If μ_{r} is relative permeability, ∈_{r} is relative permittivity, c is velocity of light f_{c} is cutoff frequency, phase velocity v_{p} (i.e., speed with which a particular phase of the wave travels down a rectangular waveguide at frequency f) is given by

In a microwave coaxial cable the inner conductor radius is a and inner radius of outside conductor is b. For TE_{11} mode the cut off wavelength is about