  PSR B0818-41 is one of the few pulsars which show multiple drift regions
having well defined phase relationship. In this paper we report new results
from the multifrequency GMRT observations of this pulsar. Significant linear
polarization is observed with depolarization at the edge of the profile, due to
orthogonal polarization. Circular polarization changes sign near the middle of
the pulse profile at 1060 MHz, but not observed at 325 and 610 MHz. Remarkable
frequency evolution of polarization angle (PA) is observed. Based on the
frequency evolution of average profile, PA swing and results from subpulse
drifting, we propose two possible emission geometries, alpha~11 deg, beta~-5.4
deg and alpha~175.4 deg, beta~-6.9 deg. Simulation of the pulsar radiation
pattern with both these geometries reproduces the observed features in the
drift pattern quite well. In addition to the remarkable subpulse drifting
observed at 325 MHz, we report subpulse drifting at 244 and 610 MHz. We observe
changes of drift rates, transitions from negative to stationary and stationary
to negative drift rates, with some connection with nulls. Though P3m is the
same for all the drift regions, P2m and Delta(Phi) values are different for the
inner and outer drift regions. The peak emission from the leading and the
trailing outer regions are offset by ~ 9 P1. Utilising this information, we
solve the aliasing problem and predict P4~ 10 s, which makes it the fastest
known carousel. The drift pattern from the two rings are phase locked for PSR
B0818-41. The same is found to be true for, all pulsars showing drifting in
multiple rings of emission and puts constraints on the theoretical models of
pulsar emission mechanism and, favors a pan magnetospeheric radiation
mechanism.
