Dual circular polarisation microstrip array antenna for WLAN/WiMAX applications

A planar 2 × 2 microstrip array antenna with dual circular polarisation (CP) is presented. This array can be reconfigured and operated with either the right-handed (RH) or left-handed (LH) CP by controlling the input state of the branch-line coupler. A prototype has been fabricated with a 0.4 mm-thick FR4 top layer for radiating elements and a 0.8 mm-thick FR4 bottom layer for a feeding network, where a 5 mm air spacing is inserted between them. Wide operating frequency ranges for RHCP and LHCP states can be achieved at about 1.55 GHz and 1.54 GHz, respectively. Good radiation properties across the operating band are also obtained so that the proposed array antenna is suitable for WLAN and WiMAX applications.