OPTIMIZED FEEDS FOR THE WIRE-GRIP LENS HF ANTENNA AT THE FAA RECEIVER STATION, MOLOKAI, HAWAII.

The report describes the development and testing of optimized feeds for the Wire-Grid HF Lens Antenna at the FAA International Flight Service Receiver Station at Molokai, Hawaii. Utilization of these optimized feeds in the lens greatly increases its gain as well as reducing the theoretical azimuth pattern side lobes, particularly at the low frequency end of the HF band. During the course of this program the originally installed Samoa and Nandi-Canton feeds were replaced with optimized feeds. Measurements made on these optimized feeds confirmed their predicted high efficiency of approximately 50 percent. The calculated efficiency of the optimized feeds is greater than that of the originally installed feeds by approximately 10 db at the low frequency end of the band and 8 db at the high frequency end of the band. Using a ground-based transmitter the measured power gain increase of the lens using the optimized feeds was approximately 7 db at the low frequency end of the band and approximately 4 db at the upper end of the band. Measured gain increases more closely approximating the feed efficiency increases would be expected if the ground-based transmitter were replaced with an airborne transmitter located at the elevation angles corresponding to the peak of the lens elevation patterns. Author