A circularly polarized (CP) transmitarray with 1-bit phase resolution is proposed in X-band. It consists of two-layer metallic patterns connected by a metallized via-hole. The top layer of metallic pattern composed of a square ring patch with two triangle corners along diagonal is utilized to produce circular polarization, and two diodes are inserted in this pattern to achieve 0 degrees/180 degrees phase tuning of the outgoing wave. The bottom layer of metallic pattern is made of a U-slot rectangular patch to receive incident wave. The experimental results show that the proposed transmitarray produces circularly polarized wave around 10.2 GHz when illuminated by a linearly polarized wave, and its insertion loss is less than 1.4 dB. Furthermore, we present the design of a dual circularly polarized transmitarray. The numerical simulation is performed to show that it can achieve dynamic polarization manipulation of the emitted wave between left- and right-handed circular polarizations and also has the ability of tuning the phase of the outgoing wave by 180 degrees. The proposed transmitarray, as a promising and simple solution to produce circular polarization, has potential application in many communication systems.