RF, Digital Radio and Metamaterial Fundamentals

Project 1

Time-domain pulse reflections


Overview

Work in assigned project groups. 

The objective of this project is to simulate and measure time-domain pulse reflections.

NOTE: Use the Project Report Template and keep answers to questions on consecutive sheets of paper with all plots at the end.

IN NO CASE may code or files be exchanged between students, and each student must answer the questions themselves and do their own plots, NO COPYING of any sort! Nevertheless, students are encouraged to collaborate in the lab session.



Part 1: Measurements

  • Pulse reflection measurements:
  • Organize the pulse reflection experiment as shown below
  • In 2018, do not use the following "Fig 001," use the alternate setup in "Fig 001 alternate"

  • xx
    Fig 001

  • Make sure that channel1 and channel2 of the oscilloscope are set to 50 ohm input impedance.

  • Alternative setup using equipment in open lab area:
  • zz
    Fig 001 (alternate)
     
  • Connect the cables as shown with the 18 foot long cable (20 feet long for the alternate setup) connected between the tee on the pulse generator and the tee on the channel2 input of the oscilloscope.  A shorter cable connects the pulse generator tee to the channle1 input of the scope. 
  • At channel2 of the oscilloscope, two tees are used to add a pair of 50 ohm terminations in parallel with the channel2 input.  These three 50-ohm impedances effectively terminate the cable in 16.7 ohms when the two terminations are combined in parallel with the 50 ohm scope impedance.
  • Similarly the 50 ohm impedance of scope channel1 acts as a voltage divider in series with the 50 ohm impedance of the signal source, resulting in a net Thevenin source impedance of 25 ohms. 
  • Note that the pulse voltage of the pulse generator is rated into a matched load.
  • Set the pulse generator for 2 V max, 0 V min, 5 MHz frequency, 20 ns pulsewidth, 5ns rise/fall time.
  • If you are using the alternate setup in Fig001 alternate above, then adjust the signal generator amplitude  so you have a 1 V peak pulse when the signal generator is drectly connected to channel 1 of the oscilloscope, including the two 10 dB attenuators, but excluding all other terminations/connectors/cables/etc.   Adjust the offset voltage of the signal generator so that the baseline of your waveform is at zero volts.
  • Set the oscilloscope display as follows, and the pulses should appear similar (not the same) as below:

  • xx
    Fig 002

  • Detach the long cable from the tee at the pulse generator, what is the voltage when only the 50 ohm oscilloscope as a load? 
  • Reattach the long cable and save a copy (use USB and raphic with clear background) of your measured input (top) and output (bottom) pulses as shown above  
  • What is the measured velocity of the pulses in the line, expressed as a fraction of the speed of light, such as 0.4c? 
  • The oscilloscope traces should be nearly the same as your simulation below!

  • Part 2: Simulation

    Start the software:

  • From a Linux terminal, ADS should be available in the  menu (Applications::ElecEngineering::KeysightAdvancedDesignSystem)
  • From a PC terminal, you must first open a remote Linux session, then proceed as for a Linux terminal
  • For snapshots use the Linux menu Applications::Graphic::Ksnapshot and select the option to take a legible snapshot of a window rather than a full screen snapshot.
  • Note: (the following note may not be valid after 2009) 
  • If you find that you have printing problem, see if you have a file ".XprinterDefaults" in your home directory. Move this file to ".XprinterDefaultsOld", and restart ADS ... it will write a new copy of this file that should enable printing.
    if this does not work, move your current ".XprinterDefaults" file to ".XprinterDefaultsOld", and try downloading .XprinterDefaults to your home directory. (To download you may need to hold down the "shift key" while you click on the link.) Select the LPDEST printer by File-->PrintSetup-->Options and select Default Printer ($LPDEST) on default_queue
  • FIRST: create a folder/directory in your home directory named apps and a subfolder in apps named ads
  • After ADS starts you should get a starting window similar to this (navigate into your apps/ads folder):


  • Click the help menu item in the upper right (MenuBar::Help) and read through the on-line manuals (see the help tab in ADS), for particular questions it is usually best to use the help index from the ADS window MenuBar::Help to search the manuals.
  • Note: there might be a bug with the main help items, in that you may need to have a web browser such as fireffox open before help will appear in the browser window .
  • Load and run the pulse example as follows:
  • Download the 7zap archive as follows:
  • x

  • You should find a new directory RFcourse2012_pulse1a_wrk created in apps/ads

  • Run ADS and open the new RFcourse2012_pulse1a_wrk workbook by double-clicking it

  • Go down through the directory tree to pulse1/schematic and double click that schematic file, and the following schematic should appear.  (1 mil = 1/1000 inch)


  • Double-click the transmission line and look at the variables in the pop-up menu. 
  • Use the mouse to select the variables and observe the changing description at the bottom of the pop-up.
  • Double-click the "gear" icon (shown below) in the upper right of the window to simulate.

    z

  • The data plotting window should appear.
  • Click the "rectangular plot" icon (shown below) in the left of the new popup window to get a plotting grid by dropping the plotting box in the visible area.

    z

  • In the pop-up window:

    Select DataSet -> V1 -> Add
    Select DataSet -> V2 -> Add
    Select DataSet -> Vsrc -> Add

  • Click OK at the bottom of the popup
  • Drop a second plotting box in the visible area, and in the pop-up window:
  • Select DataSet -> V1 -> Add
  • Click OK, and the following Time-domain plot should appear.
  • As an optional exercise:
  • Compute the impedance of the line using ADS::ToolsLinecalc
  • Use linecalc tool to compute the impedance and electrical length of the line at 1GHz as illustrated below. 
  • Note that the MSub component in the schematic specifies the thickness and dielectric constant of the substrate.
  • Make sure to change the "Er" dielectric constant to the appropriate value (Er is defined in the MSub component on schematic)
  • Make sure to change the "H" dielectric height/thickness to the appropriate value (H is defined in the MSub component on schematic)
  • Make sure to change the "W" width to the appropriate value (the width is defined in the MLIN component on schematic)
  • Make sure to change the "L" length to the appropriate value (the length is defined in the MLIN component on schematic)
  • Press the "Analyze button, and you should see a result for the transmission line impedance of near 50 ohms (approx 52.2)
  • In linecalc, change the width of the line slightly, until you find the proper width for a 50-ohm line
  • Copy the linecalc window and save it for future reference For snapshots use the Linux menu Graphice::Ksnapshot

  • Save your schematics and plots before exiting ADS


  • xx
    Fig 003

  • Save a snapshot of your new schematic and paste it into your report.
  • (SEE BELOW FOR THE REPORT TEMPLATE)
  • Make sure that your plots, component values, legends, axes, and fonts are legible in your report!

  • Run the simulation and plot the voltages at the input and output  of the transmission line, and add 4 markers to show the pulse voltages of the first two pulses at the input and output of the transmission line as shown below:
  • xx
    Fig 004

  • Save a snapshot of your input/output pulses as shown above, with markers added,  and paste it into your report.
  • Compute Gamma 1 from the component values on the schematic (reflection coefficient at 1st reflection, at interface between source and transmission line)
  • Does the simulated voltage agree with your computed reflection coefficient?
  • Compute Gamma 2 from the component values on the schematic (reflection coefficient at the reflection at far end of line, at the load)
  • Compute Gamma 3 from the component values on the schematic (reflection coefficient at input, after "round-trip" return)
  • At the input of the line, for the first pulse reflection, what is the reflection coefficient Gamma1? 
  • At the input of the line, for the first pulse reflection, what is the incident pulse voltage, reflected pulse voltage, and total voltage? 
  • At the output of the line, for the first output, what is the reflection coefficient Gamma2? 
  • At the output of the line, for the first pulse output, what is the incident pulse voltage, reflected pulse voltage, and total voltage?

  • Save your schematics and plots before exiting ADS


    Report Data


    NOTE ReportTemplate: Use the Project Report Template 

      YOU MUST ADD CAPTIONS AND FIGURE NUMBERS TO ALL FIGURES!! 

    Copyright 2010-2018 T. Weldon

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