266 Keysight N9927-90001 User’s Guide
IQ Analyzer (IQA) – Option 351 (CPU2 Only)
I/Q Analyzer (IQA) Mode Settings
— Res BW (Spectrum only) – Sets the resolution bandwidth of the FFT
analysis. Changing this value changes the FFT window size, analysis
length, and the sweep time (data acquisition capture length). This
softkey is only available when IQA is set to Spectrum (Freq Domain).
When the resolution bandwidth value is set to Auto (default) the
FieldFox automatically sets the optimum resolution bandwidth value.
(Default: 200 kHz, Minimum: 0.1 Hz, maximum: 3 MHz).
— Analysis Length Sets the FFT analysis length that is the length of the
complex I/Q data points (I/Q–pairs) vector that is used for spectrum
analysis, expressed in the number of samples. (Couplings: In Auto,
this setting is directly coupled to the Res BW and to Span. Minimum:
8, Maximum: 524,288. Where each FFT length "point" is equal to 1 I
and 1 Q point. So, 237 is equal to 237 I and 237 Q points).
— FFT Window
Sets the FFT filtering window (spectrum analysis
window) shape for the I/Q data. Default: Flat Top
Then select one of the following:
There is a significant difference between resolution BW in FFT
measurements and the resolution BW of a traditional "sweeping"
spectrum analyzer (SA) measurement. The resolution BW in FFT
measurements does not directly control the IF BW like a traditional SA
swept measurement. Resolution bandwidth is directly related to the
analysis length (window) and or data acquisition capture length (sweep
time).
FFT Window Description
Uniform No windowing
Triangular Barlett windowing
Hanning This is a Hann window, sometimes called Hanning or "raised
cosine".
Hamming This window has lower side-lobe peaks than the Hann window,
but has worse main-lobe flatness and poor side-lobe roll-off.
Blackman This window is similar to the three-term Blackman-Harris
window, but it has simpler fixed-form coefficients and better
side-lobe roll-off.
Blackman Harris 3 This is the three-term Blackman-Harris window. This has the
minimum side-lobe level for a three-term cosine window.
Blackman Harris This is the four-term Blackman-Harris window. This has the
minimum side-lobe level for a four-term cosine window with
60 dB/decade roll-off.
Gaussian Top This is a five-term cosine window that resembles a Gaussian
window.
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