A circularly polarized planar and slender antenna using helical element and back conductor

A circularly polarized slender shaped helical antenna is presented. The helical antenna can generate circular polarization (CP) in the normal direction to the helical axias under a condition of structural parameters. However, when a planar and slender antenna shape is required, it may be difficult to satisfy the condition. In the proposed antenna, the ratio of the thickness : vertical : horizontal sides is approximately 1:2:8 which has been obtained generating circular polarization using a back conductor. The back conductor is installed at a close position behind the helical element using a capacitive feed structure in order to keep a low-profile structure. This antenna can be resonated at around 1 GHz with the size satisfying k₀ a=0.35 (k₀: wave mumber at the resonance frequency, a:radius of a hypothetical sphere circumferencing the antenna). Reasonable agreements have been obtained between simulated and measured results in S₁₁, axial ratio, and radiation pattern.