Design, Simulation and Measurements of Graphene-based THz Antennas for Future 6G Communications

The terahertz (THz) frequency band is among the key technologies being investigated for future 6G communication systems. Over the past years, wireless communications have increasingly used higher frequency bands in pursuit of greater bandwidth and integration capabilities. This technological advancement has facilitated the emergence of short-range applications, including data kiosks, wireless chip interconnects, and intra-body networks, electronic components placed within the body to monitor health. Additionally, because passive devices are smaller at higher frequencies, it is possible to fit more antennas into the same area, resulting in arrays that produce increasingly focused beams. Given the significant spreading losses and molecular absorption at this frequency range, THz communications are particularly well-suited for short-range applications where spatial limitations are key or extremely high bandwidth is necessary. Moreover, the THz and millimeter wave (mm-wave) wireless communications for intra-chip and chip-to-chip connections can enhance the already constrained wired interconnects within computing packages, helping to alleviate communication bottlenecks in future computing platforms that may contain hundreds or thousands of processors in a single package. Adopting compact antennas and transceivers as wireless interconnects within computing packages will lead to low-latency and reconfigurable communication pathways, reducing the complexity of the dense wired interconnect network.
The main problem with the current wireless network inside chips is the size of the antenna. Reducing the size of a metallic antenna to just a few micrometers leads to poor performance due to the low conductivity of the metal at these small dimensions, and using such small antennas would require very high frequencies, around hundreds of THz, which are not suitable for radio frequency (RF) wireless communications due to issues with signal loss and transceiver design. Hence, technological advances in antenna development are essential for implementing future communication systems at THz frequencies. Thus, graphene-based antennas appear as the ideal complement to traditional metallic antennas due to their potential for smaller dimensions and frequency tunability in the THz range. Graphene antennas operating at THz frequencies are smaller than their metallic counterparts functioning at the same frequency,
thereby advancing the boundaries of integration further. The research, design, and investigation of THz graphene-based antennas are the focus of this thesis.
This work addresses the graphene material characteristics and plasmonic behaviors directly related to a functioning THz graphene-based antenna. Moreover, three different graphene-based antenna types, with different working principles, operating at THz frequencies are investigated, i.e. two different types of photoconductive antennas (graphene dipole and graphene patch antennas), and an electronic antenna (graphene patch and graphene stack patch antennas). Theoretical explanations regarding the principles of THz emission of each antenna type are presented, as well as descriptions regarding the measurement systems utilized to characterize these antennas. Studies regarding antenna emission are made by electromagnetic (EM) simulations and proper measurements. The further investigation of antenna frequency tuning and antenna efficiency in the THz range is based on simulations varying important graphene antenna characteristics. The measurements show not only THz emission from the graphene-based antennas but also the THz emission tuning of the antennas based on an electrostatic bias. Additionally, a THz graphene antenna array is studied by means of simulations. Finally, the challenges and feasibility of having efficient THz graphene-based antennas are discussed, and possible future development steps are suggested.