There is disclosed a feed network including a circular common waveguide having an axis and terminating in a common port and a first port for coupling a first linearly polarized mode to the circular common waveguide. A phase shifting element may be disposed within the circular waveguide. The phase shifting element may be adapted to cause a predetermined phase shift between a first signal and a second signal propagating in the common waveguide. The phase shifting element may be rotatable about the axis of the common waveguide.