| abstract |
An antenna system having a central radiator element and one or more surrounding rings of parasitic elements which can be tuned or actuated separately in each ring by electrical commutation to provide a stepped cardioid radiation or receiving pattern. When the radiator element and a ring of parasitics are used to transmit a cardioid, its stepped pattern contains a fundamental sinusoidal component which can be extracted by a filter at a receiver and used to provide a TACAN/VORTAC bearing determination by comparing its phase with a reference signal transmitted once per revolution of the pattern to mark a predetermined position in its rotation, as is common in TACAN systems. When the cardioid pattern comprises transmitted squitter pulses, care is taken to ensure actual transmissions marking each stepping of the antenna pattern in order to provide optimum bearing information. |