The condition for circularly polarised radiation fields from waveguide apertures is discussed. It is shown that ideal circular polarisation cannot be achieved in practice for elliptical hybrid-mode waveguides, neither for corrugated nor for partly filled dielectric (dielcore) waveguides. The crosspolar performance of the elliptical dielcore waveguide supporting the fundamental hybrid-mode is calculated accurately, confirming its good crosspolar performance which has been previously shown by experiments.