Advanced sounding: 1. The FMCW alternative


  • A. W. V. Poole


HF radar employing linear frequency-modulated continuous wave or “chirp” modulation provides an alternative to the more conventional pulsed amplitude modulation technique in advanced ionosphere sounding. An analysis is presented which shows that the phases of the discrete Fourier components of the receiver output can be used in the same fashion as the phases of pulsed, fixed frequency ionospheric echoes to evaluate the standard digital parameters, including group path by the method of stationary phase. This can be used to overcome the group path/Doppler velocity ambiguity of linear frequency modulation. A description is given of a sounding structure from which unambiguous group range, angle of arrival, O/X mode, and Doppler velocity can be evaluated. A simple error analysis is also given.