A novel design of microstrip antenna with reconfigurable band rejection for cognitive radio applications

This article discusses the use of compact ultrawideband (UWB) microstrip monopole antenna with reconfigurable band rejection in cognitive radio. Frequency characteristics of the antenna can be reconfigured electronically to have a variable single band‐notched function to block interfering signals from 5 to 6 GHz wireless local area network (WLAN), 5.79–6.40 GHz intelligent transport system (ITS) and 8.02–8.4 GHz international telecommunication union (ITU). Using pairs of C‐shaped and L‐shaped parasitic structures in the ground plane, additional resonances are excited and hence much wider impedance bandwidth can be produced. Using these modified structures, the usable upper frequency of the antenna is extended from 10.4 to 14.5 GHz which provides a wide usable fractional bandwidth of more than 135%. To generate a reconfigurable band‐stop performance, we use three PIN diodes within the embedded structures in the ground plane. By changing the ON/OFF conditions of the PIN diodes, the antenna can be operated as UWB, and is reconfigurable in terms of the ability to selectively have band stops in the WLAN/ITS/ITU bands. The proposed monopole antenna has compact size with simple structure. Good VSWR and radiation pattern characteristics are obtained in the frequency band of interest. Experimental results show that the proposed antenna could be a good candidate for ultrawideband cognitive radio application.