Diffraction coefficients for a slot-excited conical antenna

First-order diffraction coefficients for a slot-excited conical antenna are calculated, beginning with integral expressions for the radiation field. Simple formulas based on these coefficients are presented for the radiation patterns that correctly reproduce the interference structure as well as predict the magnitude of the field down to quite low frequencies. Plots of the diffraction coefficients are given for both symmetric and asymmetric excitation of a circumferential slot. Radiation fields are compared with those obtained by summing the exact normal mode series.