| Featuring of the zero reflection phase at a special frequency, artificial magnetic conductor (AMC) has been widely researched for the applications of electromagnetic transmission, radiation and scattering. This dissertation is mainly focusing on AMC to improve the performance of antennas and reduce the radar cross section (RCS) of reflection screens.First of all, advances on electromagnetics metamaterials are introduced. And the theory and design methodology of AMC, development of Fabry-Pérot (F-P) antenna system, researches of RCS reduction are expatiated. Then, the numerical method and simulation system utilized in this dissertation are presented as well.If an AMC ground plane is used to replace the metal ground, the height of an F-P antenna can be reduced by half. The design method of F-P antennas is summarized in this dissertation. A ray model is used to explain the principle of the F-P antennas, and several F-P cavities are constructed, including different sizes of the cavities, different types of superstrates and AMCs. The methods of periodic image and receiving mode are used to analyze the F-P cavities. Dipole and microstrip antennas are utilized to excite the cavities. For the cavity of large size, two exciters will get better gain than only one. And the height of the F-P antenna with AMC ground can be reduced more by utilizing characteristic of the AMC phase, though the gain will be reduced only a little. Moreover, several F-P antennas with single microstrip antenna exciter are designed and fabricated. The experiment results have a good agreement with the simulation.Several artificial ground planes, including conventional dielectric substrate backed by a metal ground, a loop type of AMC, and a spiral type of AMC, are studied for their application in dipole and microstrip antennas. And one dipole antenna radiating circular polarized wave is proposed by utilizing the reflection magnitude and phase characteristics of the spiral AMC. Compared with the dielectric substrate, both the loop and spiral types of AMCs reduce the resonant frequency of the microstrip antenna, while maintaining the patch’s linear polarization. Furthermore, the spiral AMC can not only reduce the antenna’s working frequency, but also realize circular polarization at a different frequency, and it realizes the design of dual-band dual-polarization microstrip antennas. Two patch antennas with different circular polarizations are fabricated, and the experiment results agree well with the simulation.Applications of mixed AMCs for designing low-RCS reflection screens are investigated. By utilizing the phase differences between different AMCs, the energy will be cancelled at some directions and redirected into other directions, and then the RCS at some direction is reduced. Two types of AMC blocks are arranged in a checkerboard structure. For normal incident electromagnetic wave, the monostatic RCS will be reduced in a wide frequency band and the energy is redirected into four diagonal directions of the screen. If the two types of AMC blocks are arranged in a fan-type to construct a screen, the reflection energy will be redirected into more directions. For oblique incidence, the RCS characteristics of the two screens are investigated. The method of array factor is used to establish the computational model for AMC screens, in which the different AMC blocks are located in arbitrary ways. An example with random distribution of AMC blocks is studied. The results of the model are validated with simulation, and verify the effectiveness of the methodology. |
