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Six-Sector Antenna for the GPS-Squitter En-Route Ground Station.

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A six sector antenna for a pole mounted GPS-Squitter en-route ground station was designed, built, and tested. The fan beam of each of the six sectors of the antenna covers a 60-degree azimuthal sector. Together, the six uniformly spaced, contiguous 60-degree sectors cover the complete 360 degrees of azimuth at the two Mode S frequencies 1030 and 1090 MHz. When equipped with its receivers, the antenna achieves a maximum operational squitter reception range in excess of 200 nmi. Physically, the antenna consists of six vertical 12-element linear arrays spaced uniformly around the circumference of an imaginary vertical circular cylinder and lying parallel to its axis. Six reflectors in the form of parabolic cylinders are mounted behind the linear arrays, one per array, to define the six separate sector beams. The complete radome enclosed assembly is a cylinder 8 feet tall and 23 inches in diameter. It weights 250 pounds. Antenna range measurements of the antenna gain pattern verified that it meets its design goals. Reception tests in which the antenna was used to collect short squitters broadcast by air traffic being tracked by the MODSEF Mode S sensor demonstrated its system performance. Three additional aspects of the antennas use were demonstrated. These are, first, the emergency role of the antenna for direction finding in case GPS-derived position is temporarily lost, for which a potentially useful performance was exhibited second, the application of the antenna to compiling performance statistics of the current population of aircraft transponders - as example, the distribution of transponder ERPs, is included here and third, the use of the antenna on a buoy mounted en-route ground station, including the effects on the link of buoy pitching sea reflection multipath. The first two of these studies employed squitter data collected with the antenna the last

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  • Radiofrequency Wave Propagation

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