeting - Institute of Navigation
Johnson, Gregory, Ken Dykstra, Ruslan Shalaev, Peter Swaszek, and Richard Hartnett. "Airframe effects on Loran H-field antenna performance." Proceedings of the Annual Meeting - Institute of Navigation , (2005): 26-35. https://digitalcommons.uri.edu/ele_facpubs/1077