Design of Circularly Polarized Low-Profile and Slender Antenna With a Helical Element

Designs of circularly polarized, slender, helical antennas are presented. A capacitive feed structure, which has been proposed previously, with a slender helical structure is used as a back-conductor. The back-conductor is installed close behind the helical element in order to radiate circular polarization (CP) with a low-profile structure at approximately 1 GHz with k
₀
a=0.35 ( k
₀
: wavenumber at the resonance frequency, a: radius of a hypothetical sphere circumventing the antenna). Reasonable agreement between the simulated and measured results for S
₁₁
, the axial ratio (AR), and the radiation pattern have been obtained. Furthermore, the effect of the back-conductor is discussed for the helical antenna structure with a large ground plane.