  We propose a random matrix theory to describe the influence of a
time-dependent external field on electron transport through open quantum dots.
We describe the generation of the current by an oscillating field for the dot,
connected to two leads with equal chemical potentials. For low frequency fields
our results correspond to adiabatic charge pumping. Finite current can be
produced if the system goes along a closed loop in parameter space, which
covers a finite area. At high frequency finite current is produced even if the
loop is a line in parameter space. This result can be explained in the same way
as adiabatic pumping but considering the evolution of the system in phase space
rather than in parametric space.
