Yikuan Chen

EECS Department, University of California, Berkeley

Technical Report No. UCB/

May 1, 2025

As the demand for high-resolution sensing continues to rise in applications such as autonomous vehicles, human-machine interfaces, and biomedical monitoring, mmWave and sub-THz radar have become increasingly attractive. These systems offer robustness to lighting and weather conditions, fine range and velocity resolution, and the compatibility for integration with compact, low-power and cost-efficient CMOS technologies. Among different radar technologies, frequency-modulated continuous-wave (FMCW) radar is particularly well-suited for short-to-mid-range applications, offering continuous sensing and potential for low hardware complexity, especially in CMOS-integrated systems. However, a persistent challenge in monostatic FMCW radar is self-interference (SI) caused by leakage from the transmitter to the receiver, which can saturate the front-end and severely degrade dynamic range.

To address this challenge, this dissertation presents an RF-domain SI cancellation architecture to cancel the SI before the LNA. The approach uses a feedforward path with a TX IQ mixer for leakage beat frequency control by frequency shifting, and a replica IQ mixer to synthesize a cancellation chirp that aligns in frequency and time with the SI signal. A Wilkinson power combiner subtracts the replica from the received signal before the LNA stage, preserving receiver linearity and improving detection of close-range targets by avoiding the high-pass filter in the baseband. The system is implemented as a D-band radar transceiver operating at 140 GHz with 10 GHz FMCW chirps. The chip is fabricated in 28nm bulk CMOS and packaged using low-cost technologies. The prototype system demonstrates up to 44.7 dB cancellation for narrowband tones and 22 dB cancellation over wideband chirps in measurement with stable performance over time and temperature. To the author's knowledge, this is the first reported full radar chip to demonstrate wideband, multi-path SI cancellation capability realized in the RF domain with high cancellation depth and minimal baseband complexity.

Advisors: Ali Niknejad

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BibTeX citation:

@phdthesis{Chen:31705,
    Author= {Chen, Yikuan},
    Title= {A 140 GHz FMCW Radar with RF Self-Interference Cancellation},
    School= {EECS Department, University of California, Berkeley},
    Year= {2025},
    Number= {UCB/},
    Abstract= {As the demand for high-resolution sensing continues to rise in applications such as autonomous vehicles, human-machine interfaces, and biomedical monitoring, mmWave and sub-THz radar have become increasingly attractive. These systems offer robustness to lighting and weather conditions, fine range and velocity resolution, and the compatibility for integration with compact, low-power and cost-efficient CMOS technologies. Among different radar technologies, frequency-modulated continuous-wave (FMCW) radar is particularly well-suited for short-to-mid-range applications, offering continuous sensing and potential for low hardware complexity, especially in CMOS-integrated systems. However, a persistent challenge in monostatic FMCW radar is self-interference (SI) caused by leakage from the transmitter to the receiver, which can saturate the front-end and severely degrade dynamic range.

To address this challenge, this dissertation presents an RF-domain SI cancellation architecture to cancel the SI before the LNA. The approach uses a feedforward path with a TX IQ mixer for leakage beat frequency control by frequency shifting, and a replica IQ mixer to synthesize a cancellation chirp that aligns in frequency and time with the SI signal. A Wilkinson power combiner subtracts the replica from the received signal before the LNA stage, preserving receiver linearity and improving detection of close-range targets by avoiding the high-pass filter in the baseband. The system is implemented as a D-band radar transceiver operating at 140 GHz with 10 GHz FMCW chirps. The chip is fabricated in 28nm bulk CMOS and packaged using low-cost technologies. The prototype system demonstrates up to 44.7 dB cancellation for narrowband tones and 22 dB cancellation over wideband chirps in measurement with stable performance over time and temperature. To the author's knowledge, this is the first reported full radar chip to demonstrate wideband, multi-path SI cancellation capability realized in the RF domain with high cancellation depth and minimal baseband complexity.},
}

EndNote citation:

%0 Thesis
%A Chen, Yikuan 
%T A 140 GHz FMCW Radar with RF Self-Interference Cancellation
%I EECS Department, University of California, Berkeley
%D 2025
%8 May 1
%@ UCB/
%F Chen:31705