De-embedding
Understanding De-embedding
De-embedding is essential for accurate characterization of on-board components, MMIC devices, and PCB-mounted parts where the calibration plane cannot be placed directly at the DUT terminals.
De-embedding Methods
- Port extension: Simplest. Shifts the reference plane by adding electrical length. Phase correction only; does not account for fixture loss or mismatch.
- Time-domain gating: Uses IFFT to convert to time domain, gates out fixture reflections, returns to frequency domain. Good for removing connector effects.
- 2x thru: Measures a thru structure of known fixture characteristics and mathematically removes it from the DUT measurement. Very accurate for PCB fixtures.
- Matrix de-embedding: Measures the fixture S-parameters (open, short, thru standards) and mathematically cascades the inverse matrix to remove fixture effects.
Frequently Asked Questions
What is de-embedding?
De-embedding removes test fixture, trace, and connector effects from S-parameter measurements to extract the intrinsic DUT performance. Methods: port extension (simple), time-domain gating, 2x thru, and matrix de-embedding (most accurate).
When do I need de-embedding?
Whenever the VNA calibration plane is not at the DUT terminals: PCB-mounted components, MMIC in test fixtures, connectorized DUT with SMA launches. Above 5 GHz, fixture effects become significant and de-embedding is usually necessary.
What is the 2x thru method?
The 2x thru uses a test structure that is twice the length of one connector/fixture half. By measuring this thru and mathematically splitting it, the fixture characteristics are extracted and removed from the DUT measurement. Very popular for PCB measurements.