A composite antenna radiating circularly polarized conical and axial beams

The increasing popularity of mobile communication systems has created the need for an antenna with circularly polarized (CP) axial, conical, and tilted beams that operate at different frequencies. A loop antenna radiates a linearly polarized (LP) wave. A recent study shows that the LP wave can be transformed into a CP wave by adding perturbation elements to the loop (see Nakano H., Computer Physics Commun., vol.68, p.441-50, 1991). Also, a curl antenna radiates a CP wave, without the need for perturbation elements. The curl is a simple derivative of the single arm spiral antenna. A composite antenna composed of two loop radiation elements and one curl radiation element, each having a separate feed system, is analyzed using the method of moments. The analysis shows that the excited radiation element has a traveling wave current, while the remaining elements have negligibly small currents. This contributes to forming the desired CP beams. It is found that the CP axial, conical, and tilted beams have axial ratio bandwidths of 1.3%, 0.23%, and 5.8%, respectively, while having VSWR bandwidths of 6.6%, 1.5%, and 30%, respectively. It is also found that increasing the height of the outermost loop contributes to widening the VSWR bandwidth of the conical beam.