A New Method for Suppressing the Axial Divergence of G.T.D. in the Study of the Circular aperture in its Rayleigh's Zone

For a circular radiating aperture, the G.T.D. diverges on the axial caustic. We show that the caustic correcting factor proposed by Keller can only be used in farfield zone for, in near field zone, it gives different (and inacurrate) results in the E or H plane. We demonstrate that the exact value of the diffracted field on the axis is the average of Keller's results in the E and H planes, and we generalize this calculus in the case of two any orthogonal planes. On the axis and in its neighborhood, the results obtained by this new method well agrees with that given by Kottler's formulas and progressively fit together with that of G.T.D.