Tri-band planar monopole antenna with two circularly polarised bandwidths for WiMAX applications

A tri-band planar monopole antenna with one linearly polarised band, two circularly polarised bands, and bidirectional radiation patterns is presented in this study. The antenna consists of a monopole with seven arms etched on the top side of a FR4 substrate, and a slitted ground plane on the bottom side. Measured results show that the antenna has a S-11<-10dB impedance bandwidth of 9.7% (2.05-2.26GHz) for the lower band, 11.3% (3.41-3.82GHz) for the middle band, and 60.2% (4.89-9.11GHz) for the upper band. The circular polarisation (CP) is radiated within the middle (left hand CP) and the upper (right hand CP) bands, and the measured broadside 3dB axial ratio bandwidths are 4.9% (3.53-3.71GHz) and 58.6% GHz (4.69-8.58GHz), respectively. The proposed antenna has a total size of 25x35x1.6mm(3) and can be employed for the 2.1GHz UMTS, whereas the CP bands can be used for the 3.5/5.5GHz WiMAX, 5.5GHz Wi-Fi, and 5.2/5.8GHz WLAN applications.