What to Look For in Matching Network S-Parameters
After designing a matching network (L-network, Pi, or stub), you can verify its performance by measuring the combined DUT + matching network as a 2-port network or analyzing the simulation output. Key metrics:
| S-Parameter | What It Shows | Target |
|---|---|---|
| S11 (at matched input) | Input impedance match quality | <−10 dB across target band |
| S21 (through matched network) | Signal transmission loss | Device S21 − matching IL (should be small loss) |
| S22 (at load) | Output impedance seen by load | <−10 dB |
S11 Bandwidth Comparison: Ideal vs Real Components
Load 3 files into RF View simultaneously:
1. Ideal simulation (RF View Circuit Sim → Send to Plot as Sim_Result):
S11_ideal = −25 dB at 900 MHz, −10 dB bandwidth = 250 MHz
2. Real Match simulation (Murata components):
S11_real = −18 dB at 900 MHz, −10 dB bandwidth = 220 MHz
(slightly worse due to finite component Q)
3. Measured PCB (VNA .s2p):
S11_measured = −14 dB at 900 MHz, −10 dB bandwidth = 195 MHz
(worse due to PCB trace parasitics)
Insertion Loss Budget
Ideal matching network IL: 0 dB (ideal reactive elements, no dissipation)
Real matching network IL contribution:
Inductor: ΔIL_L = 4.34 × Q_match / Q_L ≈ 0.2–0.5 dB
Capacitor: ΔIL_C ≈ 0.05–0.1 dB (C0G, high Q)
PCB trace: ΔIL_trace = loss × length ≈ 0.05–0.2 dB
Total matching network IL: 0.3–0.8 dB typical for cellular frequencies
Analysis Steps in RF View
- Load all three .s2p files (ideal sim, real sim, measured)
- S11 overlay: see degradation at each stage
- BW Marker on each: quantify bandwidth reduction from ideal to measured
- S21 overlay: see insertion loss addition from matching network (small, <0.5 dB)
RF View Matching Verification: Use Circuit Simulator to generate simulation .s2p, load alongside measured PCB .s2p, and overlay for instant comparison. Identify whether mismatch is from components or layout. Free on Android.