What is the difference between coherent and non-coherent integration in radar signal processing?

• A. Coherent integration preserves phase across pulses for Doppler processing.
• B. Non-coherent sums amplitudes with phase information.
• C. Coherent integration reduces range resolution.
• D. Non-coherent processing is used for weather detection.

Answer: (A)

Preserving phase information across successive radar returns is what coherent integration is all about. Each pulse gives a complex value that has both magnitude and phase. By summing those complex values over many pulses, the target's contributions add up coherently if the phase relationship stays consistent, while random noise tends to cancel out. This not only boosts the signal-to-noise ratio more strongly, but it also keeps the phase information needed to measure Doppler shifts and estimate target velocity.

Non-coherent integration, by contrast, discards the phase. You convert each return to a magnitude or power and then add those magnitudes. Without phase, you lose Doppler information, and the SNR improvement is weaker (roughly proportional to the square root of the number of pulses) because the signals don’t add constructively with respect to phase.

So the correct statement emphasizes that coherent integration preserves phase across pulses to enable Doppler processing, whereas non-coherent processing does not. The other options describe behaviors that don’t match how coherent versus non-coherent integration actually work.