DESIGN AND ANALYSIS OF RECONFIGURABLE ANTENNAS FOR WIRELESS APPLICATIONS

Abstract

In this thesis, frequency and compound reconfigurable antennas (frequency and pattern, frequency, pattern, and polarization) are designed and analyzed for sub-6 GHz 5G, Wi-Fi 6E, vehicular, and Internet of Things (IoT) applications. However, already existing reconfigurable antennas are limited to narrow bandwidth and large size and utilize more RF switches for their reconfiguration. Due to these, the complexity of wireless systems increases, and the performance may be degraded. Therefore, to maintain better performance over a wide frequency range, a partial ground concept and fewer RF switches are utilized to achieve compound reconfiguration with a compact size. Initially, a compact-size hexagonal-shaped frequency reconfigurable antenna is investigated by implementing the switchable slot on the ground plane, operating at 3.8 GHz and 3.6 GHz for new C-band 5G networks. Further, a V-shaped slit frequency reconfigurable antenna is implemented by incorporating the PIN diode MADP000907-14020 P at a suitable position on this slit and operating its ON and OFF states, obtained dual-band, operating at 3.9 GHz and 6.37 GHz in the ON state of the PIN diode. In the OFF state of the PIN diode, a single band is obtained, operating at 5.5 GHz for Wi-Fi applications with compact size and wideband operation. For IoT close-range applications, along with frequency reconfiguration, a pattern reconfiguration is also required for better spectrum utilization with minimal interference. Therefore, a frequency and pattern reconfigurable antenna is investigated in further chapters based on the Yagi-Uda principle. The reported structure provides omnidirectional and directional patterns that operate at 5 GHz and 4.3 GHz, respectively, at three distant modes by connecting and disconnecting the two parasitic stubs on the ground plane through two PIN diodes. However, this structure is limited to frequency and pattern reconfiguration. To obtain three reconfigurations, namely frequency, pattern, and polarization in a single structure with a lesser number of PIN diodes for wireless and automotive applications operating in the sub-6 GHz (n77/n78 bands), a compound reconfigurable electronically switched parasitic monopole antenna is designed and analyzed. The design has two inverted L-shaped parasitic stubs and a half-hexagonal radiating element, both of which are coupled to a PIN diode for reconfiguration in frequency. Furthermore, comparable parasitic stubs are integrated into the ground plane via PIN diodes, allowing for pattern tilting and polarization reconfiguration. The antenna supports three polarization states, namely linear, left-hand circular, and right-hand circular polarization, and it achieves pattern tilting from boresight to end-fire at the target bands. The PIN diode operating configurations enable the realization of these polarization states. Multiband antennas are desired instead of implementing different radiating structures for each band in modern communication systems. Along with multiband, for long-range coverage, high- gain antennas are v preferable. So, here, a structural symmetry of a half hexagonal-shaped radiating element and split ring resonators is proposed for multiband and pattern tilting capability. Further, a Frequency Selective Surfaces (FSS)-based reflector is kept below the radiating element, and a gain is improved to 50% compared to without a reflector. Also, pattern tilting is obtained independently of frequency in three directions from this structure. A full-wave electromagnetic simulator such as ANSYS High-Frequency Structure Simulator (HFSS) predicts the reported reconfigurable antennas' performances, which are fabricated and measured by the required parameters. They are compared with other cutting-edge antennas proposed for similar applications to verify the concepts and design performances.