Response of a Polarimetric Antenna to Ionospherically Propagated Signals

The Earth’s magnetic field causes the ionosphere to be birefringent at radio frequencies, which means that any system using ionospherically propagated radio waves, such as long-distance broadcasting, high-frequency (HF) skywave communications, over-the-horizon radar, and oblique incidence sounders (OIS) will receive pairs of waves with different polarizations. In this article, we develop a model for the polarization of ionospherically propagated radio waves; the polarization is dependent only upon the strength and direction of the magnetic field at the location where the radio wave exits the ionosphere. This leads to the hemisphere of possible incoming directions of arrival to any particular receiver being divided into three distinct regions. We then use this model to predict the response of a polarimetric antenna to a transmitted OIS signal and validate the model against real ionograms, including cases where all three polarization regions can be clearly observed.