Beam Pointing Error Mitigation Capabilities of the Cassiopeia Array for Frequency Offset Retrodirective Space Based Solar Power

It is a common understanding that frequency offset retrodirective antennas produce a beam pointing error between the received pilot beam signal and the retransmitted signal. If this was the case, this could be a major issue when using a retrodirective antenna for space based solar power applications, where the satellite is required to lock to a pilot beam from the earth based rectenna and retransmit the power beam back in the same direction. Any mis-pointing of the beam could point the power beam completely off-target. This paper concludes that the retrodirective beam pointing error researched so far only applies to planar arrays. When a 3-dimensional helical "Cassiopeia" type array is simulated as a frequency offset retrodirective antenna, it was found to have inherent capabilities to mitigate beam pointing error. Instead of producing significant beam pointing error, the frequency offset has more of a defocusing effect, with only minor beam pointing error effects compared to a linear array. Beam pointing error was found to reduce by a factor of 8 for an 8x1 linear array compared to an 8x8 helical array. It is anticipated that these unwanted effects could be quite minimal for small frequency offsets, to the point where their effects could be accurately quantified for a large SBSP array and thus incorporated into the design parameters of such a system.