Bandwidth-Enhanced Circularly Polarized Spiral Antenna With Compact Size
Ling‐Lu Chen, Lei Chang, Zhuang‐Zhi Chen, Qiaona Qiu
Abstract
A compact circularly polarized (CP) spiral antenna with enhanced impedance and 3-dB axial ratio (AR) bandwidths that is fed by a tapered coax balun is presented. The antenna is composed of a two-arm nonself-complementarity planar equiangular spiral, a z-directional helix, absorbing material with a stepped cylindrical honeycomb structure, and a ground plane. The z-directional helix is used to extend the current path and to improve the impedance matching and AR in the low-frequency band. The coupling between the nonself-complementarity planar spiral arms is increased, which improves the impedance matching in the low-frequency band and the AR at approximately 5.55 GHz. The stepped cylindrical absorbing material can reduce the reverse current and improve the AR in the high-frequency band. The measured results show that the impedance bandwidth and 3-dB AR bandwidths range from 0.5 to 6 GHz and from 0.5 to 5.8 GHz, respectively. The overall size of the proposed antenna is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.189\lambda _{L} \times 0.065\lambda _{L}$ </tex-math></inline-formula> (diameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> height, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{L}$ </tex-math></inline-formula> is the free-space wavelength at the starting frequency).