openSNPKit370: Virtual IEEE P370 De-embedding Kit

A free, open-source training kit for learning fixture de-embedding.

This library provides synthesized S-parameter files demonstrating de-embedding concepts, pitfalls, and best practices..

Part of the OpenSNPTools ecosystem.

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🎯 Who Is This For?

• Signal integrity engineers learning de-embedding for the first time
• Students in RF/microwave or high-speed digital courses
• Practitioners who want hands-on examples without buying expensive test fixtures

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📦 What's Included

Virtual P370 Kit (kit/)

File	Description	Equivalent P370 Board
dut_microstrip_6cm.s2p	6cm bare microstrip (ground truth)	Board #1
dut_microstrip_3cm.s2p	3cm bare microstrip	Board #1a
2xthru_50ohm_6cm.s2p	6cm 2x-THRU, 50Ω nominal	Board #2
2xthru_52ohm_6cm.s2p	6cm 2x-THRU, 52.5Ω (105% Z₀)	Board #3
fixture_with_vias.s2p	Fixture with via transitions	Board #4
beatty_50_25_50.s2p	Beatty impedance standard	Board #5

Pitfall Examples (examples/)

#	Pitfall	What Goes Wrong
01	Good Reference	Baseline: what "correct" looks like
02	Impedance Mismatch	±5% Z₀ causes 1-2 dB ripple
03	Poor Return Loss	RL < IL violates 5 dB rule → noise amplification
04	Non-Causal	Phase error → "ghost limbs" in TDR
05	Mode Conversion	Differential asymmetry → Scd/Sdc artifacts
06	Port Ordering	(1,3)/(2,4) vs (1,2)/(3,4) confusion
07	Calibration Drift	Thermal drift → passivity violations
08	Bandwidth Truncation	Measuring to 28 GHz for 25 Gbps → ringing
09	Wrong Algorithm	Symmetric method on asymmetric fixture
10	Microprobing	De-embed GSG probes (alt to $15K ISS cal)
11	Measured Striplines	Real-world data for correlation. We hope to build up a dataset over time!

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🚀 Quick Start

# Clone the repo
git clone https://github.com/OpenSNPTools/openSNPKit370.git
cd openSNPKit370

# Install dependencies
pip install -r requirements.txt

# Run your first example
cd examples/01_good_reference
python example_01.py

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📁 Repository Structure

openSNPKit370/
├── README.md
├── LICENSE                      # BSD-3-Clause
├── requirements.txt
├── CHANGELOG.md
│
├── kit/                         # Virtual P370 S-parameter files
│   ├── README.md
│   ├── dut_microstrip_6cm.s2p
│   ├── dut_microstrip_3cm.s2p
│   ├── 2xthru_50ohm_6cm.s2p
│   ├── 2xthru_52ohm_6cm.s2p
│   ├── fixture_with_vias.s2p
│   └── beatty_50_25_50.s2p
│
├── examples/                    # Pitfall demonstrations
│   ├── 01_good_reference/
│   ├── 02_impedance_mismatch/
│   ├── 03_poor_return_loss/
│   ├── 04_noncausal/
│   ├── 05_mode_conversion/
│   ├── 06_port_ordering/
│   ├── 07_calibration_drift/
│   ├── 08_bandwidth_truncation/
│   ├── 09_wrong_algorithm/
│   ├── 10_microprobing/
│   └── 11_measured_striplines/
│
├── synthesis/                   # Scripts that generate the kit
│   └── generate_kit.py
│
└── docs/
    ├── pitfall_guide.md
    ├── theory_review.md
    └── figures/

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🔧 Technical Specifications

PCB Parameters (P370-equivalent)

Parameter	Value
Material	Rogers RO4350B-equivalent (Dk=3.48, Df=0.0037)
Frequency	10 MHz – 67 GHz
Trace geometry	~22 mil width on 10 mil dielectric → 50Ω
Copper	1 oz (35 µm) with surface roughness
Via model	Pi-network (L ≈ 80 pH, C ≈ 35 fF) --> TBD!!
Connector	1.85mm end-launch model

Realism Features --> ALL THIS TBD!!

• ✅ Frequency-dependent conductor loss (skin effect)
• ✅ Dielectric loss (Djordjevic-Sarkar model)
• ✅ Surface roughness (Huray model)
• ✅ Via resonances and parasitics
• ✅ Connector discontinuities
• ✅ Measurement noise floor (~-60 dB)

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📊 The 10 Pitfalls — Detailed

01. Good Reference (Baseline)

Purpose: Establish what "correct" looks like
Expected results:

• IL: -0.5 dB @ 10 GHz, -1.5 dB @ 50 GHz
• RL: < -25 dB across band
• Self-deembed residual: < 0.05 dB

02. Impedance Mismatch

Purpose: Show ripple from ±5% manufacturing tolerance
Setup: 50Ω 2x-THRU with 52.5Ω fixture
Symptom: 1-2 dB ripple, standing waves
Lesson: Match your 2x-THRU impedance to your fixture

03. Poor Return Loss

Purpose: "Cannot see through a wall" failure
Setup: Fixture with RL = -8 dB, IL = -10 dB
Symptom: Noise amplification, passivity violations
Lesson: Maintain RL - IL ≥ 5 dB headroom

04. Non-Causal

Purpose: Show "ghost limbs" from phase error
Setup: Add 15° phase error (simulates connector mismatch)
Symptom: Pre-cursor energy in TDR (t < 0)
Lesson: Verify causality before trusting magnitude

05. Mode Conversion

Purpose: Show Scd/Sdc artifacts from asymmetry
Setup: One trace 0.5mm longer in differential pair
Symptom: Scd, Sdc rise from -40 dB to -25 dB
Lesson: Balance your differential fixtures

06. Port Ordering

Purpose: Convention confusion
Setup: Same fixture, different port numbering
Symptom: Sdd21 shows zero, signal in wrong S-param
Lesson: Document and verify port conventions

07. Calibration Drift

Purpose: Show thermal degradation
Setup: T=0 (fresh cal) vs T=60 min (drifted)
Symptom: Directivity drops 50→35 dB, RL degrades
Lesson: Re-calibrate, especially for sensitive measurements

08. Bandwidth Truncation

Purpose: Show artifacts from insufficient frequency range
Setup: Measured to 28 GHz vs 40 GHz for 25 Gbps
Symptom: Time-domain ringing, causality issues
Lesson: Measure 10% beyond your target frequency

09. Wrong Algorithm

Purpose: Symmetric method on asymmetric fixture
Setup: Via fixture with different left/right lengths
Symptom: > 1 dB self-deembed residual
Lesson: Use NZC (non-zero-centered) for asymmetric fixtures

10. Microprobing

Purpose: De-embed as alternative to expensive ISS cal substrates
Setup: GSG probe-to-probe THRU + probe-DUT-probe
Result: Removes pad parasitics, reveals structure Lesson: de-embedding could be an easier path than ISS

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🔗 Related Tools

Tool	Description
openSNPQual	S-parameter quality checker (passivity, reciprocity, causality)
openSNPlot	S-parameter visualization
scikit-rf	Python RF/microwave library
IEEE 370 Reference Code	Official MATLAB implementation

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🤝 Contributing

Contributions welcome! See CONTRIBUTING.md for guidelines.

Ideas for contributions:

• Add measured S-parameters (anonymized) for comparison
• Improve synthesis models
• Add more pitfall examples
• Create interactive Jupyter notebooks
• Translate documentation

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📄 License

BSD 3-Clause License — see LICENSE.

Free to use, modify, and distribute. Attribution appreciated.

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📚 References

• IEEE 370-2020: "Electrical Characterization of Printed Circuit Board and Related Interconnects up to 50 GHz"
• IPC-2141A: "Design Guide for High-Speed Controlled Impedance Circuit Boards"
• Keysight App Note 5989-5765EN: "The ABCs of De-Embedding"
• scikit-rf documentation

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📧 Contact

Author: Giorgi Maghlakelidze
Email: giorgi.snp [at] pm.me
LinkedIn: linkedin.com/in/giorgim
Issues: GitHub Issues

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