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).
Highlights
Wideband antennas have attracted widespread attention for application in many communication and radar systems
In [19], in order to reduce the size of an Archimedean spiral antenna, two arms were extended on the profile and connected together at the end
We studied the effect of the nonself-complementarity spiral on the antenna performance
Summary
Wideband antennas have attracted widespread attention for application in many communication and radar systems. In [4], by using chip resistors inside the substrate, a planar equiangular spiral antenna achieved an impedance bandwidth of 2-18 GHz. A two-arm Archimedean spiral with a stepped ground plane cavity operating in the frequency band of 2-10 GHz was designed as a feed for a parabolic reflector [5]. A differential-fed Archimedean spiral with a novel loading structure and a ring-shaped absorber was studied to achieve miniaturization design with an overall size of 0.21λL × 0.21λL × 0.09λL [18] This antenna operated from 0.5 to 1.4 GHz. In [19], in order to reduce the size of an Archimedean spiral antenna, two arms were extended on the profile and connected together at the end. The design procedure of the proposed antenna, the simulated and measured results are presented and discussed
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