1ECE 435INTRODUCTION TO THE MICROWAVENETWORK ANALYZERLatest revision: October 1999IntroductionA vector network analyzer (VNA) is a device capable of measuring both the magnitude and phaseof a sinusoidal voltage signal. This makes it very similar to a vector voltmeter. However, anetwork analyzer is more advanced than a vector voltmeter in many ways. Complex RF circuitry isused to make the analyzer much more accurate, with a typical dynamic range of 70-110 dB. Microprocessor circuitry allows flexible processing of data including smoothing, averaging and avariety of displays. Most importantly, a VNA is capable of acquiring measurements over a sweptband of frequencies, allowing the rapid wideband characterization of a wide range of microwavenetworks. To compensate for the frequency dependent phase and amplitude characteristics of the cables andreceiving system, it is necessary to calibrate using the known responses of standard loads (open,short, and 50Ω terminations). The calibration procedure is an important part of network analysis,and must be done repeatedly (ideally, each time a new measurement is taken).The HP 8720B network analyzer incorporates in one package each of the three components of anetwork analyzing system: a swept frequency source, a receiver, and an S-parameter test set. Thesweeper produces a sinusoidal signal with a frequency that can be swept between 130 MHz and 20GHz with a 100 kHz resolution. The receiver allows the measurement of complex voltage. The S-parameter test set incorporates directional couplers to send the signal into the chosen port of a two-port network while measuring either the transmitted or reflected signal. More advanced networkanalyzers (such as the HP 8510C) consist of separate components assembled into an analysissystem.In this lab you will characterize the reflection and transmission characteristics of a 100Ωload, an open-ended coaxial cable, a cavity wavemeter and a 10 dB attenuator. You will be able tomake in a few minutes measurements which might take days using the slotted line or vectorvoltmeter techniques studied in earlier labs.NOTE: The HP 8720B network analyzer, cables and calibration kit cost about $70,000. Please treat the equipment KINDLY so that students may use them for years tocome.2IMPORTANT NOTE ON CONNECTORS ************************************The connectors on the 8720B S-parameter test set cables and on the standard loads areabout the only things that can be easily damaged. Accurate measurements depend on thecareful handling of all connectors. (HP has a special publication just on the cleaning andhandling of connectors.)PLEASE follow these rules when using connectors:1. Do not touch the connector threads.2. Always keep caps on unused connectors.3. Do not force the connectors. If they don't seem to be meshing, you don'thave them aligned properly.4. Don't adjust the APC connectors. Only the N-type connectors are used bythe students. (APC connectors require a torque wrench for proper adjust-ment.) If the APC connectors need adjusted, ask the lab instructor to do itfor you.5. Don't turn the device being connected! Only turn the sleeve on the male N-type connector.6. Hand-tighten the N-type connectors snugly, but not so tight they can't beeasily loosened.7. Don't bang the connectors on the table top.8. Don't bend the cables past where they move freely.*****************************************************************3I. REFLECTION MEASUREMENTSA. Power-up1. Turn on 8720B and PC.2. Insert your formatted floppy into computer. Type SCAN A: (or B:). If thereare viruses on your disk REMOVE IT IMMEDIATELY and see yourinstructor.3. Note: all measured data should be stored with the .NDF extension (NewData Format).B. Set instrument state1. Run all programs from the C:\USR directory on the PC. Type NAM3 (net-work analyzer measurements) to start the measurement software. Control isnow with the PC.2. Push LOCAL on VNA to return it to local control.3. Push START and set starting sweep frequency to 0.2 GHz. Push STOP andset ending sweep frequency to 2.2 GHz.4. Push MENU and set no. pts to measure to 201.5. Push AVG and set average to ON. The VNA will now take 16 sets ofmeasurements and average the results. Set IF bandwidth to 300 Hz. This isthe IF filter width.6. Push MEAS and set the measurement to S11.7. Push CAL and select CAL KIT. Set to N 50Ω.C. Save instrument state1. From main menu of NAM3, enter instrument state menu.2. Choose to save the instrument state.3. Push LOCAL.3. Push any key. The VNA will now transfer the instrument state.4. Enter a filename. Choose something you will remember (try S11.IS). Theinstrument state will now be saved to disk.5. Return to the main menu of NAM3.6. The instrument state is now saved and can be recalled at any time.D. Recall instrument state1. From the main menu of NAM3, choose to exit the program.2. Press LOCAL and PRESET on the VNA to return instrument state to itsinitial setting.3. Start NAM3.2. From main menu of NAM3, enter instrument state menu.3. Choose to upload the instrument state to the VNA from disk.4. Enter your filename. The VNA should return to your instrument state.45. Return to main menu of NAM3.E. Calibrate the VNA1. Press LOCAL on the VNA.2. Press CAL to enter the CAL menu.3. Press CALIBRATE MENU.4. Choose S11 1-PORT.5. Calibrate by connecting the following standard loads in succession. (Be sureto read the section on connector care.)a. Attach the open.b. Press OPENS.c. Indicate the sex of the connector. (Male N-type connectors have therotating sleeve).d. Wait until averaging is finished and OPEN is underlined.e. Press DONE: OPENS.f. Repeat for short and 50Ω load. For the load indicateBROADBAND.g. If you make a mistake, start the calibration procedure from thebeginning.h. When done, press DONE 1-PORT CAL.i. The VNA will now compute the CAL coefficients it will use tomake phase and amplitude compensation.F. Save CAL coefficients1. From the main menu of NAM3, enter the CAL coefficient menu.2. Choose to save the CAL coefficients to disk.3. Enter your filename (try S11.CAL). The CAL coefficients will bedownloaded to the PC.4. Return to main menu of NAM3.G. Recall CAL coefficients1. If you goof up something and have to start over, you do NOT have torecalibrate (unless a day or more has elapsed since your last calibration). Just recall the instrument state and CAL coefficients from disk. (Don't dothis unless you have to).H. Swept-frequency