| Left-handed metamaterials(LHMs)are a kind of man-made electromagnetic metamaterials,which have both equivalent negative permittivity and permeability,that exhibit a series of unique characteristics,attracting great attentions in the areas such as cloaking,absorbing materials,antennas,microwave circuits,and so on.However,LHMs with only one left-handed band no longer satisfies the requirements of science and technology development,but multi-band and tunable characters have become a hot research topic.Based on this situation,this dissertation starts from the generating mechanism for equivalent negative permittivity and permeability,with the help of the equivalent circuit analysis method,the full-wave simulation analysis method,and the S parameters retrieval method,surrounds the design of multi-band LHMs and its applications in miniaturized antennas.Detailed work is listed as below:1?Aiming at the problem that it is difficult to add frequency bands with LHM property in multi-band LHM designs,proposed a novel design method that is based on the coupling between neighbouring units to introduce additional magnetic resonance to build multi-band LHMs,designed a dual-band LHM.Firstly,designed a single band magnetic negative metamaterial,then neighbouring metallic structures are connected through metallic short wires to bring in new magnetic resonance,and further combined with arrayed metallic wires hence designed a dual-band LHM.This dissertation used equivalent circuit method analyzed the magnetic resonance based on the coupling between units in detail,together with full-wave simulation and S parameters retrieval analysis,identified the dual-band double negative property of the designed LHM,and also the efficiency of the proposed method.Studied the multi-band LHM design method based on the coupling between substrate to introduce additional magnetic resonance,designed a triple-band LHM.Firstly,designed a single-sided single band rectangular split ring structured LHM,then copied this structure to the other side of the substrate and central rotated 90 degrees,designed a triple-band LHM.This dissertation used equivalent circuit method to analyze the magnetic resonance based on the coupling between the substrate in detail,together with full-wave simulations and S parameters retrieval analysis,identified the triple-band double negative property of the designed LHM.2?Aiming at the problem that the lack of basic units brought difficulties in the design of multi-band tunable LHMs,proposed a tunable LHM basic unit,which is composed of a variable capacitor loaded coplanar short wire pairs.Through the theoretical analysis of the mechanism of generating negative permeability for metallic split ring resonator basic unit,pointed out that negative permeability is irrelated with the structure's style,and combined the analysis on short wire pairs LHMs,hence designed this tunable LHM basic unit which has simple structure and easy to fabricate.Simulation study indicated that this basic unit exhibits wide band negative permittivity and tunable negative permeability.This dissertation designed a dual-band tunable LHM by composing the tunable LHM basic unit with double slits ring resonator,a triple-band tunable LHM by composing the LHM basic unit with single loop resonator.Using full-wave simulations and S parameters retrieval method to analyze the dual-band and triple-band tunable LHM,and fabricated and tested the triple-band LHM,identified that the proposed LHM basic unit can efficiently reduce the difficulties in the design of multi-band tunable LHMs.3?Proposed a novel LHM multiplexing design strategy for miniaturized multi-band LHM antennas,which applys LHM to improve antennas' performance while using the LHM unit itself as a radiation unit to generate another working band without physical changes on the LHM antenna's structure,hence brought convenient in the design of miniaturized multi-band LHM antennas.Designed two miniaturized WLAN/WiMAX antennas based on LHMs.The first antenna is composed of a single-band LHM and a ‘T' style antenna with a physical size of 22mm×13mm×1mm.Full wave Simulations and radiation performance analysis on this LHM antenna indicated that the designed antenna fulfilled the requirements of WLAN/WiMAX antennas.The second antenna is composed of a ‘G' style antenna surrounding the multi-band LHM based on the coupling between substrate,and its physical size is only 24mm×18mm×1mm.The designed antenna was simulated and measured,and the generating mechanism for each working band weere analyzed in detail.The studied results indicated that the designed antenna exhibits good radiation performance,satisfying the design requirements of WLAN/WiMAX.Compared to recent reported miniaturized WLAN/WiMAX antennas that exhibit similar radiation performance,the designed antenna in this dissertation has the smallest size.This design also identified the efficiency and advancement of the proposed LHM multiplexing design method. |
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