Limiting polarisation of radio waves of medium and high frequency reflected from the ionosphere

Heights of limiting polarisation are evaluated by means of the criterion of Budden for selected models of electron density and collision frequency in the lower ionosphere. For these models, limiting polarisation occurs typically at heights of between 50 and 70km at medium and high frequencies. The electron-collision frequency at these heights is sufficient to influence the polarisation significantly. The dependence of the power available from a linearly polarised receiving aerial on the limiting polarisation of a downcoming skywave signal is investigated.