Performance enhancement of small antennas and applications in RFID: Dissertation

The focus of this thesis is on the performance enhancement of small antennas and design and verification of antennas for radio frequency identification (RFID) and wireless sensors. The work is presented in eight scientific papers and in a summary, which introduces relevant fundamental concepts and previous work done in the field of small antennas. Previously, several performance enhancement methods have been proposed to improve the antenna performance especially in mobile communication applications. However, solutions for the fundamental small antenna problem, high reactive energy and low radiation resistance, which in practice lead to narrowband and low efficiency operation, are rarely provided. In this thesis, alternative methods to alleviate the high reactive energy and low radiation resistance like material loading, non-Foster tuning and multi-port loading are discussed. Also, lately antennas for RFID and wireless sensor applications have gained growing interest. However, several characteristic design features exist for these antennas. Especially, the concept of platform insensitivity is essential and discussed in detail. Also, antenna designs and dual-band tuning technique applicable to RFID antennas are presented. In addition, wireless measurement techniques for RFID antenna verification are reported.