From kHz to THz: Exposing Limitations of Rao-Wilton-Glisson Basis Functions in Method-of-Moments Simulations of Practical Monopole Antennas

The radiation efficiency and gain of all-metal antennas are critically influenced by their geometric design, particularly the cross-sectional and axial configurations, due to the conductive losses governed by the frequency-dependent skin effect. This study numerically investigates these effects through computational simulations of one-quarter-wavelength monopole antennas—common in vehicular applications—using a dedicated MATLAB-based Method-of-Moments (MoM) solver. Unlike idealised perfect electric conductor (PEC) models, we analyse practical copper-based square-rod monopoles with finite conductivity, evaluating their performance for devices across an ultra-wideband spectrum (1 kHz–200 GHz) relevant to emerging wireless and 5G/6G vehicular systems. Our analysis quantifies metallic losses, computational limitations of MoM solvers at extreme frequencies, and trade-offs in antenna design for mobile platforms. The results provide key insights into conductor loss trends and numerical modelling challenges, offering guidelines for optimising antenna efficiency in high-frequency regimes.