
I am doing S21 and S11 measurements with a plus4 on a Noolectric LANA and am seeing strange results. The bottom graph shows the results port1 connected to the input and port 2 connected to the output. I used 12" cables and calibrated at the end of the cables. This results in a ripple on the S21 with the average less than 10 dB. The top graph has added a 20 dB attenuator between the port 1 cable and the input. The ripple only at the lowest frequencies and the S21 value starts at about 27 dB and tapers off around 16 dB at 2 GHz, taking the 20 dB attenuator into account. This is more in line with the part spec. I am trying to understand what is causing the incorrect S21 values without the attenuator. I tried adding extra cable length to the input and varied the input power from -30 to 0 dBm, these made no discernable difference in either case. I thought it might re related to the S11 value, but neither the S21 value nor the ripple rate or magnitude seem to correlate in the second graph. Also, I see similar results when I drive the input with a Pluto. Any ideas?
Thanks,
Bruce
KO4PRE