ONE PORT RETURN LOSS MEASUREMENTS (S11) AND TWO PORT TRANSFER FUNCTION (S21) MEASUREMENTS SETUP
Here I would simply clarify the difference of setup we talked about between this two measurements with the following two drawings .
The two 10 dB attenuator are used to guarantee a perfect matching in the section after the cables .
Of course they limit the dynamic range of the measurements . For this reasons they are not always used or used with lower values .