The objective of our ComSenTer effort is to realize energy-efficient transmitters and PAs for digital beamformers designed to support MIMO at 140, 240, and 340 GHz. The opportunity is staggering; currently PAs and communication systems operating above 100 GHz operate at less than a few percent of energy efficiency. To gain broad commercial and defense interest in upper millimeter-wave bands, we seek to demonstrate the potential for advanced transistor technologies to realize efficiency exceeding 20%.


We are investigating the co-design of III-V and silicon integrated circuits to optimize energy efficiency for different array sizes. The availability of high fmax InP and GaN IC technologies are investigated for high-power and high-efficiency at 140 GHz. Architectures and signal processing approaches that maintain high efficiency under the average power levels in a MIMO array are compared for circuit innovations and approaches to digital signal processing.

We are collaborating with Ali Niknejad and Mark Rodwell on features of IC and packaging for digital beamformers, Umesh Mishra on advanced GaN device technologies, and Sundeep Rangan on power consumption analysis in arrays.


Our most significant accomplishments, so far, include

  1. Tapeout of high-efficiency InP power amplifiers at 140 GHz.
  2. Design of high-power GaN power amplifiers at 140 GHz.
  3. Development of new average efficiency architecture for 140, 240 and 340 GHz.

Team Leader

James Buckwalter

James F. Buckwalter (S’01–M’06–SM’13) received the Ph.D. degree in electrical engineering from the California Institute of Technology, Pasadena, CA, USA, in 2006. From 1999 to 2000, he was a Research Scientist with Telcordia Technologies. In 2004, he joined the IBM T. J. Watson Research Center, Yorktown Heights, NY, USA. In 2006, he joined the Faculty of the University of California at San Diego, La Jolla, CA, USA, as an Assistant Professor and became an Associate Professor in 2012. He is currently a Professor of electrical and computer engineering with the University of California at Santa Barbara, Santa Barbara, CA, USA. Dr. Buckwalter was a recipient of the 2004 IBM Ph.D. Fellowship, the 2007 Defense Advanced Research Projects Agency Young Faculty Award, the 2011 NSF CAREER Award, and the 2015 IEEE MTT-S Young Engineer Award.



E. Lam, K. Ning,, A. Ahmed, M. Rodwell, & J. F. Buckwalter, “A 2-stage, 140-GHz Class-B Power Amplifier Achieving 22.5% PAE at 17.3 dBm in a 250-nm InP HBT Technology,” presented at the 2022 IEEE/MTT-S International Microwave Symposium - IMS 2022, Denver, CO, June 19-24, 2022.

J. F. Buckwalter & S. Chien, “A Compact, 114-GHz, High-efficiency Power Amplifier in a 250-nm InP HBT Process,” presented at the 2022 IEEE/MTT-S International Microwave Symposium - IMS 2022, Denver, CO, June 19-24, 2022.

E. O'Malley, A. Arias-Purdue, M. Guidry, & J. F. Buckwalter, “Gallium Nitride HEMTs for Power Amplifiers above 100 GHz,” presented at the 2022 IEEE 22nd Annual Wireless and Microwave Technology Conference (WAMICON), Clearwater, FL, April 27-28, 2022.

K. Ning, Y. Fang, M. Rodwell, & J. F. Buckwalter, “A 140-GHz Power Amplifier in a 250-nm InP Process with 32% PAE,” presented at the 2020 IEEE Radio Frequency Integrated Circuits Symposium (RFIC), Los Angeles, CA, August 4-6, 2020.