Phased helical antenna array design for CubeSat application

Abstract

The following study investigates the feasibility of a low power, high speed downlink connection for the purposes of Cubesat application. Using a 2×2 phased helical antenna array operating on the 802.11b standard protocol with cots parts, a low cost 1U system is conceived with beam steering functionality and 11 Mb/s down link capability; unprecedented in traditional Cubesat communication links that are typically slow as a result of their strict power, size, and cost limitations. Applying a steerable antenna array also allows a small satellite to better maintain a secure link connection, directly forming the beam to the ground station, where a small, low-cost attitude control system (as usually found in CubeSats) would be unable to provide accurate physical antenna pointing. Due to time restraints, this paper only seeks to establish what is reasonably achievable in a CubeSat form factor, and to provide a rudimentary systems design and RF analysis for proving the feasibility of such a system. No hardware development or physical testing was done. The course of the study began with a review of previous work, defining 1U CubeSat limitations to set target goals for power consumption, physical size, overall cost, and downlink speed. From there a preliminary systems architecture was developed, which included high level design, component selection, frequency/protocol usage, and power and link budget analysis. Once establishing system capability, the design was further refined, creating and modelling the helical antenna design, MATLAB modelling the phased array behavior, and constructing and simulating a Wilkinson RF power divider board layout. The overall 1U CubeSat communication system design was determined to be able to theoretically transmit up to 11Mb/s downlink speeds using an 802.11b module in CCK mode, utilizing a 60 degree range for the steerable beam. The helical antennas, designed to operate at 2.4 GHz in a 2×2 configuration fit snugly on one 10cm × 10cm face of a CubeSat, and the one-to-four RF power divider split the signal with only .3db losses below ideally split signal power. Perhaps most importantly however, all components accomplishing these specifications were low cost and within typical telemetry system power allocations of a 1U CubeSat, pulling less than 3.5W total. If implemented, this communication system design would be by far the most capable 1U CubeSat data link, and would be the first operating 1U CubeSat utilizing a phased array antenna. As such, the design allows for stronger signal reception at the ground station, pointing the beam directly where a low-cost CubeSat ADCS would fail to point the satellite and its antennas accurately.