Double-Conversion FMCW Radar for Extension of Maximum Unambiguous Range

This article presents a double-conversion frequency-modulated continuous-wave (FMCW) radar to overcome the maximum unambiguous range (MUR) limitation imposed by the sampling rate in stretch processing. The proposed radar integrates a double-quadrature topology and employs a second frequency conversion for beat signals. This conversion allows the sampling of the beat signals in the desired frequency band. In other words, the proposed radar can detect targets in a broader range of interest (ROI) with a limited sampling rate. As a result, the MUR can be extended by concatenating data from each ROI. This approach preserves the maximum unambiguous velocity (MUV) by maintaining the pulse repetition interval (PRI). A 24 GHz prototype radar was implemented using commercial off-the-shelf components, and a comprehensive calibration for channel imbalances was performed. The experimental results showed that the proposed radar effectively extended the MUR from 78.78 to 157.5 m by concatenating two range-Doppler (R-D) maps with different ROIs. Moreover, this was realized without requiring any costly hardware or complicated signal processing, thereby providing a practical solution for extending the MUR of FMCW radars without sacrificing the MUV.