What Limits RF Circuit Simulation Accuracy
Linear circuit simulation (using ABCD cascade) is exact for the assumed component models. Discrepancies between simulation and measurement arise from model inaccuracies, layout parasitics not included in the model, and interconnect effects at higher frequencies.
Simulation Accuracy vs Frequency
| Frequency | Simulation Accuracy | Dominant Error Source |
|---|---|---|
| DC to 500 MHz | ±0.1 dB typical | Component value tolerance |
| 500 MHz to 3 GHz | ±0.3–0.5 dB | PCB trace inductance, pad capacitance |
| 3 GHz to 10 GHz | ±0.5–2 dB | Via inductance, substrate mode coupling |
| Above 10 GHz | >±1 dB typical | EM coupling, radiation, non-TEM modes |
Ideal vs Real Component Models
Ideal inductor: L = const, no parasitics
Real SMD inductor (Murata LQP15 10nH):
Q = 50 at 900 MHz (ESR ≈ 1.1 Ω)
Self-resonant frequency SRF ≈ 5 GHz
Package capacitance Cp ≈ 0.08 pF
Using ideal model at 900 MHz: IL error ≈ 0.3 dB
Using ideal model at 2.4 GHz: IL error ≈ 1.0+ dB
Using ideal model at 5 GHz: completely wrong (at SRF!)
When VNA Measurement Is Essential
- Above 5 GHz: Layout parasitics become comparable to lumped element values
- After first PCB build: Always measure to catch unexpected resonances from ground plane geometry
- Component qualification: Manufacturer S2P models may not include process variation or temperature drift
- Yield prediction: Monte Carlo simulation still needs verified nominal model before statistical runs are meaningful
RF View Simulation: What It Does Well
RF View's circuit simulator uses the same ABCD cascade mathematics as commercial EDA tools for the linear frequency-domain behavior. The accuracy of results depends entirely on the component models used:
- S2P DUT blocks: exact (uses measured VNA data) — excellent accuracy
- Ideal R/L/C elements: exact for the stated values — accuracy depends on how well ideal matches real
- Real Match (Murata data): uses manufacturer-measured S2P — high accuracy up to SRF
RF View Simulation Workflow: Use ideal elements for initial design exploration, switch to Real Match for pre-assembly accuracy, then compare with VNA measurement after assembly. Free on Android.