Characteristics of S and X band scatter signals

If a signal is propagated by a scatter mechanism through a turbulent medium, the characteristics of the signal at a receiving site beyond the horizon are a function of: 1. The size of the important scattering volume 2. The velocity of the scatterers The size of the important scattering volume is determined by the scattering coefficient of the turbulent medium and the geometry of the radio link if the antenna beam-angles are large, or by the intersection of the transmitting and receiving beams if the beam-angles are small. The size of the volume determines a length at the receiving site over which signals are correlated and this in turn controls the height-gain function, and the maximum aperture of an antenna which yields its full theoretical gain. The volume size also controls the multipath effects and, hence, signal distortion and bandwidth. If the scatterers are moving with a certain drift velocity and a turbulent velocity, the signal observed at a fixed receiving site fluctuates with time. The contribution of drift velocity to the fluctuations arises from a special pattern moving by the receiving site. The turbulent velocity contributes to the fluctuations due to the beating of frequencies shifted by a Doppler effect from the carrier frequency. Measurements of height-gain, antenna-gain, correlation distances, and fading rates on S-and-X Band signals propagated over a 100 mile path are in agreement with predictions.