The shape function

of a planar aperture

is defined ashaving value one inside

and zero outside. The two-dimensional Fourier transform of

when

is an

-sided polygon is considered, and a closed-form exact solution is presented. Applications of these results are described for 1) the calculation of the secondary pattern of a reflector antenna with a noncircular aperture, and 2) high-frequency transmission through a periodic frequency selective surface.