Compact Dual-Band Dual-Mode Antenna with Omni-/Unidirectional Radiation Characteristics

A novel dual-band dual-mode antenna that operates at 2.45/5.8 GHz is proposed in this letter. The antenna exhibits linearly polarized omnidirectional radiation in the low band, and circularly polarized broadside radiation in the high band. To improve the 3 dB axial-ratio (AR) bandwidth, both truncated patches and a sequential rotation technique are combined together in the antenna design. The omnidirectional radiation in the low band is achieved by exciting four open-ended slots etched in the ground plane for the first time. The four slots form a magnetic-dipole-like current distribution along the edge of the ground plane, resulting in omnidirectional radiation. The low- and high-band operations are seamlessly integrated into a common design, sharing the same structure. This work provides a novel approach for improving the versatility of a radio frequency front-end subsystem without increasing footprint. The proposed antenna is prototyped and measured, showing good results in terms of impedance/AR bandwidths, isolation, radiation, and polarization.