Low frequency radio signal polarisation sensor with applications in attitude estimation

A novel system for estimating the attitude (orientation) of a platform using measurements of Low Frequency (LF) radio signals is reported. The sensor system consists of an array of three orthogonal solenoid coil antennas, a three channel radio receiver circuit, a datalogging and control module and data processing algorithms. Traditional low-cost attitude estimation systems typically combine accelerometers, magnetometers and gyroscopes, but produce estimates that are sensitive to platform acceleration. This is a particular problem in high-acceleration, cost-constrained environments such as small fixed-wing Unmanned Aerial Vehicles. The system presented here is shown to accurately measure the axis of polarisation for signals with linear or almost linear polarisation, subject to a sign ambiguity. A representative AM radio broadcast in the LF band is shown to have a substantially linear polarisation, which is used to provide information about the sensor's attitude and shown to exhibit no drift over a period of 24 hours.