Optimization of terahertz sub-wavelength limited waveguides for 6G applications

For the effective use of 6G and beyond applications, it is important to make the terahertz frequency band available with features such as having a large amount of free bandwidth and being able to share data at the terabit level per second with low latency. In order to benefit from these unique features of the terahertz frequency band, there is a need to develop terahertz integrated circuits and terahertz passive circuit elements with the best performance at terahertz frequencies, which will enable the connection of active elements in a terahertz integrated circuit. In this context, it is anticipated that Spoof Surface Plasmon Polariton-based circuits, which consist of metal on the dielectric substrate with corrugations on both sides and have previously performed well at microwave and low terahertz frequencies, will also perform well at real terahertz frequencies. The studies carried out in this thesis aim to develop a universal method for the design of passive circuit elements such as waveguides, phase shifters and power dividers, and the optimization of these circuits by using the Spoof Surface Plasmon Polariton phenomenon at real terahertz frequencies. For this purpose, first of all, transition circuits that will enable the transition from coplanar waveguides to Spoof Surface Plasmon Polariton circuits with minimum loss are designed to operate at 1 THz frequency. In the design of transition circuits, attention has been paid to impedance matching and mode conversion. Then, radiation, conductive and dielectric loss analyses of circuits with different physical dimensions were made using simulation programs. These loss analyses were used to optimize the circuits and Spoof Surface Plasmon Polariton circuits working with the best performance at 1 THz frequency were obtained. For optimized circuits, a model based on the effective waveguide and therefore the guided wavelength has been developed. In this way, the physical dimensions of Spoof Surface Plasmon Polariton circuits, which also work with the best performance at other frequencies, have been determined. These designs can be easily produced with a single layer, and the production steps have been optimized accordingly. The designs were realized with optimized production steps by adding the structures required for measurement. The measurement of the produced structures was completed by applying calibration and the designs were compared with the simulation results to confirm. In addition to these studies, Spoof Surface Plasmon Polariton circuits operating at a frequency of 0.3 THz were designed and produced. With these structures, the best loss per unit length (dB/mm) and degree per loss (°/dB) results were obtained at 0.3 THz frequency.