Low-Profile Broadband Vertically Polarized Antenna with Archimedes Spiral Slits

In this paper, a low-profile antenna with broadband vertically polarized omnidirectional radiation is presented. The bandwidth is broadened by adding Archimedes spiral slits on the outer side of a circular patch located in the center of the antenna. The simulation results show that the antenna fractional bandwidth, related to the values of the reflection coefficient lower than −10 dB, is increased from 7% to 20% when the Archimedes spiral slits are used. The designed antenna has a vertical polarization and omnidirectional radiation and an overall thickness of $0.038 \lambda$, considering the wavelength at the central operating frequency of 5.7 GHz.