problem in simulation of antenna with 3D-FDTD

hi to all.
I wrote a 3D-FDTD code in matlab.
I have a cylindrical dielectric antenna that surrounded by air(epsr=1).I know maxwell equations and discretized forms of them both in vaccum and dielectric.but I donn't know how import a coaxial feed to my dielectric antenna.this antenna is like of monopole antenna.
I placed a differentiated gaussian pulse with 1 amplitude in bottom of antenna.but all of field components are zero.
I have a two problem in my project:
1-how import coaxial cable feeding and it's descretized equations in matlab?
2-how treat with different permitivity in vaccum and my antenna regions?
I used from both Mur ABC and PML.
how can I correct my FDTD code?
configuration of my antenna is like of attachment.

1. Coaxial feeding is not trivial, basically you need to use a wave port to solve the correct (2D eigen value problems) modes supported in the matching interface and then you can calculate S-params input impedance and so on.
A easier way is to use a lumped port to do the excitation, your field will still be correct, but you are not able to accurately calculate your S-param and others, since lots of evanescent waves will be reflected to the lumped port and will disturb your calculation.

2. You need to locate if your FDTD cell locates within your dielectric medium region, if it is, then your update coefficient of that particular FDTD cell should change based on the permitivity.

Hope this helps

hi rodgerwxh
I'm confused really.
what do you mean from lamped port or wave port in FDTD?I want write a 3D-FDTD matlab code.how model them?as yet,I can to model geometry of my antenna & PML and I can write code of them.i,e code of descretized maxwell eqautions of my antenna (that is dispersive medium) and free space and CPML.
now I want excite my antenna from it's bottom.like of a monopole antenna above a Grounded box.How write it's code?
how do this work?plese help me step by step...
my antenna has a dispersive medium that I know it's descretized rquations.
this antenna is within a free space that is truncated by CPML.now how excite my antenna with a modulated gaussian pulse by coaxial cable or a simple probe?
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in addition to excitation with coaxial cable and Probe,this is an another configuration of my antenna.how model feed in this picture?

in this picture,from metal connection of between of GND plane and metal sleeve is used for excitation.how model this configuration?