A S-parameter data viewer with tools to RF circuit design. This tool is part of the Qucs-S project.

Online documentation https://andresmmera.github.io/qucs-s-spar-viewer/

Release page https://github.com/andresmmera/qucs-s-spar-viewer/releases/

Qucs-S Project https://github.com/ra3xdh/qucs_s

Features

Data Import

Touchstone File Support: Read standard .snp files (S1P, S2P, S3P, etc.)
Qucs Dataset Support: Import data from both Qucsator and NGspice formats

Visualization

Multiple Plot Types:
- Rectangular plots (Magnitude/Phase, Impedance, Stability, VSWR, Group Delay)
- Smith Chart (Z and Y chart options)
- Polar plots
Trace Management: Add, remove, and customize traces with color, width, and line style
Markers: Place frequency markers with automatic value readout
Limit Lines: Define pass/fail criteria with frequency-dependent limits

Session Management

Save/Load Sessions: Preserve complete workspace including:
- All loaded datasets
- Plot configurations
- Trace properties
- Markers and limits
- Notes

Synthesis Tools

Filter Design: Canonical and Direct-Coupled LC filters. Transmission line filters
Matching Newtwork Design: L-section, Stub-matching, impedance transformers
Power Combining Design: Various power combiner and coupler topologies including Wilkinson, Bagley, Gysel, Lim-Eom, etc.
Attenuator Design: Pi, Tee, Bridged-Tee and tuned attenuators, including power dissipation calculations.
Netlist Scratchpad: Text-based tool to simulate the S-parameters of a netlist as you type
All the tools can export the synthesized circuits to Qucs-S via clipboard.

Building

Requirements

Qt 6.x
C++11 or later compiler
CMake

Dependencies

Qt Widgets
Qt XML

Compilation

mkdir build && cd build
cmake ..
make
sudo make install

Usage

Loading Data

File → Open to load Touchstone or Qucs dataset files
Select parameters from the matrix-style parameter selector
Choose display mode (Magnitude/Phase, Smith, Polar, etc.)
Click Add Trace to visualize

Adding Markers

Navigate to the Markers tab
Enter frequency and scale
Click Add Marker
View values in the marker table

Setting Limits

Go to Limits tab
Define frequency range and value thresholds
Limits appear as shaded regions on plots

Saving Work

File → Save Session to preserve entire workspace
Session files (.spar) store all data and settings
File → Recent Files for quick access

File Formats

Touchstone (.snp)

Standard format for N-port S-parameter data. Supports:

Frequency sweeps
MA (Magnitude-Angle), RI (Real-Imaginary), DB (dB-Angle) formats
Reference impedance specification

Qucs-S Dataset

Qucs-S format supporting:

Qucsator format: S[i,j] matrix notation
NGspice format: ac.v(s_j_i) voltage source notation
Multiple parameter types (S, Y, Z)

Session Files (.spar)

XML-based format storing complete application state.

License

GNU General Public License v3.0 or later

Author

Andrés Martínez Mera - andre.nosp@m.smme.nosp@m.ra@pr.nosp@m.oton.nosp@m.mail..nosp@m.com