Two-Port (.s2p) Convention
Standard: Port 1 = Input, Port 2 = Output Data row: freq S11 S21 S12 S22 S11 = input reflection (port 1 looking in) S21 = forward transmission (port 1 → port 2) S12 = reverse transmission (port 2 → port 1) S22 = output reflection (port 2 looking in)
Three-Port (.s3p) Conventions
| Device | Port 1 | Port 2 | Port 3 |
|---|---|---|---|
| Wilkinson divider | Input | Output 1 | Output 2 |
| 3-port duplexer | TX Input | Antenna | RX Output |
| Circulator | Port A | Port B | Port C (clockwise) |
| Directional coupler | Main In | Main Out | Coupled |
Four-Port (.s4p) Data Layout
Touchstone 1.0: data written in 4 rows per frequency point Row 1: freq S11 S21 S31 S41 (first column of S-matrix) Row 2: S12 S22 S32 S42 Row 3: S13 S23 S33 S43 Row 4: S14 S24 S34 S44 Note: Column-major order (Sᵢⱼ: i = row, j = column) i.e., Row k contains S₁ₖ, S₂ₖ, S₃ₖ, S₄ₖ
Duplexer Port Assignment
| Convention | Port 1 | Port 2 | Port 3 | Port 4 |
|---|---|---|---|---|
| 3GPP standard | TX | Antenna | RX | — |
| Some vendors | Antenna | TX | RX | — |
| 4-port (with GND) | TX | Antenna | RX | GND/Shield |
Always verify port assignment from the vendor's datasheet before analysis. Incorrect port assignment shows reversed S11/S22 and wrong isolation path.
Fixing Port Order with RF View
Use RF View's SNP Converter → Port Change to remap ports: define the new port-to-port mapping and RF View rewrites the S-matrix with permuted rows/columns. Batch apply to multiple files.
RF View Port Change: Visually remap port numbering for S2P, S3P, and S4P files. Preview the change before applying. Batch process entire folders. Free on Android.