Chapter 5 NA (Network Analyzer) Mode

Learn more about NA Mode measurements in the FieldFox Supplemental Online Help: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm.

 

In this Chapter

“About S-parameters”

“Mixed-Mode S-Parameters”

“Parameter Conversion”

“Receiver Measurements”

“Multi-Trace Configurations”

"Quick Settings”

“Calibration Settings”

“Format”

“Frequency Range”

“Scale Settings”

“Magnitude Offset”

“Electrical Delay”

“Phase Offset”

“Averaging”

“IF Bandwidth”

“Smoothing”

“Single or Continuous Measure”

“Resolution (Number of Data Points)”

“Sweep Time”

“Triggering (NA)”

“Output Power”

“System Impedance (Z0)"

“Port Extensions”

“Velocity Factor”

“Increase Dynamic Range"

 

See Also

“Why and When to Calibrate”

“All about Markers”

“All about Limit Lines”

“All about Trace Math”

Learn how to make 75Ω (ohm) Measurements in the Supplemental Online Help: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm.

NA Mode Settings

Select NA Mode before making any setting in this chapter.

 

How to select NA Mode

  1. Press Mode.
  2. Then NA.

 About S-parameters

S-parameters (scattering parameters) are used to describe the way a device modifies a signal. The FieldFox can measure four S-parameters. The syntax for each parameter is described by the following:

 

S11 | S22 (out | in)

 

out = FieldFox receiver port

in = FieldFox source port

 

The FieldFox automatically switches the internal source and receivers to make both forward and reverse measurements. Therefore, the FieldFox can measure all four S-parameters with a single connection.

 

When the source comes from port 1, the measurement is said to be in the forward direction.

 

When the source comes from port 2, the measurement is said to be in the reverse direction.

 

S11 and S22 reflection measurements are used to measure the amount of reflections off the corresponding DUT port. Low reflections means there is a good impedance match between the source and DUT.

 

S21 and S12 transmission measurements are used to measure the loss or gain through a DUT over a specified frequency range. Both ends of the DUT must be connected to the FieldFox. The FieldFox signal source is transmitted out one of the test port connectors, through the DUT, and into the other test port connector.

How to measure S-parameters

  1. Press Preset then Mode Preset (Factory)

  2. Press Measure 1 then choose from the following:

OR select a multi-trace configuration. Learn more on “Multi-Trace Configurations”.

  1. Press Freq/Dist then either Start and Stop or Center and Span to enter a Frequency Range for the measurement.

  2. Press BW 2 then IFBW to select the IF Bandwidth for the measurement. Narrower bandwidths require more time to sweep, but lowers trace noise.

  3. Press Sweep 3 then Resolution to select the number of data points for the measurement. More data points require more time to sweep.

  4. Press Cal 5 to calibrate the measurement. Learn more in “How to Perform a Calibration”.

  5. All other settings can be made AFTER calibration without compromising measurement accuracy.

Mixed-Mode S-Parameters

In NA Mode ONLY, mixed-mode S-parameters (also known as Balanced measurements) are available with Option 212.

 

Because the FieldFox has only two test ports, only reflection measurements are available. Connect the balanced input or output of your DUT to the FieldFox ports 1 and 2

For highest accuracy, a Full 2-port calibration is required.

 

All FieldFox settings and features are supported (except Parameter Conversion) with mixed-mode S-parameters.

 


 

Learn more about Balanced Measurements with the FieldFox in the FieldFox Supplemental Online Help: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm

 

How to make mixed-mode S-parameter measurements

  1. Press Measure 1.

  2. Then More.

  3. Then choose from the following:

 

To make balanced reflection measurements at the DUT output, connect the DUT output to the FieldFox ports.

 

Parameter Conversion

In NA Mode ONLY, converts the active S-parameter trace to an equivalent impedance (Z), admittance (Y), or reciprocal 1/S-parameter.

 

How to select parameter conversions:

  1. Press Measure 1

  2. Then select an S-parameter

  3. Then More

  4. Then Conversion

  5. Then choose from the following:

 

Receiver Measurements

In NA Mode ONLY, you can make unratioed, uncorrected receiver measurements. These measurements are typically used as diagnostic tools for service personnel.

 


 
Receiver measurements are NOT corrected for absolute power. They are only useful for making relative measurements. The Y-Axis and markers are labeled in dB - NOT dBm. Specifically, R1 and R2, do NOT indicate the actual power levels out of the source ports.

 

How to make receiver measurements

Press Measure 1

Then More, then Advanced

Then choose from the following:

A Port-1 test port (*1) B Port-2 test port (*2)
R1 Port-1 reference receiver (*1)

R2 Port-2 reference receiver (*2)

(*) indicates the Auto-selected source port for the measurement

Source Port The FieldFox port to provide the source signal. Choose from the following:

  • Auto The FieldFox sets the source port based on the selected receiver.

  • Port 1 Select when measuring transmission at B receiver.

  • Port 2 Select when measuring reverse transmission at A receiver.

 

 Learn more about Raw Receiver Measurements at the FieldFox Supplemental Online Help: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm

 

Multi-Trace Configurations

In NA Mode you can display multiple traces on the FieldFox screen.

The graphic above shows a x3H configuration. Tr2 is the ACTIVE trace as indicated by the highlighted Tr2.

Trace Setting Notes


 
IMPORTANT! For CAT and NA modes, limit lines do not apply where  F1 = F2.

 

How to select a multi-trace configuration

  1. Press Trace 6 > Num of Traces

  2. Then choose from the following:

The default measurements depend on the options that are installed

x1

x1 1 trace standard configuration

x2
 

x2 2 traces overlayed on a single graticule

x2H
 

x2H 2 traces on separate graticules

x3H
 

x3H 3 traces on separate graticules

x3
 

x3 3 traces overlayed on a single graticule

x4
 

x4 4 traces overlayed on a single graticule

x4H x4H 4 traces on separate graticules

How to activate a trace in order to change a setting

How to maximize the viewing of the active trace

  1. Press System 7 > Full Screen

  2. Press any key to return to the standard display.

Quick Settings

Both CAT and NA Modes allow you to view and change most relevant settings from a single location. All of these settings are discussed in this chapter and, unless otherwise noted, ALL of these settings can also be made using the standard softkey menus.

How to view and change Quick Settings

Otherwise, use the numeric keypad,  arrows (), or rotary knob to change the value.

Calibration Settings

NA Mode has a page specifically for making settings that pertain to Port Extensions, including Velocity Factor and Media Type.

 

Learn more in “Port Extensions”.

 

Learn more about Media Type in “Waveguide Calibrations”.

 

See also, Chapter 6 “Calibration for NA, CAT, and VVM Modes” and to “Apply Nearest (NA Mode Only)”.

How to view and change Calibration Settings

Format

Select the display format in which to present measurement results. This setting can be changed at any time without affecting calibration accuracy.

 


 

Learn more about Display Formats in the FieldFox Supplemental Online Help: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm

 

The marker on screen readout can be changed to formats other than the display format. Learn more in “Marker Format”.

How to select a NA Format

  1. Press Measure 1 > Format [current setting].

  2. Then choose from the following:

 


 

Phase is unwrapped by comparing the phase from one data point to the next. If the phase difference between two data points is greater than 180 degrees, or if the phase of the first data point is greater than 180 degrees from DC, than the phase measurement is probably NOT accurate. To ensure that the phase measurement is accurate, increase the resolution setting. When making a narrow band measurement, reduce the start frequency for the unwrapped phase measurement to ensure the first data point is less than 180 degrees from DC.

Frequency Range

Set the range of frequencies over which you would like to make measurements.

 

When the frequency range is changed after a calibration is performed, the calibration becomes interpolated. Learn more in “Interpolation *”.

How to set Frequency Range

This can be done in two ways:

Scale Settings

Adjust the Y-axis scale to see the relevant portions of the data trace. The Y-axis is divided into 10 graticules.

 

This setting can be changed at any time without affecting calibration accuracy.

How to set Scale

  1. Press Scale / Amptd.

  2. Then choose from the following methods:

 

Scale annotation on the FieldFox screen

  • Reference Line = red arrow

  • Ref Level = –40 dB

  • Ref Position = 1

  • Scale = 2 dB per division

Magnitude Offset

Magnitude Offset allows you to offset the magnitude (not phase) data by a fixed and/ or sloped value in dB. If the display format is Linear Magnitude or Real (unitless), the conversion from dB is performed and the correct amount of offset is implemented.

 

The Magnitude offset setting affects only the active trace.

How to set Magnitude Offset

  1. Press Scale / Amptd
  2. Then More

Electrical Delay

Electrical delay is a mathematical function that simulates a variable length of lossless transmission line. Use the electrical delay feature to compensate for the linear phase shift through a device and view only the deviation from linear phase of the device.

 

You can set the electrical delay independently for each measurement trace. To apply an electrical delay to all measurement traces, use Port Extensions. Learn how in “Port Extensions”.

 

Learn how to set Phase formats in “Phase Offset”.

How to set Electrical Delay

  1. Press Scale / Amptd > More > Electrical Delay

  2. Enter a time value using the numeric keypad, the  arrows (), or the rotary knob.

  3. Press a multiplier key. Learn about multiplier abbreviations in “Multiplier Abbreviations”.

 

Electrical Delay can also be set using the Mkr->Delay feature. Learn how on “Marker Functions”.

Phase Offset

Phase offset mathematically adjusts the phase measurement by a specified amount, up to 360°. Use this feature in the following ways:

 

Improve the display of a phase measurement. This is similar to the way you would change the acquisition in an amplitude measurement. Change the phase response to center or the response on the screen.

 

Emulate a projected phase shift in your measurement. For example, if you know that you need to add a cable and that the length of that cable will add a certain phase shift to your measurement, you can use phase offset to add that amount and simulate the complete device measurement.

 

You can set the phase offset independently for each measurement trace.

How to set Phase Offset

  1. Press Scale / Amptd > MorePhase Offset

  2. Enter a value in degrees using the numeric keypad, the  arrows (), or the rotary knob. Press Enter.

Averaging

Averaging helps to reduce the effects of random noise on a measurement. You specify the number of measurements to be averaged. The more measurements averaged, the greater the amount of noise reduction. An average counter is shown in the left edge of the screen as Avg <n> where <n> is the number of measurements that are averaged.

 

Averaging can be set before or after calibration. When set before calibration, each calibration standard is measured <n> times and averaged. More time is needed to perform the calibration, but there will be less noise in the resulting error terms which means that subsequent measurements will also have less noise. In addition, noise is further reduced by continuing to average after calibration.

How to set Averaging

  1. Press BW 2.

  2. Then Average <n> where <n> is the number of measurements to average.

  3. Enter a value using the numeric keypad. Enter 1 for NO averaging.

  4. Press Enter.

  5. Then Average Mode Choose from the following:

  1. While averaging is in process, press Sweep 3 then Restart to restart the averaging at 1.

IF Bandwidth

The FieldFox converts the received signal from its source to a lower intermediate frequency (IF). The bandwidth of the IF bandpass filter is adjustable. Reducing the IF receiver bandwidth reduces the effect of random noise on a measurement. However, narrower IF bandwidths cause longer sweep times.

How to set IF BW

  1. Press BW 2 > IF BW.

  2. Then choose from the following:

More 30 Hz | 300 Hz | 3 kHz | 30 kHz

Smoothing

Trace smoothing averages a number of adjacent data points to smooth the peak-to-peak noise values on a displayed trace. The number of adjacent data points that are averaged is known as the smoothing aperture. Aperture is set by specifying a percentage of the X-axis span.

 

Trace smoothing does NOT significantly increase measurement time.

 

Smoothing is used in Group Delay measurements, although it can be used with any NA format EXCEPT Polar or Smith Chart. Learn more about NA Mode formats, including Group Delay, in “Format”.

 

When enabled, Smo appears on the FieldFox screen.

How to set Smoothing

  1. Press BW 2 > Smoothing ON OFF

  2. Then Sm. Aperture and enter a value between 0 and 25 (percent) using the numeric keypad.

  3. Press Enter.

Single or Continuous Measure

This setting determines whether the FieldFox sweeps continuously or only once each time the Single button is pressed. Use Single to conserve battery power or to allow you to save or analyze a specific measurement trace.

 

This setting can be changed at any time without affecting calibration accuracy.

How to set Single or Continuous

  1. Press Sweep 3.

  2. Then choose one of the following:

Resolution (Number of Data Points)

Data points are individual measurements that are made and plotted across the X-axis to form a trace. Select more data points to increase measurement resolution. However, more data points also takes more time to complete an entire measurement sweep.

 

When the Resolution is changed after a calibration is performed, the calibration becomes interpolated. Learn more in “Interpolation *”.

How to set Resolution

  1. Press Sweep 3 > Resolution.

  2. Then choose from the following:

101 | 201 | 401 | 601 | 801 | 1001 | 1601 | 4001 | 10001.

 

Using SCPI, Resolution can be set to ANY number of points between 3 and 10001. See the Programming Guide at Keysight FieldFox Library, Help and Manuals | Keysight.

Sweep Time

The fastest possible sweep time is always used as the default setting. Use the Min Swp Time setting to slow the sweep time when measuring long lengths of cable. Learn more, refer to the FieldFox Supplemental Online Help.

 

The actual sweep time is shown on the FieldFox screen. See the Screen Tour on “Screen Tour”. To increase the sweep time, enter a value that is higher than the actual sweep time. The increase will not be exactly the amount that you enter, as the actual sweep time is the composite of many factors.



 

Measurement speed specifications do NOT apply in Temperature Control Mode. Learn more in “Temperature Control Mode”.

How to set Sweep Time

  1. Press Sweep 3.

  2. Then Min Swp Time.

  3. Enter a value using the numeric keypad.

  4. Press a multiplier key. Learn about multiplier abbreviations in “Multiplier Abbreviations”.

Triggering (NA)

External triggering (NA and SA modes ONLY) allows you to initiate a sweep when an external DC voltage is sensed at the Ref In/Trig In connector on the FieldFox top panel. See External Triggering for SA Mode in “Triggering (SA)”.

Trigger Source

  1. Press Sweep 3 > Trigger > Trig Source

  2. Then choose from the following:

 

IMPORTANT!

If trigger signals come faster than the FieldFox can process them, some triggers may be ignored or lost.

 


 

To ensure triggers are recognized and processed in order, use the external trigger output function to indicate when the FieldFox is ready for another input trigger. Alternatively, slow the external triggers coming in from external equipment to a rate where FieldFox does not miss a trigger.

 

The External Trigger output signal is only selectable when Point Mode Trigger is enabled. Not supported in other trigger modes.

External Trigger output signal is sent as soon as FieldFox has processed the last trigger signal that was detected.

 

As each point is acquired, the data will show up on screen. If a trigger has not been detected, a yellow Wait indicator will show on the sweep status icon area.

 

Error Handling and Recovery

Trigger Slope

Determines which edge of an External trigger signal initiates a sweep.

 

  1. Press Sweep 3 > Trigger > Trig Slope

  2. Then choose from the following:

Output Power

Set the power level out of the FieldFox to High, Low, or manually set power level to a value between High and Low.

 

Generally, the high power setting is used when measuring passive, high-loss devices to place the signal farther from the noise floor. However, for devices that are sensitive to high power levels such as amplifiers, use the Low power setting.

 

For best measurement accuracy, use the Manual power setting at -15 dBm. After calibration, the power level can be decreased for amplifiers, or increased for higher dynamic range.

 

Power Level settings in this mode will NOT change Power Level settings in other modes. To help prevent damage to your DUT, use caution when changing modes with your DUT connected to the FieldFox test ports..

How to set Output Power

  1. Press Meas Setup 4.

  2. Then Output Power

      1. Then press Power Level

      2. Then enter a value using the numeric keypad, the  arrows (), or the rotary knob.

      3. Press Enter.

System Impedance (Z0)

To accurately view data presented in Smith Chart format, first set the System Impedance.

 

Learn how to select Smith Chart format in “Format”.

 

Learn how to make 75Ω measurements, by referring to the FieldFox Supplemental Online Help.

How to set System Impedance

  1. Press Meas Setup 4 > Settings .

  2. Then scroll to System Z0 and press Edit

  3. Then type either 50 or 75 and press Enter

Port Extensions

Port extensions allow you to electrically move the calibration reference plane on either port 1 or port 2 after you have performed a calibration.

Why use Port Extensions

Use port extensions if you are unable to perform a calibration directly at your device because the location is not accessible. Perform a calibration at a convenient place, then use port extensions to compensate for the time delay (phase shift) to the desired reference plane. On the FieldFox, port extensions does not compensate for the loss of the additional electrical length, nor any mismatch errors beyond the calibration reference plane.

 

Also, use port extensions if you have already performed a calibration, and then decide that you need to add a length of transmission line in the measurement configuration. Use port extensions to “tell” the FieldFox that you have added the length to a specific port.

 

 

Port extensions and Electrical Delay differ in the following ways:

 

Port Extensions and Electrical Delay can be set independently. When both are set, the delay adds together. Learn more about Electrical Delay in “Electrical Delay”.

How to apply Port Extensions

  1. Press Meas Setup 4 > Port Extensions > Port Extensions ON > Port1 Extension

  2. Then enter time value using the numeric keypad, the  arrows (), or the rotary knob. Press Enter or select a seconds (time) multiplier.

 

You can also set Port Extensions by pressing Meas Setup 4 then Calibration (settings).

While setting Port Extension, the physical length of the extension, at the current Velocity Factor setting, is visible to the right (red box in above image).

Velocity Factor

The electrical delay or port extension value is entered as delay, or electrical length, in units of time.

 

Entering the velocity factor causes the FieldFox to accurately display the equivalent physical length in meters (NOT available in feet) that corresponds to the entered electrical delay.

 

Velocity factor is the ratio of the velocity of wave propagation in a coaxial cable to the velocity of wave propagation in free space. This velocity depends on the relative permittivity of the cable dielectric (er).

 

Velocity factor = 1/sqrt(er)

 

VF = 0.66 corresponds to wave propagation through a polyethylene dielectric.

 

VF = 1.0 (default setting) corresponds to wave propagation through free space (a vacuum).

How to set Velocity Factor

  1. Press Meas Setup 4 > Port Extensions > Velocity Factor

  2. Then enter a value between 0.1 and 1 using the numeric keypad, then press Enter.

 

You can also set Velocity Factor by pressing Meas Setup 4 then Calibration Settings.

Big Marker Display States (A and B)

This feature, available ONLY in NA Mode, allows you to view up to three Big or Super Big marker readouts. This is done by using up to two different display states called A and B. Each display state is comprised of the settings listed below. When the Big Readout setting is toggled through A and B, these display states are recalled.

How to create Big Marker Display States

To have big readouts, markers MUST be created using the following procedure.

 

If you have already set up your display and do not want to lose it, then save the current state to a state file. Learn how in “State Files”. The following procedure will overwrite your display state.

 

  1. Press Mkr ->/ Tools

  2. Then Big Readout

  1. With A or B selected, then press Edit Big Marker (A or B)

  2. Then edit the following display state settings:

 


 

—To move a marker, press Marker, then Marker, then scroll to the marker number to be moved. The new marker position can NOT be saved with the A or B display state.

— Settings that are NOT listed above are NOT affected by the recalled display states.

— Changes to the above settings outside the Big Readout menu will be overwritten when Big Readout (A or B) is selected. For example, suppose the display format for the B state is Log. If you change the display format to Lin using the standard menu (Meas 1, Format), the setting will show on the display. But if you then use the Big Readout (A | B | OFF) setting, when B is recalled, the Lin setting will be overwritten with the original Log setting.

Increase Dynamic Range

Dynamic range is the difference between maximum input power to the FieldFox receiver (without compressing the receiver), and the minimum measurable power (noise floor). Measurement accuracy is increased when the DUT response is at least 10 dB above the noise floor. For a measurement to be valid, input signals must be within these boundaries.

The following settings will increase the dynamic range of your NA mode measurement.

 

The following procedure MAY increase the dynamic range of your NA mode measurement. The results you see will depend on the performance of your DUT.

 

With an S21 trace active:

  1. With RF OUT (port-2) open, press Trace 6 then Math and Memory then Data->Mem

  2. Re-connect the DUT.

  3. Press Data Math then Data-Mem