Aperture Synthesis for HF Radio Signals Propagated via the F Layer of the Ionosphere

Abstract : A portable high-frequency (HF) radio aperture up to 70 km in length was synthesized by receiving ionospherically propagated signals in a DC-3 airplane. By thus moving a small antenna rapidly over a long distance, a narrow receiving beam width (high azimuthal resolution) was achieved. It is believed that the synthetic aperture described here is the first in the world developed for HF, although the concept has been used successfully at microwave frequencies.