The University of Michigan-Shanghai Jiao Tong University Joint Institute (UM-SJTU JI, JI hereafter) Assistant Professor Xuyang Lu and undergraduate student Zhehao Yu have published a research article “mmWave Spatial-Temporal Single Harmonic Switching Transmitter Arrays for High back-off Beamforming Efficiency” in IEEE Transactions on Antennas and Propagation, a top journal in microwave and antenna society.

The article proposes an electromagnetic and circuit co-designed transmitter array that includes time as an additional degree of freedom for power back-off efficiency enhancement. Xuyang Lu is the corresponding author, Zhehao Yu is the first author.

Modern wireless communication system takes advantage of both beamforming and high-order modulation schemes to achieve directional fast signal transmitting. One major drawback of transmitting high-order modulated signals is that it forces the transistors to operate in the linear region with a large input back-off. This will degrade efficiency of power amplifiers. On the other hand, conventional phased array requires complex weight multiplications in different signal paths and, consequently, the beamforming efficiency degrades due to poor matching of the device.

In the published article, a novel time-modulation transmitter array is designed to simultaneously achieve high efficiency beamforming and back-off signal transmitting. The article shows the modeling, analysis, and design of the modulation signal in detail. Additionally, a corresponding integrated system is also designed and simulated. From the simulation, the drain efficiency of the architecture exhibits a 57% improvement at 3-dB PBO, 100% improvement at 6-dB PBO, and 190% improvement at 9-dB PBO compared with conventional class A/B amplifiers.

Background Information

Zhehao Yu (Student Member, IEEE) is a senior dual-bachelor-degree-program student of the University of Michigan-Shanghai Jiao Tong University Joint Institute majoring in electrical and computer engineering at the joint institute and electrical and electronic engineering at the University of Michigan, Ann Arbor. He is pursuing the Ph.D. degree at the Department of Electrical and Systems Engineering, University of Pennsylvania, as a recipient of the university’s Dean’s Fellowship. His current research interests include CMOS mmWave and terahertz integrated systems, integrated photonics, and electronic-photonic integration.

Xuyang Lu (Member, IEEE) received his B.S. degree in electrical engineering from Rice University, Houston, Tx, USA, in 2014, and the M.A. and Ph.D. degrees in electrical engineering from Princeton University, Princeton, NJ, USA, in 2016 and 2020, respectively. He joined the University of Michigan-Shanghai Jiao Tong University Joint Institute as an assistant professor in 2021, with a joint appointment with the department of Electronic Engineering, Shanghai Jiao Tong University. He is also a member of the MoE Key Laboratory of High-Speed Electronic Systems, Shanghai Jiao Tong University. His research interests include high-speed programmable RF and mmWave integrated systems, integrated terahertz systems, inte- grated photonics, on-chip Antenna optimization, and machine- learning in analog circuit design.