A wideband technique for micro-ranging in OTHR

A method for utilizing wideband transmissions (>100 kHz) in OTHR is proposed. The technique involves the aggregation of multiple narrow band signals into a wideband composite through digital synthesis. The multi-channel signal is received digitally and after normal correlation and Doppler processing is recombined using Whitehead-Malekpsilas phase-frequency technique to provide an orthogonal micro-ranging dimension. The technique is described, and then modeled in an attempt to gauge its effectiveness. The demanding application of OTHR height finding is chosen in the modeling as it requires separation of ionospheric micro multi-path signals to be effective. The modeling shows that ionospheric dispersion limits a direct application of the micro-ranging technique when propagating through an IRI mid-latitude ionosphere with typical frequency selection rules. A simple method of estimating and removing the ionospheric dispersion is proposed and demonstrated to be effective in progressing the technique to provide range resolution approaching that expected with the wideband signal.