Phase Noise Suppression System for Microwave Photonic FMCW Radar Based on Deskew Filtering

Frequency-Modulated Continuous-Wave （FMCW） radar is widely used in military， autonomous driving， and other fields for its high resolution， low power consumption， and strong anti-interference. However， traditional microwave electronic radars fail to meet broadband signal generation/processing needs， leading to the development of microwave photonic radar. By combining photonics and electronics， it overcomes the “electronic bottleneck，” with optical frequency multiplication and dechirping reception architectures gaining attention for large bandwidth and simple structure. Nevertheless， in this architecture， frequency multiplication degrades phase noise （by 20 log₁₀（n） dB for multiplication factor n）， while electro-optic/optoelectronic conversion worsens it. Phase noise impairs radar accuracy， resolution， and anti-interference， limiting broadband advantages. Existing suppression technologies for microwave photonic radar often suffer from complexity， high cost， or new noise introduction， demanding more effective compensation.This paper proposes a phase noise compensation scheme for microwave photonic FMCW radar using deskew filtering. The system adopts an optical quadrupling structure （boosting distance resolution） plus reference delay and mixing branches. The baseband linear frequency-modulated （LFM） signal splits into two paths： one drives the microwave photonic quadrupling module to generate a transmitted signal （4× baseband frequency/bandwidth， 4× phase noise）， whose echo is processed via a microwave photonic mixer to get an echo dechirped signal with phase jitter； the other undergoes reference delay/mixing to produce a reference dechirped signal. Deskew filtering compensates the echo dechirped signal as follows： apply Hilbert transforms to both signals for complex signals， estimate phase noise via the reference， remove phase noise's delay dependence in the echo using the deskew filter， and eliminate phase noise to mitigate radar performance impacts.An experimental setup was built to verify the feasibility of the proposed scheme. The initial frequency of the baseband linear frequency-modulated signal was 5 GHz， with a bandwidth of 100 MHz. After passing through the microwave photonic quadrupling module， a quadrupled frequency signal in the range of 20~20.4 GHz was generated， effectively expanding the bandwidth. The reference and echo dechirped signals were collected and processed using the deskew filtering algorithm. To evaluate the effectiveness of phase noise compensation in the dechirped echo signal， we analyze two key aspects： first， comparing the stability of the half-period of the dechirped echo signal before and after compensation， and second， examining its phase noise characteristics. A reference group processed using the equal phase interval sampling method was introduced for comparative analysis. The results show that before compensation， the standard deviation of the half-period was 0.54 ns. After compensation with the equal phase interval sampling method， this value decreased to approximately 0.24 ns. Further compensation using the deskew filtering method reduced the standard deviation to 0.15 ns， representing a 3.6 times improvement in stability compared to the pre-compensation state. This indicates that the phase noise compensation achieved through the deskew filtering method significantly enhances the stability of the half-period of the dechirped echo signal. Regarding phase noise characteristics， the experimental results demonstrate that within the frequency offset range of less than 10 kHz， the deskew filtering method outperforms the equal phase interval sampling method in suppressing phase noise， resulting in a lower phase noise level in the processed signal. Additionally， a time-frequency analysis was conducted on the signals before and after compensation to compare the range profiles. The results reveal that the target energy in the compensated range profile becomes more concentrated， and the deviation range of the distance measurement results is effectively suppressed. Specifically， the distance corresponding to 10 dB bandwidth decreased from 49.57 m （pre-compensation） to 41.28 m （post-compensation）， while the standard deviation of distance measurement results reduced from 0.97 m （pre-compensation） to 0.78 m （post-compensation）. Collectively， these findings demonstrate that the deskew filtering method effectively improves the range resolution and distance measurement stability of the radar system.