The slot admittance is calculated for a slot radiating into a waveguide of radius 5 to 10λ. The radius of the wide waveguide is selected so that the slot admittance is equal to the admittance for a semi-infinite half space in absence of plasma. This slot admittance is an approximation to the admittance of an inhomogeneous half space in presence of a plasma layer. The calculated slot susceptance is shown to be nearly constant for various thicknesses of the plasma layer, while the slot conductance and radiation conductances are decreased by increasing plasma thickness. This approximate calculation appears to be particularly good for thin layers of electrically contrasting plasma (εp/εo= 1 and/or tan 5δ>> 1). The calculations indicate an admittance similar to that of earlier calculations for a rectangular slot radiating into a wide rectangular waveguide.
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