About Resolution Bandwidth

Resolution Bandwidth is a qualitative measure of the minimum separation required between two frequency components to be able to visually separate them and, for the VSA, is defined as the Equivalent Noise Bandwidth of the filter, which is determined by the window type that you select and the length of the window.

Resolution bandwidth (ResBW or RBW Resolution Band Width (RBW or ResBW): specifies the minimum frequency bandwith that two separate frequency spectra can be resolved and viewed seperately. For FFT (digital) based VSA's the process is equivalent to passing a time-domain signal through a bank of bandpass filters, whose center frequencies correspond to the frequencies of the FFT bins. For a traditional swept-tuned (non-digital) spectrum analyzer, the resolution bandwidth is the bandwidth of the IF filter which determines the selectivity.) affects the following:

The frequency resolution for spectrum traces
How fast the VSA makes a measurement

ResBW parameter: Specifies the measurement RBW. The VSA will adjust the RBW to the closest value that satisfies the current measurement setup.

Because resolution bandwidth is directly related to measurement time, manually selecting a narrower resolution bandwidth can slow down a measurement more than necessary. Selecting a resolution bandwidth that is too wide, on the other hand, may not provide adequate resolution and can obscure spectral components that are close together.

Auto ( Power Spectrum, Adjacent Channel Power and Spectral Emissions Mask measurements only) - When checked (default setting), automatically changes ResBW to match the ratio set by Span to ResBW Ratio.

Swept analyzers generally define ResBW (also called window BW in swept analyzers) as the 3 dB bandwidth of the window. The 89600 VSA defines ResBW as the "equivalent noise bandwidth" of the window, which is the bandwidth of a rectangular filter that passes the same noise power as the filter specified by the window.

It is recommended that Auto Frequency Points mode be enabled. Auto Frequency Points mode provides the most flexibility in choosing a ResBW or Main Time Length for a given Span and Window Type.

Power Spectrum Measurements

For details about Resolution Bandwidth when making Power Spectrum measurements, see Resolution and Video Bandwidth (Power Spectrum).