Design Approach of a Single Circularly Polarized Patch Antenna with Enhanced AR-Bandwidth under Triple-Mode Resonance

A novel design concept to widen axial-ratio (AR)-bandwidth of a single circularly polarized (CP) patch antenna is presented by resonating its TM $_{1/2,0}$ , TM $_{1/2,1}$ , and TM $_{3/2,0}$ modes. First, a set of shorting pins is loaded around the edge of the patch with decreased width, aiming to suppress undesired nonbroadside modes. Second, the far-zone radiated fields of the antenna are theoretically studied by using equivalent magnetic currents (EMCs). The results demonstrate that its broadside $\vert {E}_{\theta }\vert $ , $\vert {E}_{\varphi }\vert $ , and $-\vert {E} _{\theta }\vert $ components of xo z plane radiation patterns could be orthogonally generated under TM $_{1/2,0}$ , TM $_{1/2,1}$ , and TM $_{3/2,0}$ modes, respectively. Most importantly, these three broadside EMCs must be sequentially rotated. Third, the resonant frequencies of these triple radiative modes ( ${f}_{1/2,0}$ , ${f}_{1/2,1}$ , and ${f}_{3/2,0}$ ) are extensively analyzed and reallocated by loading the shorting pins. It proves that the ${f}_{1/2,0}$ and ${f}_{1/2,1}$ could be progressively pushed up to around the ${f}_{3/2,0}$ , resulting in generating the CP radiation as expected. With these arrangements, the AR-bandwidth of the proposed CP antenna is significantly widened under triple-mode resonance. In final, the proposed antenna is fabricated and measured. Simulated and measured results are in good agreement with each other. The measured results depict that the CP antenna has acquired an enhanced AR-bandwidth with two minima poles, covering a fractional bandwidth of about 5% from 3.25 to 3.41 GHz, which is about 3.3 times wider than the traditional counterpart (1.5%). Besides, its profile is kept only about 0.03 free-space wavelength. Particularly, the single-layer, single-fed, single-radiator, and high-efficiency properties are simultaneously maintained for the CP antenna without needing to rely on any extra feeding networks, patches, or resisters.