| This thesis is concerned with wave propagation on superconductive strip transmission lines which incorporate Josephson tunneling along the length. Attention is primarily focused on fluxon propagation and its effects on the volt-ampere characteristics of the Josephson junctions. Analytical solutions, computer simulations, and a mechanical model are used to explain the experimental measurements on long junctions. These devices were fabricated using niobium and lead superconductors with a niobium oxide barrier formed by rf or thermal oxidation.; Our experimental measurements of the DC Josephson current show that in most practical cases, this current is concentrated near the boundaries of the junctions. This causes the junction to switch prematurely to a dynamic state by admitting fluxons from the edges. Consequently, long Josephson junctions, regardless of their geometries, support DC Josephson currents which are usually much less than values predicted using uniform current distribution.; The current singularities, at well defined voltages, on the volt-ampere characteristics of the Josephson junctions are due to resonant propagation of fluxons. We have shown that, for proper bias conditions, a fluxon may be reflected back, not as one antifluxon but several. Over a period, a certain number of fluxons propagate in one direction in part of the cycle and a different number of antifluxons propagate in the opposite direction in the remainder of the period. These additional asymmetric modes result in steps centered between the previously known steps of the volt-ampere characteristics.; Flux flow propagation of fluxons is, on the other hand, defined as a situation where fluxons are generated at one boundary and expelled from the opposite one. The unidirectional motion of fluxons is manifested by a branch on the volt-ampere characteristics with a voltage location depending on the rate at which fluxons enter the device. We have demonstrated that the current-voltage curves and the dependence of DC Josephson currents on an external magnetic field may be symmetric or asymmetric for such devices depending on the current density distribution. Furthermore, we have shown, both experimentally and by using a computer simulation, that such asymmetries can be observed and changed on a single device by using several different entry points for current electrodes. Finally, the feasibility of oscillators and amplifiers, based on the two types of fluxon propagation, were investigated using both experimental and simulation results. |
