What is the role of de-embedding in electromagnetic simulation of RF structures?
Simulation De-Embedding Techniques
De-embedding is a critical step in extracting meaningful S-parameters from EM simulation. Incorrect de-embedding is one of the most common sources of simulation-measurement discrepancy, especially for structures where the connecting lines are not simple uniform transmission lines.
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
Frequently Asked Questions
What happens if I forget to de-embed?
If no de-embedding is applied: S21 phase includes the electrical length of the connecting lines (the DUT appears electrically longer than it actually is). S21 magnitude includes the loss of the connecting lines (the DUT appears lossier). S11 includes the round-trip phase through the connecting lines (the return loss ripples with frequency as the phase rotates). For short connecting lines (
Can I de-embed a connector launch pad?
Yes, but it requires more than simple distance de-embedding because the connector-to-PCB transition is not a uniform transmission line. Best approaches: (1) Model the entire connector (include the full 3D connector geometry in the simulation) and place the wave port at the coax reference plane. No de-embedding needed because the simulation already includes the transition. (2) TRL de-embedding: simulate a thru-line, reflect, and line standard that include the connector launch pad at each end. De-embed to extract the DUT without the connector transition. (3) Manufacturer S-parameter files: some connector manufacturers (Rosenberger, Samtec) provide full-wave EM models or S-parameter files for their connectors. Import these into the circuit simulator and cascade with the DUT simulation results.
How does de-embedding affect noise figure simulation?
Noise figure simulation is not directly affected by distance-based de-embedding because de-embedding removes only the phase and loss of passive connecting lines, which contribute thermal noise at the physical temperature of the line. If the connecting line is at the same temperature as the simulation reference: de-embedding correctly removes both the signal loss and the noise contribution of the line. However, if the line temperature differs from the noise reference temperature (e.g., a cryogenic line at 4K connected to a room-temperature port): the de-embedding must account for the different noise temperature. In practice: for standard room-temperature simulations, de-embedding of passive lines has minimal impact on noise figure results (<0.05 dB for low-loss lines).