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