The invention discloses a dual frequency feed assembly for receiving signals of both a first band and a second band lower than the first band, or transmitting signals of one of the first band and the second band while receiving signals of the other band. The dual frequency feed assembly includes an orthogonal-mode transducer, which includes: a core unit having an inner waveguide, an outer waveguide with a diameter larger than that of the inner waveguide and the two waveguides being concentric, a first band output/input port connected to the inner waveguide, and a second band output/input port; and two or four detachable branch waveguides connected to the core unit. An O-ring is provided at each connection between the core unit and the branch waveguides. The dual frequency feed assembly further comprises a first band polarizer made of a metal septum and/or a second band polarizer made of dielectric slabs, when receiving circularly polarized signals. Both of them can be provided in the inner waveguide or the outer waveguide, respectively, which makes the feed assembly design more compact and suitable for mass production.