Investigation On The Miniaturization Of Microstrip Antennas Based On The Backward Wave Property Of Lefthanded Medium

Left-Handed Medium (LHM) represents a novel artificial electromagnetic material with periodic structures, demonstrating negative refractive index and backward wave properties resulted from simultaneously negative permittivity and permeability parameters. And its future is indeed very promising in applications of microwave antennas and circuit components, and significant for both scientific and engineering disciplines. Based on the fundamental analysis of unusual electromagnetic characterizations, this thesis will mainly focus on engineering design of novel LHM structures with high performance, verified by the practical applications in microstrip antennas, to develop comprehensive research on miniaturization techniques based on the phase-compensating effect of practical LHM structures.Firstly, this thesis proposes the theoretical mechanism of LHM phase-compensator acting by the backward wave property, and develops the mathematic models for one-dimensional (1-D) subwavelength cavity resonators in which a combination of a Right-Handed Medium (RHM) and a LHM possessing negative permittivity and permeability has been inserted. Then the ideal is extended to microstrip patch antennas partially loaded by RHM-LHM substrate. Theoretical results illustrate that the RHM-LHM combination can, in principle, both obtain small 1-D cavity resonators and microstrip patch antennas whose resonance relation may not depend on the sum of thicknesses of the RHM-LHM combination, but instead it depends on their constitutive relation parameters. Consequently, the predictions provide important theoretical support for further realization of small microstrip antennas based on practical LHM structures.Then, a cavity-type LHM (CTLHM) structure is proposed with small electrical sizes. It exhibits LHM properties from 9.2 GHz to 11.8 GHz, whose electrical size is only 0.11 wavelengths and reduced by 41% compared with other reported LHM structures. The presence of the left-handed properties of the CTLHM is verified by an investigation on double negative property and backward wave property. And then CTLHM unit cells are stacked and periodically embedded into a host dielectric material to construct a phase- compensating substrate for small patch antennas. Results illustrate that the electrical length of the patch antenna is successfully reduced by 66% based on the CTLHM structures instead of theoretical mathematic models, and breaks through the limitation of half-wave length of conventional patch antennas. Moreover, both near field distribution and radiation patterns of the miniaturized patch antenna are in good agreement with the theoretical predictions.Lastly, based on the technique of reducing working frequency for split ring resonators (SRR) and parallel inductance effects of Defected Ground Structure (DGS), this paper presents two novel distributed planar left-handed microstrip line units, the double layers SRR/DGS (DLSRR/DGS) unit and miniaturized SRR/DGS (MSRR/DGS) unit. By retrieving their effective permittivity and permeability, respectively, their double negative property is verified. And the backward wave property is also verified by the numerical simulations conducted to an array including eight MSRR/DGS LHM units, which demonstrates that the MSRR/DGS array can support unique backward wave very well. Compared with conventional cases, this structure has been reduced 60% in electrical sizes. Finally, a small microstrip loop antenna, partially loaded with MSRR/DGS LHM units, has been designed and simulated. Simulation results indicate that the physical length of the loop antenna has been reduced 26.5%, while its area has been reduced about 54.6%。This paper systematically proposes the fundamental theory of the miniaturization techniques based on the backward wave property of LHM, develops novel approaches for engineering realization and applications. Therefore, the research will significantly promote the progress of LHM toward practical applications, and provide important references and engineering value for the research in related fields.