Embed Size (px)
Citation preview
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
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? – 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
Coaxial Measurements – Common Mistakes & Simple Solutions
30
Thank You
• Rusty Myers for his input
• Elton Mosher for all the test data
