Abstract: This specification discloses a microwave circular polarizer for converting a linearly polarized microwave signal to a circularly polarized microwave signal and vice versa. A transducer, such as an Orthomode junction is used to obtain a power split or a power recombination of two orthogonal linear polarizations. To obtain the phase delay required to generate a circularly polarized signal from two linearly polarized signals, the polarizer includes a phase compensator with a pair of waveguides which have appropriate width and length so that signals passing therethrough develop a phase difference therebetween and a composite circularly polarized signal results. The amount of phase shift occurring in each of the waveguides varies with the frequency of the signal in such a way as to produce a high purity circular polarization over a broad frequency band. A phase shift of 90.degree.