State the impact of PRF on unambiguous range and velocity measurements.

• A. PRF is Pulse Repetition Frequency; higher PRF improves velocity unambiguity but reduces maximum unambiguous range; lower PRF increases range unambiguity but worsens velocity accuracy.
• B. PRF stands for Phase Range Factor; affects angular resolution only.
• C. PRF stands for Pulse Repetition Focus; increases range.
• D. PRF is Pulse Repetition Frequency; higher PRF improves velocity unambiguity but reduces maximum unambiguous range; lower PRF increases range unambiguity but worsens velocity accuracy.

Answer: (D)

PRF is Pulse Repetition Frequency, and it sets how often a radar sends a pulse per second. This timing creates a trade-off between how far away a target can be resolved without ambiguity and how accurately its velocity can be measured.

For range, the maximum unambiguous distance is roughly c/(2*PRF). So increasing PRF makes the interval between pulses shorter, which means echoes from farther targets can be misassigned to the wrong pulse and become ambiguous. In short, higher PRF reduces the maximum unambiguous range. Lower PRF lengthens the pulse interval, increasing the unambiguous range.

For velocity, the Doppler information is sampled at the PRF. The unambiguous Doppler (velocity) range is ±PRF/2, so higher PRF expands the speeds you can measure without aliasing. Lower PRF shrinks that range, causing velocity measurements to be ambiguous or less accurate.

Thus, increasing PRF improves velocity unambiguity but reduces the maximum unambiguous range, while decreasing PRF increases range unambiguity but worsens velocity unambiguity and potential accuracy.