Printed dual spiral-loop wire antenna for broadband circular polarization

A Printed dual spiral-loop wire antenna above a ground plane is proposed and implemented for circular polarization (CP) with broadband axial ratio (AR) and wide elevated angle. The two spiral loops are formed on the two opposite interfaces of a thin dielectric substrate while they are located symmetrically with respect to the feeding point. In the design, the two unequal side lengths of each spiral loop are properly adjusted to achieve a circularly polarized radiation at the frequency of 1.5 GHz. After extensive investigation is executed on the AR and input impedance versus varied side lengths, the proposed CP antenna is optimized, fabricated and tested. The predicted and measured results are found in good agreement with each other, achieving the 3-dB axial-ratio bandwidth of ∼15% and the 10-dB return-loss bandwidth of ∼6.7%. In addition, the overall dimension of this antenna is reduced by ∼24% in length.