Resonance spacecraft antenna calibration: Rheometry and numerical simulations

We report on the calibration effort for the monopole antennas onboard the Resonance spacecraft. The calibration is performed for four boom antennas and four cylindrical sensors at the boom tips. These antennas are devised for the measurement of electrical fields and plasma parameters. We apply two methods for the antenna analysis: first, electrolytic tank measurements (rheometry), which is a method to determine the effective length vectors of electrically short antennas; second, numerical computer simulations which enable us to study also the transition to higher frequencies. The accuracy of the applied methods is about 1 degree for directions of effective axes and some percent for effective lengths and antenna capacitances. It is shown that the electrical representations of the antennas, the effective length vector, differ from their mechanical originals, are shortened and tilted by several degrees of angle. The knowledge of the acquired parameters is of great benefit to the Resonance mission. In particular, goniopolarimetry techniques like polarization analysis and direction finding depend crucially on the effective axes. For the first time this kind of analysis is performed for a spaceborne antenna system consisting of boom monopoles and cylindrical tip antennas.