Radio propagation through ionospheric sporadic-E

Mid-latitude sporadic-E is a thin layer of dense ionisation at heights around 100km. It is important for radio propagation because it allows beyond line of sight communication at much higher frequencies than standard propagation via the normal E and F layers. The exact propagation mechanism at VHF radio frequencies is not well understood because although it is clear that at lower frequencies it is refraction, that has not been clearly demonstrated at VHF. I am making novel measurements of signal amplitude, phase (and derived doppler), polarisation and potentially time delay to discover the nature of sporadic-E propagation at VHF.