  We present a systematic study of the circular polarization in pulsar
integrated profiles, based on published polarization data. For core components,
we find no significant correlation between the sense-change of circular
polarization and the sense of linear position angle variation. Circular
polarization is not restricted to core components and, in some cases, reversals
of circular polarization sense are observed across the conal emission. In conal
double profiles, the sense of circular polarization is found to be correlated
with the sense of position-angle variation. Pulsars with a high degree of
linear polarization often have one hand of circular polarization across the
whole profile. For most pulsars, the sign of circular polarization is the same
at 50-cm and 20-cm wavelength, and the degree of polarization is similar,
albeit with a wide scatter. However, at least two cases of frequency-dependent
sign reversals are known. This diverse behaviour may require more than one
mechanism to generate circular polarization.

Astrophysics