Time Domain Transformation

The Analyzer measures and displays parameters of the DUT in frequency domain. Time domain transformation is a function of mathematical modification of the measured parameters in order to obtain the time domain representation.

For time domain transformation Z-transformation and frequency domain window function are applied.

The time domain transformation can be activated for separate traces of a channel. The current frequency parameters (S₁₁, S₂₁, S₁₂, S₂₂) of the trace will be transformed into the time domain.

Note		Traces in frequency and time domains can simultaneously belong to one channel. The stimulus axis label will be displayed for the active trace, in frequency or time units.

The transformation function allows for setting of the measurement range in time domain within Z-transformation ambiguity range. The ambiguity range is determined by the measurement step in the frequency domain:

The time domain function allows to select the following transformation types:

- - Bandpass mode simulates the impulse bandpass response. It allows the user to obtain the response for circuits incapable of direct current passing. The frequency range is arbitrary in this mode. The time domain resolution in this mode is twice lower than it is in the lowpass mode;
  - Lowpass mode simulates lowpass impulse and lowpass step responses. It is applied to the circuits passing direct current, and the direct component (in point F=0 Hz) is interpolated from the start frequency (Fmin) of the range. In this mode the frequency range represents a harmonic grid where the frequency value at each frequency point is an integer multiple of the start frequency of the range Fmin. The time domain resolution is twice higher than it is in the bandpass mode.

The time domain transformation function applies Kaiser window for initial data processing in frequency domain. The window function allows to reduce the ringing (side lobes) in the time domain. The ringing is caused by the abrupt change of the data at the limits of the frequency domain. But while side lobes are reduced, the main pulse or front edge of the lowpass step becomes wider.

The Kaiser window is described by β parameter, which smoothly fine-tune the window shape from minimum (rectangular) to maximum. The user can fine-tune the window shape or select one of the three preprogrammed windows:

- - Minimum (rectangular);
  - Normal;
  - Maximum.

Table 28 Preprogrammed window types

Window	Lowpass Impulse	Lowpass Step
	Side Lobes Level	Pulse Width	Side Lobes Level	Edge Width
Minimum	– 13 dB		– 21 dB
Normal	– 44 dB		– 60 dB
Maximum	– 75 dB		– 70 dB

Time Domain Transformation Activating

		To enable/disable time domain transformation function, use the following softkeys:
Note		Time domain transformation function is accessible only in linear frequency sweep mode.

Time Domain Transformation Span

To define the span of time domain representation, you can set its start and stop, or center and span values.

		To set the start and stop limits of the time domain range, use the following softkeys:
		To set the center and span of the time domain, use the following softkeys:

Time Domain Transformation Type

		To set the time domain transformation type, use the following softkeys:

Time Domain Transformation Window Shape Setting

		To set the window shape, use the following softkeys:
		To set the window shape for the specific impulse width or front edge width, use the following softkeys:
		To set the window shape for the specific β-parameter of the Kaiser-Bessel filter, use the following softkeys:
Note		The impulse width and β of the Kaiser-Bessel filter are the dependent parameters. When you set one of the parameters the other one will be adjusted automatically.

Frequency Harmonic Grid Setting

If lowpass impulse or lowpass step transformation is enabled, the frequency range will be represented as a harmonic grid. The frequency values in measurement points are integer multiples of the start frequency Fmin. The Analyzer is capable of creating a harmonic grid for the current frequency range automatically.

	To create a harmonic grid for the current frequency range, use the following softkeys:
Note	The frequency range will be transformed as follows:
	Fmax > N x 0.3 MHz	Fmax < N x 0.3 MHz
	Fmin = Fmax / N	Fmin = 0.3 MHz,