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Message ID: 2359     Entry time: Thu Jun 27 17:06:57 2019
Author: ScottA 
Type: DailyProgress 
Category: RFAM 
Subject: Bias Tee S Matrix 

In order to better characterize the Bias Tee, I measured the non-diagonal components of it's S matrix using the network analyzer(NA). I did not measure the reflection coefficients due to the inability of the NA to measure this without specialized components, and attempts at solving numerically were unsuccessful. Bias Tee's model number is ZFBT-4R2GW-FT (Link: https://www.minicircuits.com/WebStore/dashboard.html?model=ZFBT-4R2GW-FT%2B).

Measurement Details:

  • My first step was to solder a BNC connection onto the DC Port of the Bias Tee, and attach SMA to BNC connectors on the RF and RF+DC Ports to connect to the NA. 
  • I split the signal out of RF OUT on the NA and plugged one side into R, and the other into the port on the Bias Tee I was interested in inserting a signal into. The port I wanted to measure the signal out of was connected to A through BNC.
  • The port which was not in use was terminated with 50 ohms.
  • Utilizing WideTFMeas.py and its param and config file I acquired the data to be plotted in a jupyter notebook. 
  • I repeated this process 6 times until every port of the Bias Tee had both been injected with and received the signal from RF OUT.


  • I defined the RF port as Port 1, DC as Port 2 and RF+DC as Port 3.
  • I made 4 plots from this data, three showing the data for each port individually and one showing the transfer functions that will apply when using the bias as expected.
  • The first three plots give the signals read from the two alternate ports when the signal is injected into the port mentioned in the title.
  • The last plot shows the coupling between the RF and RF+DC ports as well as between the DC and RF+DC ports, which characterizes the transfer functions we expect to see in practice.


  • It is clear that any signal from the RF to RF+DC port will pass at high frequencies, but will be attenuated near DC.
  • Also, any signal from the DC port to RF+DC will pass at low frequencies but will be attenuated at high frequencies.
  • The DC attenuation in the RF port should be on the order of 10^(-3) at our operating RF frequency of 37 Megahertz, or around -60db.
  • The RF attenuation in the DC port should be around 10^(-2) up to 400Hz, or around -40 dB.
Attachment 1: Bias_Tee_S_Matrix_6_27_2019.pdf  155 kB  Uploaded Thu Jun 27 18:54:46 2019  | Hide | Hide all
Bias_Tee_S_Matrix_6_27_2019.pdf Bias_Tee_S_Matrix_6_27_2019.pdf Bias_Tee_S_Matrix_6_27_2019.pdf Bias_Tee_S_Matrix_6_27_2019.pdf
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Attachment 3: Bias_Tee_S-matrix_Data_6-27-2019.zip  485 kB  Uploaded Thu Jun 27 19:01:31 2019
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