PART III LABORATORY MANUAL 202 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman 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 203 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman 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 204 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman (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 205 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman 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 ] Rg=50Ω I (0, t) + + Z0 =75 (Ω) Vg (t) = 150 U(t) V (0, t) 8 (µ0,2.25 ε0), v =2x10 m/s RL=120(Ω) - - z=0 z= ℓ 206 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman 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 Network Analyzer Time domain display Transmission line terminated by a load Network Analyzer Port #1 Port #2 ZL Rg Cable (Z0) Vg Z0, εr ZL z = 0 z = l 207 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman 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 208 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman Capture Display on the computer with Agilent Intuilink - click on the Agilent Intuilink Desktop shortcut or go to START Æ PROGRAM Æ Agilent Intuilink Æ Intuilink Data Capture Application - Connect to the Network Analyzer: o Go to INSTRUMENT menu Æ Network Analyzer o Select SET I/O Æ Click on FIND PORTS Æ Select AVAILABLE ADDRESS “GPIB0:: 16: INSTR” Æ 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 Æ 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. 209 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman Pre Lab for Experiment III – SW Pattern and SWR ˆ Zg ~ , Z 0 εr V g Z$ L z =-l z =0 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 ) V (z) | ) + | vs z (in cms) V0 • Normalize with respect to the maximum • Plot the normalized SW pattern ) V (z) [ | ) + | / Vmax ] vs z (in cms) V0 • Calculate SWR for each load. 210 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman 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. Network SW Pattern Analyzer Probe Carriage slotted line GR874-B ZL Zˆ g ~ Z 0 ,εr ˆ Vg ZL z = 0 z =l 211 Electromagnetic Waves and Transmission Lines By Dr. Jayanti Venkataraman 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.