The scalar network analyzer, SNA is considerably less common in RF design circles than the VNA, but it can provide some useful insights.
As the name indicates a scalar networj analyzer, SNA, measures only the amplitude response of an RF network to an applied stimulus.
Scalar network analyzers can be very useful in measuring aspects like the amplitude response of a filter or other network. In this way a good insight can be obtained into a number of the aspects of the operation of the network.
Effectively, a scalar network analyzer, SNA, works just as a spectrum analyzer in combination with a tracking generator. When a tracking generator and spectrum analyser are used together, their operation is electrically closely linked.
The tracking generator generators a swept signal on exactly the same frequency that the spectrum analyser is receiving. Thus if the output from the tracking generator was connected directly to the input of the spectrum analyzer, then a constant line would be seen across the screen of the analyzer indicating the amplitude of the tracking generator output.
If a device is placed between the two items, then the spectrum analyser will note any amplitude variations. In this way for example, the response of a filter can be plotted. The constant output of the tracking generator will pass into the filter, where the response of the filter will change it according to the frequency and the response of the filter at that frequency, and in this way the spectrum analyzer will be able to display the response of the filter. From this it can be seen that scalar network analyzers, SNA, are very useful for measuring the amplitude response of a variety of components.