ECE Undergraduate Laboratory
ECE 469 - RF/Microwave and Optics Lab

ECE 469 - RF/Microwave and Optics Lab

Lab 1: Introduction to Vector Network Analyzers (VNA)

VNAs probe devices with sine waves (the incident waves) and measure both (1) the magnitude and (2) the phase of the outcome signals in terms of reflected and transmission coefficients. Those two numbers can be put into a 1x2 vector format: [Magnitude, Phase]. The VNA may come as one, two or N-port device. The word Analyzer refers to the network portion of the system, meaning the ability to measure outputs of the system under test to a variety of inputs.

Primarily, VNA is used to analyze the response of the Device-Under-Test (DUT) to a collection of sine waves at various frequencies. These frequencies are delivered one by one either in one or multiple scans. The frequency response may be also be presented as a temporal response by a simple Fourier analysis. The Vector Network Analyzer measures magnitude and phase of incident, reflected, and transmitted waves to provide full characteristics of the DUT.

Incident waves are transmitted from the input source (or port) and the VNA deduces the relationships between transmitted, incident, and reflected waves. The key part of the VNA is its ability to see all three waves, separately. Each VNA port has a bridge, or a coupler, which separates the incident and reflected signals.


Figure  1.1
One-port VNA

Figure  1.1
Two-port VNA

The reflection and transmission coefficients may be described by the S parameters:

b1=S11a1+S12a2

b2=S21a1+S22a2

Here,

S11=b1/a1 for a2=0

S21=b2/a1 for a2=0

S22=b2/a2 for a1=0

S12=b1/a2 for a1=0

You may refer to this link for more information and videos

Operating Manual is in the S2VNA\Doc directory or may be downloaded from the CMT website.


Acquaint yourself with the VNA

  1. Open the program in Demo mode: System – Misc Setup – Demo Mode - ON
  2. Experiment with different display settings.
  3. Change display settings.
    • Various font size: Display – Properties – Font Size - Choice
    • Add more traces: Display – Number of Traces – 4 - allocate traces
    • Add traces: Display – Allocate Traces - configure 4 absolute traces
      • Click on Tr1, Measurement – Absolute – Receiver R1 (source port)
      • Click on Tr2, Measurement – Absolute – Receiver A (source port)
      • Click on Tr3, Measurement – Absolute – Receiver R2 (source port)
      • Click on Tr2, Measurement – Absolute – Receiver B (source port)
    • Add title label Display -Title Label
    • Edit Title Label – Enter Absolute Measurements
    • Save the state file: Save/Recall – Save State -
    • Rename State01.sta in C:\VNA\S2VNA\State to:
      EENN_Lab1_YourName_Absolute_Measurements.sta
    • Preset VNA to the original state - System – Preset – OK
    • Recall the state file to make sure it configures VNA - Save/Recall – Recall State – File
    • Save *.sta file at easily accessible location. You will need it for the lab exercises.

Objectives

To become familiar with the instrument software and principles of operation


Laboratory Procedure


Section 1

  1. Connect VNA to the computer. Note: all safety and ESD precautions should be strictly adhered to.
  2. Power up VNA
  3. Start the software
  4. Recall EENN_Lab1_YourName_Absolute_Measurements.sta file
  5. Scale - either manually or automatically
  6. Save the image for your report.

Section 2

  1. Connect RF cables to ports. Use TW-N and TW-SMA torque wrenches. Note: Torque wrenches are calibrated tools. As soon as the handle bends, then torqueing should stop.
  2. Connect SMA-SMA adapter between cables. Use TW-S SMA torque wrench.
  3. Configure the software to show four traces (either magnitudes, phases or Smith charts.
  4. Save the image for your report.

Section 3

  1. Preset VNA
  2. Configure Display to show 4 different traces with four S-parameters – S11, S21, S22, S12
  3. Change IFBW (intermediate frequency bandwidth - understand what it generally means for local oscillators), number of points, trace format, scale, power levels, start/stop frequencies.
  4. Experiment with IFBW and number of points changes. Observe how changing IFBW and number of points changes measurement speed

Figure  1.1
S-parameters

Section 4

  1. Obtain the time domain signals
  2. Calculate the Fourier Transform of the obtained time domain curves to obtain the frequency domain curves. You need to print the curves in .txt format into a file and use MatLab or the like to perform the Fourier Transform on the set of point.
  3. Experiment with assembled two, or more cables with and without an attenuator: what do you see? Record the frequency and time domain signals. and assess the attenuation (this value is also written on the element)

Report

  1. One report per group. No timeline for the lab's final report until, of course, the end of the semester; however, if the report is submitted early, comments may be provided and the final grade may be improved.
  2. Follow the template that is provided in the Welcome announcement.

In addition: