Radiation pattern and impedance of a quarter wavelength monopole antenna above a finite ground plane

This study deals with the radiation pattern and impedance calculation for a quarter wavelength monopole antenna placed at the center of circular and square perfect electric conductor (PEC) ground planes. The analysis is based on analytical approximations as well as on two different numerical methods, namely the Method of Moments (MoM) and the Finite-Difference Time-Domain method (FDTD). The previously known analytical expressions for a quarter wavelength monopole antenna above a circular ground plane were studied in more detail, particularly with regard to their validity constraints. Antenna radiation pattern and impedance were studied for various ground plane dimensions. The simulation results were validated by comparison with analytical results. Achieving excellent agreement for the examined circular ground planes, the MoM was further used to investigate several square ground planes with areas equal to the examined circular discs. Moreover, the convergence of the antenna parameters towards the values for an infinite ground plane was examined. The results showed very slow convergence of the radiation pattern, but quite rapid convergence of the input impedance.