EEE161 Applied Electromagnetics Laboratory 1

Transcription

1 Dr. Milica Marković Applied Electromagnetics Laboratory page 1 EEE161 Applied Electromagnetics Laboratory 1 Instructor: Dr. Milica Marković Office: Riverside Hall milica@csus.edu Web: milica 1 Learning Objectives In this lab you will 1. Analyze the effects of coaxial cable to step and sinusoidal voltage at the input and the output of the cable. 2. Interpret phase and time delay as they relate to voltages and currents on transmission lines. 3. In ADS create a workspace, schematic diagram 4. perform Transient simulation with a coaxial cable 5. Label nodes, then use an equation in data window to display results 6. display simulation data, tune the circuit parameters and save files. 2 Report Consult with your lab instructor what kind of report they want to see! For example, in a doc file, snip the text of the problem assigned, then just cut and paste in a word file the circuit and the simulation you performed. Explain the steps you are taking, and thoroughly explain each simulation results figure. Have you expected these results or not? Do you think the simulation is correct? How does the simulation relates to other simulations performed? Submit ONE report per group in SacCT. 3 ECS Login You need to have ECS login and password. This login is different from CSUS login (aka Saclink login) that you use to check your . If you don t have the login, go to the Riverside Hall second floor computer lab and request a login from IT. You will not be able to login to ECS computers unless you have ECS login.

2 Dr. Milica Marković Applied Electromagnetics Laboratory page 2 4 Coaxial Cables - Background Coaxial cables are used extensively in electrical engineering. Some examples are: Distribution of Cable TV, Connection between antennas and power amplifiers in base stations for cell phones, some internet cables are coaxial (what is usually called an Ethernet cable is a twisted-pair cable, not coax). Figure 3 shows an RG-59 coaxial cable. Figure 1: RG-59 Coaxial Cable. A-Plastic Cover, B-Woven Copper Shield, C-Dielectric Insulator, D-Solid Copper-Clad Steel Wire. cable Google Search for and download Data Sheet for Pasternack RG-59 coaxial cable. An excerpt from RG-59 data sheet is shown if Figure 4. 5 Speed of electromagnetic waves Electromagnetic waves propagate in air (ɛ r = 1) with the speed of light c= m. However, in s dielectrics where ɛ r > 1, the speed is: v = c ɛr (1) Which dielectric is used in RG-59? Calculate the speed of waves in RG-59, then compare it with the data sheet. How is data sheet expressing the speed? Can you explain what is this the percentage of? Now you know how to calculate the speed of electromagnetic wave. How much time will an electromagnetic wave need to travel over an 11.5 inch line if the dielectric in the line is PE (Polyethylene)? This time is called time-delay τ. Remember that the waves travel with constant speed, Equation 2. If the distance traveled is d, and the speed is v, what it the time τ, Equation 3, that the signal needs to travel distance d? Be careful with units. The speed of em waves, c, is given in m s and the distance is given in inches. You need to convert units first.

3 Dr. Milica Marković Applied Electromagnetics Laboratory page 3 Figure 2: Excerpt from RG-59 Data Sheet v = d t τ = d v (2) (3) Next, we want to know if a sinusoidal signal at frequency f = 0.5 GHz is delayed for about the time τ, what will the phase shift be? The sinusoidal signals are written as v(t) = sin ωt. If the signal is delayed for the time τ, then the delayed signal v(t τ) is given in Equation 4. If we multiply through ω with t and τ to get Equation 5 v(t τ) = sin (ω(t τ)) (4) v(t τ) = sin (ωt ωτ) (5) From here, by inspection, we see that the phase is given by Equations 6-7. In degrees, using unit conversion, the phase shift is θ rad = ωτ (6) θ rad = 2πfτ (7) θ deg = 360 f t (8)

4 Dr. Milica Marković Applied Electromagnetics Laboratory page 4 6 Coaxial Cables - Background Coaxial cables are used extensively in electrical engineering. Some examples are: Distribution of Cable TV, Connection between antennas and power amplifiers in base stations for cell phones, some internet cables are coaxial (what is usually called an Ethernet cable is a twisted-pair cable, not coax). Figure 3 shows an RG-59 coaxial cable. Figure 3: RG-59 Coaxial Cable. A-Plastic Cover, B-Woven Copper Shield, C-Dielectric Insulator, D-Solid Copper-Clad Steel Wire. cable Google Search for and download Data Sheet for Pasternack RG-59 coaxial cable. An excerpt from RG-59 data sheet is shown if Figure 4. 7 How to login to Hydra to access ADS We will use Keysight s (former Agilent, even former-er HP) ADS. You can simulate circuits using various simulation techniques in ADS: AC simulation, Transient simulation, Small-Signal simulation, Harmonic Balance simulation, Envelope simulation etc. Each of these is targeted to a specific type of circuit and application. In this class we will first use Transient simulation. This is a simple time-domain simulation, which means that the circuit is solved by solving differential equations for voltages, just like what you did in ENGR17. Transient simulation results will display transients as well as steady-state solution for voltages and currents. Transients are voltages and currents that occur in the circuit when we turn on the generator, and before they settle to their permanent, steady-state values. First login to the computer that your lab is held in with ECS login and password. 1. If you are accessing Hydra from computers running Linux (for example from RVR3009), follow directions provided by the instructors. 2. If you are accessing Hydra from computers running Windows, search for Remote Desktop Connection. To Login use

5 Dr. Milica Marković Applied Electromagnetics Laboratory page 5 Figure 4: Excerpt from RG-59 Data Sheet ECS\USERNAME and your password. 3. It is very important NOT to close any black windows that will start poping up when you login to Hydra. If you do close one by accident, just log out, and log back in again. 4. Find ADS on the list of programs. It is usually called Advanced Design System (year). 5. Open a new workspace, by following step-by-step instructions given in Figure You have to save this new workspace on T: drive. ADS will not allow you to save it to C: drive! If you don t have the T: drive, check step c) above! 7. Click on the Schematic icon on the top bar of the Advanced Design System (year) (Main) window. 8. Do not select any templates, and cancell Schemtic Wizard window 9. The Schematic Window should open. 8 Setup a transient simulation of a coaxial cable with step voltage in ADS Sometimes it is not quite clear why do we need to study coaxial cables. After all, in EEE117 lab we use coaxial cables to connect the generator to the breadboard, but we don t make any assumptions

6 Dr. Milica Marković Applied Electromagnetics Laboratory page 6 (a) Go to Start, All Programs, Advanced Design System (b) Close this window (c) This is the main ADS window. (d) Create new workspace. (e) Name your new workspace as HW1 wrk, then click next, next,...,finish Figure 5: Create a new workspace.

7 Dr. Milica Marković Applied Electromagnetics Laboratory page 7 or considerations about it. This is because the frequency of the signals we re using in EEE117 is very low. When the frequency increases, transmission line effects become significant. In this section we ll start studying how and why transmission lines effects occur in circuits. We will use ADS to setup the simulation shown in Figure 9(a) on a schematic diagram. Open a schematic diagram in ADS and under TLines ideal, select COAX MDS, and place it on the schematics, as shown in Figure 6(a). Now, using data sheet from Figure 4 enter the correct parameters A, Ri, Ro. For Ro use the outside radius of the coax. Set T=0, Er=2.25 (Coaxial cable s dielectric is PE - Polyurethane), leave Cond1 and Cond2, Mur, TanD as they are. As shown in Figure 7, from time-domain sources pull-down menu, select VtStep, and from Lumped Elements pull-down menu select a resistor. Set the resistance of the resistor to 75Ω. From Simulation- Transient pull-down menu select TRANS. To setup the transient simulator, double click on the Transient Simulation on your schematic diagram. Then: 1. Set Start time to 0 ns (it is likely already set to 0ṅs) 2. Set Stop time to 10 ns 3. Set MaxTimeStep to 0.1 ns (this is the sampling rate - you will learn more about that in EEE180) 4. Click on the Integration tab and set the Time step control method to Fixed. This means that the simulator will use only the time step specified. Now, label the input and output voltage nodes with V in and V out by using NAME icon on top of the schematic diagram window: To simulate the circuit, click on the Simulate pull-down menu from the top of the schematic diagram, then click on Simulate (or click on the gear icon on top of the schematic diagram, or press F7 on the keyboard). New Data Display window will open. Follow directions as shown in Figure 8 to display input and output voltage. You should end-up with the Data Display as shown in Figure 9. Q Why is the otput signal delayed for about 1.43 ns? In your answer, use at least the following vocabulary words: speed of electromagnetic waves, dielectric, dielectric constant, coaxial line length, time delay. 9 Setup a transient simulation of a coaxial cable with sinusoidal voltage in ADS Now, you will repeat the previous simulation with a sinusoidal generator. Save the schematic diagram you made with a different name. For example, sinusoidalsignal. Then remove the step voltage and from the same pallete (time-domain signals) replace it with V_1 Tone

8 Dr. Milica Marković Applied Electromagnetics Laboratory page 8 (a) Placing a model of a coaxial cable in ADS (b) Schematic representation of a coaxial cable model parameters in ADS (c) Description of coaxial cable model parameters in ADS. Figure 6: Simulation of coaxial cable in ADS.. Label the input node with V in and output node with V out. Simulate the circuit and display the input and output voltages as a function of time (this is the default for transient simulation). Observe the time delay, as shown in Figure 11. Q How does this time delay compare with the step simulation? Explain why is this so. Now, follow instructions on how to add an equation to the Data Display as shown in Figure 12. Display the rest of the plots as shown in Figure 11. When you are ploting input and output voltage, you have to select Add Vs then select equations, and new variable you just defined. See Figure 12.

9 Dr. Milica Marković Applied Electromagnetics Laboratory page 9 (a) Resistor under the Lumped-Element pallete. (b) Time-domain step voltage under Time-Domain voltages. (c) Transient simulation under the Aimulation-Transient pallete Figure 7: Location of various circuit elements under Palette.

10 Dr. Milica Marković Applied Electromagnetics Laboratory page 10 (a) Click on rectangular plots and place it in Data Window. (b) Select the variable that you want to display, click add. Figure 8: Presenting simulation results in ADS.

11 Dr. Milica Marković Applied Electromagnetics Laboratory page 11 (a) Transient simulation of voltages at the input and output of a coaxial cable. (b) Simulation results. Figure 9: Simulation of coaxial cable in ADS.

12 Dr. Milica Marković Applied Electromagnetics Laboratory page 12 Figure 10: Schematic diagram of a setup for transient simulation of a sinusodial signal on a coaxial cable.

13 Dr. Milica Marković Applied Electromagnetics Laboratory page 13 (a) Transient simulation of sinusoidal voltages at the input and output of a coaxial cable. (b) Simulation results. (c) Simulation results. Figure 11: Simulation results of the sinusoidal voltages at the input and output of a coaxial cable in ADS from Figure 10.

14 Dr. Milica Marković Applied Electromagnetics Laboratory page 14 (a) Select Eqn (b) Type your equation. (c) Your equation is displayed. (d) Click on rectangular plots in Data Window(not shown above), then select Equations as shown, and pick gain from the list. Figure 12: Plotting equations example.