Over-the-Air Phase Noise Spectral Density Measurement for FMCW Radar Sensors

Phase noise significantly degrades the performance of frequency-modulated continuous wave (FMCW)- and chirp sequence (CS)-based radar sensors. Knowledge of the power spectral density (PSD) of these sensors is therefore essential for estimating their limitations. This work presents a test setup where over-the-air (OTA) tests can be carried out and the PSD extracted directly from the signal radiated from a radar sensor operating in the $76 \,\mathrm{G}\mathrm{Hz}$ – $81 \,\mathrm{G}\mathrm{Hz}$ automotive frequency band. For this, the radar signal is demodulated in the analog domain by mixing it with a delayed version of the received signal. Demodulation compresses the signal bandwidth, simplifying hardware requirements for sampling and signal processing. The remaining systematic errors are compensated and the range correlation effect is corrected by an appropriate signal processing scheme. Our approach eliminates the need for prior knowledge of modulation parameters, leading to both increased precision and reduced potential for errors. The proposed setup is validated comparing system measurements with data obtained from established testing methods and simulations.The presented setup successfully demonstrates the capability of performing OTA test measurements of a PSD from a FMCW sensor. Our results demonstrate good agreement between the PSD test results and the expected outcome.