Coaxial Measurements – Common Mistakes & Simple Solutions Sathya Padmanabhan Rocky Teresa Maury Microwave Corp. For electronic copy of presentation go to

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

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

Coaxial Measurements – Common Mistakes & Simple Solutions 4 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

Coaxial Measurements – Common Mistakes & Simple Solutions 5 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?

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

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

Coaxial Measurements – Common Mistakes & Simple Solutions 8 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

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

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

Coaxial Measurements – Common Mistakes & Simple Solutions 11 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

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

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

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

Coaxial Measurements – Common Mistakes & Simple Solutions 15 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

Coaxial Measurements – Common Mistakes & Simple Solutions 16 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 Fixed vs. Sliding load SOL calibration

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

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

Coaxial Measurements – Common Mistakes & Simple Solutions 19 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

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

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

Coaxial Measurements – Common Mistakes & Simple Solutions 22 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

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

Coaxial Measurements – Common Mistakes & Simple Solutions 24 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

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

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

Coaxial Measurements – Common Mistakes & Simple Solutions 27 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

Coaxial Measurements – Common Mistakes & Simple Solutions 28 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

Coaxial Measurements – Common Mistakes & Simple Solutions 29 More Info Connectors – Precision or Not? – Verifying accuracy of calibration – – –

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