ANS:A - guide diameter

Some applications require dual polarization capability. Circular waveguide has this capability. These analysis uses cylindrical coordinates. In circular waveguide TE₁₁ mode has the lowest cut off frequency and is the dominant mode. If D is diameter of waveguide λ_c = 1.706 D for TE₁₁ mode λ_c = 1.029 D for TE₂₁ mode λ_c = 0.82 D for TE₀₁ mode λ_c = 1.306 D for TM₀₁ mode.