Question

When using FMCW radar, what specific signal property is compared between the transmitted and reflected wave to calculate the target&#x27;s precise distance?

Accepted Answer

When using Frequency Modulated Continuous Wave radar, the specific signal property compared between the transmitted and reflected wave is the instantaneous frequency difference. FMCW radar works by transmitting a signal that continuously increases in frequency over time, known as a frequency ramp or chirp. Because the radar wave travels at the speed of light, it takes a specific amount of time to reach a target and bounce back to the receiver. By the time the reflected signal returns, the transmitter has already moved on to a higher frequency. The receiver mixes the transmitted signal with the received signal to produce a beat frequency, which is the numerical difference between the two frequencies at that exact moment. Because the frequency of the transmitted signal increases at a known, constant rate, this beat frequency is directly proportional to the time delay caused by the round trip to the target. For example, if a target is further away, the return signal takes longer to arrive, resulting in a larger frequency gap and a higher beat frequency. By measuring this beat frequency, the system calculates the precise distance to the target using the relationship between the slope of the frequency ramp, the speed of light, and the detected frequency difference.

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When using FMCW radar, what specific signal property is compared between the transmitted and reflected wave to calculate the target's precise distance?