Theoretical and Numerical Analyses of a Quasi-Isotropic Antenna With Almost Everywhere Isotropy

A fundamental radiation limit for quasi-isotropic antennas is rigorously presented utilizing vector spherical modes within the framework of a mode-matching technique. The theoretical derivation is substantiated through diverse numerical analyses demonstrating that quasi-isotropic radiation employing an omnidirectional antenna is realizable with unity gain across nearly all angles and a minimizable antenna gain of 1.1929 (0.7660 dBi) at specific finite angles attributable to the Gibbs phenomenon. Ideal implementation necessitates the introduction of a linear array comprising traditional element antennas such as Hertzian dipoles, half-wave dipole antennas, and microstrip patch antennas. The validation of our array configuration is conducted using the NEC-2 software package, and the resulting quasi-isotropic radiation patterns demonstrate a high degree of agreement. The ratio between the numbers of element antennas and effective Legendre modes governs a relative convergence that influences radiation characteristics, thereby indicating the existence of an optimal ratio for achieving quasi-isotropic radiation while minimizing the mean absolute error (MAE).