Graphene is a 2D material which is consisted of carbon atoms arranged in hexagonal lattice and because of special electrical, thermal and mechanical characteristics is attracted a lot of attention in recent years. Graphene, due to the supporting surface plasmons propagation, is used in design and fabrication of many microelectronic and nanoelectronic devices such as waveguides, transistors, filters, absorbers and antennas in terahertz. Most impoatant feature of graphene, in comparison to metals, is its tunability. The surface conductivity of graphene is tunable with the aid of electric bias field and on the other hand, it turns into tensor in the precense of static magnetic field. For this reason, graphene shows gyrotropic and nonreciprocity effects and causes Faraday rotation in transmitted wave. The nonreciprocity of graphene can be used in design of circulators and isolators. Faraday rotation is almost independent of frequency in microwave and is about of a few tens of degrees. On the other hand, it is low in terahertz and increasing of it, is a challenge in this area. Using graphene in design of different devices needs to suitable numerical methods for its analysis. There are two ways for graphene modeling. In the first way, graphene is considered as a dielectric by very small thickness. This method needs to fine meshing which increased the requirement memory and simulation time and so, it is not suitable from point of view of computational resources. In the second way, the thickness of graphene is assumed zero and effect of graphene is taken into account in boundary conditions. In the present, most of commercial EM solvers cannot analyze magnetically biased graphene while the others model the graphene using dielectric approach. Using graphene in periodic structures can be result in design of tunable devices for controling the reflection, transmission and polarization of electromagnetic waves. Therefore, in this thesis, for the first time, a transmission-line formulation which is a Fourier-based numerical method is used to diffraction analysis of magnetically-biased periodic structures. To increase convergence rate, true Fourier expansion which is inverse rule is recognized based on Li’s factorization rules. The surface conductivity is zero in some area of unit cell and the true Fourier expansion is not applicable. So, the approximate boundary condition which is proposed for analysis of unbiased graphene arrays, is expanded. Using the implemented numerical method, some of available structures in papers are simulated to verify the high accuracy and speed of method. Moreover, a wideband absorber is designed and simulated by this method. The high attention is devoted to analyze Faraday rotation effect and its challenges in terahertz regime. In according with the applications of Faraday rotation and its challenges, more exact investigation and exploiting new structures to increase this effect are proposed for future researches. Key Words : 1- Graphene, 2- Plasmonics, 3- Transmission Line Formulation, 4-Periodic Structures, 5- Non-reciprocal Devices, 6- Faraday Rotation.