1 Transmission Line (TL) Basics
1.1 LAUNCH CST
1. Find and open CST STUDIO SUITE 2018
1. Click on Circuits & Systems >> Schematic.
2. You are now in the circuit schematic capture app of CST. We will be working with this window for a few weeks, so familiarize yourself with the interface.
3. “Block selection tree” is where you set up the simulation. While “Navigation tree” is where you view results and adjust simulation parameters later.
1.2 Matched Termination
4. Select Block selection tree >> Ideal TL >> Drag the Transmission Line Block to the schematic window
5. Now that we have a transmission line (TL) click the block to change its specification in the block parameter list to the values your instructor provides. Which can be found on the bottom of the window in the Block Parameter List.
Default Values:
Impedance: 50
Epsilon: 4.7
Length: Last Digit of student ID # X 1 cm (if 0, use 1)
Mu: 1
Attenuation: 0
6. Next, add two external PORT blocks, , which act as the measurement reference for the Device Under Test (DUT), in this case, is the TL.
7. Double click each of the external terminals (PORTs) to make a connection to the TL.
8. Once you have wired the blocks, we need to set the program to simulate the parameters of interest. To set up the simulation, click add tasks, , under the Home Tab. A pop-up window will appear, similar to the one on the right.
9. Under Circuit >> Double click on S-Parameters, enter the values your instructor provided. Click “OK.” Then Click
Default Values:
Fmin: 0 Hz
Fmax:
10. Next, navigate to the results, by clicking Navigation Tree >> Tasks >> S-Parameters
11. Navigate to each of the four S-Parameter plots. Use your engineering judgment to correct the Magnitude dB (Y-Axis) scaling to a realistic range. This will be graded, make sure the scale makes sense, over the range of values. You may want to convert the dB to linear scale if that helps you.
12. Once you have confirmed that the scales make sense, save the CST file for your record, and take screenshots of the S11, and S21 plots.
13. For the load matched circuit, calculate the value for the last frequancy of the simulated range from the S21 plot, and include the calculation in your report.
14. Use the calculated value to find the value of, include the calculation in your report.
15. Using the calculated value, find in your report.
1.3 Mis-Matched Termination
2. Follow the instructions to the matched circuit above to build a similar circuit.
Default Values for TL Block:
Impedance: 50
Epsilon: 4.7
Length: Last Digit of student ID # X 1 cm (if 0, use 1)
Mu: 1
Attenuation: 0
16. Here we set a different impedance value for the PORT 2 block. You can change the properties of a block by double-clicking it. A window popup similar to the one on the right will appear. Ask your instructor for the values.
Default Values for PORT 2 block:
Fixed Impedance
Impedance Real: Last Digit of student ID # X 100 (if 0, use 1)
Impedance Imaginary: Zero
17. Look at the results, run a sanity check then pat yourself on the back and save the CST file.
18. Use the two CST files, the calculated from above and knowledge from your ECE 302 class to write a MATLAB code replicating the S11 CST results for the same mismatched load used above for the last frequancy point in your range. (3 GHz / Last ID#).
19. Include your MATLAB result, your formulation for the problem, and a full-TEXT copy of the code in your submitted lab report.
20. In your report, discuss your formulation (Math implemented in MATLAB)
21. Compare the MATLAB and CST S11 results for a mismatched load, include both plots.
1.4 Short Termination
22. Next, we study a transmission line terminated with a short circuit. Here we only need a single port.
23. The block used here is a “Transmission Line Open” from the “Ideal TL” folder, as displayed in the schematic.
24. Sample values are shown here; follow your instructor provided values.
Default Values:
Impedance: 50
Epsilon: 4.7
Length: Last Digit of student ID # X 1 cm (if 0, use 1)
Mu: 1
Attenuation: 0
25. In your lab report, include the screenshots and explain the significance to the energy transmitted and reflected at each port.
26. Draw on your ECE 302 course to explain what is happening with the S11magnitude and phase values
27. What is an analougus value to S11 have you calculated in your ECE 302 course?
1.5 Open Termination
Next, we study a transmission line terminated with an open circuit. Here we only need a single port. Sample values are shown below, follow your instructor provided values.
Default Values:
Impedance: 50
Epsilon: 4.7
Length: Last Digit of student ID # X (if 0, use 1)
Take a screenshot of the linear (NOT dB) S11 value for both the magnitude and phase, explain the meaning of the result in your report.