2.4 GHz Matching Challenges
- SMD inductor SRF: 0402 10 nH SRF ≈ 5 GHz → safe at 2.4 GHz; 0201 2.7 nH SRF ≈ 8 GHz → even safer
- PCB trace inductance: at 2.4 GHz, 1mm trace ≈ 1 nH → noticeable (keep layout compact)
- Via inductance: at 2.4 GHz, 1mm via ≈ 1 nH → use multiple vias for shunt elements
- Component Q at 2.4 GHz: inductor Q drops to ~35–50 (0402 10 nH); capacitor C0G Q still >500
Example: 2.4 GHz WiFi LNA Input Match
LNA (e.g., Qorvo QPL9065A) input impedance at 2.4 GHz:
z_in = 0.45 − j0.32 → Z_in = 22.5 − j16 Ω
Design on FR4 (H=1mm, W=1.84mm for 50Ω):
Step 1: Cancel −j16 Ω: series L = 16/(2π×2.4GHz) = 1.06 nH → pick 1.0 nH
Step 2: Match 22.5Ω → 50Ω:
Q = √(50/22.5 − 1) = 1.11
X_shunt = 50/Q = 45 Ω → C = 1/(2π×2.4GHz×45) = 1.47 pF → pick 1.5 pF C0G
X_series = Q × 22.5 = 25 Ω → additional series L = 1.66 nH → pick 1.5 nH
Total series L = 1.0 + 1.5 = 2.5 nH (combine into one 2.7 nH inductor)
Component choice: Murata LQP15MN2N7 (2.7 nH, Q=42 at 2.4GHz)
Murata GRM0335 (1.5pF, C0G)
Estimated matching network IL ≈ 4.34×1.11/42 + 4.34×1.11/1000 ≈ 0.11 + 0.005 ≈ 0.12 dB
PCB Layout Tips for 2.4 GHz
- Total trace length between components: <2 mm (1 mm = 1 nH at 2.4 GHz → significant)
- Ground via directly under shunt capacitor: <0.5 mm via length
- Solid ground plane: no slots or cuts under the 50Ω trace
- Substrate: FR4 acceptable for short matching network traces (<5mm total)
RF View 2.4 GHz Matching: Load WiFi LNA .s2p, Auto Match at 2.4 GHz, Real Match with Murata LQP15 + GRM C0G components, Monte Carlo for yield under ±5% tolerance. Free on Android.