Bandfilter   

Opens a submenu to search for trace segments with a bandpass or bandstop shape and determines characteristic filter parameters.

Bandfilter search and filter parameters

• Bandpass Search Ref to Max activates the search for a bandpass region in the active trace.

• Bandpass Search Ref to Marker activates the search for a bandpass region in the active trace, starting at the position of the active marker.

• Bandstop Search Ref to Max activates the search for a bandstop region in the active trace.  

• Bandfilter Tracking causes the bandfilter search to be repeated after each sweep.  

• x dB Bandwidth... sets the level defining the filter bandwidth.  

• Search Range... confines the search to a subrange of the sweep.

• Search Markers and Result Off hides the markers and bandfilter parameters in the diagram area.

Bandfilter mode can be selected for a broad range of measured quantities (Trace – Measure), provided that the display format is dB Mag. To obtain real filter parameters, the measured quantity must be a transmission S-parameter and a frequency sweep must be performed. For other quantities (e.g reflection parameters), the Bandfilter functions are still useful to analyze general trace properties. In some display formats (e.g. Phase) the bandfilter search is disabled.

Bandpass Search Ref to Max

Activates the search for a bandpass region on the active trace and activates bandfilter Tracking. A bandpass region is the tallest peak in the search range with a minimum excursion specified by means of the x dB Bandwidth parameter.

When Bandpass Search is activated the analyzer uses (or creates) the four markers M 1 to M 4 to locate the bandpass region.

The bandfilter search results are displayed in the bandfilter info field.

To search for a bandpass region in the vicinity of the active marker, use Bandpass Search Ref to Marker.

Bandpass Search Ref to Marker

Activates the search for a bandpass region on the active trace in the vicinity of the active marker and activates bandfilter Tracking. The bandpass region is the frequency range between the lower and the upper band edge; the band edges are defined by the magnitude of the trace at the marker position minus the x dB Bandwidth parameter:

In contrast to a Bandpass Search Ref to Max, the Bandpass Search Ref to Marker does not change the position of the active markers. The Loss is the response value at the marker position; the bandfilter search results are displayed in the bandfilter info field. The Lower Band Edge and the Upper Band Edge must fall into the search range, otherwise the bandfilter search results are invalid.

Bandpass Search Ref to Marker is particularly suitable for bandfilters with known center frequency, with the active marker placed onto this center frequency. You can also use a peak search to place the active marker on the maximum of the trace. Notice that, if the active marker is off the peak, both band edges are more than x dB below the peak response value.
To search for a bandstop region in the vicinity of the active marker, use Bandfilter Tracking – Bandstop Search Ref to Marker.

Bandstop Search Ref to Max

Activates the search for a bandstop region on the active trace and activates bandfilter Tracking. A bandstop region is the lowest peak (local minimum) in the search range, provided that its level is at least <x dB Bandwidth> below the maximum (passband value).

When Bandstop Search is activated the analyzer uses (or creates) the four markers M 1 to M 4 to locate the bandstop region.

The bandfilter search results are displayed in the bandfilter info field.

To search for a bandpass region in the vicinity of the active marker, use Bandpass Search Ref to Marker. Use Bandfilter Tracking to select other search modes.

Bandfilter Tracking

Causes the bandfilter search to be repeated after each sweep: When tracking mode is active the markers typically change their horizontal and their vertical positions as the measurement goes on.  

Tracking for the different bandfilter search modes is enabled or disabled in a selection box. Selecting a search mode for tracking also activates this mode.  

The search modes have the following effect:

• Bandpass Ref to Max / Bandstop Ref to Max: The bandpass / bandstop is the tallest / lowest peak in the search range.

• Bandpass / Bandstop Ref to Marker: The bandpass / bandstop is the peak in the vicinity of the active marker position. The response values for the lower and upper band edges are calculated as the response values at the active marker position plus / minus x dB, where x is equal to the <x dB Bandwidth>. To be valid the peak must be above / below the response value for the band edges, and the band edges must fall into the search range.

• Bandpass / Bandstop Absolute Level: The bandpass / bandstop is the tallest/lowest peak in the search range. To be valid, the peak must be above / below –x dB, where x is numerically equal to the <x dB Bandwidth> value. The Lower Band Edge and Upper Band Edge values are given by the frequencies where the trace is equal to –x dB.

Tracking is a toggle function: Selecting the function repeatedly switches the tracking mode on and off.  

x dB Bandwidth

Opens the numeric entry bar for the minimum excursion of the bandpass and bandstop peaks.

• A bandpass peak must fall off on both sides by the specified x dB Bandwidth to be considered a valid peak.

• A bandstop peak must be x dB Bandwidth below the maximum level in the search range (bandpass value) to be considered a valid peak.

Search Range...

Opens the Search Range Dialog to confine the bandfilter search to a subrange of the sweep.  

It is possible to define and store up to ten different search ranges for each trace. The bandfilter search is performed using the markers M 1, ..., M 4, irrespective of the selected search range.  

• Search Range Selects a search range for the bandfilter search. Full Span means that the search range is equal to the sweep range. Besides, it is possible to store up to 10 customized search ranges.  

• Start defines the beginning of the search range. Start must be smaller than the Stop value, otherwise the search will not be initiated.

• Stop defines the end of the search range. Stop must be larger than the Start value, otherwise the search will not be initiated.

• Range Limit Lines On displays two vertical lines indicating the Start and the Stop value of the current bandfilter search range in the diagram area. This function is enabled as soon as one of the search ranges 1 to 10 is selected.

Search range properties

Search Markers and Result Off

Hides the info field with the results of a bandpass or a bandstop search and disables bandfiter tracking. The info field is displayed again (and tracking is re-enabled) when a new bandfilter search is performed.  

The analyzer provides an alternative, short version of the bandfilter info field; see System – System Config... – General.

Bandfilter parameters