Lowprofile antenna for NAVSTAR receivers

Describes the design of a low-profile antenna which is used to receive signals from NAVSTAR Global Positioning System satellites to enable a receiver on board an aircraft to calculate its position to high accuracies. The basic requirements of the NAVSTAR system are that the antenna be right-hand circularly polarised and dual frequency (1228 MHz and 1575 MHz) with a 20 MHz bandwidth at each. In addition the antenna must receive signals simultaneously from a number of satellites at elevation angles greater than 5° above the horizon. The antenna installation under consideration is a single unit externally flush-mounted on top of the fuselage of the aircraft with the thickness of the antenna being minimised to keep aerodynamic drag low