Close-Spaced Diversity Antenna for HF Transmission

The advantages of ionospheric communications over satellite communications for the military are reduced cost and lower vulnerability to physical attack. However, the long haul ionospheric signal is not as reliable as the satellite communications signal, and experiences both long-term and short-term fading. Frequency management shows good promise in the reduction of long-term fading. Short-term fading, caused by waves reflecting from multiple layers changing in real time, can be reduced by space diversity schemes. However, a spacing of 10 wavelengths is generally needed for HF space diversity and is not practical for the highly mobile military requirements of today. This paper reports a field component [ (electric) and (magnetic) fields] diversity scheme in which two antennas are spread much less than one wavelength (λ/16) resulting in typical correlation between the two signals of less than 0.7. A theoretical analysis was made and experiments verified the concept of this new scheme.