Early results are presented from high power ionospheric modification experiments with the SPEAR (Space Plasma Exploration by Active Radar) HF facility, which is used to generate artificial field-aligned irregularities (AFAI) in the polar cap ionosphere. These AFAIs are detected both through HF coherent backscatter radar and bistatic HF Doppler experiments. The AFAIs created with SPEAR are demonstrated to provide an important geophysical diagnostic of the polar cap ionospheric electric field, and may also scatter radio waves out of the ionospheric waveguide, even when they have propagated over very considerable distances. ; This is the author's final draft of the paper published as Advances in Space Research, 2007, 40 (3), pp. 384-389. The final version is available from http://www.sciencedirect.com/science/journal/02731177. Doi: 10.1016/j.asr.2007.02.059