Low-Power Ka-Band Radar Chip Achieves Record Efficiency for Next-Generation Sensing Applications

A Low-Power Ka-Band Transceiver With 5.2-GHz Bandwidth for FMCW Radar Applications | IEEE Journals & Magazine | IEEE Xplore

Researchers at Zhejiang University demonstrate breakthrough transceiver design with 5.2-GHz bandwidth while consuming just 107.6 mW

A team of researchers from Zhejiang University and Donghai Laboratory has developed a low-power Ka-band frequency-modulated continuous wave (FMCW) radar transceiver that achieves unprecedented energy efficiency while maintaining high performance across multiple operational modes. The advancement, published in IEEE Transactions on Circuits and Systems—II: Express Briefs, represents a significant step toward making millimeter-wave radar technology practical for battery-powered Internet of Things (AIoT) devices, health monitoring systems, and portable sensing applications.

Technical Innovation and Performance

The transceiver, fabricated in 65-nm CMOS technology, achieves a maximum transmitter output power of 15.6 dBm with 35.3% drain efficiency at 34.6 GHz, while the receiver demonstrates a 49-dB conversion gain and a minimum double-sideband noise figure of 4.9 dB. What sets this design apart is its innovative low-voltage operating mode, where it achieves 7.68-dBm transmitter output power with 23.8% drain efficiency while consuming only 107.6 mW total power.

Led by Professors Zhiwei Xu and Nayu Li from Zhejiang University's State Key Laboratory of Ocean Sensing, the research team addressed critical challenges in millimeter-wave circuit design. The low-noise amplifier employs current multiplexing and Gm-boosting techniques to enhance energy efficiency, while a novel primary-coil current splitter improves gain and minimizes crosstalk between I/Q mixers.

Architectural Advantages

The team's primary-coil current splitter represents a notable innovation in power distribution for millimeter-wave receivers. Traditional approaches either use secondary-coil splitters that face combined large load capacitances or coupling-domain splitters that suffer from I/Q imbalance and crosstalk issues. The primary-coil current splitter achieves higher passive efficiency and reduced crosstalk by allowing two transformers to separately face the parasitic capacitance of single-branch mixers, effectively increasing inductance with better quality factors.

The system operates across 32.4–37.6 GHz with measured phase noise of -100.6 dBc/Hz at 1-MHz offset with a 32.4-GHz carrier, and demonstrates an RMS frequency error of just 2.94 MHz (0.073%) for a sawtooth chirp with 4-GHz chirp bandwidth and 200-µs chirp-up time.

Performance Analysis Across Radar Modalities

Synthetic Aperture Radar (SAR) Applications

While not explicitly designed for SAR operation, the transceiver's characteristics suggest promising capabilities for short-range SAR imaging. The 5.2-GHz instantaneous bandwidth translates to theoretical range resolution of approximately 2.9 cm, making it suitable for high-resolution imaging applications. The low power consumption becomes particularly advantageous for SAR systems mounted on small unmanned aerial vehicles (UAVs) or mobile platforms where battery life is critical.

The phase noise performance is crucial for SAR coherency requirements. With phase noise variation of only 3.1 dB across the 32.4–36.4 GHz chirp band, the system maintains sufficient phase stability for coherent integration over multiple pulses. However, the relatively modest transmit power of 15.6 dBm would limit operational range compared to traditional airborne SAR systems, positioning this technology more appropriately for ground-based or close-range imaging scenarios.

Doppler Radar Performance

The transceiver excels in Doppler velocity measurement applications. Over-the-air testing demonstrated successful detection and velocity estimation of moving targets using two-dimensional FFT processing to analyze Doppler components. The Ka-band operating frequency provides excellent Doppler sensitivity, with velocity resolution capabilities suitable for automotive, gesture recognition, and vital signs monitoring applications.

The system successfully detected multiple targets simultaneously, with testing showing concurrent detection of corner reflectors positioned at ranges from 7.6 m to 33.8 m. The low phase noise characteristics prove particularly beneficial for Doppler processing, where phase coherency directly impacts velocity measurement accuracy.

The receiver's in-band input-referred 1-dB compression point of -36.1 to -31.2 dBm and out-of-band compression point of -27 to -21 dBm indicate reasonable dynamic range for typical short-to-medium range Doppler radar scenarios. For applications requiring extended dynamic range, reducing mixer and baseband gain to 0 dB improves both compression points to -15 dBm.

Digital Communications Potential

Though designed primarily for radar, the transceiver architecture shows interesting potential for joint radar-communication systems—an emerging area of research. The wide instantaneous bandwidth of 5.2 GHz could theoretically support multi-gigabit per second data rates in communication applications.

However, several factors would need consideration for communication deployment. The transmitter's linearity, while adequate for FMCW radar where constant envelope modulation dominates, would require characterization for amplitude-modulated communication waveforms. The measured drain efficiency of 35.3% at maximum power suggests class-B operation, which typically exhibits nonlinear amplitude response.

Recent research has explored dual-use radar-communication systems at Ka-band. Zhao et al. from Tsinghua University demonstrated a Ka-band phased-array transceiver supporting both radar and communication functions, though with significantly higher power consumption. The Zhejiang University design's emphasis on power efficiency could enable similar dual-mode operation in portable applications where previous solutions proved impractical.

Antenna Integration and System Validation

A critical innovation lies in the complete system integration approach. The team designed an inverted shunt-fed patch antenna array fabricated on Rogers 4550F substrate, achieving 13.43-dBi gain with sidelobe levels below -11.78 dB and 3-dB beamwidth of 16.3° in the vertical plane and 60.2° in the horizontal plane.

The antenna exhibits simulated gain ranging from 10.73 dBi to 13.43 dBi with input reflection coefficient below -8.2 dB across 32–38.5 GHz. This antenna design overcomes traditional bandwidth limitations of microstrip patches through multi-layer coupling structures and optimized ground plane configuration.

The transceiver chip uses flip-chip chip scale package (FC-CSP) technology mounted on a 6-layer substrate with solder bumps, then integrated onto a printed circuit board via ball grid array, minimizing parasitic effects of chip-package-board interconnections.

Competitive Landscape and Industry Context

The millimeter-wave radar market has seen intense development activity, particularly for automotive and consumer applications. Major semiconductor manufacturers including Texas Instruments, NXP, Infineon, and Analog Devices have released Ka-band radar chipsets, though most target automotive applications with different power and cost profiles.

Compared to recent state-of-the-art Ka-band FMCW radar transceivers, the Zhejiang University design demonstrates the lowest front-end power consumption while maintaining competitive bandwidth. Prior work by Ding et al. achieved 2-GHz bandwidth but consumed more power, while Deng and Wu's design provided high output power at the cost of increased power consumption.

The emphasis on dual-mode operation (normal and low-voltage) distinguishes this work from commercial offerings. This flexibility enables system designers to trade performance for battery life depending on application requirements—a critical capability for wearable and portable devices.

Market Implications and Applications

The research addresses growing demand for low-power millimeter-wave sensing in several emerging markets:

Healthcare Monitoring: The fully integrated design with baseband accelerator enables vital signs monitoring applications, where contactless detection of respiration and heartbeat provides advantages over traditional contact-based sensors. The low power consumption makes continuous monitoring feasible in wearable form factors.

Gesture Recognition and Human-Machine Interfaces: Millimeter-wave radars enable fine-grained gesture recognition for IoT applications, with recent research demonstrating 4-D gesture sensing capabilities at 60 GHz. The Ka-band frequency provides similar resolution capabilities with potentially better range performance.

Industrial Sensing: The high bandwidth enables precise distance measurement for industrial automation, robotics, and material handling applications where sub-centimeter accuracy is required. Measured distance errors of less than ±0.12 m demonstrate practical accuracy for these applications.

Automotive Applications: While the automotive radar market has largely standardized around 77-79 GHz, the 35-GHz Ka-band offers advantages for specific applications. The frequency allocation supports large modulation bandwidth for high-precision detection, with lower atmospheric loss compared to W-band.

Technical Challenges and Future Directions

Despite impressive performance, several challenges remain for widespread adoption:

Range Limitations: The relatively modest transmit power of 15.6 dBm limits detection range compared to higher-power alternatives. While adequate for many AIoT and consumer applications, automotive and longer-range industrial applications may require power amplifier enhancements.

Integration Complexity: The system requires careful co-optimization of chip, package, and antenna through electromagnetic simulation to ensure optimal impedance matching. This complexity increases manufacturing cost and development time.

Regulatory Considerations: Commercial deployment requires navigation of frequency allocation regulations, which vary by region and application. The Ka-band includes frequency ranges allocated for different services, requiring careful frequency planning.

Research Team and Institutional Support

The research was conducted by a collaborative team from Zhejiang University's State Key Laboratory of Ocean Sensing and Donghai Laboratory's Institute of Intelligent Marine Sensing and Communications. Lead researchers include Shengjie Wang, Wenyan Zhao, Jiangbo Chen, Quanyong Li, Jingwen Xu, Nayu Li, Huaicheng Zhao, Gaopeng Chen, Chunyi Song, Xiaokang Qi, and Zhiwei Xu.

The work received support from the National Natural Science Foundation of China Key Project (Grant 62434008), the National Key Research and Development Program of China (Grant 2023YFB4403304), and the Key Research and Development Program of Zhejiang Province (Grant 2022C01231).

Conclusion

The Zhejiang University team's Ka-band transceiver demonstrates that millimeter-wave radar technology can achieve the power efficiency necessary for battery-operated applications without sacrificing bandwidth or sensitivity. The dual-mode operation and integrated antenna solution provide a pathway toward practical implementation in size- and power-constrained applications.

As millimeter-wave sensing continues expanding beyond traditional automotive and military applications into consumer electronics, healthcare, and industrial automation, innovations in power efficiency become increasingly critical. This research contributes important circuit techniques and system integration approaches that enable next-generation portable radar systems.

The primary-coil current splitter technique and current-multiplexing low-noise amplifier design may find application in other millimeter-wave systems beyond radar, including 5G/6G communications and high-resolution imaging systems. The demonstrated performance across multiple operational modes suggests a design methodology applicable to broader classes of millimeter-wave transceivers where power efficiency cannot compromise functionality.

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Sources

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