  Measurements of the polarization of radio emission are subject to a number of
depolarization effects such as bandwidth depolarization, which is caused by the
averaging effect of a finite channel bandwidth combined with the
frequency-dependent polarization caused by Faraday rotation. There have been
very few mathematical treatments of bandwidth depolarization, especially in the
context of the rotation measure (RM) synthesis method for analyzing radio
polarization data. We have found a simple equation for predicting if bandwidth
depolarization is significant for a given observational configuration. We have
derived and tested three methods of modifying RM synthesis to correct for
bandwidth depolarization. From these tests we have developed a new algorithm
that can detect bandwidth-depolarized signals with higher signal-to-noise than
conventional RM synthesis and recover the correct source polarization
properties (RM and polarized intensity). We have verified that this algorithm
works as expected with real data from the LOFAR Two-metre Sky Survey. To make
this algorithm available to the community, we have added it as a new tool in
the RM-Tools polarization analysis package.
