Design of circularly polarized and electrically small antenna with omnidirectional radiation pattern

This paper presents an electrically small and circularly polarized antenna with an omnidirectional radiation pattern. The antenna consists of a horizontal loop element enclosed by two U-shaped elements and a vertical element from the feeding point. The radiation pattern of the circular polarization is omnidirectional and has a maximum gain of -2 dBic in parallel to the ground plane at the 900 MHz band. The antenna dimensions are 48 × 20 × 13.8mm (0.14 λ × 0.06 λ × 0.04 λ) with ka = 0.476 (i.e. < 0.5), where k is the wavenumber at the resonant frequency and a is the radius of a sphere surrounding the antenna. The dimension corresponds to the definition of an electrically small antenna. The omnidirectional circularly polarized pattern of a prototype antenna shows good agreement with that of the simulation. In addition, this paper introduces a mechanism that generates omnidirectional circular polarization from electrically small antennas.