What is the physical meaning of X(s)and X(T) for different circumstances in the X-parameters?
To your first question:
What is the physical meaning of the same frequency ?
When an amplifier is not linear, and the amplifier is producing a large signal at F0 out of the DUT, and a signal is applied from the output to the port 2 of the DUT at frequency F0+dF, , then there will be a reflected signal at F0+dF and this is essentially the Xs*a2 (a2 is the applied signal at port 2, essentially from some reflective load) term, and another signal that is the cross-modulation of the main signal and the reflected signal at F0-dF. The size of this signal is the Xt.a2* term. The total voltage coming out is the main output B2+Xs.a2+Xt.a2*; there will be 3 signals coming out. Now if you take the limit as dF goes to zero you have the case of all the signals at the same frequency, with phase of Xs portion changing with a2, and the phase of Xt portion changing in the opposite direction. Page 410 of my book has an illustration.
(1)If there are signal interacts with , what signals are interacting with ?
(2)If the understanding of X is not correct, how to understand?
The terms your refer to are B2,2 which is the second harmonic of the signal coming out of port 2 B2 is signal at port 2, second ,2 is at the second harmonic. X2,2,2,2 is the reflected signal at port 2, caused by an applied signal at port 2, where the applied signal is at the second harmonic frequency, and the measured reflected signal is at the second harmonic frequency. This means it tells you how much signal you will get out of the DUT caused by a load reflection at the second harmonic of the measurement frequency.
all your mixer questions such as:
（2）How to understand the effcet of
on ? are answered the same way. Each small signal can mix and create more signals at any frequency combination. Each term represents the mixing product efficiency for the signal applied, XSabcd means apply a signal at port c at frequcny index d, measure the signal at port a at frequency index b, that tells you how much signal is created in the X term; same is true for the T term except with the phase reversal issue.
But, this is a difficult forum to discuss some complicated issues. Did you get a copy of David Root's book?
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