On the use of null-steering arrays to enhance the quality of HF skywave communications

The quality of HF skywave transmissions is degraded by the presence of multiple propagation paths between transmitter and receiver. Multipath signals are characterized by amplitude fading and associated phase variations as well as a spread in the propagation times and arrival angles of the skywave components. The use of null steering array techniques (either manual or adaptive) to attenuate all but the dominant component of a multicomponent wavefield is discussed. Propagation measurements are presented which give an insight into the type of ionospheric conditions required for null steering arrays to lead to a significant enhancement in the quality of skywave transmissions.