Broadband circular polarizers:


Typical design: dielectric slab in circular waveguide
1/4-wave retardation at 45 degrees
Typical problem: it's only 1/4-wave at one frequency!
New solution: use combinations of retarder elements at different angles
Formalism: retarders are elements in SU(2) or SO(3)


Find achromatic solutions analytically or with computer search