Lab Experiment 1

Transmission Lines – Calibration of a Network Analyzer and Finding a Cable`s Impedance

(Revised on 3/10/12)

Notes to the students:

Please be very careful when you use the Network Analyzer. DO NOT remove any connectors. Please change the cables very gently! If you use the calibration tools, make sure everything goes back into the box and return the box to its original place. Keep the lab clean! Make sure you sign the signup sheet.

Required components

 

Lab Submission: This is a FORMAL lab report. Please print double-sided to save papers! Each plot must have a figure number and description. Figures must be referred in the text. Each lab step/question must be clearly referenced in your lab report. Everything must be typed. Each student must submit a separate report. You can work in groups and share the snap shots.

Your lab report must contain the following:

1.     Abstract (state the objectives of the lab in Parts I and II)

2.     List of instruments used in the lab

3.     General setup for Part I and Part II – must include diagrams and brief description of each setup (what is the purpose of the setup)

4.     Answer all the questions in Part I and Part II – include the question and question number. Reference the lab setup if required.

5.     Conclusion (what did you learn in this lab (seriously)?

a.      PRE-LAB

b.     Part I

c.      Part II

6.     References (references must be cited in the lab – use the correct format)

7.     Answers to your Pre-lab questions.

8.     On a separate sheet answer the following survey questions:

a.      Was this lab helpful? Evaluate each part on scale of 1-10: Pre-lab / Part I / Part II

b.     Did this lab help you learn about transmission lines more?

c.      How much time did you spend to complete this lab?

d.     Do you feel you learned about Network Analyzers and what they do?

e.      Any suggestions about this lab (other than the fact that is long)?

 

Pre-lab

A-    Carefully read the provided handout first.

B-    Redo the transmission line problem on page 475 (fig. 26-6) of the provided handout.

a.      Use your own Smith Chart to show all the parameters.

b.     In addition, write a Matlab program to obtain all the answers.

c.      Make sure your results are consistent with the results shown in pp. 479.

d.     Submit your Smith Chart, Matlab program, and the final results in tabulated form.

A-    Clearly, define the following parameters and clearly explain their impact:

a.      Return Loss,

b.     Reflection Loss,

c.      Transmission Loss Coefficient.

B-    For the example above, find the value of the inductor. Then, show all the load impedances on a Smith Chart for the following 10 frequencies: 100M, 200MHz, 300 MHz to 1GHz (use your program).

a.      Plot the values on the Smith Chart. Explain your observations.

b.     Use the Simulator (Module 2.4 and 2.5) to verify your answer. Show at least one snap shot supporting your answer.

Lab - Part I  - Calibrating the Network Analyzer

A-    Describe the steps required to calibrate the Network Analyzer at 1 GHz. Be clear! Note: Make sure the COR on the top left hand side of the screen is ON after calibration!

B-    After the calibration is completed, show the impedance and SWR for open, short, 50-ohm loaded system on a Smith Chart. You can use your snap shots from the Network Analyzer (NA).

C-    What is the source impedance of the system (NA)?

D-    If the system happen to be matched with a 75-ohm load, show where the impedance will be on the Smith Chart. Explain your answer.

E-    Show the impedance and SWR results for the 50-ohm load (in the calibration tool box) for a range of frequencies e.g., 100MHz, 200MHz, 500MHz, 800 MHz and 1GHz. Explain your observations. Show snap shot of your results. Note: Make sure the system is calibrated for EACH frequency! (COR must always be visible)

F-    Repeat the step above (part E) but this time set the START and STOP frequencies to 900MHz, and 1GHz, respectively (don`t forget calibrating the NA first). Explain your observations. Show snap shot of your results.

G-    How much power (in Watt) is being transmitted by the source? (don`t change it)

H-   Within the START and STOP frequency range how many frequency points are being measured? (don`t change anything)

I-     Using the LINEAR MAG display (use FORMAT button) record the values for 100 MHz and 1GHz when the 50-ohm load is in place. Explain your observations.

J-      Using the LOG MAG display (use FORMAT button) record the values for 100 MHz and 1GHz when the 50-ohm load is in place. Explain your observations.

K-    What is the relationship between the LOG MAG and LINEAR MAG values? How are they related to one another?

Lab - Part II – Characterizing a Transmission Line

  1. Refer to the Operation and Service Manual in the calibration kit and explain breifly how the NA measures the ratio of reflected/incident waves.
  2. Measure the impedance of the combined THICK coax cable (Type-N connector) and AMPHENOL connector at fo=1GHz and span=10 MHz. Explain how you performed the measurements.
    1. What is the impedance of the coax at 1GHz?
    2. What happens if the frequency increases or decreases?
  3. Connect the cable to the 50-ohm load.
    1. Observe the the impedance using Smith chart. What do you see? What does it mean?
    2. How is SWR changing?
    3. Check the LOG MAG. How is it chaging?
  4. Connect the same cable to the load with a resistor attached to it. Use the NA to
    1. Observe the the impedance using Smith chart. What do you see? What does it mean?
    2. Observe how SWR is changing over different fequencies.
    3. Check the LOG MAG. How is it chaging?
  5. Make a table and quantitatively compare the impedance results for different loads. You can do this by connecting different resistors or a capasitor to the provided connector. Explain your results.
  6. Recalibrate the frequecies for 2-3 GHz. Then, connect the type-N THICK cable to the NA. Make sure the 50-ohm load is NOT attached to the coax; that is the far end of the cable should be open.
    1. What do you observe on the Smith chart? Are the circles overlapping or spiral? Are what happens as the frequency increases?
    2. What do you observe for PHASE? At what frequency the phase is zero? (call it fp)
    3. Assume the length of the cable is L=1.83 ft (use 0.3048 m/ft to convert). Note that we should add 2.5 cm to account for the N jack adaptor connected to the NA. Calcualte the total length from the NA to the end of the cable.
    4. The time (delta_t) that a wave takes to travel down a transmission line of length L and return to the network analyzer. By measuring the delta phase (delta_phi) for a small frequency increment (delta_omega), we get the actual delay over a small group of frequencies. Calculate delta_t.
    5. Phase velocity can be found from 2L/delta_t. Calculate the phase velocity.
    6. Compute phase constant for the transmission line (assume u_1 = 1 and f = fp)
    7. Calcualte the relative permitivity of the cable, use c=3x10E8.
    8. Assuming Zo is 50 and u _r =1 find L' and C'. Compare your answes with RG217 Spec sheet (C' is 30.8 pF/ft) [I am not sure how close your values will be].
    9. Calcualate the percentage of reflected average power.

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