I am trying to measure the S parameters of two ADL 5523 evaluation boards in series, but the S21 is oscillating.
In the attached file is the S21 measured.
What could be the problem ?
Thanks in advance,
ADL5523 has both poor input and output return loss. When cascaded in series the reflected power cause by the mismatch is likely the cause for the oscillation. You could try to put a attenuator in between the stages to see if you can stabilize it or try to match the output of the first ADL5523 to the input of the second ADL5523.