1. Field of the Invention
The present invention relates to antenna tracking systems and to antenna tracking systems mounted on unstable platforms. More particularly, the present invention relates to step track systems using a computer signal process generally known as a Kalman Filter.
2. Prior Art
Conventional methods for using an antenna to track a radio frequency (RF) source, such as from a satellite, use expensive monopulse or conical scan (conscan) methods. For example, the conscan method determines pointing errors by using extra hardware to intentionally off center the antenna bore-sight in a conical beam pattern about the RF source. Moreover, when the antenna is mounted aboard a vessel subject to heavy seas, maintaining antenna tracking of the satellite""s RF beacon requires positioning data of the antenna relative to the ship""s roll and yaw motion; otherwise known as the attitude and heading reference of the antenna relative to the ship""s attitude and reference. The ship""s attitude and heading information is typically provided by expensive inertial navigation systems mounted to the ship. However, inertial navigational systems are not typically suitable, due to weight and size, to mount directly to the antenna pedestal or dish. For this reason the attitude and heading reference of the antenna is typically derived from the ship""s inertial navigation system thereby introducing errors into the closed loop tracking system. Thus, it can be readily appreciated that the lack of an antenna attitude and heading reference source is a disadvantage when the antenna is mounted on a mobile platform such as a marine vessel subject to heavy seas.
It is therefore an object of the present invention to provide an improved tracking system on a mobile platform. It is further an object of the present invention to provide a system and method whereby the intentional mis-pointing of the antenna bore-sight is accomplished without the necessity of extra hardware as is typical when using conscan or monopulse methods. It is a further object of the present invention to provide attitude and heading reference data by directly mounting an attitude and heading reference system (AHRS) directly to the antenna reflector or pedestal base.
In accordance with one embodiment of the present invention an apparatus for an improved antenna tracking system for antennas mounted on an unstable platform is provided. The improved system comprises a directional antenna, an attitude heading reference system (AHRS) mechanically connected to the directional antenna reflector, and an antenna controller connected to the AHRS.
In accordance with one method of the present invention, a method for closed loop radio frequency (RF) tracking of an energy source by a directional antenna mounted to an unstable platform is provided. The method comprising the steps of mechanically attaching an attitude heading reference system (AHRS) to the directional antenna, receiving the mobile platform""s internal navigation data or alternatively, receiving navigation data from the attitude heading reference system (AHRS), searching a satellite orbit pattern for an RF beacon, detecting the satellite RF beacon, and initiating self scan tracking upon detection of the satellite RF beacon.
In accordance with another embodiment of the present invention a self scan radio frequency (RF) tracking antenna apparatus with a mechanically mounted attitude reference heading system (AHRS) system, for use onboard a seagoing platform is provided. The antenna apparatus comprising at least one directional antenna, at least one AHRS mechanically connected to the at least one directional antenna; and at least one antenna controller connected to the at least one directional antenna.