Experimental and theoretical studies are reported of the electrodynamic behaviours, such as current - voltage characteristics (IVCs), microwave self-radiations and dynamic resistances, dV/dI, of granular high- superconducting (HTSC) (YBCO) and (BSCCO) film bridges. We show that the granular structure of bridges can be understood as series-connected independent and inhomogeneous resistively shunted junction (RSJ) arrays.