It is easy to come to the conclusion that the S11 phase angle as seen on the nanoVNA (CH0 PHASE 90..) is the relationship in a device under test between the voltage and current in that device, and I once fell down that hole myself. Haha! After finding that the S11 phase readings on the nanoVNA didn't make sense when thought of as representing the voltage vs current relationship in the device under test I quickly knew that I must have missed something in my understanding of how the VNA works.
After doing some studying on the fundamentals of the VNA, I found that the phase angle that the nanoVNA measures and displays as ¡°CH0 PHASE 90¡± is in fact the phase angle between the incident and reflected waves being measured by the VNA at it's port.
Are they related? I once had an engineer who frequents nanoVNA forums try to emphatically tell me that there was no relationship.. and argued profusely producing charts and graphs and explaining and explaining, to no avail, how he was so certain of this. I see he has now changed his tune after having given it some time and thought, but, YES, there is a relationship.
Are they the same thing? NO.
The VNA works by producing a stimulus wave at it¡¯s port, then measures the amplitude and phase of the returning wave that bounces back off of the device under test. From this, the VNA is able to calculate all of it¡¯s (S11) information.
Think of it as a device used to poke at an unknown black box.. you can tap and shake the box and listen to the sound it makes and can make educated guesses as to what¡¯s inside.. the VNA is similar, but a bit more capable than simply tapping and listening and guessing.
The VNA looks at the amplitude and phase of the signal that comes back, in relation to the signal it has sent out. The S11 phase displayed on the nanoVNA is simply this relationship between those two things, however, this is not the same as the phase relationship between the voltage and current in the device under test.
If you wish to read a bit more on how the S11 phase (as displayed on the nanoVNA) and the current vs voltage phase in the device under test is mathematically related, a conversation took place here back in 2018 that I think explains it well.. (See reply #4)
It seems there are some who tend to want to confound and obfuscate the nanoVNA and it¡¯s function in their ¡®explanations¡¯ inundating people with graphs and math to impress you with how smart they are.. with the end result being that the person asking the question winds up more confused than when they started.
Things can be explained simply and clearly if one chooses to do so . Often times, I find it's best to only use as much complexity as is necessary to sufficiently convey one's thoughts.
Regarding how the nanoVNA works.. I explain this very simply and quickly in my video, here at 1:15
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