MODELLING AND CHARACTERIZATION OF A WIDEBAND PIFA-PAIR MIMO ANTENNA FOR IMPROVED EFFICIENCY IN 5G SMARTPHONES

Abstract

The rapid rise in demand for high-speed data has driven the adoption of 5G technology, which achieves large bandwidth by exploiting high-frequency bands: the millimetre-wave (mm-wave) range and the sub-6 GHz range, jointly referred to as the 5G New Radio (NR) frequencies. The sub-6 GHz band, or Frequency Range 1 (FR1), extends up to 6 GHz, while the mm-wave band, or Frequency Range 2 (FR2), spans 24 GHz to 100 GHz. Smartphone antennas operating in the sub-6 GHz band are constrained by limited bandwidth and efficiency, which restricts the data rates achievable by 5G-enabled devices. This is the problem addressed by this study. A previously reported Planar Inverted-F Antenna (PIFA), adopted in this study as the reference (benchmark) antenna, covered only 78% of the required 3.0–7.5 GHz sub-6 GHz band and achieved an overall efficiency of between 40% and 78% within this band. The main objective of this study was therefore to improve on both the bandwidth and the total efficiency achieved by the reference antenna. To achieve this, a wideband, Planar Inverted-F Antenna (PIFA) based on Multiple-Input Multiple Output (MIMO) antenna intended for 5G smartphones operating over 3.0–7.5 GHz was designed. Four antenna models with constant substrate and ground-plane dimensions but varying patch and slot thickness (0.2 mm, 0.4 mm, 0.6 mm and 0.8 mm) were modelled and simulated using Computer Simulation Technology (CST) Studio Suite, which was adopted because it was readily accessible to the researcher, is widely used and validated in the antenna-design literature, and offers a user-friendly finite-integration solver suited to the scope of this study. Relative to the reference antenna (the benchmark), the four proposed models did not improve the impedance bandwidth, which remained at approximately 4.0–7.5 GHz (78%) for a -6 dB reflection-coefficient criterion. However, the overall efficiency improved considerably, ranging from a minimum of 43.8% (0.2 mm patch, 3.3 GHz) to a maximum of 99.19% (0.4 mm patch, 5.0 GHz), compared with the reference antenna's 40-78% over the same band. A key assumption and limitation of the study is that the substrate used (FR-4, relative permittivity 4.3) differs slightly from the 4.4 permittivity of the reference antenna's substrate, which may partly account for the shortfall in bandwidth improvement and means that the comparison with the benchmark, while indicative, is not a strictly like-for-like validation. Fabrication and physical measurement of the antennas were not undertaken, and only the sub-6 GHz band was considered. Further research is recommended to fabricate and measure the proposed designs, to repeat the comparison using a substrate of identical permittivity to the reference antenna, and to extend the design to the mm-wave band. Since the efficiency gains achieved are significant, the design approach also merits further evaluation for adoption by antenna and smartphone manufacturers seeking to improve radiation efficiency in sub-6 GHz 5G handsets.