چكيده به لاتين
In this thesis, the concept, analysis and synthesis of 1D and 2D graphene leaky wave antenna (LWA) at terahertz band are presented. First, it is shown that the fundamental limitation of devices based on the planar graphene waveguide (PGW) is their low quality factor (resulting from the high attenuation constant due to the graphene losses). High attenuation constant limits the radiation efficiency and beam-width of LWAs. Then two novel 1D LWAs are proposed based on the cylindrical graphene waveguide (CGW). The proposed structure has overcome the fundamental limitations of the planar LWA characteristics, such as radiation efficiency and beam-width. The designed antenna in comparison with planar leaky wave antenna has significantly improved radiation efficiency by 20% to 50%. Next, the analysis and synthesis of 2D graphene LWA is studied. The analysis and equivalent circuit of complementary graphene patch (CGP) cell are presented for the first time. The graphene patch (GP) cell, which is commonly used in the design of terahertz metasurfaces (specially antennas), suffers from several challenges, such as additional lines for DC connecting cells and their effects on the radiation patterns, the limited range of structure for supporting TM surface plasmonic polariton (SPP) waves, the low confinement and quality factor of structure and impractically small synthesized dimensions. It is shown that the proposed CGP structure overcomes all these challenges. Then a novel 2D leaky wave antenna based on CGP unit cell is designed using the holographic antenna theory. The proposed structure is realized by a single bias voltage applied to the graphene sheet. Consequently, the radiation direction can be easily swept by tuning this bias voltage. Next, for the first time, the concept, analysis and equivalent circuit of Phoenix Graphene Patch (PGP) unit cell is presented. It is shown that a full 360o phase range can be realized by this unit cell unlike the common Graphene Patch (GP) unit cell by only changing separately the physical or electrical parameters. Then a reflectarray antenna based on PGP cell is designed. The required phases are easily realized only by changing the element dimensions of cell. Finally, a programmable vortex beam reflectarray is proposed whereby the required phases are realized only by the chemical potential of graphene sheet. The structure is discretized to five sections in the radial direction and eight sections in the azimuth direction. In comparison to other structures, the proposed design can easily generate different vortex beams in real-time by changing the biasing voltages of these sections.
