Calibration removes the systematic errors that are associated with measurements in NA, CAT, and VVM Modes. Key presses are identical in all of these Modes.
In this Chapter
| “Why and When to Calibrate” |
See Also
Learn How to Make 75 ohm Measurements by referring to the FieldFox Supplemental Online Help.
There are well-defined and understood systematic errors that are measured and calculated during the calibration process. These errors are caused by leakage signals inside the FieldFox, by the frequency response of the FieldFox receivers, and by reflections inside the FieldFox that interact with the DUT. After calibration, these errors are removed from subsequent measurements.
To maintain highest measurement accuracy, perform a new calibration when any of the following changes occur:
DUT (Device Under Test) The cable, antenna, transmission line, amplifier, or anything else that is connected to the FieldFox that is to be measured.
Calibration Standards - OPEN, SHORT, LOAD, and THRU
Calibration Reference Plane is the point (or points) at which the DUT and calibration standards are connected during a calibration. This can be at the FieldFox test port connectors, or at the end of jumper cables or adapters.
Every FieldFox contains a factory calibration that was performed at the port 1 and port 2 connectors, with -15 dBm input power, over the entire frequency range of the FieldFox using a number of data points that allows reasonable interpolation over the FieldFox frequency range
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This calibration, known as CalReady, allows you to immediately make measurements of a DUT that is connected directly at the test ports (PORT 1 and/or PORT 2). CalReady corrects measurements when the FieldFox is turned ON and when a measurement is created with no other correction in place.
When measuring a DUT using a jumper cable or adapter - NOT a direct connection to a test port connector – then a Mechanical Cal is recommended. CalReady can also be used to check the integrity of the jumper cable that is attached to the test ports.
CalRdy is shown when a measurement is corrected using CalReady.
You can change the properties of the CalReady calibration. Learn more in “CalReady”.
Learn how to see when your factory CalReady calibration was performed in “System Information”.
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Press Esc at any time to end the calibration process. When performing a calibration that contains a large number of points (5000 to 10,001 points) be aware that the calibration progress bar may not move for 2 or 3 minutes during the calibration process. |
In CAT, NA, or VVM Mode, press Cal 5.
The following appears:
Choose Calibration Method screen
Response Cal – Used to quickly calibrate ONE type of measurement using mechanical standards. Measurement accuracy is generally low. Learn more in “Simple Response Cals”.
Mechanical Cal/ECal – Using mechanical calibration standards from a cal kit, perform an accurate calibration at one or both test ports, adapters, or jumper cables. Full 2-port mechanical calibration is the most accurate calibration available with FieldFox. Learn more in “ECal”.
User Cal OFF ON – Turns ON and OFF the effects of the user calibration that you performed. The OFF state reverts to CalReady.
View Cal – Shows the properties of the current calibration. Learn more in “View Cal”.
More – Learn about Cal Ready Properties in “CalReady”.
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Source Unleveled errors - During calibration, the frequency range of the measurement MAY be extended to provide maximum flexibility. During the calibration, the output power may become unleveled at the added high frequencies. You can ignore the “Source Unleveled” error, or to avoid the error, select either High power or -15 dBm before calibrating. Learn more about setting Output Power in “Output Power”. |
Mechanical Calibration is performed using discrete standards from a Cal Kit. Several Cal Kit definitions are built into the FieldFox. To learn about Cal Kit definitions, refer to the Application Note, “Specifying Calibration Standards and Kits for Keysight Vector Network Analyzers,” available online at https://www.keysight.com/us/en/assets/7018-01375/application-notes/5989-4840.pdf.
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Visit www.keysight.com/find/fieldfoxsupport to see a complete list of supported Cal Kits. Also at this website, download Data-Link software that allows you to edit Cal Kit definitions or add a new Cal Kit. |
Mechanical Cals are extremely accurate when performed using the correct Cal Kits with standards that are clean and in good repair, and when using correct connection procedures.
This page summarizes the Mechanical Cal to be performed and allows you to make changes. For best results, review the screen and make changes in the following order:
If the DUT connector type, gender, or Cal Kit is NOT correct for the DUT ports to be calibrated, then:
) or rotary
knob to change the DUT connector type. ) or rotary
knob to select the Cal Kit that you have, and are going to
use, for the specified ports.
To select a different Cal Type:
Press Change Cal Type.
) or
rotary knob, select a Cal Type,
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If an error appears (“Failure to compute calibration steps…”), check to ensure that the frequency range of the Cal Kit covers the frequency range of the measurement. You can verify the frequency range of your Cal Kit at: www.keysight.com/find/fieldfoxsupport. Click Cal Kits. |
CAL ON U is shown on the screen for all displayed measurements that are corrected with the Mechanical Cal.
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ECals each have a recommended input power level. Depending on the measurement setup, the FieldFox may default to an input power level that exceeds your ECal’s recommended input power level. Refer to the reference guide for your ECal module to determine the correct input power levels. Exceeding an ECal’s recommended input power level results in a compression and an invalid data condition. Refer to www.keysight.com/find/ecal. |
ECal is a complete solid-state calibration solution. Every ECal module contains electronic standards that are automatically switched into position during a calibration. These electronic standards have been measured at the factory and the data stored within the memory of the ECal module. The FieldFox uses this stored data, along with the measured data, to calculate the error terms for a measurement calibration.
You can perform the following calibrations with ECal:
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Simple ECal ON: When choosing Full 2-port calibration, if you are able to connect your ECal simultaneously to both device ports, you should use Simple ECAL (i.e., this ensures that you are using the correct Thru calibration model).
Simple ECal OFF: Set simple ECal to OFF when you have a test setup where you cannot connect port 1 and port 2 simultaneously to the ECAL module (Then during the calibration when prompted: “Connect port 1 to port 2", use a coaxial cable or an appropriate thru adapter to connect port 1 to port 2).
’Unknown THRU’: When prompted: “Connect port 1 to port 2", then you can connect them, using a coaxial cable or an appropriate thru adapter. Do NOT use the internal ECal THRU, because the thru calibration will be incorrect.
‘Flush THRU’: When prompted: “Connect port 1 directly to port 2", then you must connect the ports directly together at the calibration reference plane with no adapter or other cabling.
Learn more in “Calibration Type”. |
All Keysight USB ECal modules are supported. ECal modules are available in a variety of connector types, covering many frequency ranges. For information about available ECal modules, see http://www.keysight.com/find/ecal.
Select an ECal module that has connectors of the same type and gender as the DUT. If such an ECal module is not available, a module with connectors different from the DUT can be used by selecting a User Characterization. This selection is located on the Mechanical Cal Setup page of the CalWizard. However, a User Characterization can NOT be PERFORMED using the FieldFox. It must be performed using a bench top Keysight VNA, such as the PNA or ENA. Learn more about "User Characterization" at the PNA Help website here: https://rfmw.em.keysight.com/wireless/helpfiles/N52xxB/S3_Cals/ECal_User_Characterization.htm.
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The frequency range of the measurement MUST be within the frequency range of the ECal module or an error will appear when “Calculating Steps” during the calibration. |
"Error correction disabled. Stimulus outside calibrated range."
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’Unknown THRU’: When prompted: “Connect port 1 to port 2", then connect port and port 2, using a coaxial cable or an appropriate thru adapter. Do NOT use the internal ECal THRU, because the ECal thru calibration model is incorrect for this calibration type.
‘Flush THRU’: When prompted: “Connect port 1 directly to port 2", then you must connect the ports directly together at the calibration reference plane with no adapter or other cabling.
Learn more in “Calibration Type”. |
Simple Response Cals are used to quickly calibrate the magnitude and phase of a measurement using any Open, Short, or Thru component. These may be calibration standards, but because a Cal Kit is not selected, they are not modeled. Measurement accuracy is generally low. Use a Simple Response Cal to make quick measurements when using a jumper cable to connect the DUT to the FieldFox. Otherwise, CalReady is usually more accurate.
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IMPORTANT! The Simple Response calibration assumes an ideal response for the standard. DUT measurements after a Simple Response calibration will have a measurement bias equivalent to the deviation of the response of the device used as the Simple Response standard from the ideal response. Note, that an Open Response is simply a normalization, a Short response is a normalization with 180 degree phase offset. When selecting a standard from the 85058B calibration kit for a Short Response we suggest using short # 1 because it has the smallest delay of the four shorts and would thus be most similar to an ideal short.
For better accuracy, perform a mechanical calibration by referring to “Mechanical Cal”. |
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You can perform a Simple Response Cal for either: S11, or S22, or S21 AND S12. |
When prompted, choose a standard based on the displayed measurements to be calibrated. For example, to calibrate S11, connect either an OPEN or SHORT to the port 1 reference plane.
When Simple Response Cals are performed, the source match and reflection tracking terms from CalReady are updated by the measured Short or Open that is used during the calibration.
1-port response cals are also available from the Mechanical Cal menu. Learn more in “Calibration Type”.
Normalize uses a THRU standard or cable between port 1 and port 2 to cal an S21 and S12 Transmission measurement (NA Mode) and a 2-port Insertion Loss measurement (CAT Mode). In VVM Mode, this is performed using Zero.
When a Normalization is performed, the forward and reverse transmission tracking terms from CalReady are updated to account for the THRU that is used during the normalization process.
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With a Normalization Cal, all subsequent insertion loss measurements are made relative to the insertion loss of the cable used as the THRU standard. For example, if you use a cable with 1 dB of loss, then after Normalization, the display will show 0 dB of loss with this cable in place. Therefore, for highest accuracy, when measuring the DUT also attach the cable that was used in the normalization cal. |
CAL ON U is shown on the screen when a User Cal (Ex: Response Cal) is correcting ONLY the appropriate measurement. For example, when an Open Response Cal on Port 2 is performed, CAL ON U is shown for an S22 measurement only.
From the Choose Calibration screen (see “How to Perform a Calibration”), press View Cal to see the following screen:
The top box shows the properties of the current calibration that you performed and the displayed S-parameters that it is correcting.
The bottom box shows the S-parameters that are displayed but NOT corrected by the current performed calibration, but rather the CalReady calibration. Learn more about CalReady in “CalReady”.
The FieldFox simplifies the calibration process by recommending the most accurate and efficient calibration type based on the displayed S-parameters.
However, there may be times when you may want a little more accuracy or a little faster sweep time. The following information can help you learn about the various calibration choices.
Non-insertable DUT – A device whose connectors could NOT mate together. They either do not have the same type of connector or they have the same gender. This also means that the test port cables could NOT mate together as in the above diagram. Insertable DUT – A device whose connectors could mate together. They have the same type of connector and opposite or no gender. This also means that the test port cables could mate together, as in the above diagram.
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| Non-insertable DUT – A device whose connectors could NOT mate together. They either do not have the same type of connector or they have the same gender. This also means that the test port cables could NOT mate together as in the above diagram. | Insertable DUT – A device whose connectors could mate together. They have the same type of connector and opposite or no gender. This also means that the test port cables could mate together, as in the above diagram. |
Defined THRU – A THRU standard for which there is a Cal Kit definition such as in the 8551xA Cal Kits.
Flush THRU (also known as Zero length THRU) – When the test port cables mate together when measuring an Insertable DUT. No actual THRU standard is required because the test port cables are directly connected. Flush THRU is also a Defined THRU with a definition of zero loss and zero length.
Unknown THRU - Any THRU connection between the test ports. For more information, refer to the FieldFox Supplemental Online Help.
Sweep Directions – Both FULL 2-Port Cals listed below result in correction that requires background measurements sweeps in both directions, regardless of the displayed measurements. The displayed traces are updated at a slower rate than Enhanced Response and 1-port calibrations, which require sweeps in one direction only.
DUT: No restrictions
S-parameters Corrected: S11 or S22
Standards: OPEN, SHORT, LOAD
Sweeps in ONE direction.
Most comprehensive calibration. Corrects all S-parameters
DUT: Non-Insertable or Insertable
Standards: OPEN, SHORT, LOAD on BOTH ports. Any THRU between ports.
Based on the SOLR/Unknown THRU calibration. For more information on the Unknown THRU process, refer to the FieldFox Supplemental Online Help).
Sweeps in BOTH directions.
Quicker to perform QSOLT than Full 2-port. Corrects all S-parameters.
DUT: Insertable only
Standards: OPEN, SHORT, LOAD on port 1. Flush THRU between ports.
Recommended cal type for Insertable DUTs. A Cal Kit is NOT required for port 2.
Sweeps in BOTH directions.
Faster measurements than Full 2-Port.
DUT: Non-Insertable or Insertable. S-parameters PARTIALLY Corrected: S21 and S11 (Forward) OR S12 and S22 (Reverse)
Standards: OPEN, SHORT, LOAD on ONE port. Defined or Flush THRU between ports.
Sweeps in ONE direction.
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Also select an Enhanced Response Optimization. Learn more in “Enhanced Response Optimization”. |
A complete 2-Port calibration with potentially better accuracy than Full 2-port. Corrects all S-parameters.
DUT: Non-Insertable or Insertable
Standards: Thru, Reflect, Line or variations of these. A TRL Cal Kit MUST be selected to see this Cal Type
Sweeps in BOTH directions.
Learn more about TRL Calibration, refer to the FieldFox Supplemental Online Help.
Calibrate the magnitude and phase of a measurement using ‘modeled’ mechanical standards. Measurement accuracy is better than Simple Response Cals (available on the main Cal page - see “Calibration Type”) but NOT as good as full 1-port cal. Corrects either S11 or S22. Can be used with Isolation (see following section). Learn more in “Simple Response Cals”.
DUT: Non-Insertable or Insertable
S-parameters Corrected: S11 or S22
Standards: OPEN or SHORT on ONE port
Sweeps in BOTH directions.
The optional isolation step of a calibration corrects for crosstalk which is the internal signal leakage between the test ports. The Isolation step measures Load standards that are connected to one or both FieldFox test ports.
Perform an isolation calibration when you are testing a device with high insertion loss, such as the stop band of a filter or a switch in the open position.
The isolation step can add noise to the error model when the measurement is very close to the noise floor of the analyzer. To improve measurement accuracy, set a narrow IF Bandwidth during the calibration.
The Isolation step is NOT allowed with ECal.
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If the first calibration step does NOT prompt you to connect Load standards, then the Cal Kit probably does not contain an Isolation standard. You can use DataLink software to edit the Cal Kit and add an isolation standard using a Load standard. See Data Link Help for more information: Keysight FieldFox Library, Help and Manuals | Keysight . |
In general, calibrating with Waveguide is very similar to calibrating with coax. However, most coax mechanical Cal Kits have standards that can be used over a very wide frequency range. Waveguide Cal Kits are used over a narrow frequency range. Therefore, it is VERY IMPORTANT to set the frequency range of the measurement WITHIN the frequency range of the waveguide Cal Kit. Otherwise, an error message will appear during the ‘Calculating Steps’ portion of the calibration.
Keysight sells two waveguide Cal Kit series: the premium 11644A series and the economy N9911X series. Both are available online at www.Keysight.com
Velocity factor is the speed at which an electromagnetic signal passes through the transmission medium relative to the speed of light. This value is important when distance is being calculated in DTF measurements (CAT mode) and Time Domain (NA mode).
When the media is waveguide, the velocity factor changes with frequency. FieldFox calculates this ‘effective’ velocity factor automatically. However, the settings are different for CAT mode and NA mode.
These settings are necessary ONLY when making DTF measurements.
These settings are necessary ONLY when your measurement requires electrical delay or port extensions, or if using Time Domain Transform.
When Enhanced Response Cal Type is selected, either for one calibration or for CalReady, this setting optimizes the calibration based on the type of DUT being measured. See also: CalReady Properties in “CalReady”.
This setting does NOT survive Preset.
Highest measurement accuracy is achieved when the frequency range or resolution settings remain the same during the measurement as when the FieldFox was calibrated. If these settings change after performing a calibration, the FieldFox will interpolate the calibration so that VERY accurate measurements continue to be made.
Interpolated Calibrations are only slightly less accurate than a calibration performed at the measurement settings. Learn more about the relative accuracy of FieldFox calibrations in “Cal ON? – Questionable Accuracy”.
When a calibration that you performed is being interpolated, an asterisk is added to the Cal annotation. For example: Cal ON U* is shown on the screen when the current Response or Mechanical cal is being interpolated. An * is never added to a CalRdy.
When the Output Power, Interference Rejection, or IF BW (NA Mode ONLY) setting is changed AFTER performing a calibration, a question mark is added to the Cal annotation.
The resulting measurement accuracy depends on how much the setting has changed. For highest accuracy, recalibrate using the new settings.
The FieldFox can have only ONE calibration present for all modes. Because NA, CAT, and VVM modes are very similar, a calibration that is performed in one mode can also be applied in the other modes with the same type of measurements (1-port or 2-port).
To apply a Cal that was performed in a different mode, press Cal 5 then select User Cal ON.
After performing any type of calibration, you can save the FieldFox settings along with the calibration into a STATE (*.sta) file. These settings and calibration can then be recalled as necessary. To learn how, see “Saving and Recalling Files”.
There are several factory calibrations (CalReady) on every FieldFox. These can be selected based on the type of DUT that you measure most often, and the compromise that you prefer to make between measurement speed versus measurement accuracy. Remember, CalReady was performed at the test ports. Therefore, a CalReady calibration is most accurate when the DUT is directly connected to the test ports. Learn more in “CalReady”.
This setting does NOT survive Preset or Power ON/OFF.
To find the best choice for your DUT:
When Apply Nearest is pressed, interpolation is turned off and the nearest calibration point is applied when the start stop frequencies are changed for the current sweep.
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IMPORTANT! – Apply Nearest needs to re-selected after each pair of start and stop frequency points is entered, because the Apply Nearest feature is disabled when a new start stop frequency pair is selected. – Apply Nearest calculates the number of points based on the start and stop frequency points entered. – Apply Nearest will display the following error when there is no valid calibration found: “Error: 225, The required user calibration is not present." |
To use Apply Nearest:
Press Cal 5 > More > Apply Nearest
After calibrating, it is important to verify that the calibration is good. When using a jumper cable, also verify that the cable is of high quality.
Connect a LOAD standard at the calibration reference plane (where calibration standards were connected). This may be at the end of the jumper cable or at FieldFox PORT 1 connector.
Verifying Phase Accuracy
With the LOAD standard still connected, move the jumper cable while observing the trace.
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