  We present a multi-frequency, dense radio monitoring program of the blazar
OJ287 using the 100m Effelsberg radio telescope. We analyze the evolution in
total flux density, linear and circular polarization to study the jet structure
and its magnetic field geometry. The total flux density is measured at nine
bands from 2.64 GHz to 43 GHz, the linear polarization parameters between 2.64
GHz and 10.45 GHz, and the circular polarization at 4.85 GHz and 8.35 GHz. The
mean cadence is 10 days. Between MJD 57370 and 57785, OJ287 showed flaring
activity and complex linear and circular polarization behavior. The radio EVPA
showed a large clockwise (CW) rotation by ~340$^{\circ}$ with a mean rate of
-1.04 $^{\circ}$/day. Based on concurrent VLBI data, the rotation seems to
originate within the jet core at 43 GHz (projected size $\le$ 0.15 mas or 0.67
pc). Moreover, optical data show a similar monotonic CW EVPA rotation with a
rate of about -1.1 $^{\circ}$/day which is superposed with shorter and faster
rotations of about 7.8 $^{\circ}$/day. The observed variability is consistent
with a polarized emission component propagating on a helical trajectory within
a bent jet. We constrained the helix arc length to 0.26 pc and radius to $\le$
0.04 pc as well as the jet bending arc length projected on the plane of the sky
to $\le$ 1.9-7.6 pc. A similar bending is observed in high angular resolution
VLBI images at the innermost jet regions. Our results indicate also the
presence of a stable polarized emission component with EVPA (-10$^{\circ}$)
perpendicular to the large scale jet, suggesting dominance of the poloidal
magnetic field component. Finally, the EVPA rotation begins simultaneously with
an optical flare and hence the two might be physically connected. That optical
flare has been linked to the interaction of a secondary SMBH with the inner
accretion disk or originating in the jet of the primary.
