A Novel Dual Circularly Polarized Microstrip Antenna

In this paper, we propose a novel design of dual circularly polarized microstrip antenna of the cogwheel-like annular ring structure. The microstrip sector stubs are added periodically in the outer and inner edges of the microstrip annular ring and an additional microstrip line as a diameter is also placed across the inner circle to enhance performance of the axial ratio. When operated in TM₁₁ mode, this cogwheel-like microstrip annular ring antenna has a relatively wider bandwidth and a relatively smaller size than those of the traditional microstrip annular ring antenna. The three-wire transmission line and branch-line hybrid is employed as the feeding network to excite the righted-handed or left-handed direction of circular polarization