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Flap Antenna for Communications

In-flight satellite communication systems are finding a growing number of applications on commercial and military aircraft. In-flight satellite communication systems provide access to many valuable and real-time services such as DirecTV, XM radio, and high-speed internet services to both passengers and crew. An in-flight satellite link utilizes a high-gain antenna mounted on the aircraft, which continuously tracks a geosynchronously-orbiting satellite during flight. Depending on the service features and the performance requirements, the high-gain antenna could be either a phased-array or mechanically-scanned antenna. A phased-array antenna has the ability to scan very quickly and can be manufactured in a flat and conformal package. However, phased-array antenna electronics are expensive. Furthermore, their beam performance tends to degrade with an increase in scan angle. In comparison, a mechanically-scanned antenna is inexpensive and provides scanned beam performance that is independent of scan angle. However, a mechanically-scanned antenna typically has a high profile and relatively slow scan speed. In this presentation, a low-cost, low-profile mechanically scanned antenna is proposed. This antenna, called a "flap antenna," is a form of a dual reflector system on a rotating ground plane. The flap antenna assembly consists of a reflector, a feed horn, a tiltable flat flap, and an aerodynamic radome. The feed horn is used to illuminate a parabolic reflector sector with a spherical wave. The reflector reflects and collimates the rays. The flap reflects the collimated rays to form a far-field pattern and varying the tilt angle of the flap achieves elevation beam scanning.