Abstract:

Small antennas with optimized radiation efficiency and bandwidth are highly demanded in wireless communications. However, it is well known that small size, high radiation efficiency, and wide bandwidth need a design trade. As a fundamental limit, the bandwidth of an antenna is limited by its size as an efficient radiator. However, the fundamental limit theory implicitly assumes that the antenna is linear time-invariant (LTI). In other words, if this assumption does not hold for an antenna, the bandwidth of the antenna may not be limited by its size.

This talk focuses on utilizing the transient response of a narrow-band antenna to create additional resonances based on a time-variant switching mechanism. It is shown that if an antenna is switched at different resonances with a proper speed, reactive energy stored outside of the source region is sufficient to maintain a continuous radiation at each resonance. Using switched capacitors as tuning elements, a multi-band radiator can be realized with a single structure. Furthermore, if the switched capacitors are replaced by a voltage-controlled capacitive load, the resonant frequency can be modulated to result in a wider impedance bandwidth.

Speaker:  

Mohsen Salehi is a Ph.D. candidate of Bradley Department of Electrical and Computer Engineering, Virginia Tech. He received a B.S. degree in Electrical Engineering from Isfahan University of Technology, Iran, in 2003 and an M.S. degree from University of Central Florida in 2009, where he investigated miniaturized frequency selective surfaces. He conducts Ph.D. dissertation research on time-domain radiation and time-variant antennas under Prof. Majid Manteghi's supervision and is a member of the MICS group.