In-Situ Pattern Measurement of the Johns Hopkins University Applied Physics Laboratory 60-foot Parabolic Reflector Antenna

摘要

In-situ pattern measurement of JHU/APL's 60-foot parabolic reflector antenna (S-band), using a low-earth orbit satellite as the source is described. The signal strength and X and Y tracking error voltages are measured as the antenna dish sweeps a matrix of points around the position of the moving satellite. The swept region is approximately ±0.30° from the antenna's boresight. This technique was evaluated during April 1998.rnThis measurement was used to baseline the current performance of the ground station before the feed underwent significant modifications. Before the new feed assembly was installed, the position of the current feed was translated to the new feed assembly. Once installed the performance of the reflector was verified. Misalignment of the feed broadens the main beam and increases the sidelobes. More importantly, the inclusion of new components inside the feed also has the potential to introduce phase errors onto the tracking signals. These phase errors will be translated by the auto-track electronics into pointing errors causing the antenna system to inaccurately follow a target. This paper describes the measurement of the reflector antenna pattern and tracking pattern before the new assembly was installed. Results of pattern measurements with the new assembly will be presented at the conference.