| Travelling-wave antenna is one kind of common used antenna. As one kind of traveling-wave antenna, leaky-wave antenna is usually designed based on traveling-wave structures and is now widely used in many areas. In recent years, the emergence of novel materials and new structures brought new opportunities to the development of leaky-wave antennas. For instance, the studies on the novel leaky-wave antennas based on the composite right/left-handed (CRLH) transmission line structure and the substrate integrated waveguide (SIW) becomes one of the hot research topics in antenna area. This dissertation aims to study the radiation mechanism of travelling-wave structures, and to investigate new structures for leaky-wave antennas employing the new electromagnetic materials and new technologies, in order to improve the radiation performance of the leaky-wave antennas. Specifically, the novel CRLH transmission line leaky-wave antenna, the radiation mechanism of periodic leaky-wave structure with finite length, and the controlling approach of the spatial distribution of the radiation fields of leaky-wave antennas are studied in this dissertation.The main work and innovation points of this dissertation are concluded as follows:1. A novel metal-insulator-metal (MIM) parallel-plate capacitor structure is proposed, whose per-unit-area capacitance can be four times as much as that of the available parallel-plate capacitor, and this kind of capacitor can be used to further compact the CRLH structures. This type of capacitor is then applied in the design of novel CRLH structure, and the transmission property is studied. Based on this new CRLH structure, a kind of leaky-wave antenna is proposed, which is capable of beam scanning continuously with the frequency, while the radiation field around the broadside direction keeps continuous.2. Two kinds of methods for estimating the radiation patterns of CRLH leaky-wave antenna are put forward. One is the improved array factor approach (with oriented current elements as the array elements), and the other is the traveling-wave line-source integration method. Compared with the conventional approaches, these two methods can give accurate results in all the directions of the antenna.3. The theory of effective radiation section (ERS) is proposed for both slow wave and fast wave, and a new explanation on the radiation mechanism of travelling wave is presented based on the ERS. This theory indicates that the far-field radiation is mainly determined by the ERSs, while the radiations of all other sections can be cancelled and have little contribution to the total far fields. The formulas for computing the radiation pattern is derived based on the ERSs, and the effects of the locations of ERSs and the attenuation constant of the traveling-wave structure on the calculation results of the radiation patterns are analyzed.4. Based on the theory of ERS, the approach for generating radiation null region in the radiation pattern of leaky-wave antenna by suppressing the radiations of ERSs is proposed. The relationships of the angular range and depth of the null region with the antenna structural parameters are studied. Then this approach is employed to realized the radiation null region in some particular directions of the long-straight-slot leaky-wave antennas fabricated on the substrate integrated waveguide (SIW), and also the cross polarization can be controlled in a relatively low level.5. The approach for suppressing the sidelobe level of leaky wave antenna is proposed using the ERSs. This approach is then applied in the study of SIW long-straight-slot leaky-wave antennas, and the sidelobe level of the leaky-wave antenna is efficiently reduced, and low cross polarization is achieved.6. The near field constitution of the periodic leaky-wave structure is studied using the spatial harmonic expansion (mode expansion) method. The expansion formula for the harmonic modes contained in the near field is derived in Cartesian coordinate. The convergence of this method is investigated for different aperture field distribution. Based on the analysis, the near-field constitution and the far-field radiation performance of the periodic leaky-wave structure with finite length is analyzed in the case of single-mode radiation, and the influences of the bound modes on the far field are analyzed. The ERSs corresponding to the spatial harmonics are studied. By using the reconstruction method for the far field, it is proved that the radiation fields of the periodic leaky-wave structures with finite length can be calculated by the summation of the fields generated by the corresponding ERSs of the spatial harmonics. |
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