A wideband strip-helical antenna with a parasitic patch

This paper presents a new wideband and low-profile strip-helical antenna with a parasitic patch for circular polarization (CP). A helix with 2.5-turns and pitch angle of 5°, made of wide metallic strip, excites a circularly polarized wave with an axial ratio (AR) bandwidth (AR ≤ 3 dB) of 17%. With the aim of improving AR bandwidth, a circular patch is capacitive coupled to the open end of the strip-helix. The parasitic patch not only reduces the reflection at the open end of the strip-helix, but also excites another nearby circularly polarized resonance. Simulated results show that the proposed antenna has an impedance bandwidth (voltage standing wave ratio (VSWR)≤ 2) of 56%, and an AR bandwidth (AR ≤ 3 dB) of 41% in its low axial height of 0.25λ₀, where λ₀ is the wavelength in free space at center operation frequency. Due to the small pitch angle and low profile of the helix, the radiation patterns are symmetric across the AR bandwidth and the corresponding gain is stable with 9α1 dB.