A rapid beam-swinging experiment in transhorizon propagation

By using a broadside phased array for an antenna, a narrow beam can be swung rapidly and in quick succession through a limited sector by fast control of the phasing, rather than by movement of the entire antenna structure. This technique is used at the receiving end of a 101-mile beyond-the-horizon transmission path in order to probe the portion of the troposphere through which the signal is propagated. At the frequency employed of 3.12 kmc, a 0.49- degree beam is swung in azimuth through a 4.2-degree sector each tenth of a second. A variety of phenomena are observed with this technique which have not been directly apparent in slower beam-swinging experiments. The beam-broadening effect attributed to atmospheric scattering is not always evident on any one sector scan. However, the change from scan to scan is frequently rapid enough so that a time average would show the broadening. At times the scan-to-scan changes are systematic and show a continuity indicative of a motion of the scattering or reflecting regions; in some cases this motion is too rapid to be accounted for by transport of air, thus implying a wave motion rippling through the atmosphere. At other times the atmospheric structure is too fine to be resolved by the beamwidth employed, and the time variations are too rapid to reveal a continuity from one scan to the next.