Studies on waveguide-fed slot antenna

The paper presents investigations of the effect of stored energy inside a waveguide, near a displaced narrow longitudinal slot, on the immittance properties of the radiating slot. It is shown that internal stored energy accounts for the discrepancy between the theoretical and experimental results of the immittance characteristics observed in earlier studies. The effect of stored energy is to contribute an additional reactive term in the expression for the immittance of the slot. By the addition of this extra reactive term to the theoretical expression for the immittance, it has been possible to predict the point of resonance with better accuracy. Further, an expression is derived for the immittance presented by a slot to the transmission-line representation of the waveguide, as a function of slot length, displacement etc. by the application of the principle of duality to the dipole antenna.