Optically controlled reconfigurable band-notched UWB antenna for cognitive radio systems

A compact optically controlled ultra-wideband (UWB) antenna with reconfigurable band-notched characteristics is investigated for cognitive radio (CR) applications. The rejection mechanism is realised by etching one symmetric folded slot on the U-shaped radiation patch and the essence of the reconfigurable function is achieved by laser controlling photoconductive switches to change the effective length of the folded slot. A prototype with an overall size of 25 x 25 x 0.8 mm(3) is designed and constructed. On the basis of simulated and measured results, the proposed antenna exhibits good radiation behaviour and operates in a wide band with the performance of switchable band rejection of the wireless local area network (WLAN) 2.4 GHz (2.2-2.9 GHz), worldwide interoperability for microwave access (WiMAX) (3.2-4.7 GHz), WLAN 5 GHz (4.8-6.6 GHz) and the ITU 8 GHz (7.5-8.7 GHz).