An Improved Automatic Tracking System for Linear and Circular Polarization

A multimode tracking system to track geostationary satellites transmitting both linear and circular polarized beacon signals is proposed. The system is based on amplitude and phase characteristics of the higher mode TE21 only, generated on the aperture of the antenna when the boresight axis is shifted from the satellite direction. An automatic rotation of the tracking coupler by a servo-control, which also drives a coordinate converter of the feed system, allows to obtain directly the correct elevation and azimuth pointing errors for any incident polarization. A new compact mode coupler composed by four longitudinal narrow slots, parallel to the circular waveguide axis, is described. The main results of the theoretical study and experimental data, obtained with a prototype operating at the beacon-frequency of 11.575 GHz, are presented. A good agreement between theoretical and experimental results confirms the validity and the accuracy of all the system.