PART 1: Some Theory and Factoids -- Future AMSAT missions will use "smart"antenna arrays in order to achieve the gain needed for solid links to the ground. Inthis paper we will describe the underlying theory that can be used to predictperformance of an array. Since the theoretical basis involves some math, we willattempt to de-mystify arrays and provide some simple rules-of-thumb.In this discussion, we will demonstrate the similarity between time-frequencySpectrum Analysis and antenna arrays. Just as we have learned in all our SDRactivities, time (seconds) and frequency (cycles/second) are related by FourierTransforms, the antenna pattern (Le. power as a function of angle) on the sky isrelated to the "spatial frequencies" that describe the illumination of the antenna. Wewill attempt to explain these concepts with lots of practical analogies.PART 2: Applications to EAGLE - Based on this brief exposure to array theory, wewill use the concepts introduced in Part 1 to describe possible implementation for theEAGLE spacecraft. Eagle will be a spin-stabilized spacecraft; as the satellite movesaway from apogee, the "antenna farm" will no longer face the earth. In professional3-axis stabilized satellites, the antenna platform might be mechanically pointed tomaintain the antenna pointing at the earth; but AMSAT prefers to move electronsinstead of metal, and we have designed phased array antennas that can steer thebeam with no moving parts. In this paper we will describe some of the possible arrayconfigurations and present MATLAB simulations of the beam patterns that the usercan expect.
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