A multiple beam integrated antenna system for a satellite including a support structure having an alignment plate. The antenna system further includes a plurality of feed horns mounted to the alignment plate, where each feed horn includes a plurality of tapered sections that support propagation modes for both up-link signals and down-link signals. A septum polarizer is mounted to an input end of each feed horn that converts linearly polarized signals to circularly polarized signals for the up-link signals and converts circularly polarized signals to linearly polarized signals for the down-link signals. A Y-shaped waveguide is coupled to each of the polarizers and includes separate receive reject and transmit reject filters so as to keep the up-link signals and the down-link signals from interfering with each other. Flex waveguides couple the transmit leg and the receive leg of each Y-shaped waveguide to RF modules.