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

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-Ω 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 (S
₁₁
), AR, and radiation patterns, are studied. Measured results shows that the proposed antenna has an impedance bandwidth (S1
₁
≤-10 dB) of 53%, an AR bandwidth (AR 3 dB) of 44%, and a peak gain of 9.4 dBi in its volume of 0.43λ
₀
× 0.43
_λ0
× 0.25
_λ0
, where λ
₀
is the wavelength in free space at the center operation frequency.