in accordance with the present invention , a traveling wave coupler generates tracking signals from a circularly polarized microwave signal and includes a waveguide manifold for exciting circular tm 01 and tm 11 modes of said circularly polarized microwave signal . the waveguide manifold includes an input port , a propagation length , and an output port . a coupling arm waveguide includes an auxiliary input port and an auxiliary output port and is aligned and connected to the waveguide manifold along a portion of the propagation length . a coupler located between the waveguide manifold and the coupling arm transforms microwave energy of a tm 01 mode of the circularly polarized microwave signal into a rectangular te 10 mode in the coupling arm waveguide . the coupling arm waveguide and the coupler generate a difference signal , used to generate the tracking signals , at the auxiliary output port related to the coupled te 10 mode .