The tapered line theory in circuit can be applied to the design of the special-shaped monopole antenna in order to obtain better electrical characteristics. So a novel Klopfenstein taper monopole antenna is proposed. The impedance matching characteristic of the Klopfenstein tapered line is the best, and the Klopfenstein taper monopole antenna is designed based on it. On this basis, the coplanar waveguide-fed planar Klopfenstein taper monopole antennas are designed. The simulation and measurement results prove that the Klopfenstein taper monopole antennas have small size and good performance. And the planar printed antenna can be convenient integrated with other radio frequency circuits. The idea to design antenna by using of tapered line theory directly can be used in practical operations.