A 60-GHz artificial magnetic conductor (AMC)-based circularly polarized (CP) on-chip antenna has been designed and fabricated using standard 0.18-μm six metal-layer CMOS technology. The design consists of a wideband circularly polarized loop antenna at the top layer M6 and a novel AMC structure at the bottom layer M1. The size of the antenna including the modified AMC structure is 1.8 × 1.8 × 0.3 mm3. The circular open-loop structure is employed for antenna design because the gap within the loop can excite traveling wave current and then achieve circular polarized radiation. In addition, it is found that the bandwidth of circular polarization can be significantly increased by introducing one more inner parasitic loop. With the modified AMC structure integrated into the bottom layer, the antenna performance can be optimized and improved as more design freedom is introduced. The proposed antenna can offer a simulated peak gain of -3.7 dBi and a measured gain of -4.4 dBi, respectively, as well as simulated and measured axial ratio (AR <; 3) bandwidth to cover from 57 to 67 GHz.