Choosing the number of faces of a phased-array antenna for hemisphere scan coverage

Phased-array antennas utilizing fixed, planar apertures and designed to provide electronic-beam scanning throughout a hemisphere require a minimum of 3 apertures or faces. Each face covers one-third of the hemisphere and scans to an angle from broadside. This causes a ratio of broadside beamwidth to maximum-scan beamwidth of 0.45. Also, assuming no power reflected from the aperture broadside scan, a large amount of power would be reflected at maximum scan because of mutual coupling. These two effects cause a variation in realized gain of 4.1 db. By using 4, 5, or even 6 faces to scan the hemisphere, the antenna performance may be considerably improved. Each face of the 6-face array scans to an angle of only from broadside, and exhibits a beamwidth ratio of only 0.76. The power reflected from the aperture is greatly reduced, and the variation in realized gain is only 1.3 dB. The relative number of elements required by the various designs depends on the particular basis of comparison. Equalizing poorest performance by specifying equal realized gains at the respective maximum scan angles requires about 18 percent more elements for 3 faces than for 6 faces. Three of the four chosen bases for comparison yielded fewest elements for the 4-face array.