Comparison Between Transmission line and Wave guide : Transmission line Wave guide Small cross-section transmission lines (like coaxial cables) can only transmit low power levels due to the relatively high fields concentrated at specific locations within the device Metal waveguides can transmit high power levels. The fields of the propagating wave are spread more uniformly over a larger cross-sectional area than the small cross-section transmission line. Large cross-section transmission lines can transmit high power levels. Large cross-section (low frequency) waveguides are impractical due to large size and high cost .