You can create a cross section from scratch, as described in section 5.2, or you can start with one of the example cross sections that is distributed with TNT, and modify it according to your needs.
The example cross sections are in the TNT installation directory, under .../TNT/examples. Choose File Open from the menus, navigate to the example directory, and choose one of the cross section files. You may then modify it and save it elsewhere with File Save As.
To create a new cross section, you can choose File New from the menu. This will clear any existing structures from the layer stackup and the drawing window.
Enter a model title in the Title field. The model title should be descriptive, and will be saved with the cross section model. Set the units to match the physical dimensions of your transmission line structure.
Start adding structures to the layer stackup by creating a ground plane, then adding layers of dielectrics and conductors. Clicking on the New Ground Plane button will open a new window allowing you to define the structure name and the thickness. Clicking Add on the dialog will add the ground plane to the layer stackup and the drawing.
Continue by adding dielectric layers. Click on the New Dielectric Layer button to open the dielectric properties entry form. Each layer has a name, thickness and material characteristics. Make sure that the default units selected at the top of the screen match your intentions for the layer dimensions. (You don't really want a 42 meter thick dielectric, do you?)
Layers will appear in the cross section drawing as you add them, and layer names will appear in the layer stackup. If you do not add a top ground plane (i.e., microstrip), then air is assumed to be above the top defined layer.
Add conductors to the cross section by selecting one of New Rectangle, Trapezoid, or Circular Conductors buttons, which will open a new properties dialog for the conductors. Each conductor structure has dimensions and material properties. When you Add these conductors, they will rest atop the last defined dielectric layer. You can add a single conductor, or a group of identical conductors with a specified pitch. You can specify X and Y offsets to the conductors.
You can also define New Dielectric Blocks which are arbitrary rectangles of dielectric material. These blocks can be used to define non-planar (conformal) dielectric structures.
Select cross section elements by clicking on them either in the Layer Stackup window or on the cross section drawing. Double-clicking on a cross section element opens its properties dialog. You can choose to Modify the properties or Delete the structure.
You can rearrange the order of the layer stackup by clicking and dragging structures in the Layer Stackup window.
The cross section drawing is supposed to give you a graphical depiction of your transmission line cross section. Unfortunately, the scale of many conductor definitions makes it difficult to see the drawing easily. You may need to use the zoom buttons to get a better view of the structures.
You can print the cross section picture on a postscript printer by choosing File Print from the menu. The print dialog offers several options, including paper size, orientation, and output specification.
On Unix systems, the default printer command is lpr, which should work for most installations. Choose a different print command, or add options, if you choose. On Windows systems, the default printer command is PrFile32.exe, which is a small utility program that directs the postscript to a Windows print queue. If you do not have a postscript printer, you will likely get many pages of printed postscript commands.