HomeResearch → Time-varying Electromagnetic Subsystem

A very important part of the group's research in Electromagnetic systems is to explore the nonlinear dynamics and time-varying operation of the system with the hope to break the conventional performance barrier that is imposed in a linear, time-invariant system.

Direct Antenna Modulation (DAM) that Breaks the Antenna Bandwidth Limit

Such concept has been well embodied in the proposal and the development of the Direct Antenna Modulation (DAM) technique. My group first envisioned the concept of DAM in 2004 and proposed its application to electrically small antennas subsequently in 2006. The DAM technique takes the advantage of the transient property of the antenna by integrating antenna with active, non-linear devices. Due to the non-linear dynamics in the radiation process, antennas under this new scheme are capable to radiate signals with much broader spectrum than what its original bandwidth allowed yet with high radiation efficiency. The proposed scheme may overcome the well-known fundamental bandwidth limit associated with electrically small antennas imposed by the Harrington-Chu’s Q limit and revolutionize the state of the art in electrically small antenna design. Recently, the group published a complete description of the DAM concept with both theoretical derivations and experimental validations in a VLF system in IEEE TCAS-I in March, 2014. It is validated that DAM can help to achieve an efficiency bandwidth product much greater than what is limited by Chu's limit, provide that a high speed, low loss switch is available.

H. C. Jing, X. J. Xu and Y. E. Wang, “Direct Antenna Modulation (DAM) with switched patch antenna – performance analysis,” Journal of Applied Computational Electromagnetics Society (ACES), May, 2014.

U. Azad and Y. E. Wang, “Direct Antenna Modulation (DAM) for enhanced capacity performance of near-field communication (NFC) link,” IEEE Transactions on Circuit and Systems I, Vol.61, No.3, pp.902-910, March, 2014.

X. J. Xu and Y. E. Wang, "A direct antenna modulation (DAM) transmitter with a switched electrically small antenna", 2010 International Workshop on Antenna Technology (iWAT),, IEEE, 1-4 (03/01/2010).

X. Xu, H. C. Jing and Y. E. Wang, "High speed pulse radiation from switched electrically small antennas", IEEE Antennas and Propagation Society International Symposium 2006.

Non reciprocal Components with Distributedly Modulated Capacitors (DMC)

Another major breakthrough leveraging on the time-varying property of the system is the proposal of a novel circulator concept based on time-varying transmission line. This approach brings non-reciprocity to transmission lines consisting of only reciprocal material by introducing the time-varying property to the material. The detail of the theory and a complete experimental demonstration is published in IEEE MTT Trans. Oct. 2014. The proposed structure has proven to be broadband, low noise and with good power capacity. It may open up a new way in designing the RF front-end of full duplex radio systems or cognitive radios by providing isolation between the transmitting and receiving paths without the need of a frequency diplexer or a T/R switch.

S. Qin, Q. Xu and Y. E. Wang, “Non-reciprocal components with distributedly modulated capacitors,” IEEE Transactions on Microwave Theory and Techniques, Oct. 2014.

Y. E. Wang, "Time-varying transmission lines (TVTL) - A new pathway to non-reciprocal and intelligent RF front-ends," 2014 IEEE Radio and Wireless Symposium (RWS), vol., no., pp.148,150, 19-23 Jan. 2014.

S. Qin and Y. E. Wang, “Parametric conversion with distributedly modulated capacitors (DMC) for low-noise and non-reciprocal RF front-ends,” IEEE MTT-S Int. Microwave Symp. Dig., Seattle, June 2013.

Y. E. Wang, “Non-reciprocity with time-varying transmission lines (TVTLs),” in IEEE Int. Conf. on Wireless and Information Technology Systems, Maui, HI, Nov. 2012.