Systematic study of the cross polarization introduced by broadband antireflection layers at microwave frequencies

Implementation of antireflection layers using structured materials is of common use in millimeter- and submillimeter-wave refractive optic systems. In this work we have systematically studied the effect of such structures in the optical propagation with special emphasis on the cross polarization they introduce. We have performed extensive simulations and experimental verification of several commonly used structures: concentric grooves, parallel grooves, an array of boxes, an array of cylinders, and rectangular- versus triangular-shaped grooves. As a result, we propose optimal structures for demanding applications in terms of polarization and return losses over large fractional bandwidths.