An Omnidirectional Circularly Polarized Slot Array Antenna With High Gain in a Wide Bandwidth

In this letter, a novel omnidirectional circularly polarized (CP) slot array antenna with high gain is proposed. The array is based on the coaxial cylinder structure. The omnidirectional radiation is realized by four perpendicular slot pairs surrounding the axis of coaxial cylinder in the outer conductor, which can be seen as a basic omnidirectional CP element. With four of these basic elements along the axis of the coaxial cylinder, the radiation slot array is constructed with desired omnidirectional CP property and particularly stable high gain in a wide bandwidth. To match the antenna, three cascade coaxial lines with the same outer radius but different characteristic impedance are connected to its input. Measured results show that the proposed antenna performs a -10 dB impedance bandwidth (S-11 < -10 dB) of 16.4% ranging from 5.05 to 5.95 GHz and a 3-dB axial-ratio (AR) bandwidth of 14.5% ranging from 5.1 to 5.9 GHz. Within the common band ranging from 5.1 to 5.9 GHz, the measured gain in the omnidirectional plane (xy-plane) is stable and higher than 5 dBic.