Coaxial Measurements – Common Mistakes & Simple Solutions

1. Coaxial Measurements –Common Mistakes &Simple Solutions Sathya Padmanabhan Rocky Teresa Maury Microwave Corp. For electronic copy of presentation go to www.maurymw.com/presentations.htm

2. Coaxial Measurements – Common Mistakes & Simple Solutions Coaxial Measurements • DUT Measurement accuracy limited by • Test Setup • Calibration method • User practices • Common practices and assumptions in • Calibration procedures • Measurement or setup processes

3. Measurement Issues Fixed load as terminating element Use/ non use of Torque wrench Phase stability of test cables Coaxial Measurements – Common Mistakes & Simple Solutions Coaxial Measurements • Calibration Issues • Cal kit and definitions • Non zero thru calibration • Adding/ removing adapter after cal • Fixed load or Sliding load cal • Calibration Issues • Cal kit and definitions • Non zero thru calibration • Adding/ removing adapter after cal • Fixed load or Sliding load cal • Measurement Issues • Fixed load as terminating element • Use/ non use of Torque wrench • Phase stability of test cables

4. Coaxial Measurements – Common Mistakes & Simple Solutions Calibration Kit and Definitions • Using incorrect definitions for calibration • Unique to each manufacturer and model no. • Electrical delay lengths of open/ short standards • Airline lengths of line standards • Calibration constants derived based on design and performance of standards

5. Coaxial Measurements – Common Mistakes & Simple Solutions Calibration Kit and Definitions • Kit definitions critical to cal accuracy • SOLT - Error co-efficients calculated from the closeness of definitions to actual measured • TRL/ LRL – Line lengths establish reference plane • Accuracy of error co-efficients?

6. Coaxial Measurements – Common Mistakes & Simple Solutions Calibration Kit and Definitions

7. Measurement Issues Fixed load as terminating element Use (or no use) of Torque wrench Phase stability of test cables Coaxial Measurements – Common Mistakes & Simple Solutions Coaxial Measurements • Calibration Issues • Cal kit and definitions • Non zero thru calibration • Adding/ removing adapter after cal • Fixed load or Sliding load cal

8. Coaxial Measurements – Common Mistakes & Simple Solutions Non Zero Thru SOLT Calibration • Assume zero length thru for an adapter cal • Zero length thru definition for cal kits – Typical • Reference plane set by length of thru • Forced at an artificial reference plane when assumed zero • DUT loss looks much better than actual • DUT phase looks falsely shorter • Define length of thru (adapter) for adapter cals • Electrical delay of adapter from physical length

9. Thru length defined Incorrect definition for thru (assumed zero) Coaxial Measurements – Common Mistakes & Simple Solutions Non Zero Thru SOLT Calibration • DUT loss and phase comparison

10. Measurement Issues Fixed load as terminating element Use (or no use) of Torque wrench Phase stability of test cables Coaxial Measurements – Common Mistakes & Simple Solutions Coaxial Measurements • Calibration Issues • Cal kit and definitions • Non zero thru calibration • Adding/ removing adapter after cal • Fixed load or Sliding load cal

11. Coaxial Measurements – Common Mistakes & Simple Solutions Non Insertable Calibration • Adding/ Removing/ Swapping adapters after cal • Calibration methods available • Adapter swap, Adapter removal, Characterized adapter, Unknown thru • Effective match – cascaded – Adding adapters • Again, where is your reference plane? • Phase equal adapters

12. Coaxial Measurements – Common Mistakes & Simple Solutions Non Insertable Calibration • Adding adapters after cal

13. Coaxial Measurements – Common Mistakes & Simple Solutions Non Insertable Calibration • Removing/ Swapping adapters after cal

14. Measurement Issues Fixed load as terminating element Use (or no use) of Torque wrench Phase stability of test cables Coaxial Measurements – Common Mistakes & Simple Solutions Coaxial Measurements • Calibration Issues • Cal kit and definitions • Non zero thru calibration • Adding/ removing adapter after cal • Fixed load or Sliding load cal

15. Coaxial Measurements – Common Mistakes & Simple Solutions Fixed vs. Sliding load SOL calibration • Which one to choose? • Definition of fixed load • SOL calibration accuracy based on definitions • Is DUT a well matched device? • Cannot measure better than fixed load • If you calibrate with a 30 dB Return Loss Fixed Load • What level of Return loss can be measured on the DUT? • Worse than 20 dB – NO problem • 20 – 30 dB – uncertainties ramp up • Better than 30 dB – Can’t determine

16. Coaxial Measurements – Common Mistakes & Simple Solutions Fixed vs. Sliding load SOL calibration • Sliding Load - • Precision Airline with movable terminating element • Change phase of imperfect termination • Use circle fitting to find center • Reduces G error to • Airline Impedance • Stability of terminating element • Lower frequency limited due to length of slide • Usually combine with Fixed load at low frequencies

17. Coaxial Measurements – Common Mistakes & Simple Solutions Fixed vs. Sliding load SOL calibration • Which one to choose?

18. Measurement Issues Fixed load as terminating element Use (or no use) of Torque wrench Phase stability of test cables Coaxial Measurements – Common Mistakes & Simple Solutions Coaxial Measurements • Calibration Issues • Cal kit and definitions • Non zero thru calibration • Adding/ removing adapter after cal • Fixed load or Sliding load cal

19. Coaxial Measurements – Common Mistakes & Simple Solutions Fixed load as terminating element • DUT VSWR = Effects (DUT + Fixed load) • Can mislead with constructive or destructive combination • Knowledge of • Fixed load – how good is it? • Expected DUT performance • Well matched fixed load

20. Coaxial Measurements – Common Mistakes & Simple Solutions Fixed load as terminating element

21. Measurement Issues Fixed load as terminating element Use (or no use) of Torque wrench Phase stability of test cables Coaxial Measurements – Common Mistakes & Simple Solutions Coaxial Measurements • Calibration Issues • Cal kit and definitions • Non zero thru calibration • Adding/ removing adapter after cal • Fixed load or Sliding load cal

22. Coaxial Measurements – Common Mistakes & Simple Solutions Use (or no use) of Torque wrench • Well connected pair – optimum signal flow path • Over tightened pair – damage mating surfaces • Loosely connected pair – high reflection at interface

23. Coaxial Measurements – Common Mistakes & Simple Solutions Use (or no use) of Torque wrench • How tight is hand tight?

24. Coaxial Measurements – Common Mistakes & Simple Solutions Use (or no use) of Torque wrench • Using open ended wrench for tightening • Applying torque at the wrong end of mated pair • Incorrect method of applying torque

25. Recommended NOT Recommended Coaxial Measurements – Common Mistakes & Simple Solutions Use (or no use) of Torque wrench • Recommended method

26. Measurement Issues Fixed load as terminating element Use (or no use) of Torque wrench Phase stability of test cables Coaxial Measurements – Common Mistakes & Simple Solutions Coaxial Measurements • Calibration Issues • Cal kit and definitions • Non zero thru calibration • Adding/ removing adapter after cal • Fixed load or Sliding load cal

27. Coaxial Measurements – Common Mistakes & Simple Solutions Test setup and handling • Minimal movements during and after calibration • Drift in cal (error co-efficients) as setup changes • Good phase stable cable • Tracking phase of zero length thru after cal • Critical for phase sensitive measurements • Check phase stability of test cables

28. Coaxial Measurements – Common Mistakes & Simple Solutions Summary • Know your standards • Proper non insertable cal technique • Select the right load • Use torque wrench • Use pin depth gage • Phase stable test setup – Good quality cables

29. Coaxial Measurements – Common Mistakes & Simple Solutions More Info • Connectors – Precision or Not? • http://www.maurymw.com/presentations.htm • Verifying accuracy of calibration – • http://www.maurymw.com/support/pdfs/5C-027.pdf • http://www.maurymw.com/support/pdfs/5C-026.pdf

30. Coaxial Measurements – Common Mistakes & Simple Solutions Thank You • Rusty Myers for his input • Elton Mosher for all the test data