What is the difference between coherent and non-coherent integration in radar signal processing?
Radar Integration
The non-coherent integration gain depends on the pre-integration SNR: for high SNR samples, non-coherent integration approaches coherent (gain ≈ N). For low SNR samples (near detection threshold): the gain is closer to √N due to the noise-on-noise bias from magnitude detection. Albersheim's equation provides an empirical formula for the required single-pulse SNR given the number of integrated pulses and desired P_d and P_fa, accounting for the non-coherent integration loss.
| Parameter | Pulsed | CW/FMCW | Phased Array |
|---|---|---|---|
| Range Resolution | c/(2B) | c/(2B) | c/(2B) |
| Velocity Resolution | PRF dependent | Direct from Doppler | Coherent processing |
| Peak Power | High (kW-MW) | Low (mW-W) | Moderate per element |
| Complexity | Moderate | Low | High |
| Typical Application | Surveillance, weather | Altimeter, automotive | Tracking, multifunction |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
When can I use coherent integration?
When: the radar is phase-coherent (stable transmitter and LO), the target's Doppler is known or can be estimated (allows phase correction before integration), and the target remains in the same resolution cell during the integration time. For a 10 GHz radar: the coherent processing interval is limited by target acceleration (1 m/s² acceleration: coherent time < 75 ms before phase smearing).
Can I combine both?
Yes, this is common. Coherently integrate over the maximum coherent processing interval (CPI), then non-coherently combine multiple CPIs. This captures the full coherent gain within each CPI and additional non-coherent gain across CPIs.