What is Sweep Speed in a VNA?

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Andreas Henkel, Product Management for Network Analysis - Rohde & Schwarz

Aug 6, 2019

The sweep speed refers to the time the vector network analyzer (VNA) requires to finish one sweep of the source signal and get all the selected data in a chosen frequency range. It is usually specified in terms of time per data point and the time required for a sweep is called cycle time.


Brian Walker - Copper Mountain Technologies

Aug 9, 2019

The sweep speed, or the time required to present a complete S Parameter measurement from the start to the stop frequency on the screen depends on three things. First, the IF Bandwidth determines how long it takes to make a measurement at each point. This is due to the delay through the Finite Impulse Reponse (FIR) filter which applies the IF Bandwidth to the signal. This delay is approximately 1.5/(IF Bandwidth) per point. 

Secondly, the number of measurement points obviously affects the sweep speed and thirdly the type of calibration in place. A full two port calibration must operate on all four S Parameters in order to calculate any single corrected S Parameter. If a full two port calibration has been performed then the VNA must sweep twice, once in each direction in order to obtain all four required parameters. This doubles the time required to present a sweep on the screen. A full four port calibration would take four times as long. 

Additionally each sweep requires a small setup time, usually a few milliseconds. 

So Sweep Time is approximately  Setup + CalFactor * NP * 1.5/IFBW

Where NP is the number of points and CalFactor is 1 for no calibration or 1 port, 2 for 2 port and so on. and Setup is perhaps 1 to 5 mS. 

 

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