Lab Procedure Mda

NUST SCHOOL OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCE

MICROWAVE DEVICES AND ANTENNAS LAB REPORT #1 118-MEHRAN MUSTAFA-BEE 3A 6/15/2009

PROCEDURE

TO

MODEL

A

COAXIAL CABLE

IN

HFSS 9

1. Start HFSS 9 software and insert and HFSS design in the project (As shown in the figure). This will open the environment which will assist in the modelling of the coaxial cable. Basically this will be an environment for any activity one wants to do in HFSS. the the

The figure (2) shows environment in which modelling is done.

Figure 1- Inserting a HFSS design

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Figure 2- The working environment

2. A coaxial cable is cylindrical in shape. To draw a cylindrical shape, go to Edit and select “cylinder” from the drop box (see figure 3). Figure 3Selecting to draw a cylinder.

3. When the cylinder option is selected, a black square accompanies the mouse. Bring it near the origin on the axis, left click and then drag outward to draw a circle as shown in figure 4. (Release the left mouse button after clicking once.)

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Figure 4a- Drawing a cylinder

4. Once an arbitrary sized circle is drawn, left click again. Move the cursor in the z direction and notice that a red arrow head is placed on the edge of the cylinder indicating the direction of the cylinder z-axis. Stretch it to an arbitrary length and then left click again. An arbitrary sized cylinder is constructed. A table similar to the one shown in figure 4c where the cylinder can be accurately edited. The options in the table are self explanatory.

Figure 4b- Drawing a cylinder

Figure 4c- Drawing a cylinder

In this lab, the coaxial cable is 50mm in length and the inner conductor has a radius of 0.5319mm. These specifications are entered in the table.

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5. While modelling a coaxial cable in HFSS, only two concentric cylinders are required. One is the inner conductor and the other is the insulation. The outside environment is made vacuum. As seen from the figure, there is an inside cylinder and an outside cylinder around it.

Figure 5- Constructing the outer cylinder

6. Once both the cylinders are drawn complete with the specific dimensions, it’s time to assign the type of material to them. Select the inner cylinder and then right click on it. A drop box will open. Go to “Assign Material” in the drop box. A library of all the materials in HFSS will open. As Page | 5

this is the inner conductor, it should be a perfect conductor. Chose “Perfect Conductor” or “Copper” from the library and click “OK”. This will make the inner conductor a perfect conductor. Similarly, the outside cylinder needs to be a dielectric insulator. A suitable material can be assigned to it in a similar manner (in this case: Teflon).

Figure 6b- Material Library

7. After the materials have been assigned, the next step is to separate the two cylinders. This can be done by subtracting the inner cylinder from the outer cylinder. The inner cylinder must not be deleted completely but it should be cloned.

3D

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Cloning it separate the two cylinders but not completely remove the inner cylinder. Figure 7- Subtracting

8. Next step is to provide boundary conditions. The boundary conditions are only required for the outer cylinder. The boundary to be applied is to the circular face of the outer cylinder. This can be done by first choosing “Face” from the drop box in the upper right corner (as shown) and then selecting the circular face of the outer cylinder. Right click the selected surface and go to assign boundaries and chose “Perfect Electric”. See figure 8 below.

Figure 8a- Setting face selection

Figure 8bAssigning boundary conditions

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9. Now it’s time to apply an excitation to the coaxial cable. Wave ports are to be assigned through which the wave will enter and leave the coaxial cable. These are the two ends to the coaxial cable. The procedure is somewhat the same as assigning the boundary conditions. In this the face of one end is selected. Go to “Assign Excitation” and then chose “Wave Port”. A box will open which will then assign a wave port to the selected end. There is only one setting to be done and that is to renormalize the port to 50Ω. Do the same to the other port as well.

Figure 9- Assigning wave port

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10.Now in the project menu, in the left most box, go to “Mesh Operations”. Select the whole object and assign a mesh to it. The links are shown in the figure. The mesh should be length based. This will create a number of meshes on the object for analysis and modelling. Figure 10- Mesh Operations

11.Now to complete the model, provide an analysis to analyse the drawing and model it in to an actual coaxial cable. Just below Mesh Operations, there’s an option of “Analysis”. Right click on it and choose “Add solution setup”. In the box, assign a number to “Maximum number of passes”. Keep this a low number so that for testing, it doesn’t take long time to analyse.

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Figure 11- Analysis

12.Now chop the coaxial cable from the middle in the XZ plain so that the wave, when applied, can be visible travelling in the coaxial cable. 13.Now, when everything is finalized, validate the design and then start the analysis. After sometime it will provide a report on the model and indicate and errors or warnings. The model will be complete after that.

Figure 12Sectioning

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Figure 13- Plotting electric fields

14.Now select one half of the sectioned coaxial cable right click on it. Now go to “Plot Fields” and in there, select “Mag E”. To see the field pattern inside the cable, go to “Field Overlay” in the project box and select “E-field”. Inside “Efield” there will be Mag_E1. Right click it and select “Animate”. Assign the number of frames and then animate.

Figure 14- Plotting fields.

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The results of the lab assignment are shown on the following pages.

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