Abstract: A low-profile, dual-band, four-beam circularly polarized (CP) folded transmitarray (FTA) antenna for bidirectional communication is presented. The antenna is composed of two receiver-transmitter (T-R) arrays operating at distinct frequency bands and two feed sources. Specifically, the T-R₁ serves a dual function: it facilitates dual CP beam radiation based on the spin-decoupling method at lower band while reflecting electromagnetic (EM) waves at higher band. Correspondingly, the T-R₂ achieves dual CP beam radiation through spin-decoupling at higher band and reflects EM waves at lower band. Finally, four independently controllable CP beams are realized in both the +z and -z directions. Simulated results demonstrate that at 13 GHz, the peak gains of the left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) beams are 23.5 dBic and 23.27 dBic along the +z axis, with corresponding aperture efficiencies of 29.3% and 27.8%, respectively. At 17 GHz, the peak gains of the LHCP and RHCP beams are 22.9 dBic and 22.34 dBic along the -z axis, with aperture efficiencies of 14.9% and 13.1%, respectively. Featuring a low profile, lightweight, and dual-band operation capability, the FTA provides an effective solution for bi-directional CP wireless communication systems.