What Makes BAW/FBAR Different
BAW (Bulk Acoustic Wave) and FBAR (Film Bulk Acoustic Resonator) filters use piezoelectric resonators in a vertical stack structure. Compared to SAW filters, BAW/FBAR offers: lower insertion loss, higher frequency operation (1.5–6 GHz), much smaller group delay (<10 ns vs 100–500 ns for SAW), and better temperature stability.
BAW vs SAW vs LC Filter Comparison
| Property | BAW/FBAR | SAW | LC discrete |
|---|---|---|---|
| Insertion Loss | 0.8–2.0 dB | 1.5–3.0 dB | 1.5–4.0 dB |
| Group delay (typ) | 1–10 ns | 100–500 ns | 5–100 ns |
| Shape factor | 1.1–1.4 | 1.3–1.8 | 1.5–3.0 |
| Frequency range | 1.5–6 GHz | 50 MHz–3 GHz | 10 MHz–3 GHz |
| Temp coefficient | <±10 ppm/°C | −35 to +35 ppm/°C | ±50–200 ppm/°C |
| Package size | Very small (WLCSP) | Small (CSP) | Medium (SMD array) |
Key BAW/FBAR S-Parameter Characteristics
S21 passband: flat insertion loss region, typically 2× narrower than SAW
Rejection: very steep transition band — BAW 5G n78 filter:
3460–3800 MHz passband IL < 1.5 dB
3000 MHz stopband: S21 < −50 dB (only 460 MHz below passband edge!)
Group delay: small but with characteristic "ripple" signature
Near resonance: group delay spikes are much smaller than SAW
Typical ripple: 1–5 ns peak-to-peak in passband
Temperature Stability Analysis
BAW filters are designed for temperature-stable operation. To verify:
- Load S2P files measured at −40°C, +25°C, and +85°C
- Overlay all three in RF View
- Use Table Marker at center frequency to compare S21 and S11 at each temperature
- Check center frequency shift: should be <±100 kHz for well-designed BAW filter
Analysis in RF View
- Load BAW filter .s2p → S21 view → BW Marker for passband width
- Place marker at transition band edge → characterize sharp rolloff
- Switch to Group Delay → verify <5 ns ripple (much flatter than SAW)
- Compare with SAW .s2p on same chart: see why BAW is superior for LTE 64-QAM
RF View BAW Analysis: Load BAW .s2p files and compare with SAW files simultaneously. Group delay view clearly shows BAW's lower delay advantage. Multi-file overlay handles temperature variant comparison. Free on Android.