Dual-Band Spiral Patch-Slot Antenna With Omnidirectional CP and Unidirectional CP Properties

A novel dual-band microstrip antenna with omnidirectional circularly polarized (CP) and unidirectional CP characteristic for each band is proposed in this communication. Function of dual-band dual-mode is realized based on loading with metamaterial structure. Since the fields of the fundamental modes are most concentrated on the fringe of the radiating patch, modifying the geometry of the radiating patch has little effect on the radiation patterns of the two modes (n = 0, + 1 mode). CP property for the omnidirectional zeroth-order resonance (n = 0 mode) is achieved by employing curved branches in the radiating patch. Then a 45^° inclined rectangular slot is etched in the center of the radiating patch to excite the CP property for the n = + 1 mode. A prototype is fabricated to verify the properties of the antenna. Both simulation and measurement results illustrate that this single-feed antenna is valuable in wireless communication for its low-profile, radiation pattern selectivity and CP characteristic.