Omnidirectional WLAN Antenna With Common-Mode Current Suppression

An omnidirectional wireless local area network (WLAN) loop-slot antenna with common-mode current (CMC) suppression is proposed in this communication. First, based on the analysis of the equivalent model of odd-even mode, the feeding coaxial line is led out at the voltage-zero point of the loop-slot element, which suppresses the CMC over the full band. Second, through the theory of array, three loop-slot elements form an array to obtain omnidirectional radiation. Finally, the physical size is reduced by loading Stubs T in the slot. The roundness of the radiation pattern is modified by the Stubs T and the chamfering edge of the antenna. A prototype of the proposed antenna was fabricated and measured. The measured results show that the antenna achieves \vert \text{S}_{11}\vert < -10 dB in bands of 2.15-2.65 and 4.85-5.92 GHz. In addition, the roundness is 0.95 dB at 2.4 GHz, 1.84 dB at 5.2 GHz, and 2.43 dB at 5.8 GHz. The antenna effectively suppresses the CMC to keep a favorable roundness over a wide band, showing its potential in WLAN communication systems.