Calculate S-Parameters in the Time Domain

In this tutorial, we'll calculate S-parameters in the time domain for a matched stripline transmission line. This line is located on the third layer of a sample 6-layer PCB stackup shown below. The board thickness is 1.5 mm.

Using time-domain analysis, you can reconstruct the signal waveform using the convolution mathematical function. For transmission lines, the S11 and S21 coefficients are typically most important.

1. First, determine the trace width required to achieve a characteristic impedance of 50 Ohm for an Offset stripline (OS-1B1A) structure, as demonstrated in the Calculate Trace Width tutorial.

   

   The calculated trace width is 0.1539 mm.

2. In the Calculation settings panel, switch calculation mode to Time domain and set the Parameters option to S-parameters. The previously entered transmission line parameters will retain their values.

   

3. Set the following calculation parameters:

   • Set LTL, Length of line to 100 mm
   • Set ZS, Source impedance to 50 Ohm
   • Set ZL, Load impedance to 50 Ohm
   • Set FREQ, Frequency to a range from 100 MHz to 2 GHz with a step of 50 MHz

   

4. Run the calculation.

5. In the Calculation results panel, select the S-parameters graph. Then set the View → S-parameter option to S11.

   

   The graph at the bottom will display the S11 parameter (the reflected signal) as a function of time.

   

Calculations for differential transmission lines can be performed in the same way.