Time-Varying Transmission Lines (TVTL): A Pathway to Integrated Non-Reciprocity for Full-Duplex Communications

Modern wireless systems such as cognitive radios often require the RF front-ends to be broadband, low noise, software reconfigurable, and robust against interferences. In addition, a full-duplex front-end offers not only higher capacity than that of a half-duplex system, but also other system benefits such as flexibility in band selections without band limiting diplexers. The implementation of such systems, however, requires non-reciprocal components that operate over a broad bandwidth, with low loss and interference suppression capability.

Time-varying transmission lines (TVTLs) are a solution to meet the aforementioned challenges. By definition, TVTLs are transmission lines whose characteristic impedance is a function of space and time. For example, the characteristic impedance can be modulated by an electromagnetic wave that travels on the same or a different transmission line. The theory of time-varying transmission line were studied in 1950's under the scope of distributed parametric amplifiers. Recently, the TVTL concept has been applied to develop broadband, non-reciprocal components that can be integrated on-chip through a device architecture called Distributedlly Modulated Capacitors (DMC). The DMC based TVTLs offer a collection of benefits that of both active and passive devices, including non-reciprocity, positive gain, high power capacity, low noise and frequency tunability, which opened a pathway to implement integrated full-duplex system front-end.

Dr. Yuanxun Ethan Wang received the B.S. degree in Electrical Engineering from University of Science and Technology of China (USTC), Hefei, China in 1993, and the M.S. and the Ph.D. degrees in electrical engineering from University of Texas at Austin, in 1996 and 1999. He became an Assistant Professor with the EE department of UCLA since Nov. 2002 and is now an Associate Professor with the same department. Dr. Wang is a senior member of IEEE and an associate Editor of IEEE Transactions on Antennas and Propagation. He has published more than 100 journal and conference papers. His research is in the general area of microwave systems with emphasis on the front-ends including antennas, phased arrays, high performance RF transmitters and receivers. His researches blend digital technologies and concepts into RF design, which often leads to novel antenna and circuit configurations with performances beyond the conventional bound. Dr. Wang is the director of the Digital Microwave Lab and the Center for High Frequency Electronics in the Electrical Engineering Department of UCLA and the leader of antenna thrust in National Science Foundation funded Engineering Research Center "“ Translational Applications of Nanoscale Multiferroic Systems (TANMS).