Touchstone File Overview
The Touchstone file format (.snp, where n = port count) is the de facto standard for exchanging S-parameter data between RF instruments, EDA tools, and analysis software. It stores S-parameter magnitude and phase data vs. frequency. RF View reads all standard Touchstone files: .s1p, .s2p, .s3p, .s4p, and beyond.
Version 1 File Structure
# [freq_unit] S [data_format] R [reference_impedance] ! Comment lines start with ! ! Option line starts with # # GHz S DB R 50 ! Freq S11_mag S11_ang S21_mag S21_ang S12_mag S12_ang S22_mag S22_ang 1.0 -15.2 -25.3 -0.5 -85.2 -30.1 -88.1 -18.3 -22.1 2.0 -18.5 -45.2 -0.6 -165.3 -32.5 -168.2 -21.5 -44.8
Options Line Parameters
| Field | Options | Default |
|---|---|---|
| Frequency unit | Hz, KHz, MHz, GHz | GHz |
| Parameter type | S, Y, Z, H, G | S |
| Data format | MA (Mag-Angle), DB (dB-Angle), RI (Real-Imag) | MA |
| Reference impedance | R [value] | R 50 |
Data Format Comparison
| Format | Column 1 | Column 2 | Best For |
|---|---|---|---|
| MA (Magnitude-Angle) | Linear magnitude (0–1) | Phase (degrees) | General use |
| DB (dB-Angle) | Magnitude in dB | Phase (degrees) | Human-readable, plot-friendly |
| RI (Real-Imaginary) | Real part | Imaginary part | Computation, numerical precision |
N-Port Data Ordering
For a 2-port file, parameter order on each line is: S11, S21, S12, S22 (column pairs in MA/DB/RI format). For a 4-port file (.s4p), each frequency requires multiple data lines:
! 4-port: 16 S-parameters, 2 values each = 32 values ! Touchstone v1 wraps at 4 pairs per line: ! Line 1: S11 S21 S31 S41 ! Line 2: S12 S22 S32 S42 ! Line 3: S13 S23 S33 S43 ! Line 4: S14 S24 S34 S44
Touchstone Version 2 Enhancements
Version 2 (.ts extension or [Version] 2.0 keyword) adds:
- Explicit port definitions with impedances per-port
- Mixed-mode S-parameters (differential/common mode)
- Noise parameters embedded in the file
- Better support for n-port files with unambiguous data ordering
- Comment blocks and data integrity checksums
RF View Compatibility
RF View reads Touchstone version 1 files in all three data formats (MA, DB, RI) and all standard frequency units. The app automatically detects the format from the options line and correctly parses data for 1 to 4+ port files. If a file fails to load, check for:
- Missing or malformed options line (must start with #)
- Inconsistent number of data columns
- Non-standard line endings (Windows/Unix mixing)
- Frequency points not in ascending order