A mm-wave dual-frequency circularly polarized feed for an offset reflector antenna is being developed for a portable satellite ground terminal. The two frequency bands are Q- and K-bands for transmit and receive, respectively. Requirements for the antenna feed design are: low cost, compact size, rugged construction, high efficiency, and low sidelobes in both of the frequency bands. The chosen feed design consists of a single corrugated horn designed for the two separate frequency bands with two circular waveguide concentric openings at the horn throat. The inner circular waveguide is used for transmit, and the outer coaxial circular waveguide is used for receive. In these waveguides, separate circular polarizers, orthomode transducers, and impedance matching elements for each frequency band are designed and integrated in a compact and solid fashion. Electrically, good impedance match and small axial ratio are obtained for both frequency bands. Radiation patterns with approximately equal illumination taper at the reflector edge and coincident phase centers are obtained in both frequency bands. Detailed design considerations and measured performance data are presented. (Author)