A waveguide has distal, medial and proximal sections. The distal and medial sections rotate relative to each other and to the proximal section. In a first configuration, the waveguide transforms linearly polarized electromagnetic radiation at the proximal end of the proximal section to linearly polarized electromagnetic radiation at the distal end of the distal section and vice versa. In a second configuration, the waveguide transforms linearly polarized radiation at the proximal end of the proximal section into circularly polarized electromagnetic radiation at the distal end of the distal section and vice versa. Preferably, the distal and medial sections include respective eight-wavelength polarizers and the proximal section includes a quarter-wavelength polarizer. A multi-band antenna feed includes two such waveguides, one nested inside the other, for transforming electromagnetic radiation of respective frequency bands.