A Three-Arm Metaspiral Antenna

This paper presents a low-profile, multi-beam antenna that radiates circularly polarized (CP) waves in three azimuth directions. The antenna, with a height of approximately one-hundredth of the wavelength at the operating frequency, is designed in three steps. First, we clarify the dispersion characteristics of an n-type meta-atom. Then, we investigate a single spiral radiation element, made up of n-type meta-atoms, to achieve a CP radiation beam. Lastly, we array three CP spiral radiation elements separated by 120 degrees in the azimuth plane, having feed points <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$F_{\mathrm{m}}(\mathrm{m}=1,2,3)$</tex> near the coordinate origin. This compound of radiation elements is called a three-arm metaspiral antenna (3-MTSA). Analysis reveals that, when the feed points are excited in turn, a CP radiation beam rotates around the z-axis, with a half-power beamwidth (HPBW) of 121 degrees. Thus, the designed 3-MTSA is capable of covering the entire azimuth direction of 360 degrees with three CP radiation beams. Further analysis shows that the input characteristic at each feed point has a voltage standing wave ratio (VSWR) of less than two, and that the gain in the beam direction is 4.3 dBic.