ALPHASAT - Ka/Q Band Ground Propagation Terminals for the Alphasat TDP5 Scientific Experiment

In the framework of the ALPHAST mission a highly accurate beacon receiver for 20 and 40 GHz is developed in cooperation with Joanneum Research under contract by the European Space Agency. ALPHASAT is the largest communications satellite built so far by European industry. ALPHASAT carries a number of technology demonstration Payload. The ALPHASAT TDP 5 experiment has the goal to investigate novel communications techniques for the next generation of communications satellites utilising the so-called Q/V-band (40 and 50 GHz). These very high frequencies are significantly influenced by weather effects (rain, hail, snow). The traditional approach to implement large fade margins is not suitable, as it leads to prohibitively expensive ground stations. Adaptive coding and modulation (ACM) are efficient methods for fade mitigation. In order to design good ACM algorithms a detailed knowledge of the wave propagation properties of millimetre waves is needed. This is done by precisely measuring the signal attenuation of a constant carrier (beacon) transmitted by the satellite. Any variation is a measure of the propagation conditions. The Institute has developed a beacon receiver based on a software-defined radio platform. Sophisticated tracking algorithms have been implemented to take care of frequency errors of the incoming signal. The four-channel receiver allows to measure not only the signal attenuation at 20 and 40 GHz, but also depolarisation effects of the electromagnetic waves. Data are automatically recorded for later analysis. It is planned to reproduce this device for entities in Europe engaged in propagation studies.