Design of a UHF phased array ground station antenna for small satellites

Abstract

Universities and amateur radio communities have been major drivers in the launch of small satellites. These communicate mostly in the VHF and UHF bands with ground stations consisting of mechanically steerable Yagi-Uda antenna systems. Advances in miniaturization have allowed the more recent trend of launching multiple nanosatellites operating in a similar frequency range. UoMBSat is a 1p PocketQube operating in UHF half-duplex mode designed by the Astrionics Research group at the University of Malta. It is intended to be launched as a 2x2x2 cluster whereby the individual satellites will disperse gradually and must be individually tracked. Such satellite formations pose a new challenge for the conventional ground station which must be capable of distinguishing one satellite from several others in close proximity and identify individual members of a constellation, with capability to possibly track multiple satellites. A system with the capability to electronically steer the beam is required. Phased array antennas (PAAs) allow this to be achieved. They are rarely implemented in small satellite ground stations of this nature due to complexity, cost and the physical challenges associated with the large wavelength. Constraints and requirements arising from the UoMBSat have been considered and a novel design for a low-cost, functionally-scalable, Geodesic Dome PAA (GDPAA) with a compact footprint is proposed, to meet the general needs of small satellites. A design paradigm for a PAA design for small satellites is proposed and adequately documented to serve as a chronologically optimised sequence of design decisions which other academics interested in implementing a low-cost PAA in their ground stations may consider. It is demonstrated that if antenna elements are placed in a circular lattice on each face of the icosahedron structure, the overall footprint of the system is reduced by 20% and the overall array performance is improved when compared to the next best triangular lattice counterpart. A low-cost electronics solution utilizing 4-channel Direct Digital Synthesizers is used for phase and amplitude control with reduced complexity. A Python software library to drive the GDPAA has been designed and developed to be interoperable with existing tools and the SatNOGS ground station network. A planar face together with the supporting radome hardware components has been designed and fabricated and measured results are in good agreement with simulations. It is overall demonstrated that a low-cost UHF Phased Array ground station antenna for small satellites is feasible through an active GDPAA with analogue beamforming (BF).