| The electrical permittivity e and the magnetic permeability μ are the fundamental characteristic quantities that determine the propagation of electromagnetic waves in matter. Almost all of the natural materials have positive permittivity, e and permeability,μ . In 1968, Veselago introduced the concept of left-handed metamaterial------a mediumin which both the permittivity and permeability are simultaneously negative. Although metals have a negative ε and ferromagnetic or antiferromagnetic materials have α negative μ, no known materials exist in nature with simultaneously negative e and μ. Veselago's analysis with ε and μ both negative have remained a curious exercise in electromagnetic theory and present a variety cf unusual electromagnetic and optical properties, such as Doppler shift, Cherenkov radiation, negative refraction effect and perfect lens, etc. However, in the mid-1990s, Pendry et al. suggested a model of periodic array on thin metallic wires to simulate plasma and obtained a negative ε -(eff) below the plasma frequency. An array of split ring resonators (SRRs) was adopted to realize a negative μeff at the region close to the resonance frequency. By combining SRRs and wires, Smith and his collaborators first demonstrated the negative index of refraction of LHMs. The discovery of left-handed material has been regarded as one of the ten most significant discoveries in science community in 2003, and has been the front and focus area in physics and electromagnetics research.We systematically investigate nonsymmetrical structural character of LHMs in waveguide and space and design left-handed metamaterials antennas. The original works and valuable results of this dissertation are as follows:1, The transmission and reflection phenomena of LHMs, which is a designed center nonsymmetrical structure composed of copper SRRs and wires in the X direction, and the influence of the center distance of the SRRs and wires to the left-handed peaks are investigated using a rectangular waveguide system. It shows that the transmission spectra of the LHMs demonstrate an M-like shape, namely that a stopband appears in left-handed passband, and the position of stopband is adjusted by the center distance of the SRRs and wires. And the presence of the nonsymmetrical structure increases the intensity of the transmission peak and width of the left-handed region. The reflection spectra of the center nonsymmetrical LHMs demonstrate a W-like shape, and the maximum of the reflection spectra is good agreement with the stopband of the transmission peak of the LHMs. At the same time, the W-like reflection spectra have a blue-shift compared with the M-like transmission spectra. According to the study of thenonsymmetrical structure of different types, the appearance of the stopband in the transmission spectra of LHMs can be attribute to (1) the nonsymmetrical electromagnetic coupling effect of the SRRs and wires;(2) the coupling effect of the split side with the up and down wall of the waveguide.2> The transmission and reflection phenomena of LHMs, which is a designed center nonsymmetrical structure composed of copper SRRs and wires in the Z direction, and the influence of the center distance of the SRRs and wires to the left-handed peaks are investigated using a rectangular waveguide system. It shows that the single peak of transmission spectra of the LHMs turns into an M-like double peaks when the center distance of the SRRs and wires changes from 0 to a/2, where a is the crystal lattice constant, namely that a stopband appears in left-handed passband, and changes to a single peak again with the increase of the center distance of SRRs and wires. The appearance of the stopband can increase the width of left-handed region and enhance the intensity of the transmission spectra. As a word, the center nonsymmetrical degree of the SRRs and wires can be used to the modulation of the width and intensity of the M-like left-handed transmission spectra. The width and intensity of the left transmission spectra decreased gradually along with the increase of the width and intensity of the right transmission spectra when the center distance changes from 0 to a/2. The reflection spectra of the center nonsymmetrical structure of RRs and wires in the Z direction also exhibits a W-like shape, and the stopband in the left-handed transmission spectra is good agreement with the maximum of the reflection spectra. The further study proved that the appearance of the stopband in the left-handed transmission spectra could be attributed to the nonsymmetrical coupling effect between the SRRs and wires.3-. Design microwave darkroom, buy absorber materials and cables, finally put up the testing system ,which is used to test the transmission and reflection phenomena of materials in spatial. We investigated the influence of the length of the wires to the resonance frequency co0 in spatial. It shows that the electric continuity of wires can beenhanced and the resonance frequency co0 can be reduced through adjusting the length of the wires. Design the special wires that are connected by two metal bars and find the resonance frequency co0 can be reduced more.4^ The transmission and reflection phenomena of LHMs in spatial are investigated, which is a designed nonsymmetrical structure composed of copper SRRs and wires. It shows that the single peak transmission spectra of the LHMs turns into an M-like double peaks when the position of the two rows of SRRs is adjusted, namely that a stopband appears in left-handed passband, and the position of stopband is adjusted by offset 5 of the two rows of SRRs. With the increase of offset 6 the stopband move gradually to lower frequencies which is good agreement with the law in waveguide andthe difference of intensity of the left-right transmission spectra increases firstly then gradually reduces. Comparing the transmission spectra of nonsymmetrical structure with the transmission spectra of symmetrical LHMs, we find that the resonance frequency of the transmission spectra of the LHMs moves to higher frequency. For enhancing nonsymmetry, we adjust simultaneously the position of three groups of two rows of SRRs and find the transmission spectra of the LHMs demonstrate an M-like shape, namely that the single peak of transmission spectra of the LHMs turns into an M-like double peaks. With the increase of offset 5 , the intensity of the left transmission spectra decreased gradually along with the increase of the intensity of the right transmission spectra, namely that "left higher, right lower" to "left lower, right higher". The reflection spectra of nonsymmetrical LHMs also exhibits a W-like shape when the transmission spectra demonstrate an M-like shape, and the frequency of the maximum peak of reflection move to lower frequency with the change of the position of the nine row and ten row SRRs. The appearance of the stopband in the transmission spectra of LHMs can be attribute to (1) the nonsymmetrical electromagnetic coupling effect of the SRRs and wires;(2) the nonsymmetrical coupling effect between SRRs.5,The research of patch antennas based on left-handed matematerials(LHMs) structures is a relatively new area. The goal is to improve the performance of the patch antennas by using the special features of LHMs structures. A patch antenna with LHMs as the substrate has been designed. It is shown that the surface waves are suppressed, the frequency bandwidth is improved by 125MHz, the gain in the forward direction is improved by 2.82dB. The return loss of the patch antenna is reduced, namely that the impedance matching is ameliorated. In conclusion, in the present experimental research works have been carried out intensively on patch antennas based on LHMs. It is shown that LHMs can greatly improve the performance of the patch antennas. |
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