We have investigated how the presence of a defect in two coupled quasihyphen;onehyphen;dimensional quantum wires influences the propagation properties of guided electron waves in the system. The defect potential in the two dimensional electron gas is modeled by a two dimensional dgr; function. In elastic scattering, the transfer of the electron among various eigenstates of the uncoupled quantum wires and from one wire to the other is largely affected by the defect potential. For the single mode shallow potential well system, the defect causes incomplete energy transfer between the channels. As the position of the defect varies along the channel, the characteristics of the mode amplitude functions change dramatically as the defect passes through nodes of the amplitude function of the incident waves in the channel. When the defect position is away from these nodes the amplitude functions of the transmitted waves reduce greatly due to the large reflection by the defect. And their variation never reaches zero as in the case without defect. When the defect position is near these nodes the tunneling characteristics between the two channels are as if the defect is absent since the reflection is minimal. For the strong scatterer we find a pinning effect in that the mode amplitude function of the channel where the defect is located always has one of its transmission minima pinned down to the defect. We introduce a possible way of injecting the propagating electron into a particular channel and at a given longitudinal position, by controlling the position of the defect in the structure. In the multimode deep potential well structure, the transfer from an eigenstate of the uncoupled quantum wires to the other states is greatly enhanced and the characteristics of the amplitude functions are dramatically changed by intersubband scatterings.
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