thin wire approximation

Hi, I'm having some trouble in implementing a coax probe fed DRA. I'm actually using the thin-wire approximation equation as described in many papers, such as Taflove's.
The problem is in the interface between the coax cable FDTD 1D implementation and the DRA FDTD 3D space. When I'm injecting a Gaussian pulse, when the pulse is going down to zero, the fields are going wild.
Do I need to consider any kind of interface issue?
Did anybody have the same problem and then solved?

thanks a lot

You have to define a 1D array that you will use for updating the field along the co-ax cable, you will updat the field concurrently with the 3D field during the time stepping, then you have to define a variable that will serve as your place holder for the excitation into the 3D algorthm so that at each time step you assign the the field at the opening of the co-axial cable(i.e. the field at the lattice point that correspond to the opennig of the feed cable) to the variable and assign the value of the variable to the field at the feed point of the 3D antenna.
Hope I am clear enough.