To determine if an antenna is normal (gain) or if it falls into the supergain category, let the antenna be enclosed in the smallest sphere that just surrounds all of the antenna elements. The maximum gain that can be developed by an antenna operating in the normal range is:

Gnmax = (1*PI*A/Lam)2+ 4*PI*A/Lam


Where A is the radius of the enclosing sphere, and Lam is the wavelength. This equation is plotted in the graph shown below.

A 2 element yagi beam with its elements spaced at .1 wavelength occupies a radius essentially the same as a ½ wave dipole - a ¼ wavelength radius - so the maximum normal gain is around 7.4 dBi (Shown in red). Since the measured gain of the 2 element Raibeam (with .1 wavelength element spacing) is 8.2 dBi it definitely falls into the supergain region.
Maximum Normal gain of an antenna as a function of a radius just enclosing the antenna. If the gain is less than the curve value, the antenna is in the normal (gain) range, if greater, in the supergain range.

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