Bandwidth Metrics for a Matching Network
S11 −10 dB bandwidth: range where S11 < −10 dB (VSWR < 1.92) This is the most common specification for matching network BW. Relation to Q: BW₋₁₀dB ≈ f₀ / Q_matching L-network: Q fixed = √(Z_high/Z_low − 1) Pi/T-network: Q chosen by designer (lower Q = wider BW)
Step 1: Load Simulated/Measured S11 File
- After designing and simulating your matching network in RF View:
- Send Sim_Result to S-Parameter Plot → select S11 display
- Or load measured .s1p from VNA after PCB assembly
- Verify S11 dips below −10 dB at design frequency
Step 2: Read −10 dB Bandwidth
Method A (BW Marker): set threshold to −10 dB in BW Marker settings
→ RF View automatically finds BW where S11 < −10 dB
Method B (manual):
Find f_low = first crossing of −10 dB line (left of dip)
Find f_high = last crossing of −10 dB line (right of dip)
BW = f_high − f_low
Example: matching for 900 MHz device
S11 < −10 dB from 860 to 940 MHz → BW = 80 MHz (8.9%)
Q = 900/80 = 11.25 (moderately narrow-band)
Step 3: Check If Bandwidth Meets System Requirement
| Standard / System | Required BW | Matching BW Needed |
|---|---|---|
| LTE Band 8 (single band) | 35 MHz | >35 MHz at −10 dB |
| WiFi 2.4 GHz (11b/g/n) | 100 MHz | >100 MHz |
| 5G NR n78 (sub-6 GHz) | 500 MHz | >500 MHz → wideband design needed |
| UWB (3.1–10.6 GHz) | 7500 MHz | Very wideband (usually antenna-integrated) |
Step 4: Widen Bandwidth if Needed
- Switch L-network → Pi/T network with lower Q to widen BW
- Multi-section matching (e.g., two L-networks in series) for 2–3× BW extension
- Chebyshev matching transformer for prescribed passband ripple + maximum BW
- Remember: Bode-Fano limit sets maximum achievable BW for given impedance ratio
RF View: Use BW Marker on simulated S11 to read matching bandwidth. Redesign in the Circuit Simulator and iterate quickly. Monte Carlo shows bandwidth variation under ±5% component tolerance. Free on Android.