Aplicação de superfície seletiva de frequência como refletor reconfigurável para otimização do desempenho de antena de microfita para aplicações em 5G

Abstract

This work presents the development of reconfigurable frequency-selective surfaces (RFSS) as a reflector to optimize the performance of microstrip antenna for 5G applications. Frequency-selective surfaces (FSS) are structures widely used in communication systems, with applications in the microwave to terahertz range. The research in this doctoral thesis includes computation analysis and experimental characterizations to evaluate the effectiveness of RFSS in different propagation scenarios. The initial analysis is performed by characterizing the FSS in its ideal form to predict the behavior of the reconfigurable structure. Then the proposed RFSS is designed and evaluated. The proposed structure consists of a single dielectric substrate with a conductive layer. The RFSS unit cell is based on a V-shaped element and only a single PIN diode is used as an active device per unit cell. The PIN diode on each line of the RFSS is connected in parallel with a very simple biasing network. These structures were designed, optimized, manufactured and experimentally characterized to validate the numerical results, with good agreement between them. Three biasing state configurations are analyzed: off state, on state and intermediate state. Depending on the biasing state, the RFSS can exhibit single- or multi- resonance frequency(ies). The proposed RFSS exhibits independently switchable characteristics that make it suitable for a variety of applications, in its single-band or multi-band configuration. After this analysis, the RFSS were applied to a system with a dual-band rectangular microstrip antenna. The system consists of placing the RFSS in front of the microstrip antenna, acting as a reflector. The antenna used is of the microstrip type with a rectangular patch, which is modified by inserting two T-shaped slots to provide dual-band response at 1.7 GHz and 3.7 GHz. Numerical results were obtained through simulations using the commercial software ANSYS HFSS. By changing the state of the PIN diode, the system increases the antenna gain and reconfigures its radiation pattern, reaching values of 5.6-dB and 5.5-dB gain increase for the first and second resonance frequencies, respectively. The final results demonstrate that implementing RFSS can significantly increase the gain and steering capability of microstrip antennas. It is demonstrated that the proposed approach is viable and offers substantial improvements in antenna performance, making it a promising solution and contributing to the evolution of 5G networks.