MEMS Filter vs SAW/BAW
| Property | MEMS Filter | BAW/FBAR | SAW |
|---|---|---|---|
| Q factor (unloaded) | 10,000–100,000 | 2,000–8,000 | 1,000–4,000 |
| Insertion loss | 0.1–1.0 dB | 0.8–2.0 dB | 1.5–3.0 dB |
| Fractional bandwidth | 0.1–2% | 2–10% | 2–8% |
| Temperature stability | Excellent (−10 to +85°C: <±2 ppm/°C) | Good | Fair |
| Frequency range | 100 MHz – 10 GHz | 1.5–6 GHz | 50 MHz–3 GHz |
| Power handling | Low (100 mW) | Moderate (1–5W) | Moderate (1–5W) |
MEMS Filter S-Parameter Characteristics
Ultra-narrow bandwidth MEMS filter example (GPS L1, 1575.42 MHz): Center frequency: 1575.42 MHz (GPS C/A code center) Passband: 1575.42 ± 1 MHz (2 MHz BW, FBW = 0.13%) Insertion Loss: <0.5 dB Q_L: f₀/BW = 1575.42/2 = 787.7 ← EXTREMELY high Q Stopband rejection at 1580 MHz (+4.6 MHz): >30 dB (Only 4.6 MHz away from passband edge!) Shape factor BW₋₃₀/BW₋₃ = ±10 MHz / ±1 MHz = 10 (sharp!)
Analysis Challenges with High-Q MEMS Filters
- BW Marker precision: need <1 MHz VNA frequency resolution to read 2 MHz bandwidth accurately
- Phase measurement: extremely steep phase change at band edges — ensure unwrapping is correct
- Group delay: very high peak delay at band center (proportional to Q)
- Temperature: measure at −40, 25, +85°C — MEMS advantage shows here
RF View MEMS Analysis: Load MEMS filter .s2p file. BW Marker finds ultra-narrow bandwidth. Set fine resolution if needed. Group delay view shows high Q signature (high, sharp peak). Free on Android.