Where we should use circular wave guide and where to use rectangular wave guide ?

with the coupler and the ODU

The circular or cylindrical wave guide is mostly used in the grounded radars to transmit and receive the energy from the antenna and the rectangular wave guide is used in communication systems.

1. It is used where the transmission or reception is in the range of microwave frequencies. 2. It is also used for handling the high power of energy. 3. It is mostly used in the airborne radar. 4. In ground radar’s we also use the wave guide. 5. The circular wave guide is mostly used in the ground radar to transmit or receive the energy from antenna. Which revolves in 360o bearing continuously. 6. The wave guide is also used in communication system. 7. In satellite communication the wave guide is mostly used. 8. We also use the wave guide in the devices of navigation aids. 9. In some cases the wave guide is used as attenuator where very high frequencies are involved. 10. The wave guides are also used with the cavity resonators to carry the input and out put signals. 

we can use the circular wave guide in rotary joints & the rectangular for normal transmission line