Power Calibration

How to perform Source Power Calibration

Note: Guided Power Cal can be performed during an S-parameter Guided Calibration. Learn more.

1. Setup your measurement (sweep type, frequency range, IFBW, and so forth). By default, a Source Power Cal is performed on the source port of the active measurement.

2. Connect coax cable, GPIB cable, and power sensors to the VNA as shown in graphic below.  

This image does NOT apply to USB power sensors, which are connected directly to a VNA USB port.

See Important First-time USB connection note.

3. Apply power to the power meter and allow 30 minutes warm-up time before beginning calibration.

4. Select Source Power Cal as follows:

Using Hardkey/SoftTab/Softkey

1. Press Cal > Main > Other Cals > Source Power Cal....

5. Complete the Source Power Cal dialog box (below), including Options, Loss Compensation and Power Sensor Settings, as needed.

Note: When using a Keysight N848X power sensor (sensors that do NOT have built-in calibration factors), enter the Cal Factors using the Power Sensor Settings dialog, because the VNA instructs the power meter to NOT use the Cal Factor tables internal to the power meter.

6. When complete, click Take a Cal Sweep in the Source Power Cal dialog box.

7. Follow the prompts to connect the sensors as required.

8. At this time you can change the Source Port setting and perform a Source Power Cal on a different port.

9. When calibration is finished, click OK. Correction is then applied and turned ON for the relevant ports on the active channel.

10. Remove sensor.

11. SrcPwrCal is displayed in the status bar when Source Power Correction is applied to the Active Measurement.

12. Perform a S-parameter calibration, which would use the corrected stimulus power levels for the relevant ports.

To turn Source Power Correction OFF:

• On the Calibration menu,then click Source Power Correction on/OFF.

• ONLY correction for the source port of the ACTIVE MEASUREMENT is turned OFF (regardless of port power coupling setting.)

Source Power Cal dialog box help

Note: Be sure that the frequency range of your power sensor covers the frequency range of your measurement. This does NOT occur automatically.

Cal with Frequency Extenders

If you are using a power sensor or power table to measure power over the frequency range of a frequency extender (mmWave module), the trace displays the measured power. This is done at the maximum RF input power setting for the frequency extender you are calibrating. This could be +10 dBm or +2 dBm depending on the power range you set during the source power calibration process. The default is +11 dBm to -30 dBm with a 0.5 db step size. This can be changed as needed.

Though the displayed frequency range is the range of the RF input, it is actually calibrating over the frequency range of the frequency extender being used. For example, the display shows 12.5 GHz to 18.333 GHz (RF input) but it is being calibrated from 75 GHz to 110 GHz.

Power

Cal Power  The calculated power (in dBm) at the calibration point. This value is the specified VNA source power plus the Power Offset value.

Power Offset  Allows you to specify a gain or loss (in dB) to account for components you connect between the source and the reference plane of your measurement. These components will remain during a measurement. For example, specify 10 dB to account for a 10 dB amplifier in the path to your DUT. Following the calibration, the VNA power readouts are adjusted to this value.

To account for components that will be removed when the calibration is complete, use the Loss Compensation table.

Channel and Port Selection

Channel  Specifies the channel on which to perform the calibration. This setting defaults to the active channel.

Source Port  Specifies the source port to be corrected. This setting defaults to the source port for the active measurement.

Note: External sources can be calibrated using this dialog. Learn more.

Accuracy

At each data point, power is measured using the specified Power Meter Settling Tolerance, then adjusted until the reading is within this Accuracy Tolerance or the Max Number of Readings has been met. The last power reading is plotted on the screen against the Tolerance limit lines.

Tolerance  Sets the maximum desired deviation from the specified Cal Power level in 0.005 dB increments from 0 to 5 dB.

Max Number of Readings  Sets the maximum number of readings to take at each data point for iterating the source power. Enter a value between 1 and 1000.

Calibration Status

Allows you to turn Source Power Cal ON | OFF and view Cal data for each port, regardless of the active measurement. This feature allows the Internal Second Source to be calibrated and turned ON | OFF, even when being used as an incidental source in a measurement, such as an LO.

Calibration ON  Check to turn Source Power Calibration ON for the specified source port.

The displayed text indicates when interpolation is applied for the calibration.

Buttons

Options  Invokes the Source Power Cal Options dialog. Label to the left of the button displays the current 'Options' setting.

Power Meter Config  Invokes the Power Meter Settings dialog box

Take Cal Sweep  Begins source power calibration measurement.

OK  Applies calibration. This button is disabled until the Take Cal Sweep has been pressed.

Cancel  If a sweep is in progress, cancels the sweep. Press again to close the dialog.

Attention please: the power meter is operating in 200 r/s mode.

During a measurement, some Keysight power meters may display this message on the screen: It means that the meter is operating in 200 readings/sec which is the fastest speed setting for this meter. This is normal operation.

Pass / Fail Limits

Limit lines are drawn on the Source Power Cal measurement graticule area. These lines are at the Cal Power +/- the current setting of Accuracy Tolerance.  A FAIL during the Source Power Cal sweep means that the VNA was unable to measure power to within the Accuracy Tolerance. Tight tolerances are more difficult to achieve at lower Cal Power levels. When a FAIL indication appears, increase the Max Number of Readings. If this does not cause a PASS condition, then decrease the Accuracy Tolerance value.

See Also

• Learn more about Source Power Cal

• Learn about External Testsets and Source Power Cal.

Source Power Calibration Options dialog box help

Provides options for measurement of the source power.

Note: At low power levels (less than -30 dBm) most power meters are not as accurate as a VNA receiver.

Calibration Reference  Choose power meter/VNA receiver to use to measure power.

• Use a power meter. Traditional source power calibration using only a power meter to measure the source power at each data point. Most accurate (at higher power levels) and slowest method.

Note: Because the following two settings use VNA receivers to make power measurements, they do NOT work correctly when a Frequency Offset value is being used.

• Use a power meter once, to calibrate receiver, then use receiver.  When checked, the first reading at each data point uses a power meter to calibrate the reference receiver. Subsequent readings, if necessary to meet your accuracy requirement, are measured using the reference receiver. This technique is much faster than using the power meter, and more accurate when measuring low power levels.

Note: Do NOT use this setting if there is a component before the power sensor that exhibits non-linear behavior, such as a power amplifier in compression.  Use a power meter and Calibrate the source at multiple power levels.

• Use this receiver.  Select a VNA Receiver or a PMAR (Power Meter as Receiver).

VNA receiver - For highest accuracy, first calibrate the receiver by performing a source power cal using a power meter, then a receiver cal. That receiver can then be used to quickly calibrate other VNA source ports, or used on another channel with different stimulus settings. This would be useful, for example, if the power level of the measurement was below the sensitivity of the power sensor. Calibrate the VNA receiver using a source power cal that is within the sensitivity of the sensor. Then, use the calibrated receiver to perform a second source power cal at the reduced power level.

1. • The VNA receiver is specified using either standard receiver notation or logical receiver notation.

   • It is best to use the reference receiver for the source port to be calibrated. For example, if calibrating source port 2, specify "R2" or "a2" which is the same port 2 reference receiver using logical receiver notation.

   • To ensure an accurate source power cal, the frequency range over which the receiver was calibrated must be the same or larger than the "receiver only" source power calibration.

   • All accuracy and settling tolerance and number of reading settings apply just as they do with a power meter reading.

PMAR Device -  The power meter/sensor must first be configured. Learn how to Configure a PMAR device.

• Use a power table and the analyzer reference receiver  Used to provide power leveling with mmWave test set and modules. Learn more.

Calibrate the source at multiple power levels   Used primarily with mmWave measurements.

This feature can also be used with standard VNA measurements when a component is used in the source path such as a booster amp which does NOT have linear gain or loss over frequency. If this is not true for your setup but want to improve your source power accuracy, consider using the Receiver Leveling feature.

When checked, source power is measured using the specified 'Cal Reference' device (power meter/sensor or VNA receiver) and iterated on a sweep-to-sweep basis to construct a 2-dimensional power table: Power IN, Power OUT, over all frequencies.

• Click Power Levels to launch the Source Cal Power Levels dialog box to set the power levels at which source power is to be measured.

• The source power cal is saved, but the power table is NOT accessible.

Calibrate the analyzer reference receiver   Check to calibrate the appropriate reference receiver to the power level that is measured at the calibration plane. Do this to make very accurate measurements using the calibrated reference receiver. This cal is done in addition to the standard source power cal using the any of the methods listed above. At the end of the source power cal measurement sweep, you can optionally save the reference receiver cal to a Cal Set to be recalled at a later time. The Cal is saved when the OK button is clicked to close the Source Power Cal dialog.

Source Cal Power Levels dialog box help

This dialog appears when you click Power Levels on the Source Power Cal Options dialog.

Specify the power levels at which the Source Power will be calibrated. These values should be set to a few dB more or less than the measurement power levels.

Max Power - The highest power level at which to calibrate. This value should be a few dB higher than the highest power level of your measurement.

Note: Setting the Max Power will override power settings entered manually in a Power Table (InputPower). Therefore, when using a power table, set the Max Power value to the same value shown in the Power Table (InputPower).

Min Power - The lowest power level at which to calibrate.  This value should be a few dB lower than the lowest power level of your measurement.

Power Step - Calibrate at every incremental power level, between the Max and Min Power settings.

Power Meter Settings dialog box help

This dialog appears when you click the Power Meter Config button on many dialog boxes.

Communication

• GPIB / Address  Select GPIB power meter. Then select the address for the power meter. Default is 13. The VNA will search VISA interfaces that are configured in the Keysight IO Libraries on the VNA. Note: Use this selection when using a 82357A USB/GPIB Interface,

• USB  VNA scans for USB power sensors or N191x device-side USB power meters. Select a power sensor from the list. Only ONE USB power sensor can be configured to cover the entire frequency range of the calibration.  To use multiple power sensors, perform a Guided Power Cal.

• LAN  Specify the Hostname or IP address of the Power Meter.

• Any  This can be used if you wish to spell out the exact VISA resource string/alias for your power meter’s I/O connection, for GPIB, USB, LAN or any other I/O protocol supported by VISA.  For example, you must use this to use a VDI PM5 power meter, and the VISA resource string/alias in that case must be ASRL3::INSTR.

Note: The VDI PM5 driver software must be installed to use VDI power sensors. Refer to Install VDI PM5 Driver.

Sensors  Invokes the power sensor settings dialog box.

Settling

These Settling settings do not apply when a VNA receiver is the power measurement device. Each power meter reading is "settled" when either:

• two consecutive meter readings are within this Tolerance value or

• when the Max Number of Readings has been met.

The readings that were taken are averaged together to become the "settled" reading. The settled reading is then compared to the Accuracy Tolerance requirements (tolerance and max readings) specified on the Source Power Cal dialog box.

Tolerance  When consecutive power meter readings are within this value of each other, then the reading is considered settled.

Max Number of Readings  Sets the maximum number of readings the power meter will take to achieve settling.

Sensor Loss Compensation

Use Loss Table  Select this checkbox to apply loss data to Source Power calibration correction (such as for an adapter on the power sensor).

Edit Table  Invokes the Power Loss Compensation dialog box.

Power Loss Compensation dialog box help

To Add a Row to the table, click on a row in the table and press the down arrow on either the VNA front panel or keyboard.

To Edit a value, double-click in the cell to be edited.

Compensates for losses that occur when using an adapter or coupler to connect the power sensor to the measurement port. These components will be removed when the calibration is complete. To account for components that will remain during the measurement, use the Power Offset setting.

The Frequency / Loss pairs define the amount of loss for the entire frequency range. For example, using the entries in the above dialog image:

• 0.5 dB is used to compensate power sensor measurements up to 1 GHz.

• Each data point between 1 GHz to 2 GHz is linearly interpolated between 0.5 dB and 1 dB.

• 1 dB is used above 2 GHz.

• A single frequency/loss segment is applied to the entire frequency range.

Frequency  Enter a frequency in Hz.

Loss  Enter a loss as a POSITIVE value in dB.  To compensate for gain, use NEGATIVE values.

Delete Table Segment  Deletes row indicated in the field.

Delete All  Deletes all data in the table.

The Power Loss Compensation table survives VNA Preset and Power OFF. To NOT use Loss compensation, clear the Use Loss table checkbox on the Power Meter Settings dialog.

Power Sensor Settings dialog box help

This dialog appears when you click the Sensors button on the Power Meter Settings dialog.

Note: Be sure that the frequency range of your power sensor covers the frequency range of your measurement. This does NOT occur automatically.

Sensor A (B)  Displays one of the following messages depending on type of sensor.

• Not connected  The VNA is not detecting a power sensor.

• Cal factors are contained within this sensor  This message is displayed when the Internal Reference Cal Factor and Cal Factor data are contained in the sensor and automatically accessed.

• Sensor Data  Allows the following entries for power sensor data:

• • Reference Cal Factor  Specifies the sensor's Reference Cal Factor.

  • Cal Factor Table  Specifies the frequency and corresponding Cal Factor for the sensor.

  • Delete Cal Factor  Deletes the indicated row in the table.

  • Delete All  Deletes all data in the table.

  • To Add a Row to the table, click on a row in the table and press the down arrow on either the VNA front panel or keyboard. A row is added to the bottom of the table. The table is automatically sorted by frequency when OK is pressed.

Load Cal Factors  Click to load cal factors from a *.csv file that you create from the cal factors that appear on the sensor. The first line of the file MUST have the reference Cal Factor (typically 100), followed by Freq / Cal Factor pairs as show in the following image:

Save Cal Factors  Click to save the cal factor table to a *csv file.

Use this sensor only  Check this box to use this sensor over the entire frequency span of the measurement, even if two sensors are connected to power meter.

Clear this box to allow entry of minimum and maximum frequencies for the sensor. Only ONE of the two sensors can have this box checked. You will be prompted to connect the appropriate sensor during the power calibration.

Minimum Frequency  Specifies the minimum frequency range for the sensor when using dual sensors.

Maximum Frequency  Specifies the maximum frequency range for the sensor when using dual sensors.

Zero and Calibrate the Power Sensor

For highest accuracy, Zero AND Calibrate the power sensor before measuring data. Follow prompts that may appear.

Zero - If the following settings are 'greyed', Internal or External zeroing is selected automatically based on the power meter/sensor model. Otherwise, select the appropriate type of zeroing to perform, then press Zero.

• Internal Zero - A switch inside the power sensor removes the sensor from the incident power.

• External Zero - Requires that you physically remove the sensor from incident power.

Calibrate - Available when the selected sensor has calibration capability. Calibration involves measuring an internal 1 mW source.

• Keysight P-Series sensors and U2020 X-Series USB sensors have an internal reference so you can calibrate them without connecting to a meter’s reference port.

• Keysight U2000 USB power sensors do not require calibrating.

• For other sensors, refer to the documentation to determine if it has calibration capability.

Press Calibrate, then follow the prompts.

How to perform a Receiver Power Calibration

1. Perform a Source Power Calibration.

2. Set the active measurement to unratioed. Learn How.

3. Connect a THRU line from the source port to the receiver port.

• When performing a receiver power cal on a reference receiver (source 1 and receiver R1), no connection is necessary as the receiver is internally connected to the source.

• When the source port and receiver port are the same (receiver A, source port 1), then connect an open or short to get maximum power to the receiver. This practice is not recommended. It is best to use different ports for the source and receiver.

4. Ensure correction for Source Power Calibration is ON as indicated by Src Pwr Cal or Src Pwr Cal* in the status bar.

5. Start the Calibration Wizard

Using Hardkey/SoftTab/Softkey

1. Set the active measurement to unratioed. Learn How.

2. Press Cal > Main > Other Cals > Receiver Power Cal....

Select Calibration Type for Unratioed Measurement dialog box help

Cal Type Selection  Select Receiver Power

Receiver Power Configuration

Cal Power  Specifies the power level to be displayed on the measurement when complete. (Source Port Power + Power Offset).

Source Port Power  Test port Power set for the measurement.  Learn how to change Test Port Power

Power Offset  Allows you to specify a gain or loss (in dB) to account for components you connect between the source and the reference plane of your measurement AFTER a source power cal has been performed. Following the calibration, the VNA power readouts are adjusted to the Cal Power value.

Next  Click to continue the Calibration Wizard.

Notes:

• When Receiver Power Cal is finished, 'Response' is displayed in the status bar and correction data is applied to subsequent sweeps. This is done because Receiver Power Cals are essentially Response Cals once they are stored and applied. See Saving a Receiver Power Cal below.

• To turn correction OFF, click Cal > Main > Correction > Channel Correction OFF.

Learn more about Receiver Power Cal (scroll up).