ASSIGNMENT QUESTIONS Answers to Questions

Some of the Boundary Conditions and other details is missing! All assignments are general RF/MW engineering application problems, and students may need to do some modification work to fit the simulation method and design requirements. The workshop demonstrator should explain more in the laboratories.

Also: Since we use FDM, all mesh and grid should have the same size dx=dy and all microstrip ("Thin Metal Strip) should have no thickness for FDM approach. The width of microstrip and structure size can be modified.

FDM/FEM Assignment No. 1 QUESTION The "Microstrip line on the circuit board" image does not state the boundary conditions along the sides or top (of the dielectric). (i.e. along the 'h' length and across the top, before the "Thin Metal Strip").

FDM/FEM Assignment No. 1 ANSWER The bottom ground plane must be 0V. Since this is an open field structure, the student requires to take a large simulation domain (cover more free space area), then the student can use FDM interface formula to deal with the points on the interface (around the "Low-Loss dielectric" material). The points on the boundary will be unknown (open boundary case, Nuemann boundary).

FDM/FEM Assignment No. 2 QUESTION The "Suspended-substrate microstrip line" seems to be missing dimensions. The height of the dielectric is know (1mm) but the length is not provided. Nor is the position of the metal strip given, but I assume it is to be taken as the center of the dielectric.

FDM/FEM Assignment No. 2 ANSWER The dimension should be given by the student. They are to prove if the best position is in the centre. The width of microstrip and structure size can be modified to match FDM mesh and grid size.

FDM/FEM Assignment No. 3 QUESTION The Center Strip and Ground plane widths are given, but the width of the gap between them is not known.

FDM/FEM Assignment No. 3 ANSWER Since we use FDM, the gap should have the same size as the width of centre strip. The width of microstrip and structure size can be modified to match FDM mesh and grid size. This is an open field structure, the student requires to take a large simulation domain (cover more free space area), then use FDM interface formula to deal with the points on the interface.

FDM/FEM Assignment No. 4 QUESTION The Conductor width is given, but the width of the gap is unknown. Also the boundary conditions about the "microstrip" is unknown.

FDM/FEM Assignment No. 4 ANSWER The Conductor width can be 2 times Gap width. Thickness of the strip is zero. This is an open field structure, the student requires to take a large simulation domain (cover more free space area), then student can use FDM interface formula to deal with the points on the interface.

General Question 1 QUESTION The questions are based on materials with differing interfaces with gaps. But lecture notes do not seem to give examples of calculating materials with gaps.

General Question 1 ANSWER The gap is to naturally satisfy the FDM grid. It has been covered in the lecture notes, in the example with two insulation gaps for 100V and 0V for U shaped metal case. The interface formula can do the gap problem naturally.

General Question 2 QUESTION The lecture notes, Fig. 5.5 illustrates solving with 2 different material interfaces. Yet on the Assignments (with the gaps) there will be 3 different material interfaces (at certain points).

General Question 2 ANSWER It is still treated as two materials. That is what is expected for a student to learn from the workshop and assignment. Again see the Laboratory demonstrator for more on this.

Do you need to use the COMSOL Toolbox? The COMSOL application was covered in lecturers mainly to let students know that the FDM technique is certainly utilised, and that this was a quick (easier than the student determining the huge matrix themselves) way of getting a FDM output. The student is NOT expected to know how to use COMSOL.

Do you need to use the PDE Toolbox? That was a past years requirement. The PDE Toolbox was not covered this year. The student is just to provide the results with some verification, such as refine the mesh.