The Theoretical Precision with which an Arbitrary Radiation-Pattern may be Obtained from a Source of Finite Size

It appears that it is possible to approximate as closely as desired to a specified radiation-pattern by a suitable distribution of field over an aperture of given size, though the necessary currents in the conducting elements of the source would in general be prohibitively large in comparison with the power radiated. The difficulty of obtaining a high degree of approximation, and in particular a power gain very much greater than that of a uniformly illuminated aperture, is thus a practical rather than a theoretical one. The same is true for the linear array of given length as for the continuous aperture if no limit is set to the number of elements. Even when this number is limited by the adoption of half-wavelength spacing, the broadside power gain is not a maximum when the amplitudes and phases of the elements are equal, unless the elements are ideal isotropic point-sources.