Design of a Wideband Circularly Polarized Strip-Helical Antenna With a Parasitic Patch

Abstract

A wideband strip-helical antenna with a parasitic circular patch for circular polarization is designed in this paper. A strip-helix with 2.5 turns and a pitch angle of 5° is placed over a ground plane and coaxial probe-fed by a 50- $\Omega $ SMA connector. A parasitic patch is electromagnetic-coupled to the open end of the strip-helix with an extremely small distance. By combining the strip-helix with the parasitic patch, two nearby circularly polarized (CP) resonances are produced and a wide axial ratio (AR) bandwidth is obtained. The strip-helix can excite a CP resonance in axial mode, while the parasitic patch can generate another nearby one in fundamental mode. Radiation characteristics of the proposed design, including current distributions, reflection coefficient (S11), AR, and radiation patterns, are studied. Measured results shows that the proposed antenna has an impedance bandwidth (S11 ≤ − 10 dB) of 53%, an AR bandwidth (AR ≤ 3 dB) of 44%, and a peak gain of 9.4 dBi in its volume of $0.43\lambda _{0} \times 0.43\lambda _{0} \times 0.25\lambda _{0}$ , where $\lambda _{0}$ is the wavelength in free space at the center operation frequency.