Broadband circularly polarized patch antenna

Circularly polarized (CP) antennas are attractive to wireless communications applications simply because less strict orientations are required for mobile stations (the end user) with respect to base stations. To achieve CP operation, many designs of patch antennas have been reported in the literature. However, for the designs utilizing dielectric substrates, single-feed, single-element patch antennas are usually with a narrow CP bandwidth of about 2% or less (Sharma and Gupta, 1983), which limits their practical applications. In this paper, we demonstrate that by introducing a new feed structure, a single-element patch antenna can achieve a wide CP bandwidth. With the proposed probe feed and ground configuration, good impedance bandwidth with VSWR below 1.5 over the 2.4 GHz WLAN band can be obtained. In addition, good broadside, CP radiation characteristics have also been observed. The design prototype has been built and aimed for operation in the 2.4 GHz (2400-2484 MHz) WLAN band. The proposed antenna is designed for access-point applications in the WLAN environment. Details of the antenna design are described, and experiment results are discussed.