RF PCB Insertion Loss Budget
| Loss Source | Magnitude | Mitigation |
|---|---|---|
| FR4 dielectric loss (2.4 GHz) | ~1.7 dB/100mm | Upgrade to Rogers RO4003C (~0.5 dB/100mm) |
| Conductor skin effect loss | ~0.3–0.5 dB/100mm | Low-roughness copper, wider traces |
| Via inductance (signal via) | ~0.1 dB per via | Minimize, add compensation pads |
| Connector (SMA to PCB) | ~0.1–0.2 dB | Use matched launch, compensate pad |
| Impedance mismatch (trace steps) | Variable | Maintain continuous 50Ω, no trace width changes |
Trace Length Minimization
Every mm saved on FR4 at 2.4 GHz = 0.017 dB saved For matching network: target <5mm total trace length Between filter and LNA: minimize — even 5mm adds 0.085 dB PCB layout: place components as close together as possible Use direct connections (0201 components have smaller pads)
Substrate Upgrade Analysis
Scenario: 30mm of RF trace at 5 GHz FR4: ~1.05 dB loss RO4003C: ~0.27 dB loss Savings: 0.78 dB System benefit: 0.78 dB less loss before LNA → 0.78 dB improvement in system NF → 0.78 dB improvement in receiver sensitivity For GPS L1 receiver: 0.78 dB better sensitivity is significant Rogers cost: $15 vs $2 PCB incremental cost → worth it for GPS
RF View: Compare measured S21 of test structures on FR4 vs Rogers to quantify actual PCB loss. Load both .s2p files in RF View to see the loss difference visually. Free on Android.