Cutoff frequency of the TMc11 mode in a hollow conducting elliptical waveguide

The cutoff wavelength of the TMc11 mode is treated as a function of the eccentricity of the elliptical cross-section. From the exact values calculated on a digital computer, an approximate formula is derived for the function qc11 = f(e) for eccentricities between 0.05 and 0.95. Over this range, the cutoff wavelength is given to an accuracy within 0.14%.