چكيده به لاتين
In this thesis, the designing steps for two-dimensional isotropic and anisotropic Huygens metasurfaces excited by real sources in both transmission and reflection modes are investigated. After that these designed structures are employed in a practical problem. According to the design process of one-dimensional Huygens metasurfaces, the first and most important design step is to obtain the distribution of surface parameters equivalent to these metasurfaces. Here, the necessary relations to calculate these equivalent parameters for isotropic Huygens metasurface have been obtained. Here, the proposed method is investigated for both cases even one the metasurface is located in the far-field region or near field region of excitation source. For this purpose, in the first step, spherical waves have been expanded in terms of plane waves in the spectrum domain, and then by applying the generalized layer transition conditions and using the two conditions of local power conservation and local impedance equalization, the required equivalent parameters have been obtained. The obtained relationships are useful in many practical applications. In this thesis, with the aid of the presented method, a two-dimensional Huygens metasurface has been designed to control the horn antenna pattern, and in the next step, another suitable metasurface has been designed to improve the efficiency of a transmit-array antenna. Also, to validate the results, the designed metasurfaces have been physically implemented and tested in the antenna chamber. The simulation and measurement results are compared with each other and also with other works which prove both aforementioned designed structures provide better efficiencies in comparison to the other works done in these fields.
In addition, the distribution of surface parameters equivalent to two-dimensional anisotropic Huygens meta-surfaces has been obtained. Using this type of metasurface, any desired polarization transformation can be created. The designed metasurface is realized using a novel wire / loop unit cell for the first time in this thesis. Using this method and the suggested unit cell, an LP to CP transmitarray is designed and simulated. The simulation results show the polarization conversion is done properly with a good efficiency.
Finally, two-dimensional Huygens meta-surfaces are developed in reflective mode. For this purpose, based on Floquet theory, the necessary designing steps are investigated. By setting the periods correctly and selecting the number and dimensions of the elements placed in each period, a reflective beam can be created in the desired direction with almost perfect efficiency. Then, this method has been used to design a reflectarray, the resulting structure have variable periods in both transversal directions. This structure, in addition to providing a suitable reflective efficiency in the desired direction, has the feature of the frequency scanning of the antenna beam, which could not be achieved using common reflectarrays.
