A circular dielectric polarizer can have a cylindrical shape and include a dielectric slab, a dielectric core, and at least one air cutouts portions of the dielectric core. The dielectric slab can include a first dielectric material and have a thickness centered about an axis of the cylindrical shape. The dielectric core can include a second dielectric material. Portions of the dielectric core can be located on different sides of the dielectric slab. The dielectric core and the dielectric slab can form the cylindrical shape. The dielectric constant of the first dielectric material can be higher than a dielectric constant of the second dielectric material. Parameters of the circular dielectric polarizer, the dielectric slab, the dielectric core, and the at least one air cutout are selected to obtain approximately a 90 degree difference in phase in a signal passing through the circular dielectric polarizer at a target frequency.