A low-profile omnidirectional circularly polarized antenna for WLAN access point

Omnidirectional CP antennas have the advantage that no strict orientations between the access point, and the mobile unit are required for WLAN operation. For this reason, it can be expected that the omnidirectional CP antenna should find great application in WLAN operation. For such promising applications, we propose a novel omnidirectional CP antenna with a low profile of less than 10 % of the wavelength of the center operating frequency. The proposed antenna consists of a top-loaded cylindrical monopole for generating omnidirectional vertical linear polarization (LP) radiation and four printed arc-shaped dipoles for generating omnidirectional horizontal LP radiation. The vertical and horizontal LP radiation can further be adjusted to be of equal amplitude and a 90° phase difference, thereby resulting in omnidirectional CP radiation. A prototype of the proposed antenna suitable for applications in a 2.4 GHz (2400-2484 MHz) WLAN access point is constructed and studied.