The concrete expression of an approximate construction of the field comPOnentsfor the dominant mode in a earn-rectangular waveguide

the cut-off wavelength calculated by usingBoundary Element Method and the concrete functions to determine the uncertain exponent constant of the power function in field expression confirmed by using Variational Method are given atfirst. Assuming only dominant mode propagated

the formula of the resonant conductance for longitudinal slot cut in the curved face of the earn-rectangular waveguide is derived by using the equivalence principlelan actual example is presented and the result of calculation and measurement isquite satisfactory.