Touchstone

Reference: Touchstone, TouchstoneParseOptions, TouchstoneWriteOptions.

Touchstone import and export

Touchstone.parse(text, options?) returns { samples, referenceImpedanceOhms }. It reads Touchstone 1.x S-parameters, converts RI/MA/DB into Cartesian Γ and frequencies into Hz, and throws an Error with a line number for invalid content. Invalid parser options throw TypeError.

import { Smith, Touchstone } from 'smithkit';

async function showMeasurement(file: File): Promise<Smith> {
  const ports = /\.s2p$/i.test(file.name) ? 2 : 1;
  const { samples, referenceImpedanceOhms } = Touchstone.parse(await file.text(), {
    ports,
    parameter: ports === 2 ? 'S22' : 'S11',
    output: 'packed',
  });
  const chart = new Smith({ referenceImpedanceOhms });
  chart.draw('#smith');
  chart.addTrace(samples, { name: file.name });
  return chart;
}
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Packed parsing writes directly into growing typed storage, without creating an object or coordinate array per sample. It scans lines incrementally within the supplied string; this is not a streaming file API. The returned buffer has exact length and is caller-owned. The default object result remains unchanged.

Omitted header options use GHz, S, MA, 50 Ω. The parser accepts comments, BOM, LF/CRLF/CR line endings, decimal scientific notation, and continued records. Each frequency record starts on a new line. Two-port records use S11, S21, S12, S22 order; all four parameters are validated even though only one reflection trace is returned. Two-port frequencies must increase strictly. Three or more ports, per-port/complex reference impedances, noise blocks and Touchstone 2.x keywords are rejected. See the IBIS Touchstone specification for the legacy 1.x data layout.

Touchstone.stringify(samples, { referenceImpedanceOhms }) returns .s1p text with a # Hz S RI R … header and a final newline. It accepts object samples, tuples, or packed triples, writes numeric values without a precision limit, and does not modify or renormalize the input. The reference defaults to 50 Ω; supply the actual reference of your data. Empty/invalid samples, nonpositive/nonfinite reference impedance, and duplicate or descending frequencies throw RangeError. Samples are never silently sorted or discarded.

import { RfCalculations, Touchstone } from 'smithkit';

const sourceText = '# GHz S RI R 50\n1 0 0\n2 0.5 0';
const parsed = Touchstone.parse(sourceText, { output: 'packed' });
const samples = RfCalculations.renormalizeSamples(
  parsed.samples,
  parsed.referenceImpedanceOhms,
  75,
);
const text = Touchstone.stringify(samples, { referenceImpedanceOhms: 75 });
// Save text as measurement.s1p in your application.
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For an extracted S11/S22 trace, this is one-port renormalization: the other port remains terminated in the original file reference. It is not renormalization of the complete two-port network. Exporting S22 to .s1p represents that selected port as the single port of the new file; transmission data is not exported.

The Touchstone example shows parameter selection, packed import, renormalization and download. In the demo, choose Two-port reflection before importing .s2p; the trace name includes the selected parameter. Both .s1p and .s2p use packed import.