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Abstract
Metasurfaces have many applications, from beam steering effects to polarization control. There are two main theories that are used in the creation of modern metasurfaces, one based on the Huygens-Fresnel Principle and one based on Local Transmission Line models of the metasurface. The Local Transmission Line model is the more commonly used theory, but comparing structures constructed using this method to metasurfaces created using the Huygens-Fresnel principle will show the advantages and disadvantages to each design theory.The Huygens-Fresnel Principle modeled metasurfaces operate on the principle of a duel dipole radiation which is powered by an incident wave. The duel dipoles, electric and magnetic, radiate energy forward and backward from the surface which constructively and destructively interfere with one another. This interference creates the output wavefront as well as backward propagating waves. The metasurface is constructed of various unit cells which contain electric and magnetic dipoles, which are matched to the required transmission coefficient phase and magnitude. If this matching is not perfect, then significant backward radiation can occur and cause errors. Despite this, the output wavefront can be steering in extreme steering angles and with unique behaviour if done correctly.The Local Transmission Line modelled surfaces operate with generalized Snell's Law at its core, which allows the metasurface to guide and transform the incident wave. The metasurface is modelled as a series of admittance blocks on a transmission line, with length of transmission line that correspond to dielectric layers between the admittance layers. The metasurface is also designed to operate multiple input modes simultaneously, allowing for the steering of TE and TM waves at different angles using the same structure. This application is impossible for Huygens-Fresnel modelled surfaces as that theory requires different surface configurations for each operating mode, requiring the dipoles to be oriented normally to the input electric field. However, the Local Transmission Line modeled surfaces decrease in overall length as the desired steering angle increases, which decreases the accuracy of the surface for larger steering angles.Overall, Local Transmission Line modeled metasurfaces have far more application and versatility when compared to metasurfaces designed using the Huygens-Fresnel principle. Although extreme steering angles and unique wave behaviour can be designed using the Huygens-Fresnel principle, the disadvantages in designing such a surface and the errors caused by improper matching of unit cells make this method less versatile. The Local Transmission Line theory requires a less rigorous design process for creating unit cells, and there is room for some error in the admittances that do not compromise the basic functionality of the structure. This theory also lends itself to easier design, as these surfaces can be created directly on dielectrics using current PCB technology.