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A microstrip antenna design that effectively attains circular polarization (CP) and harmonic suppression is proposed. By modifying the size and position of two peripheral cuts, two orthogonal modes that have equal amplitude and are 90 out of phase are simultaneously excited. The four right-angle slits embedded in the antenna can block the second- and third-order harmonic signals. This property is especially suitable for nonlinear circuit applications, such as active integrated antenna (AIA) and rectifying antenna (rectenna). The adopted CP antenna built on a low-cost FR4 substrate has a measured bandwidth of 137 MHz (10-dB return loss) and a 30-MHz CP bandwidth (3-dB axial ratio). A rectenna that comprises the proposed antenna and a rectifying circuit is built for verifying the characteristics of the proposed antenna. The measured results of the proposed antenna are in good performances and steady efficiency.