Manfred Sampl

Calibration of Electric Field Sensors Onboard the Resonance Satellite

Strategies and results for calibrating electric field sensors (antennas), as used in radio astronomy, onboard the spacecraft “Resonance” are presented. Calibration is performed for four boom antennas and four cylindrical sensors at the boom tips. These antennas are devised for the measurement of electric fields and plasma parameters. It is shown that the electrical representations of the antennas, the effective length vectors, differ from their mechanical originals and 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 space-borne antenna system consisting of boom monopoles and cylindrical tip antennas.

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.

First results of the JUNO/Waves antenna investigations

Waves is the radio and plasma wave instrument onboard NASAs spacecraft JUNO. The instrument utilizes an electrically short dipole antenna for the measurement of electromagnetic field parameters. The instrument is devised for frequencies from 50 Hz up to 40 MHz. Waves antenna system properties are distorted because the highly conducting spacecraft body is in close vicinity of the antennas. In addition the antenna system is not tri-axial and goniopolarimetry techniques like polarization analysis and direction finding depend crucially on the true antenna properties. In the case of the Waves instrument, mentioned techniques have to rely on a rotating dipole method for detection of parameters like the wave incident direction. In this contribution we outline the first step to acquire the true antenna properties of the Waves antennas. We present the first results of our numerical investigations, the antenna monopole effective length vectors and antenna transfer matrices for the quasi static regime.

Transfer function of a 13.56MHz RFID channel

In this contribution we derive the transfer function of a typical RFID channel as defined in ISO 14443. RFID is common technology and has applications in various contexts such as keyless entry and logistics. In the following the principle of such a system is briefly outlined and an equivalent circuit is introduced. The transfer function itself is derived via a state space model approach which are a widely used concept, especially in control engineering. Finally the resulting transfer function is compared to a conventionally derived transfer function. The results show that the derived function is correct within the inherent errors of such concepts and approximations. In addition, the resulting matrix-shape state space model is a good basis for further investigations such as mitigating intersymbol interference on the channel.