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Observations over recent years have established that large scale electron density structures are a common feature of the polar cap F-region ionosphere. Whilst experimental work has produced many useful results (Warrington, E.M. et al., IEE Proc. on Microwaves, Antennas and Propag., vol.144, p.241-9, 1997; Rogers, N.C. et al., IEE Proc. on Microwaves, Antennas and Propag., 2003; vol.144, p.91-6, 1997), they were obtained for a small number of paths and frequencies. In order to be able to develop tools to enable such effects to be considered in the design and operation of HF radio systems for which the signals impinge on the polar cap ionosphere, but for frequencies and paths not subject to experimental investigation, a ray tracing model has been developed. The results obtained from the ray tracing simulations are presented together with examples of experimental observations. However, it is well known that the high latitude ionosphere is an extremely complex HF propagation environment and, therefore, precise agreement between experiment and simulation has not been attempted and should not be expected.