Real-Time Spectrum Analyzers; Parallel-Filter Analyzers - Agilent Technologies 89410A Operator's Manual

What Makes this Analyzer Different?

Real-time spectrum analyzers

Despite the high performance of modern superheterodyne analyzers, they still can't
evaluate frequencies simultaneously and display an entire frequency spectrum
simultaneously. Thus, they are not real-time analyzers. And the sweep speed of a
swept-tuned analyzer is always limited by the time required for its internal filters to
settle.

Parallel-filter analyzers

Another way to build a spectrum analyzer is to combine several bandpass filters,
each with a different passband frequency. Each filter remains connected to the
input at all times. This type of analyzer is called a parallel-filter analyzer. After an
initial settling time, the parallel-filter analyzer can instantaneously detect and
display all signals within the analyzer's measurement range.
The particular strength of such an analyzer is its measurement speed—this allows it
to measure transient and time-variant signals. However, the frequency resolution
of a parallel-filter analyzer is much coarser than a typical swept-tuned analyzer.
This is because the resolution is determined by the width of the decimating filters.
To get fine resolution over a large frequency range, you would need many, many
individual filters—thus increasing the cost and complexity of such an analyzer.
This is why all but the simplest parallel-filter analyzers are expensive.
Typically, parallel-filter analyzers have been used in audio-frequency applications.
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