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Appendix A

Uncertainty calculations for a power measurement (settled, average power)

[Specification values from this document are in bold italic, values calculated on this page are underlined.]

Process:

1. Power level: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2. Frequency: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. Calculate meter uncertainty:

Calculate noise contribution

• If in Free Run mode, Noise

= Measurement noise x free run multiplier

• If in Trigger mode, Noise

= Noise-per-sample x noise per sample multiplier

Convert noise contribution to a relative term

= Noise/Power

. . . . . . . . . . . . . . . . . . . . . . . . . %

Instrumentation linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . %

Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . %

RSS of above three terms => Meter uncertainty

= . . . . . . . . . . . . . . . . . . . . . . . . . . . . %

4. Zero Uncertainty

(Mode and frequency dependent) = Zero set/Power

= . . . . . . . . . . . . . . . . . . . . . . . . . %

5. Sensor calibration uncertainty

(Sensor, frequency, power and temperature dependent) = . . . . . . . . . . . . . . . . . . . . . . . %

6. System contribution

, coverage factor of 2 => sys

rss

= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . %

(RSS three terms from steps 3, 4 and 5)

7. Standard uncertainty of mismatch

Max SWR (Frequency dependent) = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

convert to reflection coefficient, |

Sensor

| = (SWR–1)/(SWR+1) = . . . . . . . . . . . . . . . . . .

Max DUT SWR (Frequency dependent) = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

convert to reflection coefficient, |

DUT

| = (SWR–1)/(SWR+1) = . . . . . . . . . . . . . . . . . . . .

8. Combined measurement uncertainty @ k=1

. . . . . . . . . . . . . . . . . . . . . %

Expanded uncertainty, k = 2, = U

• 2 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . %

14. The noise to power ratio is capped for powers > 100 uW, in these

cases use: Noise/100 µW.

Max(r

DUT

) • Max(r

Sensor

) sys

rss

1 2 3 4 5 6 7 8 9 10 11 12

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