In pulsed radar, increasing PRF trades off what aspect of operation?

• A. It can improve velocity measurements but reduce maximum unambiguous range.
• B. It increases range resolution but worsens Doppler shift accuracy.
• C. It reduces power consumption.
• D. It has no effect on any measurement.

Answer: (A)

Raising the pulse repetition frequency (PRF) changes how the radar samples echoes in time, which directly affects what you can measure without ambiguity. The Doppler information comes from comparing echoes from successive pulses, so a higher PRF raises the highest Doppler frequency you can measure without aliasing. In other words, your unambiguous velocity range increases as PRF goes up, making velocity measurements more capable.

But the flip side is that unambiguous range gets smaller as PRF increases. The maximum range you can determine without range aliasing is inversely proportional to PRF (roughly c/(2·PRF)). So targets farther away risk being misread as closer ones when PRF is higher. That’s the trade-off: better, unambiguous velocity information at the expense of reduced unambiguous range.

Note that range resolution is set mainly by pulse bandwidth, not PRF, and PRF doesn’t inherently reduce power per se (though average power can vary with PRF). The key takeaway is the balance between velocity unambiguity and range unambiguity.