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Slot-Loaded Transmission Line Theory for Metamaterial Antenna Applications

  • 표성민 (대학원 컴퓨터·전파통신공학과 전파통신공학전공)

초록/요약

In this dissertation, a novel slot-loaded transmission line, especially slot-loaded composite right/left-handed transmission line (SL CRLH TL), has been theoretically presented and experimentally verified for metamaterial antenna applications. Unlike the conventional composite right/left-handed transmission line, the presented SL CRLH TL provides numerously advantageous features, that is, adjustable Q-factor and controllable TL parameters such as phase constant, characteristic impedance, phase velocity, and group velocity due to the slot on the ground plane. In other words, lowered Q-factor in the resonator of the SL CRLH TL can yield the large amounts of electromagnetic radiation so that highly efficient antenna is realized with respect to increased antenna gains. Moreover, impedance bandwidths of the resonator can also provide dramatic elevations. Thus, the SL CRLH TL may support the best candidate for antenna applications followed with the unique features of metamaterial. To verify the theory of the SL CRLH TL, several kinds of microstrip antennas are investigated. Firstly, the SL CRLH TL and its isotropically arrayed resonators for the antenna realization with improved radiation efficiency are utilized. The SL CRLH resonators with both a rectangular and hexagonal-shaped mushroom structures are investigated. When the slot size of the SL CRLH TL is increased, Q-factor of the resonator antenna is decreased in proportion to the slot size. Experimental results show the radiation efficiency improvement up to 45.6 % for the 9-rectangualr ZOR antenna and 21.4 % for the 7-hexagonal ZOR antenna without degrading radiating performances, respectively. Secondly, the bandwidth and frequency of the half-wavelength resonances in the SL CRLH antenna are investigated. As the quantities of the slot are increased, the slow wave effect in the SL CRLH antenna is elevated. Measured half wavelength resonant frequencies of the SL CRLH antennas were decreased by 1.00 GHz from 7.19 GHz to 6.19 GHz for 9-hexagonal patches and 0.98 GHz from 7.01 GHz to 6.03 GHz for 7-haxagonal patches, respectively due to the slots on the ground plane. In addition, the bandwidths of 10.6 % and 15.7 % are increased for both patches in spite of reduced resonant frequencies of 14 % at both patches, respectively. Thirdly, the SL CRLH TL with inductive ground slots is analyzed to improve bandwidth enhancement. By means of adding lumped chip element inductors on the ground slots, two kinds of resonant frequencies have compounded with neighboring frequencies. As a result, the bandwidth is obtained 16.2 % at combined modes compared with a bandwidth of 0.43 % at only single mode in the antenna without inductors. Fourthly, the offset feeding method based on the SL CRLH antenna is examined for multi-mode multi-band operation. Without complicated modification of the antenna, broad-sided and end-fired radiation patterns are accomplished with different operation frequency. In addition, the unique features of the SL CRLH TL are also adopted for multi-mode operations with improved radiation performance, simultaneously.

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DEDICATION
ACKNOWLEDGEMENTS
ABSTRACT
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
ABBREVIATIONS
CHAPTER
1. Introduction
2. Review of Metamaterial
2.1 Metamaterial and Left-Handed Material
2.2 Transmission Line Approach and CRLH Concept
3. Slot-Laded Transmission Line Theory
3.1 Unit-Cell Structure and Equivalent Circuit Model
3.2 Fundamental Characteristics of SL CRLH TL
3.3 Resonant Modes for Unit-Cell of SL CRLH TL
3.4 Concluding Remarks
4. Zeroth-Order Resonant Antenna with Improved Radiation Efficiency
4.1 Preview
4.2 Antenna Design and Analysis
4.3 Implementation of Zeroth-Order Resonators
4.4 Experimental Results of Zeroth-Order Resonator Antenna
4.4.1 Radiation Patterns
4.4.2 Radiation Efficiencies
4.5 Concluding Remarks
5. Half Wavelength Resonant Antenna with Reduced Size
5.1 Preview
5.2 Antenna Design and Analysis
5.3 Results and Discussions
5.4 Concluding Remarks
6. Inductive Zeroth-Order Resonant Antenna with Broad Bandwidth
6.1 Preview
6.2 Unit-Cell Structure and Equivalent Circuit Model
6.3 Resonant Modes of Inductive SL CRLH TL
6.4 Results and Discussions
6.5 Concluding Remarks
7. Offset-Fed Dual-Band Zeroth-Order Resonant Antenna
7.1 Preview
7.2 Antenna Configuration and Analysis
7.3 Results and Discussions
7.4 Concluding Remarks
8. Offset-Fed Zeroth-Order Resonant Antenna with Enhanced Gain
8.1 Preview
8.2 Antenna Configuration and Analysis
8.3 Results and Discussions
8.4 Concluding Remarks
9. Conclusions
BIBLIOGRAPHY

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