Field Distribution in a Slot Radiator

Abstract

The distribution of electric field in the aperture plane of a longitudinal slot in the broad wall of a rectangular waveguide is estimated. The justification of the method of measurement as also the theoretical expression for the electric field distribution are obtained with the help of a simplified theoretical model. It is shown that the axial field distribution is of the form f(z)=|sin K(L-z)| except near the ends of the slot. The amplitudes and attenuation coefficients of the significant evanescent waves beyond the ends of the slot are determined from experimental data by the process of curve fitting. Experimental results obtained for slot lengths in the range λ/2 to 3λ/2 show that the field distribution of the form f(z)= cos(πz/2L), as suggested in earlier literatures, is not valid for slot lengths far away from λ/2 and particularly for a slot of lengthλ. The field distribution is given by an even function near λ/2 mode of resonance, by an odd function near λ mode of resonance.