Graphene-based patch antenna design with switchable polarization for THz band

Abstract

Today, with the development of technology, antennas with higher bandwidth and operating at higher frequencies have become widespread. Especially in recent years, antennas operating at frequencies of 0.3 THz and above have appeared. THz band antenna applications have gained momentum in the last decade. Of course, advances in material technology have contributed greatly to reaching these frequencies and bandwidths. The most important of these, and the material that forms the basis of our work, is Graphene due to its unique electrical properties. In addition, we aimed to design a microstrip antenna with switchable polarization to eliminate losses such as polarization mismatch or omnidirectional fading. Different surface structures were obtained using copper and graphene on the microstrip antenna. The most important feature of graphene in our study is that its conductivity varies depending on the bias voltage applied to the graphene. In this way, the conductivity of the surfaces using graphene can be adjusted. This makes it possible to realize varying polarizations on a single structure. In the designs, the antenna structure provides Linear Polarization (LP), Right-Hand Side Circular Polarization (RHCP), and Left-Hand Side Circular Polarization (LHCP). The biggest problem in this study and the thesis's main focus was obtaining LP, RCHP, and LHCP with a single feed. In order to realize these polarizations in a single structure, a circular antenna operating in linear polarization was first designed. The next stage of the design was to add structures that would provide circular polarization into the same design. For this purpose, asymmetric slots were added to the structure. An asymmetric slot is actually used to show that the slots shrink clockwise or counterclockwise and are located on the antenna surface. In the study, it was seen that the direction of shrinkage of the slots is the same as the direction of rotation of the currents. To adjust the Axial Ratio, the shrinkage rate of the slots was examined parametrically. Thus, RHCP and LHCP antennas were obtained from the antenna operating as LP. Afterward, graphene was added to the changing slot structure, and the conductivity of these regions was made variable. Thus, we have realized an antenna structure with variable polarization using only one simple feed structure. All designed antennas are simulated using CST Studio Suite.