On the accuracy of physical optics

The first-order correction to the physical optics (PO) solution for the axial radiation field from parabolic reflector antennas is found. The correction is of order
k^{-1}
and is in quadrature with the PO solution. By means of the correction term the accuracy of the PO surface integral is round to be better than
0.22(\lambda/D)^{2}
dB on axis, where
D
is the diameter of the reflector. Thus, the PO solution for the directivity is extremely accurate for commun reflector sizes of several wavelengths
\lambda
.