What is required for coherent integration to be effective?

• A. Phase alignment across pulses.
• B. No phase information is needed.
• C. Only amplitude alignment is required.
• D. Random phase across pulses.

Answer: (A)

Coherent integration relies on preserving and using a fixed phase relationship across successive pulses so the signal components add up in phase. When phases are aligned, each pulse’s signal contribution stacks constructively, making the combined signal stronger while the random noise tends to cancel out. This constructive summation provides a significant SNR improvement because the signal adds linearly with the number of pulses, while noise grows more slowly (noise adds in a way that averages out). If phase information isn’t available or the phase drifts randomly, the pulses cannot be aligned coherently, so the sum does not benefit from constructive addition and the expected SNR gain is lost. Amplitude alignment alone won’t achieve the same result, because without matching the phase, the peaks and troughs won’t line up, and the signals can negate each other.