Dual‐band and omnidirectional miniaturized planar composite dipole antenna for WLAN applications

Abstract

A novel planar omnidirectional dipole antenna for wireless local area network (WLAN) applications is proposed. The antenna consists of a sleeve dipole antenna for the lower band and a cage dipole antenna for the upper band. Employing a unique planar composite structure, good dual-band impedance matching can be achieved without an external matching circuit. The lower-band dipole antenna adopts a sleeve structure, which reduces the size by bending in the middle and thickening at the end as inductance and capacitance loading, respectively. The upper-band dipole antenna is embedded in the lower-band dipole antenna, and the impedance bandwidth is broadened by adopting a cage structure and coupling with the lower-band dipole antenna. The proposed antenna occupies an area of 0.38 λ0 × 0.08 λ0 (λ0 represents the wavelength of the lower frequency) on FR4 substrate of thickness 0.8 mm. The measured results show that the impedance bandwidths with a return loss more than 10 dB are 2.27–2.65 GHz and 4.89–6.02 GHz. The antenna has an omnidirectional radiation pattern, and both E-plane and H-plane have lower cross-polarization levels. The average gain reaches 2.4 and 3.3 dBi in the 2.4- and 5-GHz bands, respectively. The antenna is compact and easy to fabricate, and can be used for small omnidirectional WLAN terminal device.