DESIGN AND ANALYSIS OF GAIN ENHANCED MICROSTRIP ANTENNAS USING METAMATERIALS FOR 5G APPLICATIONS

Abstract

The surge in demand for high data rates has resulted in the exponential growth of wireless communication systems. Thus, there is a requirement for compact, high gain, and Wideband/ Ultra-wideband (UWB) antennas capable of supporting 5G and beyond communication networks has also increased exponentially. With increasing reliance on high data rates, wide impedance bandwidths (BW), Low-latency, and seamless connectivity, antenna systems must evolve to address challenges such as spectrum congestion, gain enhancement, polarisation control, and size reduction. The antenna parameters, such as Gain, Directivity, BW, Polarisation, Radiation Patterns and Efficiency, can be ‘enhanced’ by introducing the Metamaterials (MMTs)/ Metasurfaces (MSs). This thesis presents an in-depth investigation into the design and analysis of gain enhanced microstrip antennas using MTMs/ MSs, and 3D-printed Metastructures. The research is focused on Sub-6 GHz, X-band, and millimetre-Wave (mm-Wave) frequency ranges, covering applications in Internet of Things (IoT), Internet of Vehicles (IoV), CubeSat systems, point-to-point (p2p) terrestrial 5G communication, and Small 5G Base stations. In the Sub-6 GHz band, a UWB Multiple Input Multiple Output (MIMO) antenna is designed to achieve a wide impedance BW of 2.37 GHz to 8 GHz with a fractional BW of 108.58%. The antenna, intended for IoT/IoV applications, integrates an artificial magnetic conductor (AMC) with dual rings to generate dual resonances, enhancing gain and improving port isolation. The 5 × 8 AMC array placement enhances gain up to 7 dBi from a baseline of 2.3 dBi, while isolation is improved to >19.66 dB. Furthermore, essential MIMO performance metrics such as ECC (<0.0037), CCL (<0.12 bits/s/Hz), and TARC (< -10 dB) remain within acceptable limits. The compact size and wide operational BW of the design make it suitable for IoT, WiFi, LTE, WiMAX, and WiFi-6E bands. For CubeSat applications, a circularly polarised (CP) antenna is proposed using a polarisation reconfigurable metasurface (PRMS). By forming a Fabry–Perot cavity with a 9 × 9 PRMS array, the antenna achieves an Axial Ratio BW (ARBW) of 2.31 GHz, closely matched with an impedance BW of 2.41 GHz. The design enhances the gain from 7.3 dBi to 17.1 dBi while achieving compatibility with both right-hand and left-hand CP waves. This antenna design addresses one of the critical challenges in CP antenna design, where ARBW is typically narrower than impedance BW, thereby making the antenna suitable for satellite based communication. In the X-band spectrum, a phase gradient metasurface flat lens (PGMS-FL) is introduced to attain a high gain, narrow beams for p2p terrestrial 5G communication. The PGMS-FL array achieves beamwidths between 13.2° and 16.5° with a maximum gain of 17.7 dBi at 11.2 GHz. The polarisation-insensitive nature of the PGMS unit cells ensures ± ` viii stable CP performance, making the antenna a viable candidate for terrestrial p2p 5G communication. Four distinct antennas are designed and analysed at mm-Wave frequencies to overcome propagation losses and achieve high capacity wireless links. A UWB AMC array is used to enhance the gain of a MIMO antenna from 8.5 dBi to 12.21 dBi while maintaining port isolation above 19 dB. A second MIMO antenna, integrates a PGMS lens for beam tilting to ± 24º, enabling robust non-line-of-sight (NLOS) communication to improve SNR. The third design incorporates double-negative (DNG) unit cells to achieve a gain improvement of 4 dB and a front-to-back ratio increase from 10.81 dB to 20.6 dB, enhancing link reliability. Finally, a 3D-printed metastructure array embedded in a planar dipole antenna achieves flat gain with 0.45 dB variance, i.e. 11.07 dBi to 11.45 dBi across 22 GHz to 26.6 GHz. The findings of this thesis emphasise the importance of unit cell design in gain enhancement, BW widening, and polarisation stability. On the other hand, Symmetry of the MMT/MS structure, polarisation insensitivity, and angular stability emerge as key factors for optimising metastructures for antenna applications. Integrating AMCs, PRMS, PGMS, DNGs, and 3D-printed metastructures with the different antennas across multiple frequency bands demonstrates significant gain enhancements while maintaining compact profiles. Overall, the research outcomes provide compact, high-performance antenna designs suitable for 5G communication. The proposed antennas cover diverse frequency bands, which include WiFi/ WiMAX/ Bluetooth, Mid-band, Sub-6 GHz, WiFi-6E X- band, MVDDS, and mm-Wave band, enabling its applications in IoT/IoV, terrestrial 5G networks, CubeSat communication, and broadband satellite services. By addressing challenges such as narrow BW, low gain, polarisation mismatching, and size, this thesis contributes to the advancement of antenna designs that are efficient, reliable, and adaptable to the evolving needs of modern communication systems. The major highlights of this research are: • Design antennas to cover newly defined frequencies by the FCC (WiFi-6E and MVDDS) with an enhanced gain. • To enhance the ARBW of the CP antenna and increase the gain using MMT or a metal cavity, with a small structure. • Design an antenna with gain enhancement for wide impedance BW, low profile and high directivity. • To achieve gain enhancement for UWB antennas, maintaining antenna size as minimal as possible. • Design an electrically small antenna with flat gain through the operating BW and a high front-to-back ratio.