S-Parameters

S-parameters calculations allow you to evaluate the power efficiency of transmission lines and determine the level of reflected waves.

Example

• Calculate S-Parameters in the Frequency Domain

S-parameters Calculation Walkthrough

To calculate S-parameters, follow these steps:

1. Set the initial calculation settings:

   • Set Target to Transmission line
   • Set Target type to Single-ended, Diff pair, Coplanar single-ended, or Coplanar diff pair
   • Set Mode to Frequency domain
   • Set Parameters to S-parameters

   

2. Select the required transmission line model and review it in the preview area.

   

3. Define the input parameters for the transmission line.

   

   Available parameters are listed below. Some of them may not be available for certain transmission line types.

   • H – Dielectric thickness (mm). For each dielectric layer, you can specify its own thickness using the H1..H4 parameters (the number of H(n) parameters is determined by the number of dielectric layers).
   • Er – Dielectric constant. For each dielectric layer, you can specify its own dielectric constant using the Er1..Er4 parameters (the number of Er(n) parameters is determined by the number of dielectric layers).
   • W1 – Trace width (mm).
   • W2 – Trace width after undercut (mm).
   • T1 – Trace thickness (mm).
   • C1 – Coating thickness (mm).
   • CEr – Coating dielectric constant.
   • D1 – Distance from the trace to the reference plane (mm).
   • S1 – Diff-pair trace spacing (mm).
   • TC – Conductor conductivity (S/m).
   • tgδ – Loss tangent.
   • LTL – Line length (mm).
   • TR – Rise time (ps).
   • FREQ – Frequency (MHz).

   Parameters specific to S-parameters calculations:

   • ZS – Source impedance (Ohm).
   • ZL – Load impedance (Ohm).

   Surface roughness parameters:

   • a – Nodule radius (µm).
   • N – Number of nodules in a unit area.
   • Af – Unit area (mm²).

4. Click Calculate in the lower-right corner of the calculation tab to run the calculation.

   

   Before running the calculation, you can click the dropdown arrow next to the Calculate button to choose between two calculation saving options:

   

   • Overwrite calculation – Saves the modified input parameters to the current calculation, overwriting previous data.
   • Save as new calculation – Saves the modified input parameters to a new calculation. This calculation will appear in the Projects panel.

Calculation Results for Single-Ended and Coplanar Single-Ended Lines

For single-ended and coplanar single-ended transmission lines, the following parameters are calculated:

• S11 – Input reflection coefficient.
• S21 – Forward transmission coefficient.
• S12 – Reverse transmission coefficient.
• S22 – Output reflection coefficient.

Calculation Results for Differential and Coplanar Differential Lines

For differential and coplanar differential transmission lines, S-parameters are calculated in single-ended and mixed mode. You can view these parameters in separate tables.

• Single-ended mode

  

• Mixed mode

  

The calculation results shown in the tables can be displayed in one of three presentation modes:

• Magnitude/Phase
• Magnitude (dB)/Phase
• Real/Imaginary

Use the View settings → Mode drop-down in the Calculation results panel to select the required presentation mode:

Parametric Sweep

Parametric sweeps for S-parameters calculations are performed similarly to other sweeps in SimPCB Lite: you need to specify a range of values and a step for one of the input parameters.

Calculation Results

Multiple calculated S-parameters can be displayed simultaneously in the graphs. Use the View settings → S-parameter setting in the Calculation results panel to select the S-parameters to display.

See Also

• Example - Calculate S-Parameters in the Frequency Domain