Circularly polarized conical-beam antenna with wide bandwidth and low profile

This work introduces a circularly polarized (CP) conical-beam antenna with low profile and wide impedance & axial ratio (AR) bandwidths. The antenna structure simply consists of a wideband monopolar patch antenna and eight parasitic loop stubs for generating vertically polarized electric field E_θ and horizontally polarized field E_φ, respectively. The proposed antenna is low profile but wideband because of merging the TM₀₁ and TM₀₂ modes at around the center frequency. In order to obtain the wideband CP radiation, the eight parasitic loop stubs are printed and placed sequentially along the radiating edge of the patch. With the resultant radiations from both the patch antenna and the loop stubs, the CP conical-beam radiation pattern can be obtained. In addition, a parametric study of the shorting vias effect, number of loop stub elements, and loop widths are demonstrated how to design this wideband CP antenna. The antenna exhibits the wide impedance bandwidth of 28% from 4.9 to 6.5 GHz (for the reflection coefficient ≤ -10 dB) and the 3-dB AR bandwidth of 14.4% from 5.8 to 6.7 GHz. The thickness of this antenna is only 0.06λ in terms of the free-space wavelength at its lowest operation frequency. Stable omni-directional conical-beam radiation patterns are observed over the operating bandwidth with the peak gain of 4.9 dBic. The antenna can cover the uplink of standard C band (5.85 to 6.425 GHz) for satellite communication.