Development of a Full-Duplex Retrodirective Array for CubeSat Applications

CubeSat missions rely heavily on effective communication systems in order to transmit and receive
large amounts of data quickly and efficiently. The amount of data capable of being downlinked is
dependent upon the received power and bandwidth of the signal. The transmitted power is typically
limited due to the size constraints placed upon solar panels and batteries, which ultimately limits
the received power at the ground station. Therefore, the only way to improve the signal strength is
to ensure that the maximum antenna gain is directed at the ground station through either rotating
the satellite or electronically steering the antenna.

Implementing a phased array antenna would allow for electronic steerability, also known as
beamforming. This allows the CubeSat to take advantage of a large antenna gain without having
to mechanically rotate. This project aims to achieve adaptive beamforming, where the CubeSat
would not need to know the position of the ground station to transmit, but would determine this
autonomously. A retrodirective array such as this would determine the direction of arriving signals
from the ground station and maximize gain in that direction. This requires a phased array that has
enough bandwidth to transmit and receive as well as a wide enough scan angle to downlink
maximal data throughout a pass. NASA uses separate uplink and downlink frequencies that are
too far apart for a standard planar array, necessitating a multi-band array for a 1U CubeSat.
Designing this antenna array will be the primary focus of this project. Using the retrodirective
array proposed here, data throughput could be optimized.