Which TM mode in rectangular waveguide has lowest cutoff frequency?

H_z = 0 E_x = ± Z_TM H_y E_y = ± Z_TM H_x where E₀ is the amplitude of the wave. The expressions for β, λ_c, f_c, λ_g, a are the same as for TE waves. For TM wave the lowest cut off frequency in rectangular wave guide is for TM₁₁ mode. If , the cutoff frequency for TM₁₁ mode is about 12% more than that for TE₂₀ mode.