Aerial in depression ends in no functional state (6)
I believe the answer is:
dipole
'aerial' is the definition.
(I know that dipole is a type of aerial)
'depression ends in no functional state' is the wordplay.
'depression' becomes 'dip' (dip is a kind of depression).
'ends in' suggests the final letters.
The last letters of 'no functional state' are 'ole'.
'dip'+'ole'='DIPOLE'
'in' is the link.
(Other definitions for dipole that I've seen before include "Directional TV or radio aerial" , "Type of aerial" , "I loped between two equal and opposite electric charges" .)