Phase Noise Spectral Density Measurement of Broadband Frequency-Modulated Radar Signals

• Published in: IEEE transactions on microwave theory and techniques 2022-04, Vol.70 (4), p.2370-2379
• Main Authors: Tschapek, Peter, Korner, Georg, Hofmann, Andreas, Carlowitz, Christian, Vossiek, Martin
• Format: Article
• Language: English
• Subjects: Analyzers; Broadband; Chirp; Continuous radiation; Continuous-wave (CW) radar; Demodulation; Density measurement; Digital signal processing; frequency-modulated continuous-wave (FMCW) radar; Microwave measurement; Modulation; Noise; Noise measurement; Noise prediction; Noise reduction; Orthogonal Frequency Division Multiplexing; Phase locked loops; Phase measurement; Phase noise; phase noise measurement; phase noise profiles; Radar; Radar equipment; Radar systems; Radio frequency; Signal processing; Synthesis; Synthesizers; Time domain analysis; Time measurement
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2022.3148311

In continuous-wave (CW) radar systems, such as frequency-modulated (FMCW), frequency-stepped (FSCW), or orthogonal frequency-division multiplexing (OFDM) radar systems, the range and velocity uncertainty are significantly impaired by phase noise decorrelation. Therefore, radar designers require accurate knowledge of their synthesizers' phase noise profiles to assess and predict radar performance. However, commercial phase noise analyzers cannot determine phase noise during modulation, and this may differ notably from phase noise in the pure CW mode. Recent methods for FMCW phase noise analysis usually require comprehensive {a} priori knowledge of modulation parameter and are prone to systematic deviations. To overcome these issues, we propose a new approach based on differential analysis of subsequent time-domain measurements. This method retains, statistical phase noise information while reducing systematic influences. For the first time, less {a} priori signal knowledge is required, and the method works for nearly any kind of broadband signal modulation. The concept requires only a digitizer (e.g., an oscilloscope) and some digital signal processing. The proposed method is first experimentally tested with different phase-locked-loop (PLL)-based synthesizer phase noise profiles. The obtained phase noise profiles agree perfectly with the results of an established measurement system. After this proof of basic functionality, the unique phase noise analysis capability for BB modulated signals is demonstrated with PLL-generated FMCW signals. The results reveal a significant phase noise difference between the different setups and clearly show the capability and benefit of the novel phase noise spectral density measurement concept.