Per Skov-madsen’s research while affiliated with Technical University of Denmark and other places

... It is the key part in the design of CP horn antenna. At present, the design methods of circular polarizer in this kind of antenna mainly include inserting metal or dielectric diaphragm in the waveguide, [7][8][9][10][11][12][13][14] slotting in the waveguide, [15][16][17][18][19][20] chamfering in the waveguide, 21 loading ridge structure on the inner wall of the waveguide, 22 inserting multiple groups of pins in the waveguide, 23 using corrugated waveguide, 24 using elliptical waveguide 19 and by loading various kinds of artificial hypersurfaces 25,26 or anisotropic lens structures 27,28 at the online polarization antenna terminals. In Shu et al., 18 a broadband dual-CP antenna is designed by combining the circular polarizer with symmetrical slot structure loaded on the inner wall and the orthogonal mode transducer. ...

Reference:

Design of millimeter wave broadband polarization reconfigurable horn antenna based on elliptical waveguide polarizer