Low Frequency Radio Polarization Sensor With Applications in Attitude Estimation

Abstract

A novel method of attitude (orientation) estimation is proposed, which makes use of measurements of the polarization of the magnetic (H-) field of Low Frequency (LF) radio signals. This offers advantages relative to existing accelerometer-based systems in high-acceleration, cost-constrained environments, such as small fixed-wing unmanned aerial vehicles. In order to validate this method, a sensor system is presented, which is capable of determining the H-field polarization of LF radio signals from three-axis measurements. The sensor system consists of an array of three orthogonal loop antennas, a three channel radio receiver circuit, a datalogging and control module, and data processing algorithms. This system is shown to accurately measure the axis of H-field polarization for signals with linear or almost linear polarization, subject to a sign ambiguity. A representative AM radio broadcast in the LF band is shown to have a substantially linear polarization, measurements of which are used to determine a receiver’s heading angle. The stability of these polarization measurements over time and the distorting effect of certain structures are quantified. The feasibility of this method of attitude determination is therefore demonstrated.