# 5. Compare waveguides and two wire transmission lines

## 5. Compare waveguides and two wire transmission lines

Here we are comparing waveguides and two wire transmission lines.

For frequencies higher than 3 GHZ, the transmission of electromagnetic waves along transmission lines and cables is not possible because of high loss, here a metallic tube can be used to transmit electromagnetic waves.

A hollow metallic tube of uniform cross section which transmits electromagnetic waves by successive reflections from the inner walls of the tube is called waveguide.

Similarities between two wire transmission line and waveguide :-

1. As the wave propagates, they gets attenuated in both.

2. Irregularities or mismatches in the transmission line and waveguide causes reflection and thus standing waves.

3. Reflected wave can be eliminated by proper impedance match in both.

Disimilarities :-

1. Depending upon the shape and dimension of the waveguide, there is a cut off frequency fc, frequencies f > fc can only pass through it. Thus it acts as a high pass filter with cut off frequency fc.

2. Waveguide is a one conductor system, the whole body of the waveguide acts as the ground and the wave propagates through multiple reflections from the walls of the waveguide.

3. Transmission through waveguide is governed by field theory while in transmission line by circuit theory.

4. Velocity of propagation of wave inside a wave guide is different from that through free space due to reflections.