A fixed IF 77-GHz FMCW radar sensor

In this paper a 77-GHz FMCW radar with a fixed IF bandpass filter in conjunction with adjustable frequency slopes was presented. The used method allows retrieving the range profile without the need for fast digital signal processors (DSP) required to calculate the spectral contents of the received signal. Instead a fixed IF bandpass filter is implemented with an FIR filter, which is available in modern signal converters. Thus a simple microcontroller is sufficient to read out the estimated frequency bin and to set the slope of the frequency ramp to the desired values. This enables the presented sensor to be used in low-cost applications, without suffering from performance degradations compared to the conventional FMCW signal processor. The main drawback of the described method is the extended measurement time because N_s ramps must be transmitted to obtain the range profile. Therefore, the concept is suitable for slowly moving targets only, requiring that the change in distance doesn´t exceed the range resolution during one measurement cycle.