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 × 25 × 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).