Design of antenna for cognitive radio application is proposed in this paper. The design consists of two printed monopole antenna printed over FR4 substrate, sharing a common partial ground. The first antenna is the sensing antenna for spectrum sensing, having wideband characteristic and omnidirectional radiation pattern. The second one is the communicating antenna which is a frequency reconfigurable antenna with the existing switch on the antenna's structure. The measurement shows that the reconfigurable communicating antenna is working at 2.35 GHz when the switch is OFF and it is working at 1.8 GHz when the switch is ON.