De-embedding procedure help request

[shabaz123]

De-embedding procedure help request

[keikawa]

Hi @shabaz123 ,
The code you provided looks good to me.
The OpenShort de-embedding is based on the assumption that the embedding network (here the connected cables) is shorter than the wavelength of the RF signal. Therefore, longer cables result in lower accuracy.
In this case, if the VNA has an electrical length correction function, it is recommended to use it.
Alternatively, the following methods are available for electrical length correction using scikit-rf.

import skrf as rf
import matplotlib.pyplot as plt

dut_fname = './ns-dut-148.s1p'
open_fname = './ns-open.s1p'
corrected_dut_fname = './ns-dut-corrected.s1p'

# read the two files
dut_ntwk = rf.Network(dut_fname)
open_ntwk = rf.Network(open_fname)

# Electrical length compensation
lossless_tline = rf.media.DefinedGammaZ0(frequency=dut_ntwk.frequency, z0_port=None, z0=50, Z0=None, gamma=1j)
electrical_length = open_ntwk.s_deg[:,0,0] / 2
corrected_dut_ntwk = lossless_tline.line(electrical_length, unit='deg') ** dut_ntwk

# save the corrected DUT network
corrected_dut_ntwk.write_touchstone(corrected_dut_fname)

# plot the results on a Smith chart
dut_ntwk.plot_s_smith(lw=2, label='Uncorrected')
corrected_dut_ntwk.plot_s_smith(lw=2, label='Corrected')

plt.show()

[shabaz123]

Hi @keikawa

Thank you for this! I just tried your code, and the corrected plot result is superb : )
The diagram here shows the setup I had used and the approximate lengths of cables:

Since I was only interested in 10MHz to 1GHz, I thought the lengths may have been fine. In any case, I'm very happy that the electrical length compensation method of de-embedding works, and I can run with this. My VNA is a very entry-level product, it doesn't have an automatic way of doing this.

Incidentally, to hopefully contribute back to the project a bit, I have forked scikit-rf and created a branch and hope to add code for the FPC1500 to become a supported VNA for control. I have made a start, but the command seems to be missing in the VNA user manual to retrieve vector measurements (I can retrieve scalar!), so I've raised a case with R&S, and will continue with that once they reply.

Thanks again for your help.

[shabaz123]

Closing, thank you for the help!