How to Remap S-Parameter Ports in Touchstone Files

When Port Remapping Is Needed

VNA port numbers (Port 1 = cable A, Port 2 = cable B) are physical cable positions. The component under test may label its ports differently from the datasheet convention. Without remapping, analysis shows reversed S11/S22, swapped S21/S12, and incorrect Smith chart orientation.

Two-Port Port Swap (.s2p)

  Problem: VNA Port 1 was connected to DUT output, Port 2 to input
  Measured: S11 = DUT output match, S21 = reverse path
  Need:     S11 = DUT input match,  S21 = forward path

  Swap operation (permute S-matrix rows and columns 1↔2):
  New S11 = old S22    (output reflection → input reflection)
  New S22 = old S11    (input reflection → output reflection)
  New S21 = old S12    (reverse path → forward path)
  New S12 = old S21    (forward path → reverse path)

  Update options line: no change needed (impedance stays 50 Ω)

Four-Port Remapping (.s4p Duplexer)

  VNA measured: P1=ANT, P2=TX, P3=RX, P4=GND
  Datasheet convention: P1=TX, P2=ANT, P3=RX, P4=GND
  Need to swap P1↔P2 in the 4×4 S-matrix:

  This involves permuting both rows and columns of [S]:
  New S_ij → Old S_f(i)f(j)  where f maps new port → old port
  f(1)=2, f(2)=1, f(3)=3, f(4)=4  (swap ports 1 and 2)

  In RF View: Port Change → set mapping P1→P2, P2→P1

Step-by-Step in RF View

1. Open RF View → SNP Converter → Port Change tab
2. Load .s2p or .s4p source file
3. For each output port, select which input port it maps from: Output P1 ← from Input P2 (swap), Output P2 ← from Input P1
4. Preview: RF View shows new S-parameter labels before applying
5. Tap "Apply" → saves new file with remapped ports
6. Verify: load both files, compare S11 (should now be input match)

Batch Port Remapping

If you have many files from the same VNA setup that all need the same port swap:

1. Select all files in the batch
2. Apply same port mapping to all files in one operation
3. RF View processes all files with identical port transformation

Related Topics

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