A Dual-Band Circularly Polarized Planar Monopole Antenna for WLAN/Wi-Fi Applications

This letter presents a dual-band circularly polarized planar monopole antenna. The antenna consists of a radiator, a ground plane, and a microstrip line. The radiator is composed of a “C”-shaped strip and an “L”-shaped strip. The “C”-shaped strip is mainly used for the higher band, and the “L”-shaped strip for the lower band. The overall dimension of the prototype is only 40 ×47 ×1.5 mm
³
. The proposed antenna has been built and tested. Its measured -10-dB impedance bandwidths are 380 MHz (2.32-2.70 GHz) in the lower band and 1240 MHz (4.76-6 GHz) in the higher band. Its measured 3-dB axial-ratio (AR) bandwidths in the broadside direction are 180 MHz (2.39-2.57 GHz) in the lower band and 870 MHz (5.13-6 GHz) in the higher band. The overlapped impedance and AR bandwidths can fully cover all the 2.4/5.2/5.8-GHz WLAN bands and all the 2.4/5.5-GHz Wi-Fi bands. The patterns have the characteristic of bidirectional radiation, and the gains are stable in both bands.