Type of Document	Dissertation
Author	Yang, Taeyoung
Author's Email Address	mindlink@vt.edu, mindlink@ieee.org
URN	etd-09142012-105056
Title	Fundamental Limits on Antenna Size for Frequency and Time Domain Applications
Degree	PhD
Department	Electrical and Computer Engineering
Advisory Committee	Advisor Name Title Davis, William A. Committee Co-Chair Stutzman, Warren L. Committee Co-Chair Beattie, Christopher A. Committee Member Ellingson, Steven W. Committee Member Reed, Jeffrey Hugh Committee Member
Keywords	Antenna Radiation Physics Near-Field Interaction Ultra-Wideband Antenna Antenna Transfer Function Fundamental-Limit Theory on Antenna
Date of Defense	2012-09-03
Availability	restricted
Abstract As ubiquitous wireless communication becomes part of life, the demand on antenna miniaturization and interference reduction becomes more extreme. However, antenna size and performance are limited by radiation physics, not technology. In order to understand antenna radiation and energy storage mechanisms, classical and alternative viewpoints of radiation are discussed. Unlike the common sense of classical antenna radiation, it is shown that the entire antenna fields contribute to both radiation and energy storage with varying total energy velocity during the radiation process. These observations were obtained through investigating impedance, power, the Poynting vector, and energy velocity of a radiating antenna. Antenna transfer functions were investigated to understand the real-world challenges in antenna design and overall performance. An extended model, using both the singularity expansion method and spherical mode decomposition, is introduced to analyze the characteristics of various antenna types including resonant, frequency-independent, and ultra-wideband antennas. It is shown that the extended model is useful to understand real-world antennas. Observations from antenna radiation physics and transfer function modeling lead to both corrections and extension of the classical fundamental-limit theory on antenna size. Both field and circuit viewpoints of the corrected limit theory are presented. The corrected theory is extended for multi-mode excitation cases and also for ultra-wideband and frequency-independent antennas. Further investigation on the fundamental-limit theory provides new innovations, including a low-Q antenna design approach that reduces antenna interference issues and a generalized approach for designing an antenna close to the theoretical-size limit. Design examples applying these new approaches with simulations and measurements are presented. The extended limit theory and developed antenna design approaches will find many applications to optimize compact antenna solutions with reduced near-field interactions.
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