The propagation constant γ γ of the guided wave is complex, in general. For a lossless case, the propagation constant might be found to take on either real or imaginary values, depending on the chosen solution of the eigenvalue equation and on the angular frequency ω ω . When γ γ is purely real, the mode is said to be "below cutoff", since the amplitude of the field phasors tends to exponentially decrease with propagation; an imaginary γ γ , instead, represents modes said to be "in propagation" or "above cutoff", as the complex amplitude of the phasors does not change with z .