  G156.2+5.7 is a large supernova remnant (SNR) first discovered in the ROSAT
X-ray survey but radio observations are rare because of its low surface
brightness and large size. Radio continuum and polarization images of the SNR
G156.2+5.7 at lambda 6 cm are presented for the first time to be discussed in
the context with available data to investigate its physical properties. We
obtained an integrated flux density for G156.2+5.7 of S6cm= 2.5+-0.5Jy. The
spectral index of the integrated emission is alpha=-0.48+-0.08 between lambda
74 cm and 6 cm excluding compact radio sources. We also obtained a spectral
index map, which shows little variation between the shells and the central area
of the SNR. This is consistent with the constant integrated flux density
spectrum. Highly polarized radio emission has been detected from the SNR shell,
but also from a central patch, which probably originates in the front part of
the spherical SNR shell. We derived the distribution of rotation measure from
polarization data at 11 cm and 6 cm and found RM gradients of opposite
direction in the SNR shell. The SNR G156.2+5.7 is unusual by its exceptionally
high X-ray brightness and very low surface-brightness in the radio range. The
magnetic field is very well ordered along the shell periphery as expected for a
compressed ambient magnetic field. A toroidal magnetic field component is
indicated by the RM distribution. (abridged)
