Atec Agilent-8990B - Manual (Page 17)

17
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: ..............................................................................................................................................
1 mW
2. Frequency: ................................................................................................................................................ 1 GHz
3. Calculate meter uncertainty:
Calculate noise contribution
• Noise = Noise-per-sample x noise per sample multiplier = 3 µW x 1
Convert noise contribution to a relative term 1 = Noise/Power = 3 μW/1 mW ........................... 0.3%
Instrumentation linearity ..................................................................................................................... 0.8%
Drift ...........................................................................................................................................................
RSS of above three terms ≥ Meter uncertainty = ........................................................................ 0.85%
4. Zero uncertainty
(Mode and frequency-dependent) = Zero set/Power = 200 nW/1 mW ................................. 0.02%
5. Sensor calibration uncertainty
(Sensor, frequency, power and temperature-dependent) = ........................................................ 4.0%
6. System contribution, coverage factor of 2 ≥ sys
rss
= ........................................................................ 4.09%
(RSS three terms from steps 3, 4 and 5)
7. Standard uncertainty of mismatch
Max SWR (frequency-dependent) = .............................................................................................. 1.2%
convert to reflection coefficient, | ρ
Sensor
| = (SWR–1)/(SWR+1) = ........................................ 0.091%
Max DUT SWR (frequency-dependent) = ...................................................................................... 1.26%
convert to reflection coefficient, | ρ
DUT
| = (SWR–1)/(SWR+1) = ........................................... 0.115%
8. Combined measurement uncertainty @ k=1
U
C
=
( Max(ρ
DUT
) • Max(ρ
Sensor
) )
2
+
( sys
rss
)
2
.................................................................... 2.045%
√2 2
Expanded uncertainty, k = 2, = UC • 2 = ............................................................................................. 4.09%
1. The noise-to-power ratio is capped for powers > 100 μW, in these cases use: Noise/100 μW.
Worked Example