Abstract: A new microstrip antenna fed by a coplanar stripline (CPS) operating at dual-band is proposed, one is circular polarization and the other is linear one operating at 2.4GHz and 5.8GHz respectively. The dual-band operation is realized by a pair of small square loops in the center of the rhombic loops. The circular polarization (CP) is achieved by the slot on the external rhombic loops and the gain is improved by a reflection plane. A CPS to microstrip balun is designed to measure the antenna’s performances and be applied in unbalanced feed structure. Experiment results agree with simulated ones. The relative bandwidth of S₁₁ < -10dB in 2.4GHz and 5.8GHz are 33.3% and 17.4% respectively. The maximum gain are 9.05dBi at 2.4GHz and 6.59dBi at 5.8GHz respectively. The relative CP bandwidth of axial ratio < 3dB at 2.4GHz is 15.8%. The antenna has characteristics of wide bands, high gain, simple structure and easy to be integrated. It can be used in wireless communication systems and rectennas of microwave power transmission system.