Network Analyzers using TRVNA software

Time domain gating is a function that mathematically removes unwanted responses in the time domain. The function performs a time domain transformation, selects the region in the time domain, deletes the response inside (or outside) the selected region and transforms back to the frequency domain. The function allows the user to remove spurious effects of the fixture in the frequency domain, if the useful signal and spurious signal are separable in the time domain.

The recommended procedure is as follows:

•Use the time domain function for viewing the layout of useful and spurious responses.

•Enable the time domain gating and set the gate position to remove as much of spurious response as possible.

•Disable the time domain function and view the response without spurious effects in frequency domain.

The function involves two types of time gate:

•Bandpass — removes the response outside the time gate span.

•Notch — removes the response inside the time gate span.

The sharp gate shape leads to ringing effect in the frequency domain. To reduce the ringing the gate shape can be smoothed. The following gate shapes are offered:

•Maximum

•Wide

•Normal

•Minimum

The minimum window has a sharp shape. The maximum window has a more smoothed shape. From minimum to maximum window shape, the sidelobe level increases and the gate resolution decreases. The choice of the window shape is always a trade-off between the gate resolution and the level of spurious sidelobes. The parameters of different window shapes are represented in the table below.

Gate Activation

 

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Gate Span

 

 

Gate Type

 

Gate Shape Setting