Calibrated with "0 length through", test jig connected to port2 directly:
X:
[image: image.png]
R:
[image: image.png]
Z:
[image: image.png]
On Tue, 16 Feb 2021 at 01:38, Roger Need via groups.io <sailtamarack=
[email protected]> wrote:
On Sun, Feb 14, 2021 at 12:55 PM, Dragan Milivojevic wrote:
It has been stated, by multiple members of this group, that due to
hardware
deficiencies (port 2 is not a perfect 50¦¸) and lack of 12 term error
correction,
the "S21 method" can't be used to measure high impedance reliably.
Yes this is true. The "S21 series method" is a way of calculating the
complex impedance (R+jX) of a device under test (DUT). Unfortunately it
does not work on a NanoVNA-H or -H4 which are 2 port uni-directional
analyzers for the reasons you outlined in your post.
If you try it you will find that you can calculate the magnitude of a high
impedance |Z| DUT fairly well but the phase angle is not correct except at
very low frequencies. You need the correct phase angle in order to convert
from polar (Z&angle) to polar (R+jX) format.
Users interested in trying this should use a SMD resistor as the DUT which
should have a S21 phase angle very close to zero. You will only get this
at very low frequencies. A small capacitor as the DUT should have a phase
angle near 90 degrees but this will be incorrect as you increase frequency.
I have seen this on several test jigs that I have built.
If users want to try these measurements be very careful with parasitic
capacitance on the test fixture. The capacitance across the terminals
where you connect the DUT has to be well under a pF or the S21 loss in dB
will be incorrect.
Roger
