Lab Introduction & Network Analyser Basics

Transcription

1 Lab Introduction & Network Analyser Basics Martin J. Siebers Lab Manager

2 Agenda Lab Rules and Admin Connectors and Cables Network Analyser Basics VNA Demonstration

3 Lab Rules Who may use the Labs - Permission Responsibility Available Equipment Booking Removal of Equipment

4 Lab Rules (cont ) Before Leaving the Laboratories Anechoic Chamber Work-Benches, Drawers and Cabinets No food and drinks in the Lab

5 Lab Rules (cont ) Safety, Accidents and Damage Who to talk to? Visitors If you want access to the RF and Antenna Lab you must complete a Lab Registration form and know the rules!

6 Connectors and Cables Martin J. Siebers Lab Manager

7 Connectors

8 SMA connectors SMA Male SMA Female The SMA connector is the workhorse of the RF and microwave industries. The basic design uses a 4.2 millimeter diameter outer coax, filled with Teflon (PTFE) dielectric. Their upper frequency limit is anywhere from 18 to 26 GHz, depending on the tolerances held during manufacturing. SMAs, like many other coax connector families, are sized to fit a 5/16 inch (8mm) wrench.

9 3.5mm and 2.92 connectors Both use air dielectric, and mate with each other as well as the cheaper SMA styles (see next slide) The 3.5 mm connector is the next upgrade from SMA, it performs well up to 26 GHz The 2.92 mm connector (often called "2.9 millimeter") works all the way up to 40 GHz. The K-connector is Anritsu's version of the 2.92 mm connector 3.5 mm connector (male) 2.92 mm connector (male)

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11 Mating precision and SMA connectors SMA connectors must not be used with the 3.5mm and 2.92mm precision connectors although they physically mate. E&E allows that female SMAs may be used with male precision connectors. Male SMAs must never be used with female precision connectors.

12 7 mm connectors The lowest VSWR of any connector offered Work well up to 18 GHz Unique: sexless You will find the 7 mm connector at the ports of the 8753A and at the LC-meter but you are not supposed to do anything with them! Usually hand tighten is fine. Use a wrench if you can t open one. Fortunately, most 7 mm connectors have hex-nuts that fit a 3/4 inch wrench. E&E labs stocks a torque wrench to provides repeatable and reliable connections.

13 Type N connectors These are rugged and cheaper than most of the connectors mentioned. Therefore you will find them all over the laboratory. There is a big variety of Type N adapters available at the E&E labs Type N to SMA (male and female) Type N to BNC (male and female)

14 A male-to-male or barrel adapter Adapters A female-to-female or bullet adapter A male-to-female or connector saver SMA connector saver, barrel and bullet adapter

15 Connector torque The correct mating torque for all 5/16 hexagonal-sleeved connectors is 8 inch-pounds. Use a torque wrench for precision measurements. A torque wrench is a calibrated device and people rely on its performance. Use it with care and don t play with it. Make sure it does not drop on the floor because it may loose it s calibration. Support the not turning part of the connection with a spanner Use it only to torque connectors in the way being demonstrated

16 Connector care Connectors and adapters cost a lot of money. Show respect and follow the basic guidelines: Learn how to clean connectors. Cleaning the threads is good practice, but stay away from cleaning the center conductor of an air dielectric connectors such as 3.5mm, 2.92mm and 2.4mm Don't use pliers on a connector. There are wrenches for every size connector and adapter, even for SMA bullets. Learn how to gauge connectors to determine if they are out of spec. One bad connector can damage many.

17 Connector care (cont ) Never use any part of a calibration kit other than for calibration. If you need a special adapter or a load buy it or borrow it but don t take it from the cal kit Use a torque wrench. It's OK to use less torque, but not more. When you are tightening or loosening a connector, try not to spin the mating surfaces against each other. You should only be turning the threaded sleeve. Remember, righty-tighty, lefty-loosely! The total damage done by people turning stuff in the wrong direction is enormous. The hardware you hold in your hands could very well be worth more than your automobile. So be gentle with it.

18 How to deal with stuck connectors The female to female SMA adapter is the cause of much pain in the microwave laboratory. Why? Because it tends to get stuck. Therefore we provide special wrenches to hold the bullet. So the nuts can be opened and the connectors released Never use common slipjoint pliers to remove it. A damaged thread of a bullet will damage the threads of all connectors that it mates with

19 Storing connectors and adaptors You've just bought a nice new set of coax adapters for that new lab project. They come with some plastic caps on each end... so you take off the caps and throw them out, right? WRONG! Those plastic things are called dust caps for a reason, they keep your connectors clean.

20 Connector care (cont ) Adapters and connectors are precision items, that's why they cost a fortune. So why does someone treat them like common hardware? Check out the picture, whoever "owns" a bench that stores connectors like this should never be allowed in the lab! Those two-cents worth of stainless-steel screws are full of contaminates like oil, skin, and the worst culprit, tiny pieces of metal. Store them separately, and keep the dust caps on the adapters!

21 Connector care (cont ) Check out the photo of the 7 mm connector What is wrong? The way to protect the 7mm connector is to always spin the sleeve clockwise to extend the threads, then push on a dust cap.

22 Cleaning connectors Cleaning connectors regularly will not only make them last longer, but will also provide better results for your measurements. Convention: At E&E we clean the connector before we use them Clean connectors Cables Cal kit Adapters But NOT the ones at the test instruments Never apply the cleaning solution directly onto a connector.

23 Cleaning connectors in the E&E-Laboratories Clean the SMA connector: use a toothpick, apply the cleaning solution and carefully loosen all dirt in the thread If there is dirt on the Teflon face loosen it with a wet toothpick. Be careful on the Teflon face Don t rake it up! Repeat this procedure until the toothpick doesn t show dirt. Use a cotton swab, apply little cleaning fluid and wipe the female SMA connector. Cotton swabs are too big for the male SMA so it cant be wiped. Finally use air to dry the connector. Never shake the air can! Press the knob gently to ensure economical use. Start blowing air aside of the connector moving the flow onto it. Don t blow the thread of the female connector.

24 Cleaning connectors in the E&E-Laboratories Clean the 3.5 mm precision connector: use a toothpick, apply the cleaning solution and carefully loosen all dirt in the thread of the male and the female connector. Repeat this procedure until the toothpick doesn t show dirt. There are special foam swabs for the 3.5 connectors. They may be used to very carefully wipe the male and female connector under the supervision of the lab manager. Never wipe the inside of a precision connector on your own! Finally use air to dry the connector. Never shake the air can! Press the knob gently to ensure economical use. Start blowing air aside of the connector moving the flow onto it. Don t blow the thread of the female connector.

25 Cleaning connectors (cont ) The inside of a female SMA should be wiped with a cotton swab. Don t wipe the inside of 3.5mm PC connectors Outside threads of female connectors may be cleaned using a swab but the toothpick or the paper method are more efficient.

26 Cleaning connectors (cont ) Swabs may be reused but Throw out the swab when it looks like the swab on the left in the photo!

27 Connector Handling Never clean the precision connectors fitted at the instruments. Lab maintenance is responsible for that! When connector threads are cleaned, you will be able to hand-tighten all connections to within 1/2 turn of the proper torque If you are not able to hand tighten a connector, something is wrong. Usually it is an aligning problem, or one of the connectors in the pair is already damaged. Connector damage is often the result of bad cleaning or a mechanical force being applied, causing the connector to become slightly "d-shaped" instead of perfectly round.

28 Transmission lines: Coaxial Cables The dimensions d, D, and the dielectric determine: Z0 (characteristic impedance) fc (the cutoff frequency) capacitance and inductance per meter Temperature Bending radius Connector transition

29 Network Analyser Basics Martin J. Siebers Lab Manager

30 Overview Network analysers fall into two categories The Vector Network Analyser (VNA) is capable of measuring complex reflection and transmission The scalar analyser can only measure magnitude A VNA can measure S-parameter and VSWR, loss, gain, isolation, and group delay of any two (or more) ports of a given network Key manufacturers of VNAs are Agilent (former HP), Anritsu (Wiltron), and Rohde & Schwarz. VNAs also called "ANA automated network analyser.

31 History The original network analyser (HP 8409) No Error Correction build in Error correction was done by hand Then the first automated network analysers were introduced. A minicomputer processed the vector data delivered error corrected and accurate magnitude and phase of the four S-parameters The next step was to build the error correction into the TE and display the error-corrected measurements in nearly real time (the original HP 8510, circa 1982).

32 The 8510 VNA The "classic" vector network analyser is the Agilent (HP) Depending on how much one spend, this analyser can make measurements from 45 MHz to 110 GHz. E&E has two 8510C 45MHz to 20GHz 45MHz to 50GHz

33 Simplified VNA Block Diagram Incident DUT Transmitted SOURCE Reflected SIGNAL SEPARATION INCIDENT (R) REFLECTED (A) TRANSMITTED (B) RECEIVER / DETECTOR PROCESSOR / DISPLAY

34 Characterizing Devices Incident R Reflected A REFLECTION Transmitted B TRANSMISSION Reflected Incident = A R Transmitted Incident = B R SWR S-Parameters S11,S22 Reflection Coefficient Γ, ρ Return Loss Impedance, Admittance R+jX, G+jB Gain / Loss S-Parameters S21,S12 Transmission Coefficient Τ,τ Insertion Phase Group Delay

35 S-Parameters Relatively easy to obtain at high frequencies Measure voltage traveling waves with a vector network analyzer Don't need shorts/opens which can cause active devices to oscillate or self-destruct Relate to familiar measurements (gain, loss, reflection coefficient...) Can cascade S-parameters of multiple devices to predict system performance Can easily import and use S-parameter files in electronic simulation tools Incident a1 S11 Reflected b 1 Transmitted S 21 DUT Port 1 Port 2 S12 b1 = S11 a 1 + S 12 a 2 b 2 = S21 a1 + S22 a 2 Transmitted b 2 S22 Reflected a 2 Incident

36 S-Parameters Relate to Common Measurement Terms S11 = forward reflection coefficient (input match) S22 = reverse reflection coefficient (output match) S21 = forward transmission coefficient (gain or loss) S12 = reverse transmission coefficient (isolation) Remember, S-parameters are inherently linear quantities -- however, we often express them in a log-magnitude format

37 Errors Systematic errors due to imperfections in the analyzer and test setup are assumed to be time invariant (predictable) can be characterized (during calibration process) and mathematically removed during measurements Random errors vary with time in random fashion (unpredictable) cannot be removed by calibration main contributors: instrument noise (source phase noise, IF noise floor, etc.) switch repeatability connector repeatability Drift errors are due to instrument or test-system Measured Data performance changing after a calibration has been done are primarily caused by temperature variation can be removed by further calibration(s) Errors: SYSTEMATIC RANDOM DRIFT Unknown Device

38 Systematic Measurement Errors R Directivity A Crosstalk B DUT Frequency response reflection tracking (A/R) transmission tracking (B/R) Source Mismatch Load Mismatch Six forward and six reverse error terms yields 12 error terms for two-port devices

39 What is Calibration? Measure known device Note measured value Generate error table based on the difference between known and measured values Subtract error from subsequent measurements

40 Standards Definitions Definitions are the parameters of an equivalent circuit network that represents the physical network A standard may have a combination of a delay, a loss, a capacitance, an inductance, a frequency range and a characteristic impedance Standards definitions must be known to the VNA Enter manually Load from disc A Cal Kits come with the definitions of their standards.

41 Calibration Kits Coaxial calibration kits come in type N, 7 mm, 3.5 mm, 2.92 mm, 2.4 mm, 1.0 mm and skripsie. (Bold available at E&E) Be sure not to exceed the frequency capability of the cables, adapters and calibration kit (remember session on connectors). There are waveguide calibration kits for every waveguide band. E&E has one for S-Band and one for X-Band. Remember that cal kits are expensive, and pieces of the cal kit should never be used as adapters or terminations. Always put the little plastic covers onto the cal kit pieces.

42 Verification - Validation Verification means to measure known standards which haven t been used for the actual calibration. Therefore a verification kit is used. To validate the calibration and the general health of the test system, look at a few things after calibration Check the residual error in a "through" connection. Ideally the magnitude should be 0 db and the phase should be 0.0 degrees. The reflection at both ports should be better than -40dB. Usually it is at about -60dB or lower. Depending on the cable quality and the frequency range a variation of the transmission and reflection parameters will be noticed upon the movement of the cables. If there is an issue with the calibration, figure out the source of the problem before performing another calibration. Otherwise you will be wasting your time!

43 General Considerations Before performing a calibration, answer the following questions: Frequency range? Do the cal kit, the cables and any adapters operate at the desired band? Are the cables fit for this application? Notice the effect of gently bending cables. Notice the effect of moving cables. Will the cables reach the DUT without stressing them? If possible, perform the calibration with cables in the position needed to be connected to DUT

44 General Considerations Averaging Averaging will improve the accuracy of your data, as long as you do it during the calibration as well as the actual measurement. It will slow down the measurement process Smoothing Smoothing is cheating! Smoothing reduces the "bumpiness" of a frequency response by averaging data across a couple of frequency points and using the result at one frequency.

45 General Considerations Electrostatic Discharge Always discharge yourself! Use the Static Control Wrist Straps provided. Be extremely careful when executing antenna measurements (centre conductor is often exposed) Torque The torque of the connections will have an influence on the quality and repeatability of the calibration and the actual measurements. Always apply the right torque using a torque wrench. Using less torque is your choice. Never over-torque!

46 Any Questions? Thanks for your attention! See you upstairs R551 for VNA Demonstrations!