Power Calibration   

The Power Calibration submenu configures and starts a source or receiver power calibration.

In true differential mode only the source power calibration results are used, no receiver power calibration is possible.

• Source Power Cal... opens the configuration dialog for a source power calibration.

• Receiver Power Cal... opens the configuration dialog for a receiver power calibration.

Power correction data can be stored to a cal group and applied to several channels; see description of the Calibration Manager.
In remote control it is possible to read, modify and reload power calibration data. Refer to the description of the commands SOURce<Ch>:POWer<Pt>:CORRection:DATA and [SENSe<Ch>:]CORRection:POWer<port_no>:DATA.

Source Power Cal...

Opens the configuration dialog for a source power calibration.

Purpose of a source power calibration

Calibration procedure

The Source Power Cal dialog provides the following control elements:

• Calibrate – Source contains all analyzer ports or external generators and frequency converters which can be used as a source for the calibrated wave quantity. The list contains all analyzer ports Port 1 to Port n. Generators (Gen 1, Gen 2 ...) must be configured explicitly in the System Configuration – External Generators dialog before they appear in the list. Frequency converters (Conv 1, Conv 2 ...) must be configured in the System Configuration – Fequency Converters dialog. Only frequency converters with electronic attenuator (R&S ZVA-ZxxxE) can be power-calibrated.   

• Set as Stimulus Axis causes the channel line of the active channel to show the (target) power of the calibrated source port instead of the channel base power (e.g. Port 1 Pwr 0 dBm instead of Base Pwr 0 dBm). This is particularly useful if the source port powers differ from each other and from the channel base power. For power sweeps, the original stimulus axis range is replaced by the target power range of the calibrated port. After the calibration, the selected stimulus axis is maintained and shows the calibrated source power at the reference plane.  
  Use the context menu of the channel line or the Channel – Mode – Port Configuration – Stimulus dialog to select an arbitrary stimulus axis.  

• Take Cal Sweep initiates a calibration sweep for the selected source. The progress of the sweep is monitored in the calibration sweep diagram. After the necessary calibrations have been completed, a message in the trace list indicates the status of the power calibration.  

• Abort Sweep stops a running sweep. The data acquired in the aborted sweep is discarded.  

• The Settings panel displays the essential parameters of the source power calibration, to be defined in the Modify Source Power Cal Settings dialog.  

• Source Power Correction Off can be selected/deselected as soon as power calibration data has been acquired for the selected source. If the box is checked, the calibration data is kept in memory but not applied to the source. The Power Correction Off softkey disables the power correction for all receivers and sources.  

• Modify Settings... opens the Modify Source Power Cal Settings dialog.  

• Power Meter selects an external power meter that is used to measure the exact source power at the calibration point. Power meters (Pmtr1, Pmtr2, ...) must be configured in the System Configuration – External Power Meters dialog before they appear in the list. The buttons in the Power Meter panel provide settings for the selected power meter; see Power Meter Settings.

• Perform Verification Sweep after Cal enables or disables a verification sweep that the analyzer performs after the source power calibration. The sweep is also displayed in the calibration sweep diagram. Its purpose is to test the accuracy of the source power calibration after the final correction data has been acquired. The final power calibration results are applied starting with the first sweep after the verification sweep.  

Calibration Sweep Diagram

The calibration sweep diagram displays the power measured by the external power meter while a source power calibration is performed.

• A trace is displayed for each calibration sweep.

• If Perform Verification Sweep after Cal is enabled in the Source Power Cal dialog, an additional trace is displayed after the end of the calibration.

The diagram is automatically scaled so that the center corresponds to the selected Cal Power. For frequency sweeps, a horizontal trace close to the Cal Power indicates an accurate power calibration. For power sweeps, the ideal trace is a power ramp.

Below the sweep diagram, the status messages Calibration in Progress/Finished and Verification in Progress/Finished show the progress of the calibration procedure.

Modify Source Power Cal Settings

The Modify Source Power Cal Settings dialog displays the target power for the source power calibration and defines stop criteria.

The dialog provides the following control elements:

• Port n Power (where n is the calibrated source port selected in the Source Power Cal dialog) shows the target power of the calibration (Cal Power) and the Cal Power Offset. Both parameters can be adjusted in the Port <n> Power dialog, to be opened via Modify Cal Power... For frequency converters with electronic attenuators, the analyzer opens an alternative Converter Port <n> Power dialog.

• The parameters in the Power Cal Sweeps panel provide stop criteria for the calibration procedure: Maximum Number of Readings is a limit for the number of calibration sweeps. Tolerance denotes the maximum deviation of the measured power from the Cal Power. The calibration procedure is stopped if the Maximum Number of Readings is reached or if the measured power is within the Tolerance.
  The Convergence Factor can be used to modify the amount of power correction after each calibration sweep. The deviation from the desired power at the reference plane, as measured by the external power meter or a-wave receiver, is multiplied by the selected convergence factor. The variable attenuator setting is modified by the product of <power deviation> times <convergence factor>. With a convergence factor larger (smaller) than 1, the source power correction after each power calibration step is larger (smaller) than the measured deviation from the desired power.
  Convergence factors different from 1 are indicated only if the test setup includes non-linear components. External frequency converters may require convergence factors <1 at some source powers and frequencies. In general, it is recommendable to start the calibration with a convergence factor 1 and choose smaller values (0.8 ... 0.4) in case that the iteration fails. Inappropriate convergence factors can slow down the source power calibration or even prevent convergence.  

• Includes – Flatness Cal enables the iterative source power calibration with the stop criteria specified above. This corresponds to the normal source calibration procedure. If the Flatness Cal is disabled, the analyzer performs a single calibration sweep in order to calibrate the reference receiver (see below) but without overwriting the previous source power calibration data. The Port n Cal Power and Power Meter Readings are disabled. A frequency extension with an external converter without electronic attenuator is a typical example for a measurement where the Flatness Cal should be disabled.  

• Includes – Reference Receiver Cal enables a calibration of the reference receiver of the active source port together with the source power calibration. The reference receiver reading is set equal to the power reading of the external sensor. This can replace a subsequent a-wave receiver power calibration.  

• Use Reference Receiver after <n> Power Meter Readings enables the fast power calibration mode where the external power meter is used for the first <n> calibration sweeps only. The analyzer uses its reference receiver for the following, iterative calibration sweeps. The gain in speed increases with the number of readings minus <n>. The verification sweep (if it is enabled) is also performed using the reference receiver; it may be used to estimate the accuracy of the fast power calibration. See also Conditions for fast power calibration.
  Use Power Meter only disables fast power calibration; the power meter is used for all calibration sweeps.
  Reference Receiver only is available while the Reference Receiver Cal is disabled. This method also requires an existing source power calibration of the active channel and test setup for a particular target power <Cal Power 1>, including a reference receiver calibration. The calibration for the new target power <Cal Power> is based on the existing calibration data at <Cal Power 1>. During the sequence of calibration sweeps, the source power is varied such that the reference receiver indicates the new power <Cal Power>. Assuming a sufficiently linear behavior of the components in the test setup, <Cal Power> is also available at the reference plane.  

• If Switch off All Other Sources... is checked, the power at all sources except the calibrated source is switched off during the calibration. This is advisable especially if the power calibration is intended for intermodulation measurements where different signals are combined.

The analyzer performs either a Flatness Cal or a Reference Receiver Cal, or both. The two options must not be disabled simultaneously.

Conditions for fast power calibration

Power Meter Settings

The Power Meter settings in the Source Power Cal dialog (and similar dialogs) are used to select the external power meter that is used to measure the exact source power at the calibration point and to ensure maximum accuracy of the power measurement. Power meters (Pmtr1, Pmtr2, ...) must be configured in the System Configuration – External Power Meters dialog before they appear in the list.

The Power Meter panel provides the following buttons.

• Power Meter Config... opens the System Configuration – External Power Meters dialog.

• Auto Zero initiates a zeroing procedure of the power meter; see background information below.

• Power Meter Correction... opens a dialog to define the frequency range for the sensitivity correction of the power meter and an additional transmission coefficient in front of the power meter or the DUT.  

Zeroing

Power Meter Correction

Defines the frequency range for the sensitivity correction of the power meter and an additional transmission coefficient in front of the power meter or the DUT.  

The settings appear in two panels:

• Frequency Information for Sensitivity Correction from selects the origin of the frequency information.  
  For best accuracy, power meters must know the exact frequency of the measured signal. If the signal path between the source and the power meter contains a frequency-converting device, the frequency at the power meter differs from the frequency of the calibrated source. It is recommended to define the modified frequency range for the power meter in the Port Configuration dialog and select From Power Meter Entry in Port Configuration.

• The Additional Two-Port settings allow you to modify the power calibration data in order to account for an additional two-port device with known transmission coefficients. Configuration of the transmission coefficients and activation (Take Transmission Coefficient into Account) are independent from each other.  

• In Front of selects the position of the additional two-port in the test setup.
  If Power Sensor (during Calibration) is active, the analyzer increases the measured power sensor values by the two-port transmission coefficients to ensure that a subsequent measurement without the additional two-port is correctly calibrated.
  If Device under Test (during Measurement) is active, the analyzer decreases the measured power sensor values by the two-port transmission coefficients to move the reference plane of the power calibration towards the input of the DUT. For examples see background information below.

• The Transmission Coefficient panel defines the transmission characteristics of the additional two-port in the calibrated frequency range. The required information is a list of transmission coefficients at different frequency values. It is possible to edit the list manually, use one of the traces in the active setup (Use Trace), or import the list from a trace file (Import Data...). The imported trace file must be either in Touchstone (*.s<n>p) or *.csv format; see also Trace File Formats).
  The list must contain at least one frequency point before you can enable the additional two-port correction. In a power, time or CW mode sweep, one point at the fixed CW frequency is sufficient. In a frequency sweep it is possible to enter several values to account for a frequency-dependent transmission coefficient.
  You can also save the displayed list to a power meter correction list file with extension (*.pmcl) and re-load it in later sessions (Save List..., Load List...).  

Test setups with "additional two-port" devices

Receiver Power Cal...

Opens the configuration dialog for a receiver power calibration. The receiver power calibration data is acquired in a calibration sweep after appropriate selection of the calibrated wave quantity and the source.

Purpose of a receiver power calibration

Calibration procedure and calibration sweep

The Receiver Power Cal dialog provides the following control elements:

• Wave Quantity to Calibrate provides two pull-down lists to select one of the transmitted waves an or one of the received waves bn for the calibration. Each power calibration only applies to the selected wave quantity in the active measurement.

• Receiver Power Correction Off can be selected/deselected as soon as power calibration data has been acquired for the active wave quantity. If the box is checked, the calibration data is kept in memory but not applied to the wave quantity. The Power Correction Off softkey disables the power correction for all receivers and sources.

• Used Source contains all analyzer ports or external generators which can which can be used as a source for the calibrated wave quantity. The list contains all analyzer ports Port 1 to Port n. Generators (Gen 1, Gen 2, ...) must be configured explicitly in the System Configuration – External Generators dialog before they appear in the list. Behind the source, a message indicates the status of the power calibration.

• Take Cal Sweep initiates a calibration sweep for the selected wave quantity and source. The progress of the sweep is monitored in the Sweep progress bar.   

• Abort Sweep stops a running sweep. The data acquired in the aborted sweep is discarded.

The accuracy of the receiver power calibration depends on the accuracy of the source. Depending on the test setup and reference plane, it is recommendable to perform a source power calibration before the receiver power calibration.  

Power Calibration Labels

The status of a power calibration is indicated in the trace list and in the Used Source panel of the Receiver Power Cal dialog. The following messages can be displayed:

• PCal denotes an active power calibration with unchanged sweep points (no interpolation or extrapolation).

• PCai denotes an active, interpolated power calibration (the calibration data for at least one sweep point is interpolated).

• PCa? denotes an active power calibration with changed receiver settings (changed step attenuator settings and disabled ALC).  

• PCao denotes an active power calibration with a changed source power (changed base power or generator step attenuator settings).  

• PCax denotes an active, extrapolated power calibration. The current stimulus range exceeds the calibrated stimulus range. The power calibration data of the first calibrated sweep point is used for all smaller stimulus values; the power calibration data of the last calibrated sweep point is used for all larger stimulus values.  

• Pcal Off indicates that the power calibration was deliberately switched off.

A lower label in the list has priority over the higher labels (e.g. if the power calibration is interpolated and the source power is changed, then the label PCao is displayed).

The labels appear in the trace list, provided that the measurement result is an S-parameter, wave quantity, ratio, or a derived quantity (stability factor, PAE), and that the effects of an inaccurate source or receiver power have been consistently removed. The conditions for consistency depend on the measured quantity (see also Data Flow):

• For S-parameters and quantities derived from S-parameters (stability factors), only the source power calibration is relevant. S-parameters Sxy represent the ratio of a received wave bx to a driving wave ay, therefore the absolute receiver powers are not critical. A PCal label indicates a calibrated source power at all drive ports.

• For wave quantities and derived quantities (e.g. ratios, PAE), only the receiver power calibration is relevant. Due to the linearity of the receiver, a modification of the base power or generator step attenuator settings has no effect. A PCal label for a wave quantity indicates a calibrated receive port. A PCal label for a ratio indicates that both receive ports are calibrated. Notice that wave quantities and ratios are not system error corrected.

Interpolation and Extrapolation

The analyzer can interpolate and extrapolate power correction data so that a source or receiver power calibration can be reused after a change of the frequency sweep range:  

• At new sweep points within the calibrated sweep range, interpolation is applied to calculate the correction data. A label PCai in the trace list indicates an interpolated power calibration.

• At new sweep points outside the calibrated sweep range, the correction values are extrapolated: Sweep points below the lowest calibrated frequency are assigned the correction value of the lowest frequency. Sweep points above the highest calibrated frequency are assigned the correction value of the highest frequency. A label PCax in the trace list indicates an extrapolated power calibration.  

Power Correction On

Applies all available source and/or receiver power calibrations to the active channel. This function is disabled if no power correction data has been acquired for the active channel.  

Uncheck the ...Power Correction Off boxes in the Source Power Cal and Receiver Power Cal dialogs to enable an individual source or receiver calibration. Press Power Correction Off to disable the power calibration of all sources and receivers.

Power Correction Off

Disables all source and receiver power calibrations of the active channel so that all power correction data is ignored. This function is disabled if no power correction data has been acquired for the active channel.

Check the ...Power Correction Off boxes in the Source Power Cal and Receiver Power Cal dialogs to disable an individual source or receiver calibration. Press Power Correction On to re-enable the power calibration of all sources and receivers.