  We present results of deep polarization imaging at 1.4 GHz with the Dominion
Radio Astrophysical Observatory as part of the DRAO Planck Deep Fields project.
This deep extragalactic field covers 15.16 square degrees centered at RA = 16h
14m and DEC = 54d 56', has an angular resolution of 42" x 62" at the field
center, and reaches a sensitivity of 55 microJy/beam in Stokes I and 45
microJy/beam in Stokes Q and U. We detect 958 radio sources in Stokes I of
which 136 are detected in polarization. We present the Euclidean-normalized
polarized differential source counts down to 400 microJy. These counts indicate
that sources have a higher degree of fractional polarization at fainter Stokes
I flux density levels than for brighter sources, confirming an earlier result.
We find that the majority of our polarized sources are steep-spectrum objects
with a mean spectral index of -0.77, and there is no correlation between
fractional polarization and spectral index. We also matched deep field sources
to counterparts in the Faint Images of the Radio Sky at Twenty Centimeters
catalogue. Of the polarized sources, 77% show structure at the arc-second scale
whereas only 38% of the sources with no detectable polarization show such
structure. The median fractional polarization is for resolved sources is 6.8%,
while it is 4.4% for compact objects. The polarized radio sources in our deep
field are predominantly those sources which are resolved and show the highest
degrees of fractional polarization, indicating that the lobe dominated
structure may be the source of the highly polarized sources. These resolved
radio galaxies dominate the polarized source counts at P_0 = sqrt(Q^2 + U^2) <
3 mJy.
