In this paper, a microstrip antenna is proposed with an ultrawideband (UWB) design and reconfigurability for cognitive radio. The antenna has a small size of 17*24 mm, while showing the radiation performance in the frequency band of UWB with two switchable band-rejection performances in the frequency bands of WiMAX and C-band satellite. Simulated result obtained for this antenna shows a good radiation behavior within the UWB frequency range. It has also a reconfigurable frequency band-notched function in the range of application that can eliminate the interference between UWB frequency band and other existing wireless communication systems. This paper provides a detailed discussion of the existing UWB spectrum sensing reconfigurable microstrip antenna designs for cognitive radio applications. The comparison between the simulated return loss by Ansoft HFSS and CST-Microwave Studio has been also carried out.