ANTENNA PRECISE POINTING CALIBRATION USING LOW COST DGPS

Abstract

Pan&Tilt directional antennas are present in every Airspace Test Center. They are used to receive telemetry data from the target in test (usually a rocket or an aircraft). Required telemetry range can be usually around 200nm which leaves no option but to use directional antennas (parabolic among others). The use of directional antennas greatly enhances the telemetry range by a factor of 1000. But it does it at a cost: directional accuracy. This kind of antenna has a narrow radiation pattern with its nominal gain at the center of the antenna dish. The main beam of the radiation pattern can be as narrow as 1.8 degrees (3db) in a C Band 2.4m parabolic antenna. An antenna has to be pointing its radiation pattern main lobe to the flying target with an error of less than the main lobe width in order not to degrade reception. A method has been implemented to properly calibrate the mechanical pointing vector to overlap with the radiation pattern main lobe. The calibration method presented in this paper allows a very precise calibration that can be performed locally with the aid of DGPS, RF Beacon, RF Spectrum Analyzer and software to manage the whole process.