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-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 Hfield 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 Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 2006 2. REPORT TYPE 3. DATES COVERED 00-00-2006 to 00-00-2006 4. TITLE AND SUBTITLE Airframe Effects on Loran H-field Antenna Performance 5a. CONTRACT NUMBER