A novel dual-polarization, single-layer reflectarray has been designed and manufactured to operate at receive (20 GHz) and transmit (30 GHz) frequencies for Ka-band terminal antennas. The reflectarray unit cell is composed of several types of resonant elements printed on the upper side of a conductor-backed substrate, which are designed to produce a collimated beam at 20 and 30 GHz in dual polarization. Cross-shaped loops are used to provide the required phases at 20 GHz, while crossed dipoles and modified truncated rings are used to control the phasing at 30 GHz. The resonant lengths of the proposed elements have been adjusted cell by cell by means of a two-dimensional interpolation method to achieve the required phase shift at each frequency. Two different feeds have been used to illuminate the reflectarray at 20 and 30 GHz. The measured gain is 28.02 dBi at 20 GHz and 32.14 dBi at 30 GHz. The measurement results show that the radiation patterns of the designed single-layer reflectarray antenna are in good agreement with those achieved from the simulations.