IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 1, JANUARY 2012 267 Calibration of Electric Field Sensors Onboard the Resonance Satellite Manfred Sampl, Member, IEEE, Wolfgang Macher, Christian Gruber, Thomas Oswald, Member, IEEE, Helmut O. Rucker, and Mikhail Mogilevsky Abstract—Strategies and results for calibrating electric field sen- sors (antennas), as used in radio astronomy, onboard the space- craft “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 me- chanical originals and are shortened and tilted by several degrees of angle. The knowledge of the acquired parameters is of great ben- efit to the Resonance mission. In particular, goniopolarimetry tech- niques like polarization analysis and direction finding depend cru- cially 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. Index Terms—Antenna measurements, HF antennas, numer- ical analysis, radio astronomy, satellite antennas, space vehicle antennas. I. INTRODUCTION W ITH the launch of the first space-borne radio astronomy observatories in the last century, it soon became clear that the true antenna parameters of the launched instruments differ from their mechanical representation. For reliable and correct measurements, finding the true antenna characteristics is vital. In this paper, we present two methods applied to the spacecraft Resonance to find the true antenna and instrument parameter for the quasi-static case. The applied methods are electrolytic tank measurements (rheometry), which is a method to determine the effective length vectors of electrically short antennas, and numerical computer simulations. The accuracy of the applied methods is about 1 for directions of effective axes and some percent for effective lengths and antenna capaci- tances. Two other calibration methods, in-flight calibration and Manuscript received October 29, 2010; revised March 11, 2011; accepted July 20, 2011. Date of publication September 15, 2011; date of current version January 05, 2012. This work was part of the science project “RESONANCE electric field sensors: Determination of the optimum configuration,” which was supported by the Austrian Research Promotion Agency (FFG) in the framework of ASAP 4, Project 816159. M. Sampl, W. Macher, and H. O. Rucker are with the Space Research In- stitute, Austrian Academy of Sciences, Graz 8042, Austria (e-mail: manfred. sampl@ieee.org; wolfgang.macher@oeaw.ac.at; rucker@oeaw.ac.at). C. Gruber is with the University of Graz, Graz @oeaw.ac.at, Austria (e-mail: gruber@alumni.tugraz.at). T. Oswald is with the Thomas Oswald Aerospace Software, Weinitzen 8044, Austria (e-mail: thomas.oswald@aeroware.at). M. Mogilevsky is with the Space Research Institute of the Russian Academy of Sciences, Moscow 117997, Russia (e-mail: mogilevsky@romance.iki.rssi. ru). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2011.2167918 anechoic chamber measurements, might be applied at a later stage of the project. II. MISSION RESONANCE The Russian Space Research Institute (IKI, Russian Academy of Sciences, Moscow, Russia) is leading the scientific effort for a space-borne mission, called Resonance, to investigate the inner magnetosphere and auroral region [1]. The mission is consisting of four Earth orbiting satellites, which are to be investigating the wave-particle interaction and dynamic processes in near Earth’s plasma in detail. Details of the project can be found in [2]. Among these processes are the following:  ducted propagation of electromagnetic waves of whistler- mode and ion cyclotron frequency ranges, which play a sig- nificant role in the dynamics of electron and ion radiation belts;  motion of energetic particles from the regions of auroral acceleration and magnetic reconnection;  investigation of the magnetospheric cyclotron maser instability;  source mechanism of the Auroral Kilometric Radiation (AKR). Targeted observation area of the proposed experiments are magnetospheric flux tubes. To achieve a maximized observa- tion time along a bundle of geomagnetic field lines (flux tube) the spacecraft has to fly a magneto-synchronous orbit. Since ge- omagnetic field lines corotate with Earth, the spacecraft has to move along a trajectory ensuring the presence in the flux tube. Fig. 1 outlines such a trajectory where the spacecraft moves along a selected flux tube. In Fig. 1, denotes the initial po- sition of spacecraft inside the magnetic flux, where is the po- sition at the moment of time . The spacecraft “Resonance” is planned to be launched in 2014 as an assembly of the new Russian standardized scien- tific satellite micro platform called “Karat.” This platform is intended to serve as a bus for various kinds of space science missions and is developed and built by NPO S.A. Lavochkina. The platform will have a mass of 250 kg and is going to offer a science payload capacity of up to 80 kg. It consists of a ser- vice module with standardized interfaces, telemetry and control, telecom, a power supply system, a propulsion module, and the payload module. The Resonance spacecraft will be spin stabi- lized along the -axis (Fig. 2), pointing the solar panels (located at the bottom of the spacecraft) at a maximum of the possible time towards the sun. The knowledge of the true antenna properties is of vital im- portance to the scientific results of the Resonance mission by greatly enhancing the accuracy of the acquired radio data. 0018-926X/$26.00 © 2011 IEEE