Broadband Circularly Polarized Antennas with Compact Radiator Using Characteristic Mode Analysis

In this paper, a general design procedure of simple four steps for wideband circularly polarized (CP) antenna based on characteristic mode analysis (CMA) is proposed. CMA is performed to investigate the CP generation principle of the proposed radiator. Modal currents and their corresponding radiation patterns are studied for mode selection and feeding placement to achieve CP operation. Then, two feeding mechanisms are introduced to constitute two CP antenna prototypes, which are further analyzed and optimized by CMA. With the physical insight into radiation characteristics of the prototypes, two antennas employing coplanar waveguide (CPW) as feed are designed and optimized by full-wave simulation. To validate the design procedure, both antennas with the same dimension (35 × 40 × 1.6 mm3) are fabricated and measured. The experimental results show that both of the antennas have good CP radiation performance with a peak gain of 4.0 dBic and 2.5 dBic and axial ratio bandwidth (ARBW) of 48.3% and 44%, respectively. In addition, the experimental results are in good agreement with the radiation information provided by CMA.