  This paper is devoted to the study of travelling fronts of reaction-diffusion
equations with periodic advection in the whole plane $\mathbb R^2$. We are
interested in curved fronts satisfying some "conical" conditions at infinity.
We prove that there is a minimal speed $c^*$ such that curved fronts with speed
$c$ exist if and only if $c\geq c^*$. Moreover, we show that such curved fronts
are decreasing in the direction of propagation, that is they are increasing in
time. We also give some results about the asymptotic behaviors of the speed
with respect to the advection, diffusion and reaction coefficients.
