Dual-band circularly polarised planar monopole antenna for WLAN/Wi-Fi/Bluetooth/WiMAX applications

A novel planar monopole antenna with dual-band circularly polarisation (CP) is presented here. The antenna consists of a modified L-shaped monopole, an inverted-L strip, and a modified ground. The utilisation of the modified L-shaped monopole not only generates dual-band operation, but also excites CP radiation in the lower band. In order to achieve CP in the upper band, a parasitic inverted-L strip is added on the top plane of the substrate and a modified ground is designed. The proposed antenna has been fabricated and tested, the measured -10dB reflection coefficient bandwidths are 370MHz (2.38-2.85GHz) in the lower band and 2330MHz (4.05-6.38GHz) in the upper band. The measured corresponding 3dB axial ratio (AR) bandwidths are 610MHz (2.39-3GHz) and 850MHz (5.15-6GHz), respectively. The overlapped -10dB reflection coefficient and AR bandwidths can totally cover the WLAN bands, Wi-Fi bands, Bluetooth band, and partly cover the WiMAX bands. The proposed antenna owns bidirectional radiation characteristic and reasonable gain at both the lower band and the upper band.