Importance of Directivity in Couplers and Isolation in LNA

Hello All,

Can anybody tell me, what is the importance of Directivity of couplers and Isolation of LNA in system level application?What happens if that becomes bad?

Directivity is a measure of a coupler ability to separate signals flowing in opposite directions within coupler.
If coupler directivity is bad the dynamic range of the reflection measurement is small.

If the isolation of the LNA is poor the LNA could oscillate (become unstable), because it will increase the amount of feedback from the output to the input.

Hello Mr Vfone,

thank you very much

Another problem due to a poor LNA isolation is the signals after LNA (i.e., LO, IF) will feedthrough to the input port of LNA, leading to serious disturbance.