Design of An Archimedes Spiral Ultra-Wideband Circularly Polarized Antenna

Abstract

An ultra-wideband(UWB) circularly polarized antenna based on Archimedes helix is presented in this paper. The main structure is composed of a spiral radiator, microstrip balun, absorbing material, and back cavity. Two self-complementing spiral arms are connected to the cavity to extend the electrical length and reduce the cut-off frequency. Spiral arms are connected to the SMA connector by microstrip balun to realize impedance matching and balanced feed. The introduction of the back cavity can reflect the backward waves, realize unidirectional radiation, improve the gain and front-to-back ratio. The absorbing material can suppress the interference of reflected waves, optimize the direction pattern and impedance bandwidth. The proposed antenna has the characteristic of a low profile, and it has a compact size of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$9.5 \times 22.5\times 22.5\text{mm}^{3}$</tex> . Simulation results show that the voltage standing-wave ratio(VSWR) can reach 118%(5.1GHz-19.9GHz, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{VSWR} &lt; 3$</tex> ), and the axial ratio(AR) is less than 3dB in the frequency range of 7-18GHz. The gain is better than 4.3dB in the operating band and reaches a peak gain of 9.2dB at 17GHz. A prototype of the proposed antenna is fabricated and measured, the measured results are consistent with the simulation results. The results show that the antenna has the UWB and low profile characteristics and can be a good candidate antenna for UWB wireless communication applications.