When a RADAR is being operated on the 1.5 mile range setting, what is the most appropriate pulse width and pulse repetition rate?

• A. 0.25 us PW and 1,000 pps
• B. 0.05 us PW and 2,000 pps
• C. 1.0 us PW and 500 pps
• D. 2.5 us PW and 2,500 pps

Answer: (B)

For a close-range radar setting like 1.5 miles, you want the radar to distinguish targets that are fairly near each other, and you also want a reasonable update rate without causing range ambiguity. The pulse width determines range resolution: shorter pulses give finer resolution, while longer pulses smear targets together. A pulse width of 0.05 microseconds is extremely short, which yields a two-way range resolution of about 7.5 meters (roughly c × PW / 2 ≈ 3×10^8 m/s × 5×10^-8 s / 2). That’s ample to separate targets at 1.5 miles.

The pulse repetition rate sets how far away you can unambiguously measure range (maximum unambiguous range) and how often you get updates. A PRF of 2,000 pulses per second gives a maximum unambiguous range of about 75 kilometers, so a 1.5-mile target is well within that limit, and you also get a good update rate for tracking.

So, a very short pulse width with a PRF around 2 kHz provides the right balance of good range resolution for near targets and an unambiguous, timely display. That’s why the combination of 0.05 microseconds and 2,000 pps is the best choice.