Compare coherent vs non-coherent integration for radar detection.

• A. Coherent integration uses only power summation; non-coherent preserves phase information.
• B. Coherent integration preserves phase across pulses for higher sensitivity; non-coherent relies on power summation without phase information.
• C. Both methods yield identical results; integration time is the only difference.
• D. Non-coherent integration uses phase alignment to maximize SNR.

Answer: (B)

The key idea is how phase information across multiple radar looks is used. In coherent integration, the phase of the signal is preserved and aligned across pulses, so when you sum the complex-valued returns, the signal components add constructively while the noise, which is random in phase, tends to cancel out. This makes the detected signal grow proportionally with the number of looks, giving a strong SNR gain.

In non-coherent processing, phase information is discarded; you sum the power (or envelope) of the returns without aligning their phases. Since the phase is not matched from pulse to pulse, you can’t exploit constructive addition of the signal, so the improvement in sensitivity is much smaller, scaling roughly with the square root of the number of looks rather than linearly with N.

So coherent integration preserves phase across pulses for higher sensitivity, while non-coherent relies on power summation without phase information. The other statements misstate these distinctions.