We have studied the static I-V characteristics and vortex dynamics in stacked Nb/AlO$-x$//Nb Josephson junctions. In josephson junction stacks consisting of two junctions having identical maximum Josephson supercurrent I$-c$/,I$-c$/ versus H characteristics deviating from the Fraunhofer pattern have been observed, implying that a structural phase transformation to a triangular vortex lattice occurs with increasing H. Interjunction coupling leads to splitting of the Swihart mode; which manifest itself as Fisk steps with different voltage spacings. When subjected to microwave radiation, the I-V curves of the stacked Josephson junctions exhibit new features which are absent in single junctions.
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