Network Analyzer

Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman

202

PART III LABORATORY MANUAL


203

Experiment I - Calibration of the Network Analyzer Objective:

Calibrate the Network Analyzer for Transmission Procedure: (i) Turn the Power On (ii) Set the Frequency for Measurements

MENU (for HP8753ET choose SWEEP SETUP) CW FREQ 600 M (iii) Choose appropriate Calkit

CAL CALKIT

SELECT CALKIT N 50Ω (iv) Calibrate the NA with a cable on port #1

(a) HP8752 Network Analyzer

CAL CALIBRATE MENU

RESPONSE (Connect the cable from port #1 to port #2) THRU

Remove cable from port #2 and connect a SHORT at the end of the cable from port #1

SHORT (M) Connect an OPEN at the end of the cable from port #1 OPEN (M) DONE RESPONSE NA calculates cal coefficients (b) HP8753 Network Analyzer CAL CALIBRATE MENU FULL 2 PORT (Ignore error message)

REFLECTION FORWARD


204

Connect a SHORT at the end of cable from port #1 SHORTS SHORT(M) (NA beeps and underlines) DONE SHORTS

Connect an OPEN at the end of cable from port #1 OPENS OPEN(M) (NA beeps and underlines) DONE OPENS Connect 50Ω load at the end of cable from port #1 LOAD (NA beeps and underlines) REVERSE

Connect a SHORT at port #2 SHORTS SHORT(F) (NA beeps and underlines) DONE SHORTS

Connect an OPEN at port #2 OPENS OPEN(F) (NA beeps and underlines) DONE OPENS Connect 50Ω load at port #2 LOAD (NA beeps and underlines) STANDARDS DONE TRANSMISSION (Connect the cable from port #1 to port #2) FWD TRANS THRU FWD MATCH THRU REV TRANS THRU REV MATCH THRU (NA beeps and underlines all four) STANDARDS DONE ISOLATION OMIT ISOLATION ISOLATION DONE DONE 2-PORT CAL NA calculates cal coefficients


205

(b) HP8753ET Network Analyzer

CAL CALIBRATE MENU ENHANCED RESPONSE TRAN/REFL ENH. RESP.

REFLECTION Connect a SHORT at the end of cable from port #1 SHORTS SHORT(M) (NA beeps and underlines) DONE SHORTS

Connect an OPEN at the end of cable from port #1 OPENS OPEN(M) (NA beeps and underlines) DONE OPENS Connect 50Ω load at the end of cable from port #1 LOAD (NA beeps and underlines) STANDARDS DONE TRANSMISSION

(Connect the cable from port #1 to port #2) DO BOTH FWD THRUS (NA beeps and underlines all three) ISOLATION OMIT ISOLATION DONE FWD ENH RESP NA calculates cal coefficients (iv) Verify the Calibration Connect a short at the end of the cable FORMAT SMITH CHART MEAS REFLECTION The impedance should read ‘zero’ SCALE REF ELECTRICAL DELAY Use the dial move the marker to read a ‘SHORT” on the Smith Chart


206

Prelab for Experiment II -Time Domain Analysis A 75 Ω lossless line of length 200m, filled with polyethylene (εr=2.25) is terminated by an open RL = ∞ (Ω). A DC voltage Vg from the network analyzer of the internal resistance 50 Ω is switched onto the line a t=0. Defining one transit down the line as T=l/v, develop an echo diagram and plot the voltage at the input of the line, V(o,t) vs time, t, for a time period 0<t<6T [Note: Since Vg is not given, V(o,t) will be in terms of Vg ]

Vg (t) = 150 U(t) RL=120(Ω)

z=0 z= ℓ

Rg=50Ω

Z0 =75 (Ω)

(µ0,2.25 ε0), v =2x108 m/s

+

- V (0, t)

I (0, t)

+

-


207

Experiment II -Time Domain Analysis I. Objective : (i) Step excitation of a transmission line terminated by resistive, reactive and complex loads (ii) Monitor the voltage at the input of the ine over a period of time, using a vector network

analyzer in the toime doimain (iii) Determine the magnitude and the nature of the load from the scope display. Experimental Setup

Rg

Vg

Network Analyzer

ZL Port #1 Port #2

Cable (Z0)

ZL

z = 0

Z0, εr

z = l

Network Analyzer

Transmission line terminated

by a load

Time domain display


208

II. Procedure : (i) Turn the Power on (ii) Set the number of points for measurements MENU

NUMBER OF POINTS 1601 x 1 (set number of points to 1601 (or 1201))

(iii) Set the frequency range for measurements START

300 kHz STOP

1 GHz (iv) Make note of the change in frequency range SYSTEM TRANSFORM MENU SET FREQ LOWPASS (iv) Calibrate the Network Analyzer for Reflection at port #1 (without the cable)

NOTE: Follow instructions from Lab #1 starting from CAL, Calibrate MENU, etc. (v) Verify Calibration. Use ELECTRICAL DELAY if necessary (vi) Set the NA in the Time Domain Mode SYSTEM TRANSFORM MENU TRANSFORM ON LOW PASS STEP (vii) Chose a scale for measurements FORMAT

MORE (real) START 0 x 1 STOP 20 ns (change as needed, for different loads) (viii) Set the scale zero Reference (ix) Set the velocity factor CAL

MORE VELOCITY FACTOR

0.33 x 1 (to read distance directly) (x) The NA is set to make measurements in the time domain. Connect a cable to port #1. Terminate it by the following loads and make measurements. • Resistive load ( R ) - short, open, 100 Ω, 200 Ω and 30 Ω. Measure 2T for any one of the loads.

In each load, obtain the NA display and SAVE as follows


209

Capture Display on the computer with Agilent Intuilink - click on the Agilent Intuilink Desktop shortcut or go to START PROGRAM Agilent Intuilink Intuilink Data Capture Application - Connect to the Network Analyzer:

o Go to INSTRUMENT menu Network Analyzer o Select SET I/O Click on FIND PORTS Select AVAILABLE

ADDRESS “GPIB0:: 16: INSTR” Click on SELECT ADDRESS (You should see the Instrument ID: HP 8752xx…)

o Click OK - To Capture: Click on the Icon with NA picture “Get Data” - Save your bmp file (example of filename - short.bmp)

• Take control back of the Network Analyzer

LOCAL SYSTEM CONTROLLER • Purely Reactive Loads - capacitor and inductor In each case, measure Δt and save the NA display. • Complex Load - capacitor and resistor in parallel Measure Δt and save the NA display. • Remove the 50Ω cable and connect a 75 Ω cable.

Measure Δt Plot the scope display. Calculate and plot V(0,t) vs t (From Prelab) Compare with measured response.

III. Report The report should be of the following form A title and an objective A block diagram Calculate the length of the cable using any one NA display. For each load using the experimental results calculate the following

(Show all relevant calculations) - for resistive loads, calculate R - for reactive loads, calculate C (or L) - for the complex load, calculate R and C

For the 75 Ω cable - calculate the length of the cable - Plot the predicted V(0,t) vs t (form prelab) - Compare measured and predicted V(0,t)

(Plot both on the same graph) A brief conclusion.


210

Pre Lab for Experiment III – SW Pattern and SWR For the transmission line system shown, f = 600 MHz

Zg = 50 Ω Z0 = 50 Ω

l = 0.75 λ0

εr = 1.0 1. ZL = 0 Ω 2. ZL = open 3. ZL = 100 Ω 4. ZL = ( 25 + j 25 ) Ω 5. ZL = ( 25 – j 25 ) Ω Using Matlab, obtain the following for each of the loads given above.

• Calculate the SW pattern

• Normalize with respect to the maximum • Plot the normalized SW pattern

• Calculate SWR for each load.

cms)(in z vs| V

(z) V | 0+)

)

cms)(in z vs] V / | V

(z) V | [ max0+)

)

0Z r,ε

z =-l z =0

LZ$ gV~

Zg


211

Experiment III - Measurement of SW Pattern and SWR Objective : (i) Measure SW pattern and the SWR generated by a coaxial slotted line terminated by a load (ii) Measure the wavelength in the transmission line (iii) Compare measured and theoretical results Standing wave pattern measurement system The Network Aanlyzer and the slotted coaxial line for the SWR measurement and the equivalent circuit are shown below.

SW Pattern

0Z r,ε

z = 0 z =l

ZL V~ g

Zg ZL slotted line GR874-B

Probe Carriage

Network Analyzer


212

Procedure : I. Network Analyzer Settings

• Turn the Power On • Set the Frequency for Measurements (600 MHz) • Calibrate the NA, at the end of the cable, and verify it.

II. Prepare the Automated Slotted Coaxial Line (ASCL) System

• With the power OFF, connect the cable from port #1 of the network analyzer to the input of the slotted line. Connect the cable from port #2 to the probe carriage. Make sure all the cables are positioned to allow the probe carriage to travel unrestricted along the entire length of the machine. Move the probe carriage, manually, down the entire slot to ensure this. Failure to do this, will result in damage to the motor and hardware.

• Turn the power ON for the ASCL. The probe will move to the home position if it is not already there.

III. Generate the SW plot Turn on computer and click on the halfstep.vi icon. The User Interface Screen will open The ASCL will automatically record and plot the SW pattern on screen. (ii) Plot a Normalized SW pattern

• Click on RUN. (→ button in the toolbar ) PC takes control of NA • From the MODE SELECTION box, choose AUTOMATIC • Choose RESOLUTION as MEDIUM

• Choose LOAD IMPEDANCE (Z>Z0 or Z<Z0 or Z=Z0 or Complex)

• Set DUAL PLOTTING to OFF

• Click on START.

• Click on OK when Dialog box appears to verify load.

• SW Pattern is generated as the probe moves down the slotted line. The normalized

SW pattern will be plotted on the screen when it reaches the end. (iii) Save Data

• Choose YES in the dialog box for saving data. (Ignore any ‘Timeout Expired’ error messages)

• Insert a disk and choose Drive A Name the file (name.txt)


213

(iv) Measure SWR on the Network Analyzer • On the NA panel, do the following

LOCAL SYSTEM CONTROLLER (ignore message) MEAS REFLECTION FORMAT SWR (Record the SWR)

(v) To take control of the NA through LABVIEW, click on ‘Control Devices’ button. This can also done by ABORT and RUN.

IV. Required Measurements Measure the SW pattern (that is, repeat Step III) for the following loads. Remember to change the Load Impedance option accordingly • ZL = 0 Ω • ZL = infinity • ZL = 100 Ω • ZL = 50 Ω • ZL = ( 25 + j 25 ) Ω (Tee-with- stub terminated by 50 Ω and length of stub = 6.25 cms ) • ZL = ( 25 - j 25 ) Ω (Tee-with- stub terminated by 50 Ω and length of stub = 18.75 cms )

V. Retrieve Data in MATLAB

Open the file in MATLAB. Delete the comment on the first line At the MATLAB prompt type the following - load name.txt - x = name ( : , 1 )

Redefine x, with reference to the theoretical plot - y = name ( : , 2 ) - plot ( x , y )

VI. Report The report should be of the following form. A title and an objective A block diagram For each load, experimental results and all relevant calculations should be presented

in a comprehensive manner. Calculations should be shown wherever necessary - A Table comparing predicted and measured SWR (include a sample calculation) - Computer program for the predicted SW pattern. - For each load, a ‘One page’ graph of measured and predicted SW pattern, as shown.

Calculate wavelength using one of the SW patterns. Compare with predicted value. A brief discussion


214

-70 -60 -50 -40 -30 -20 -10 00

0.2

0.4

0.6

0.8

1

1.2

z [cm]

|Vz|/|

Vm

ax|

Theoretical SWR =InfExperimental SWR =1000000ΓL =-1 Offset =-17.5cm

SW Pattern for ZL = 0 +j(0) ohms

TheoryExperimental


215

PreLab for Experiment IV -Determining Unknown Impedance (i) Design of a Load using a Transmission Line Circuit For the arrangement shown, design the load (that is, find ZL and l ) so that, at AA (a) y T, AA = 1 - j 0.83 (b) y T, AA = 1 + j 1.82 (ii) Determine the Unknown Impedance from the Following Data (f = 600 MHz) (a) With the Unknown Load (referenced at z = 0)

• Measured SWR = 4.5 • Location of first accessible minimum dmin,1 = - 40.5 cms

Replacing Unknown Load with a Short • Location of first accessible minimum dmin,2 = - 48.2 cms

(b) With the Unknown Load (referenced at z = 0)

• Measured SWR = 3.4 • Location of first accessible minimum dmin,1 = - 58.2 cms

Replacing Unknown Load with a Short • Location of first accessible minimum dmin,2 = - 49.4 cms

NOTE: Part #b is independent of Part #a

A

A

Stub

Short

Z Lˆ0Z r,ε

Tee

l

gV~

gZ$ZL slotted line GR874-B

Probe Carriage

Network Analyzer

Slotted Line


216

Experiment IV - Determining Unknown Impedance I. Objective : (i) To design a load using a transmission line circuit (ii) To measure the impedance of this load using a co-axial slotted line (iii) To compare the experimental and predicted values.

A

A

Stub

Short

Z Lˆ0Z ,ε

TeeSlotted Line

l

gV~

gZ$ZL slotted line GR874-B

Probe Carriage

Network Analyzer

d


217

II. Design of a Load using a Transmission Line Circuit (i) For the arrangement shown, use the values for ZL and l obtained in the Prelab. That is,

(a) ZL = 50 Ω and l = 7 cms (b) ZL = 50 Ω and l = 21 cms

(ii) Using the Smith Chart, calculate the total impedance, ZTAA , at plane AA for each of the above cases. III. Measurement Procedure:

A. Network Analyzer Settings • Set the Frequency for Measurements (600 MHz) • Calibrate the NA to measure Transmission (RESPONSE) in LINMAG format B. Prepare the Automated Slotted Coaxial Line (ASCL) System Set up the slotted line and the load as shown in the figure above.

• With the power OFF, set up the transmission line system as shown. Make sure all the cables are positioned to allow the probe carriage to travel unrestricted. Move the probe carriage, manually, down the entire slot to ensure this. Failure to do this will result in damage to the motor and hardware.

• Turn power ON for the ASCL. The probe will move to the home position if it is not already there.

C. Generate the SW plots Turn on the computer and click on the halfstep.vi icon. The User Interface Screen will open up.

(i) With value of ZL given above, and l=25 cms (This is the Reference)

• Click on RUN • From the MODE SELECTION box., choose AUTOMATIC • Choose OFF for DUAL PLOTTING • Choose MEDIUM for PLOT RESOLUTION • Choose Z<Z0 for Load Impedance • Click on START

Save data to file. (Ignore any ‘Timeout Expired’ error messages)


218

(ii) With l=7 cms (Load #1) • Choose Dual Plotting ON • Click on Start • Both SW patterns are displayed, corresponding to REFERENCE (Short) and the

unknown load. Save data to file. (Ignore any ‘Timeout Expired’ error messages)

(iii) Repeat step (ii) for l= 21 cms (Load #2). (iv) Retrieve data in MATLAB and complete calculations as shown in Sec#2.7 in the ‘Transmission Line Notebook’ (v) Measure SWR directly from NA for each load. D. Impedance Measurements Directly from the NA (i) Reference the measurements to the plane(AA) of the stub

• Set l = 25 cms • Measure reflection using the Smith Chart Format • Adjust the ELECTRICAL DELAY to read a short

(ii) Measure the unknown impedance at plane AA

• Set l to Load #1 • Using CAL ( MORE), set Z0 = 1 • Set Smith Chart to read Admittance (MKR and MKR MODE MENU

Choose G + jB) • Set Marker to read the admittance and compare with design value • Measure SWR • Repeat for Load #2

IV. Report The report should be of the following form

• A title and an objective • A block diagram • For each load,

- Plot the measured SW patterns - Show all relevant calculations using a Smith Chart to determine the unknown impedance -Compare with design value and with the direct measurements made

• A brief conclusion


219

PreLab for Experiment V - Design of a Single Stub Tuner

Design a single stub tuner (that is, find l and d ) to match a 100 Ω load to a 50 Ω transmission line. Calculate SWR before and after impedance matching. Preparation for Lab Report (due on the day of the lab) There will be no take-home lab report for Single Stub Tuner. Come prepared to lab with the following. Page #1 : Title, Objective and Block Diagram Page #2 : Theoretical design on the Smith Chart(prelab) Page #3 : Predicted SWR values before and after the design You will complete the report in the lab and will submit it at the end of the lab.

Cable from

Shortl

A

A

Stub

Z Lˆd

gV~

gZ$


220

Experiment V - Design of a Single Stub Tuner I. Objective (i) To design a single stub tuner to match a 100 Ω load to a 50 Ω transmission line (ii) To measure the SWR before and after matching and to compare with predicted values. II. The Circuit Diagram

Short l

A

A

Stub

Z Lˆ

Tee

d + nλ / 2 gV~

gZ$ Collapsible Line

Cable from NA

ZL Collapsible Line

Network Analyzer

Port Port #2

stub


221

III. The Theoretical Design

Design a single stub tuner (that is, find l and d ) to match a 100 Ω load to a 50 Ω transmission line. Calculate SWR before and after impedance matching. IV. Measurement Procedure (i) Network Analyzer Settings

• Set the Frequency for Measurements (600 MHz) • Calibrate the NA to measure REFLECTION in the ‘normalized admittance Smith

Chart’ format. (ii) Reference the measurements to the plane (AA) of the stub

• Set l = 25 cms • Adjust the ELECTRICAL DELAY to read a short.

(iii) Implement the design of the SST

• Set l = 12.5 cms • Adjust the collapsible line such the distance between plane AA and the plane of the

load is (nλ / 2). Record the admittance, yL and SWR • Adjust the collapsible line to a length (d + nλ / 2 ). • Record the admittance, yL,AA ( = 1 + j b) • Corresponding to the measured admittance yL,AA ,obtain yS,AA and hence, use the

Smith Chart, to calculate the length l of the stub for matching. • Adjust l to this value. Record the admittance yT,AA and SWR.

(iv) Repeat with the load arrangement of Lab IV V. Report (To be submitted in Lab) The report should be of the following form • A title, an objective and a block diagram • The theoretical design on the Smith Chart (prelab) • Predicted SWR values before and after the design • Measurements recorded ( yL, SWR (before matching), yL,AA , yS,AA , l , yT,AA and SWR • Smith Chart for calculating l from measured yL,AA • Comments and conclusion.

Documents

Network Analyzer