| Metamaterials have been becoming a hot topic in electromagnetic engineering over adecade, due to its unique and novel electromagnetic response characteristics. In thisdissertation, first of all, according to its recent development, the metamaterial responsemechanism was in-depth studied and a series of high-performance metamaterials weredesigned. Secondly, these metamaterials were applied into antenna and array designs inorder to improve their radiation performances. Moreover, a series of metamaterialinspired electronically small antennas were studied deeply and widely.In second chapter, according to the recent development of metamaterial technologyand theory, different kinds of metamaterial structures with excellent performances weredesigned. On the one hand, the operation mechanism of H-shaped electric metamaterialwas first analyzed. And then, with the help of equivalent circuit model and electricmetamaterial design principle, by loading effective inductor, effective capacitor andgrounding in steps, its electric resonance frequency was reduced, and theminiaturization of its unit cell was achieved accordingly. At the same time, a dual-bandfolded-wire shaped electric metamaterial with simple and compact configuration andlow mutual coupling between resonators within one unit cell was also introduced. Onthe other hand, according to the physical mechanism of magnetic resonance and mutualcoupling between nearby units of traditional single-ring SRR metamaterial, by loadingsecond co-directional ring and adjusting the center positions of two rings in the SRRunit, a dual-band SRR with uniform and simple configuration and tunable dual-bandoperating performance was obtained. Moreover, by loading tunable inductive arms onthe rings and the additional co-directional ring, a new magnetic metamaterial wasachieved successfully, whose operating frequency band is more than three times widerthan that of single-ring SRR. Finally, the proposed metamaterial unit was tested, and theimpact of the substrate loss tangent on the vibration of its negative effectivepermeability was discussed.In third chapter, application of metamaterial units in antenna design was employed insteps. On the one hand, etching a multiband complementary element of co-directional SRR unit, which was already introduced in second chapter, on the radiator element ofUWB antenna was proposed to attain multiple notched bands. This technique possessedthe advantages of simple structure, small area taken up, and low mutual couplingbetween resonators which provides the convenience of adjusting notched frequenciesand strengths. Further, the phase response and received waveform characteristics in timedomain within the whole UWB range of such UWB antenna were analyzed. On theother hand, with the aid of slotting complementary meander-line magnetic metamaterialunit on the ground of a traditional microstrip patch antenna, the new antenna canoperate at a frequency much lower than the fundamental mode of traditional one, whichhad good radiation performances as well. In view of its operating mode similar toTM120model, the mode of proposed hybrid patch/slot antenna structure at lowestfrequency was called as induced “TM120”. And then, the effect of the meanderline slotperiod on such antenna performance was discussed. Also, in order to expand itsengineering application, the antenna was evolved on the following three aspects: Furtherminiaturization, dual-frequency operation, and back radiation reduction.In fourth chapter, the mutual coupling between adjacent elements of antenna array,the physical mechanism of scanning blindness appearance, and the detailedelectromagnetic field distribution between microstrip antenna elements wereinvestigated. And then, abiding by the metamaterial resonance and responsemechanisms, periodic composite SRR and CSRR metamaterial, and grounded SRRmetamaterial which was already introduced in second chapter, were loaded halfwaybetween antenna elements, respectively. Both of the measurement results demonstratedthat, above metamaterials can reduce the mutual coupling significantly, and accordinglyimprove radiation performance of each antenna element and also the entire array.In fifth chapter, with the aim of developing, enriching, and improving themetamaterial inspired electrically small antenna design theory and technology, relatedresearch was carried out comprehensively. First of all, the relevant definitions andconcepts of electrically small antenna were reviewed, and fundamental theory ofmetamaterial inspired electrically small antenna was introduced. Next, innovativestudies about the metamaterial inspired electrically small antennas with excellentperformances were carried out and can be classified into the following three aspects:(1)An effective method of placing slot-modified, parasitic copper disc in the near field of Egyptian Axe Dipole (EAD) antenna to enhance its broadside directivity was proposed.A multi-antenna array model was used to explain the physical mechanism of loadingdisc into the antenna system to achieve high directivity and front-to-back ratio.(2) Aseries of CSRR loaded electrically small, low-profile, efficient antennas were developed.Compared with traditional monopole, the proposed antennas can provide radiationpatterns with near90°twist at lowest frequency, and thus demonstrated good broadsideradiation.(3) An effective non-Foster method of expanding EAD antenna frequencybandwidth with high directivity was introduced. In the design process, the active circuit,which was integrated on the symmetrical slot edges of parasitic metal plate inelectrically small antenna system, could expand electrically small antenna directivitybandwidth significantly. This method can overcome the tradeoff among impedancematching bandwidth, efficiency, and directivity of electrically small passive antenna.Finally in sixth chapter, the research of this dissertation was summarized and futureresearch was proposed. |
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