Dual-band omnidirectional antenna for in-vehicle application

In this paper, a miniaturized and high-efficiency monopole antenna for $2.4 / 6 \mathrm{GHz}$ wireless LAN (WLAN) applications is proposed. The antenna consists of a rectangular block cavity superimposed by two embedded rectangular slots. Compared with traditional monopole antennas, the antenna utilizes a grounding structure to construct a small ring antenna, which reduces the antenna size and uses more metal surfaces for radiation and impedance matching, providing greater flexibility for multi-band antenna design. In addition, in order to improve the transparency of the antenna, a prototype of the proposed antenna is fabricated from a glass substrate and the bottom ground plate is changed to a mesh structure. Stable radiation patterns are obtained in the two operating frequency bands of $2.1 \sim 3 \mathrm{GHz}$ and $5.5 \sim 6.3 \mathrm{GHz}$, and the fractional bandwidths are $40 \%$ and $13.3 \%$, respectively. It covers the internal and external communication of the human body and the frequency band of wireless LAN applications, and can be applied to vehicle antennas.