A Compact Dual-Band Slot Antenna With Horizontally Polarized Omnidirectional Radiation

A dual-band horizontally polarized omnidirectional antenna for WiFi applications is proposed in this letter, which consists of a 3-D radiation slot on a metal box and three folded patches inside. The 3-D slot is formed by connecting two trapezoid slots at top and bottom of the box with a rectangle slot at the vertical side. Then, the radiation slot is excited by a folded patch connected to the feed line and produces two resonances at 2.45 and 5.5 GHz. With the help of two parasitic patches beside the excited patch, the higher frequency band is broadened. Measured results show that the antenna has two 10 dB return loss operating bandwidths of 5.32% and 20.56%. Moreover, the measured out-of-roundness for the horizontal radiation pattern is less than 2.4 dB in lower frequency band and that of higher frequency band is less than 5.3 dB. Besides, the antenna maintains a compact size of only 22 mm × 10 mm × 25 mm (0.18
λ
₀
× 0.08
λ
₀
× 0.20
λ
₀
, where λ
₀
is the wavelength of the lowest operating frequency), with the gain about 2 dBi and the cross-polarization ratio greater than 20 dB in the entire band.