This paper proposes a circularly-polarized continuous transverse stub(CTS) array antenna for space applications. The radiating structure consists of open-ended parallel plate waveguides(PPW), supporting the propagation of the transverse electromagnetic(TEM) and first transverse electric(TE1) modes. Such modes are orthogonally-polarized in the PPW cross-section and, if properly excited, can generate circular polarization(CP). The antenna radiating section consists of 32 long slots, parallel-fed by a quasi-optical system through a PPW-based corporate feed network(CFN) and an electric field rotator. The proposed antenna is matched in the 27.5-31GHz band while scanning up to +-20° in elevation, with an axial ratio(AR) below 3dB. © 2021 IEICE.