A rapid-scanning phased array for propagation measurements

An S-band broadside antenna array is described in which each radiating element consists of a parabolic reflector which is fed by a helix radiator and local ground plane, so that the signal radiated (or susceptible of reception) is circularly polarized. Phase shifting is accomplished by mechanical rotation of each helix. If the various helices are rotated at multiple rates, the array then produces a beam which is narrow owing to the overall size of the array, and which swings rapidly, owing to the rapid rotation of individual helices. This report describes the pertinent design considerations, construction and measurements on such an antenna. The antenna has a principal-lobe half-power beamwidth of 0.5 degrees and is capable continuously of scanning a sector 4.2 degrees wide at a rate as high as 10 scans per second. This antenna is currently in operation at 3.12 kMc in connection with beyond-the-horizon propagation experiments to obtain data pertaining to propagation irregularities in the troposphere.