What is a fundamental requirement for any Doppler radar to function effectively?

For Doppler radar to function effectively, coherence is a fundamental requirement. Coherence refers to the correlation between the signals transmitted and received, which is essential for accurately determining the frequency shift that occurs due to the Doppler effect. This frequency shift provides critical information about the speed and direction of the target's movement.

In the context of Doppler radar, maintaining coherence allows the system to effectively compare the transmitted signal and the returned echo from a moving target. That way, any changes in frequency due to the movement can be detected accurately, enabling precise measurements and reliable tracking.

While signal modulation, frequency stability, and pulse shaping are all important aspects of radar technology, they do not specifically address the essential principle of coherence that directly impacts the Doppler effect and thus the radar’s ability to measure velocities accurately.