A Modal Approach to Tuning and Bandwidth Enhancement of an Electrically Small Antenna

We describe the physical phenomena that contribute to the behavior of an electrically small TM
₁₀
antenna using characteristic mode theory. The application of characteristic modes to antenna tuning and bandwidth enhancement serves as demonstration of the broad utility of the modal technique. A modal analysis of the TM
₁₀
antenna's impedance match yields several interesting observations as to the nature of resonances and antiresonances, which has implications for the impedance matching of small antennas in general. Furthermore, to overcome the bandwidth limitations inherent in small antennas, we determine that multiple resonances must be combined and use a conductance ratio as a figure of merit for design. We then investigate the TM
₁₀
antenna's potential for multiresonant operation by examining different candidate modes. Using the appropriate characteristic modes to form multiple resonances, we show how the bandwidth of the TM
₁₀
antenna can be designed to be nearly double that expected from the physical limit for a single resonance.