Agilent Spectrum Analysis Basics - Agilent Technologies

Examples
Let’s look at some amplitude uncertainty examples for various measurements.
Suppose we wish to measure a 1 GHz RF signal with an amplitude of –20
dBm. If we use an Agilent E4402B ESA-E Series spectrum analyzer with Atten
= 10 dB, RBW = 1 kHz, VBW = 1 kHz, Span = 20 kHz, Ref level = –20 dBm, log
scale, and coupled sweep time, and an ambient temperature of 20 to 30 °C, the
specifications tell us that the absolute uncertainty equals ±0.54 dB plus the
absolute frequency response. An E4440A PSA Series spectrum analyzer
measuring the same signal using the same settings would have a specified
uncertainty of ±0.24 dB plus the absolute frequency response. These values
are summarized in Table 4-2.
Table 4-2. Amplitude uncertainties when measuring a 1 GHz signal
Source of uncertainty
Absolute uncertainty of
1 GHz, –20 dBm signal
E4402B
E4440A
Absolute amplitude accuracy ±0.54 dB ±0.24 dB
Frequency response ±0.46 dB ±0.38 dB
Total worst case uncertainty ±1.00 dB ±0.62 dB
Total RSS uncertainty ±0.69 dB ±0.44 dB
Typical uncertainty ±0.25 dB ±0.17 dB
At higher frequencies, the uncertainties get larger. In this example, we wish
to measure a 10 GHz signal with an amplitude of –10 dBm. In addition, we
also want to measure its second harmonic at 20 GHz. Assume the following
measurement conditions: 0 to 55 °C, RBW = 300 kHz, Atten = 10 dB, Ref
level = –10 dBm. In Table 4-3, we compare the absolute and relative amplitude
uncertainty of two different Agilent spectrum analyzers, an 8563EC (analog
IF) and an E4440A PSA (digital IF).
Table 4-3. Absolute and relative amplitude accuracy comparison (8563EC and E4440A PSA)
Measurement of a 10 GHz signal at -10dBm
Source of uncertainty Absolute uncertainty of Relative uncertainty of second
fundamental at 10 GHz harmonic at 20 GHz
8563EC E4440A 8563EC E4440A
Calibrator ±0.3 dB N/A N/A N/A
Absolute amplitude acc. N/A ±0.24 dB N/A N/A
Attenuator N/A N/A N/A N/A
Frequency response ±2.9 dB ±2.0 dB ±(2.2 + 2.5) dB ±(2.0 + 2.0) dB
Band switching uncertainty N/A N/A ±1.0 dB N/A
IF gain N/A N/A N/A N/A
RBW switching N/A N/A N/A N/A
Display scale fidelity N/A N/A ±0.85 dB ±0.13 dB
Total worst case uncertainty ±3.20 dB ±2.24 dB ±6.55 dB ±4.13 dB
Total RSS uncertainty ±2.91 dB ±2.01 dB ±3.17 dB ±2.62 dB
Typical uncertainty ±2.30 dB ±1.06 dB ±4.85 dB ±2.26 dB
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