The combination of Microwave Office and Python provides a means of using time domain gating on one and two-port Touchstone formatted S-parameter files. Gating allows the removal of responses in the time domain. Upon transformation of the time domain data back to the frequency domain, unwanted contributors to the frequency response are eliminated.
A typical use case is the measurement of a device under test (DUT) mounted on a fixture such as a printed circuit board as depicted here:
A vector network analyzer measurement might have calibration planes at the connectors and the resulting scattering parameters measurement would include both connectors, the PCB traces and the DUT. Gating can remove the discontinuities associated with the connectors and PCB losses, only retaining the DUT response in the S-parameter data.
When the frequency domain s11 response is transformed to the time domain using a low-pass step as a stimulus, the connector responses and the DUT response can be separately identified as shown here:
To apply gating, adjust start and stop gating flags in the time domain. If the time domain filter type is bandpass, then only the response between the two flags will be retained. For band stop filter type, then the response between the two gating flags will be removed, retaining the responses outside of the gating flags range.
Even though gating flags are set in the transformed s11 data, the routine used in this solution performs gating on all the port parameters.
Performing the TDR Gating Operation
Download and unzip the TDR_Gating.zip file:
The AWRDE project can be of the user’s choosing, however TDR_Gating_Template.emp has been provided with some sample data files. Python file TDR_Gating.py has been provided. AWRDE is controlled by Python and so the measurement is initiated by running the Python script. TDR gating is limited to either one or two-port S-parameter data files in Touchstone format.
Step-by-step procedure for performing the TDR gating:
- In AWRDE, import the .s1p or .s2p S-parameter file. In the Project pane > Data Files > right mouse button > Import Data File …
- Run the TDR_Gating.py Python script
A Python dialog box will allow the user to choose which valid Data File available in AWRDE to perform the TDR gating operation:
- Select the file and click OK
In the next Python dialog box:
Use the two markers in the TDR Lowpass Step graph within AWRDE to act as the gating flags. Adjust the x-axis (time) position of the two markers.
In the dialog box choose whether the gating in the time domain should perform and bandpass or band stop operation.
- Set the markers and click OK
The gated S-parameter file will be generated and imported in the Data Files section within AWRDE. The suffix _gated will be appended to the gated file
Shown are s21 and s11 plots with gated and ungated data