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This paper introduces a compact antenna with bandwidth reconfigurable and flexible characteristics for cognitive radio applications. The antenna consists of a monopole as a primary radiator and is excited by a coplanar waveguide to have a single-layer design. To adjust the operating bandwidth (BW) by fixing the lower frequency and varying the upper one, an additional stub is connected to the feeding line. This stub causes a disturbance in the current distribution, which significantly degrades the matching performance. By controlling its length, the rejected band can be changed and thus, the upper frequency is varied. To validate the proposed approach, two stubs are used, and they are connected to the feeding line through two PIN diodes. By switching the ON/OFF state of the diodes, three different states with different operating BW are attained. The fractional BWs for these states are 18.9, 33.2, and 64.3% respectively. Besides, it is also worth noting that the antenna achieves good performance when bent over a curved surface.