Noise Figure Application


The Noise Figure Application makes fast, easy, and accurate noise figure measurements. This function is available with Opt 028, S9x029A/B, or S9x027B.

The information presented in this topic pertains to Noise Figure measurements on BOTH Amplifiers and Converters unless stated otherwise.

See Also

Noise Figure Calibration

Noise Figure on Converters (NFX)

Programming commands

PNA-X Noise Figure Options (VNA Configuration Guide)

High-Accuracy Noise Figure Measurements Using the PNA-X

Noise Figure and TRL Cal

Example Setup for U7229x Amplifier Control

See other VNA Applications

Noise Figure Hardware and Software Options Explained

See Also: PNA-X Noise Figure Options (VNA Configuration Guide) - Internet connection required

Note: Option H29 does not include an internal noise tuner.

50 GHz and 67 GHz Noise Figure Receivers

Beginning in October 2012, Option 029 (low-noise receivers) is available in the N5244B (43 GHz), N5245B (50 GHz), and N5247B  (67 GHz) models.

Beginning in Fall 2023, Option E29 (low-noise receivers to 67GHz) is available in the N5247B models.

Noise Figure Application Features

Noise Figure Application Requirements

Noise Source

Note: Support for U1832X and U1833X Noise Sources is a Licensed Feature. Learn more about Licensed Features.

A Noise Source is NOT required to calibrate the Opt 029 Noise Receivers. Instead, the Noise Receivers can be calibrated using a calibrated VNA source. Learn more.

When using a Noise Source, the following requirements apply:

  • The 346C Noise Source (recommended) produces ENR values to 26.5 GHz.

  • The 346B Noise Source can be used up to 18 GHz.  

  • The 346A Noise Source can also be used up to 18 GHz, but requires more averaging for calibration.

  • The 346C K01 (50 GHz) Noise Source typically has about 6 dB of ENR at 50 GHz which may NOT yield an adequate calibration, depending on how many noise averages are used. An alternative approach calibrates the noise receivers using a power sensor-based method.  Select Use Power Meter for the noise figure calibration. Learn more.

  • The U1831C Noise Source can be used up to 26.5 GHz.

  • The U1832(A/B/C/D) and U1833(A/B/C/D) Noise Sources can be used.

    • A: 26.5GHz, B: 50GHz, C: 50GHz D: 55GHz

    • U1832X: Low ENR models

    • U1833X: High ENR models

  • An adapter may be necessary to connect the Noise Source to the VNA port 2 reference plane during calibration. Cal Kit (or second ECal module) with same connector type and gender as DUT connectors.

Limitations with the Noise Figure Application

The following features are NOT supported in a noise figure channel:

Noise Concepts

The following conceptual information is a short summary taken from the Keysight Noise Figure App Note 57-1.

All electronic circuits have some degree of random noise. The most common form is thermal noise, which increases as the temperature of the circuit increases.

The signal-to-noise (S/N) ratio of components in a communications system is a very important parameter. To improve the S/N ratio, it is usually easier and more cost-effective to reduce noise than to increase signal power.  In order to reduce noise, an accurate method to measure noise is required.

Noise Figure

Noise Figure is the degradation in the signal-to-noise ratio as a signal passes through a device. For example, in the following images:

(a) At the INPUT of the DUT:

The noise floor is  -100 dBm, the signal is at -60 dBm,  40 dB above the noise floor.

(b) At the OUTPUT of the same DUT:

The gain has boosted the signal AND the noise floor by 20 dB.

The DUT then added 10 dB of its own noise.

The output signal is now only 30 dB above the noise floor.

Since the degradation in signal-to-noise ratio is 10 dB, the DUT has a 10 dB noise figure.

For consistency, noise measurements are calculated as if using a 1 Hz bandwidth, although measurements are almost always made at higher bandwidths.

The following formula shows the lowest possible noise power in dBm at 290° K (room temperature). The only way to measure noise lower than this is to make the measurement at a lower temperature.

How the Noise Figure Application Works

The goal of the noise figure application is to accurately measure the noise that is generated by the DUT.  This may be done using special low-noise receivers or using the standard VNA receivers depending on whether the VNA has Options 029 or 02. Learn more.  

The standard receivers are always calibrated using a power meter and a measurement of the receivers effective noise bandwidth.  The low-noise receivers can be calibrated using either a characterized noise source or using the same process as a standard VNA source. Learn more about the noise calibration process.

Some noise measurement error is caused by a poor source match presented to the DUT input. Therefore, during every measurement, the noise figure application uses an ECal module to present at least four different impedances at the input of the DUT.  This "Noise Tuner" is connected to the VNA port 1 or port 2 front-panel loops that are in the VNA internal source path (see block diagram below). From the measurements at various impedance states, the VNA calculates the noise out of the DUT as though the VNA were exactly 50 ohms. No assumptions are made regarding the input impedance of the DUT.

Here is how a vector noise figure measurement is made using Option 029. The sweep numbers are annotated on the VNA display as they occur.

  1. With the noise tuner in the THRU state, S-parameter measurements are made to accurately characterize the gain of the DUT.  This requires sweeps in both forward and reverse directions. (sweep #1 and #2).

  2. The noise measurements are performed next.  VNA source power is turned OFF and the noise tuner is switched to the first impedance state.

  3. At each frequency, the noise receiver samples a large number of readings in order to attain one valid measurement. If Noise Averaging is selected, the specified number of measurements are made and averaged together to obtain one noise measurement. This continues for all frequencies (sweep #3).

  4. The next noise tuner impedance state is switched IN and the noise measurements in step 3 are repeated. This occurs until measurements are made at all impedance states. At least four impedance states must be used. (sweeps #4, #5, #6+)

  5. Calibration error terms are applied and calculations made to simulate the measurement with a perfect 50 ohm input impedance. The sweep result is plotted on the VNA display.

  6. The VNA begins sweeping again with step 1.

Scalar Noise Figure Measurements

As described above, the noise tuner is switched to at least four different impedance states before a sweep is plotted. These sweeps are NOT made in a scalar noise figure measurement, resulting in much faster measurements. Of course, a scalar noise figure measurement is NOT as accurate as a vector noise figure measurement because scalar noise figure measurements assumes that all impedances are 50 ohms. Measurement accuracy can be improved by adding an attenuator as close to the DUT input as possible. This improves the effective system source match. The effect of the attenuator loss is removed during the calibration process.

With scalar noise figure, it is not necessary to connect the noise tuner. If a noise tuner remains connected, it is switched to the THRU state for scalar noise figure measurements. This results is a small amount of loss which slightly degrades measurement accuracy. To increase measurement accuracy, manually switch the noise tuner switch to the INTERNAL position. Learn how.

Select Scalar Noise at the first page of a Noise Figure calibration.

PNA-X Option H29 - Block Diagram with Noise Figure Components

50 GHz Noise Figure Components are shaded yellow

  • At test port 1 front-panel loops, a noise tuner bypass switch connects the noise tuner (ECal module) in series with Source1 providing several different input impedances.

  • At test port 2, a switch and coupler to route RF from the DUT output to two noise receivers. The appropriate receiver is automatically switched as required for the frequency being measured.

PNA-X Option 029 - Block Diagram with Noise Figure Components

26.5 GHz Noise Figure Components are shaded yellow

  • At test port 1 front-panel loops, a noise tuner bypass switch connects the noise tuner (ECal module) in series with Source1 providing several different input impedances. Learn more about managing the Noise Tuner switch.

  • At test port 2, a switch and coupler to route RF from the DUT output to two noise receivers. The appropriate receiver is automatically switched as required for the frequency being measured.

50 GHz Noise Figure Components are shaded yellow

See Also: 50 GHz Noise Figure - Built-in Tuner switch below.

Noise Figure Option S9x027B

Option S9x027B allows a VNA with a low-noise receiver to use specialized mechanical tuners on the input port. These tuners are designed to have a large number of impedance states that are broadly distributed on a Smith chart. There are two situations in which a mechanical tuner is advantageous:

  1. When measuring noise figure at low frequencies. While Ecals are good general-purpose tuners, they tend to have a suboptimal spread of impedance states at low frequencies.

  2. When measuring NF of a device that is poorly matched. Ecal modules are well suited to measure the noise figure of devices with a match near 50 ohms, but do not perform as well with devices that have match far from 50 ohms.

Mechanical tuners also improve the quality of the Noise Parameter measurements NFmin, GammaOpt, and Rho.

The following tuners are supported by Option S9x027B. All are manufactured by Maury Microwave or Focus Microwaves. Use of a Focus Microwaves tuner is a Licensed Feature. Learn more about Licensed Features.

Maury Microwave Tuners

Model

Description

MT981AL14

LXI TUNER, 0.227-4.0 GHZ, 7MM

MT981BL10

LXI TUNER, 0.4-4.0 GHZ, 7MM

MT981BL15

LXI TUNER, 0.4-2.5 GHZ, 7MM

MT981BL18

LXI TUNER, 0.4-8.0 GHZ, 7MM

MT981EL10

LXI TUNER, 0.8-8.0 GHZ, 7MM

MT981HL13

LXI HGT, 0.8-8.0 GHz, 7MM

MT981HL14

LXI HGT, 1.8-8.0 GHz, 7MM

MT981HL15

LXI HGT, 0.65-6.0 GHz, 7MM

MT981VL10

LXI TUNER, 0.65-6.0 GHZ, 7MM

MT981WL40

LXI TUNER, 0.6-6.0 GHZ, 7MM

MT982AL02

LXI TUNER, 1.8-18.0 GHZ, 7MM

MT982BL01

LXI TUNER, 0.8-18.0GHZ, 7MM

MT982EL30

LXI TUNER, 0.8-8.0 GHZ, 7MM

MT982GL01

LXI TUNER, 0.65-18 GHZ, 7MM

MT982GL30

LXI TUNER, 0.65-8.0 GHZ, 7MM

MT983BL01

LXI TUNER, 2.0-26.5 GHZ, 3.5MM

MT984AL01

LXI TUNER , 8-50 GHz, 2.4MM

XT981AL14

LXI TUNER, 0.227-4.0 GHZ, 7MM

XT981BL10

LXI TUNER, 0.4-4.0 GHZ, 7MM

XT981BL18

LXI TUNER, 0.4-8.0 GHZ, 7MM

XT981HL13

LXI HGT, 0.8-8.0 GHz, 7MM

XT981HL14

LXI HGT, 1.8-8.0 GHz, 7MM

XT981HL15

LXI HGT, 0.65-6.0 GHz, 7MM

XT981VL10

LXI TUNER, 0.6-6.5 GHZ, 7MM

XT982AL02

LXI TUNER, 1.8-18.0 GHZ, 7MM

XT982GL01

LXI TUNER, 0.6-18 GHZ, 7MM

XT982GL30

LXI TUNER, 0.6-8.0 GHZ, 7MM

XT983BL01

LXI TUNER, 2.0-26.5 GHZ, 3.5MM

Focus Microwaves Tuners

Model

Description

C101

0.1-1 GHz, 7/16, APC-7, N

C302

0.2-3 GHz, 7/16, APC-7, N

C304

0.4-3 GHz, 7/16, APC-7, N

C804

0.4-8 GHz, 7/16, APC-7, N

C1804

0.4-18 GHz, APC-7, N

C606

0.6-6 GHz, 7/16, APC-7, N

C606S

0.6-6 GHz, 7/16, APC-7, N (Shielded)

C806

0.6-8 GHz, 3.5mm

C806S

0.6-8 GHz, 3.5mm (Shielded)

C806R

0.6-8 GHz, 7/16, APC-7, N

C806RS

0.6-8 GHz, 7/16, APC-7, N (Shielded)

C1806

0.6-18 GHz, APC-7, N

C1806S

0.6-18 GHz, APC-7, N (Shielded)

C1807

0.7-18 GHz, APC-7, N

C308

0.8-3 GHz, 7/16, APC-7, N

C807

0.8-7 GHz, 7/16, APC-7, N

C808

0.8-8 GHz, 7/16, APC-7, N

C1808

0.8-18 GHz, APC-7, N

C1818

1.8-18 GHz, APC-7, N

C1260

6-12 GHz,3.5mm

To use a tuner supported by Option S9x027B, follow this procedure:

  1. If using a Maury tuner:

    1. Download driver files for the tuner at the Web address shown below:
      https://www.maurymw.com/Support/downloads.php

    2. Run the driver installation program.

    3. Power up the tuner and connect it to the VNA via a USB cable.

  2. If using a Focus Microwaves tuner:

    1. Download driver files for the tuner at the Web address shown below:
      https://focus2501.sharefile.com/share/view/s653a869bcc8f44c8abe1052ebea6a718

    2. Run the driver installation program.

    3. Power up the tuner and connect it to the VNA via a LAN to USB cable (USB-side connected to the VNA). Please see Focus Tuner documentation for set up and support. Once the tuner is defined in the FDCS Load Pull Explorer software, the VNA FW will automatically detect it.

  3. The tuner should now be available for use. To verify this, start the VNA application and create a Noise Figure or Noise Figure Converters channel. Start the Calibration Wizard, and expand the selections for the Noise Tuner combo box. The attached tuner should appear in the displayed list. In the example below, a Maury Microwave MT982BL01 tuner was used.

  4. Once the tuner has been recognized, it should be inserted into the signal path between port 1 and the DUT input. To increase measurement accuracy, it is best to have the tuner as close to the port 2 calibration plane as possible. This ensures that the spread of tuner impedances is as large as possible.

Calibrating with a Mechanical Tuner

No special steps are required to use a mechanical tuner for noise figure calibration. After verifying that the tuner is recognized by the PNA, simply perform a noise figure calibration in the usual way. The PNA firmware will measure all impedance states of the tuner during calibration. When the calibration is complete, the number of states used in vector NF correction can be set in the Noise Figure Setup dialog. In the example below, 15 states have been chosen, but up to 21 states are available.

Caveats when using a Mechanical Tuner

Mechanical tuners offer distinct advantages, but there are caveats to keep in mind:

The Noise Tuner Switch while making S-parameter measurements

Because of the built-in Noise Tuner in the Option 029 50 GHz noise figure models, the Noise Tuner switch is managed differently than the 26.5 GHz noise figure models.

26.5 GHz Models

The default setting for the port 1 noise tuner switch is "External" as shown in the above diagram. This setting provides incident power through the front panel loops and the Noise Tuner when connected. When connected, the Noise Tuner may NOT be in the THRU state, which is necessary for accurate S-parameter measurements.

The switch is changed in any of the following ways:

Important Note: On the 26.5 GHz Opt 029 models, once you set this switch to "Internal", you must set it back to "External" to make noise figure measurements. The switch is NOT automatically set to "Internal" during a noise figure measurement.

50 GHz Models

The switch for the built-in tuner (Opt. 029) is set to "Internal" (Tuner) ONLY when making vector noise figure measurements. Otherwise, it is set to "Bypass" (the tuner). Therefore, you should NOT need to make switch settings. However, the switch can be changed in any of the following ways:

Using the Noise Figure Application

Use the following general procedure to make noise figure measurements:

  1. Connect Tuner and Noise Source.

  2. Create a Noise Figure Measurement.

  3. Make Noise Figure Settings.

  4. For Opt 029 and H29, copy your Noise Source ENR file to the VNA "C:\Program Files(x86)\Keysight\Network Analyzer\Noise folder"

  5. Perform Calibration  

  6. Connect the DUT. Learn more about DUT input and output ports.

  7. Measure Noise Figure.

  8. Optional  Click File, then Save to save noise figure data. Learn more.

Connect Noise Tuner and Noise Source

See the VNA Configuration Guide for recommended ECal modules, cables, and adapters.

Create a Noise Figure Measurement

  1. On the VNA front panel, press Meas > S-Param > Meas Class....

  2. Select Noise Figure Cold Source, then either:

  1. A noise figure measurement is displayed. The following shows how to select or change displayed parameters.

Noise Parameters

Several noise parameters, as well as standard parameters, can be measured in the same Noise channel.

How to add Noise Parameters

  1. Create a Noise Figure channel.

  2. Then do the following:

Using Hardkey/SoftTab/Softkey

Using a mouse

  1. Press Trace > Trace N >  Trace N.

  2. Press Trace > Trace Setup >  Measure....

  1. Click Instrument

  2. Select Trace

  3. Select Add Trace

  4. Click Instrument

  5. Select Trace

  6. Select Measure...

How to CHANGE Noise Parameters

  1. Create a Noise Figure channel.

  2. Select the parameter to change.

  3. Then do the following:

  1. Select a trace by pressing Trace > Trace N >  Trace N.

  2. Press Trace > Trace Setup >  Measure....

  3. Select a parameter.

  1. Right-click on a trace.

  2. Select a parameter

Noise Measurements that are offered

The following three categories of noise measurements can be made with the VNA:

  1. Noise Figure is the amount of noise that the DUT is adding in a 50 ohm test setup. This is explained in detail in Noise Concepts.

  2. Noise Power Parameters show the amount of noise coming out of the DUT in a 50 ohm test setup. With gain measurements of the DUT, these noise power parameters are used to calculate noise figure.

  3. Noise Parameters are models of the noise that is generated in a DUT, similar to how S-parameters model how RF flows through a DUT.


ENR (in dB) = 10 log10((Thot - Tcold) / T0), where T0 = 290K.

Learn more about the ENR table and Noise Source. Learn more about Noise Source ENR measurements.

290°° K =  -174 dBm/Hz.

Te is the unknown variable

Available Gain Ga is a function of S11, S22, and Γs

Noise Power Parameters

The Noise Power parameters below are offered in the following two formats:


dBm = 10 log10(k * T * B * 1000)

where:

k = Boltzmann's constant

T = the measured noise temperature

B = bandwidth

1000 = conversion from milliwatts

dB = 10 log10(T/290)

When correction is OFF, the trace exhibits what is more accurately described as delivered power.  Delivered power is the power actually seen by the ADC.  Any mismatch between the receiver and the DUT is ignored.  The noise power contributed by the receiver is removed.

This measurement is generally expressed in dBm, normalized to a 1 Hz bandwidth. For convenience, marker and trace readout shows dBm.

You could display the power in a different bandwidth using Equation Editor.

dBm/Hz = 10 log10( k * (System Temperature - Receiver Temperature) * B * 1000)

where:

B = bandwidth

1000 = conversion from milliwatts

dB = 10 log10 ((System Temperature - Receiver Temperature) / 290)

Noise Model, Noise Parameters, and the Noise Correlation Matrix

Noise Parameters are models of the noise that is generated in a DUT, similar to how S-parameters model how RF flows through a DUT.  

Noise Model

The noise wave model of any linear 2-port network may be represented by the following image:

This shows a noiseless 2-port network with noise waves (an1 and bn1) added to the input terminals. The a1 a2 and b1 b2  are standard S-parameter waves.

The noise correlation matrix relates to the noise waves as follows:

Where:

Noise Parameters

Note: Rn, as a measurement parameter, is not normalized. When the value of Rn is written to an S2P file, it is normalized (Rn / Zo). When an S2P file is recalled, the normalized Rn is multiplied by the system impedance to obtain Rn.

Standard Parameters that are offered (Amplifiers-only)

Save Noise Data

To save noise data, click File, then Save Data As   Then select from the following Save As Types:

How to start the Noise Figure Setup dialog

Using Hardkey/SoftTab/Softkey

Using a mouse

  1. Freq > Main >  NF Setup....

  1. Click Stimulus

  2. Select NF Setup...

Noise Figure Setup dialog box help

Note: In this topic, the term Jitter is used to describe the trace-to-trace fluctuations in a measurement. In other topics, this is called 'trace noise'.

Bandwidth/Average

The following settings work together to achieve the optimum balance of measurement accuracy versus speed:  

Noise Bandwidth   Increase the bandwidth to reduce the amount of trace noise on the noise power or noise figure measurement (jitter). However, a wider setting reduces the frequency resolution of the measurement.  The noise bandwidth setting should always be smaller than the bandwidth of the DUT. The noise bandwidth setting is used only while measuring noise powers, and is independent from the IF bandwidth setting used to measure S-parameters. Noise figure is calculated from noise power and S-parameter measurements.

The calibration and measurement should be performed using the SAME noise bandwidth. When the noise bandwidth is changed after calibration, noise figure measurements can change by 0.5 dB or more, depending on the DUT frequency range, gain, and noise figure.

Note: The Noise Bandwidth may be adjusted automatically at low frequencies according to the following table. At each data point frequency, if the specified Noise BW is higher than that shown in the table, the Noise BW is set to the max value in the table.

RF Bands

10 to 25 MHz

25 to 60 MHz

60 to 150 MHz

Above150 MHz

Noise Bandwidths Allowed

.8 MHz

2 MHz

.8 MHz

2 MHz

4 MHz

.8 MHz

2 MHz

4 MHz

8 MHz

.8 MHz

2 MHz

4 MHz

8 MHz

24 MHz

36 MHz

Note: Use Power Meter calibration method is NOT available when the Noise Bandwidth is 8 MHz or 24 MHz.

Average Number  Increase the number of averages to reduce jitter. This also reduces measurement speed. For maximum accuracy, use the following recommendations for the noise calibration.

When using the noise receivers, 10 noise averages is recommended. When using the standard receivers, at least 100 averages are recommended.

During a measurement, the gain of the DUT helps overcome the noise of the VNA receivers, so the number of noise averages can be reduced to improve measurement speed with minimal or no degradation to measurement accuracy.

Use Narrowband Compensation

The mathematics of noise figure assumes that the gain of the DUT is constant over the bandwidth of the noise receiver. The following image illustrates a case in which the gain (S21) of the DUT falls off sharply outside the passband region. When the VNA measures noise figure at the frequency indicated by the solid vertical line using a 4 MHz noise bandwidth, standard noise figure calculations assume the gain to equal its midpoint value (dashed horizontal line) over the entire 4 MHz bandwidth. This assumption yields a composite gain-bandwidth value that is lower than the actual value, which in turn results in a noise figure value that is too high. This is the reason for the bump in the displayed NF value at this frequency and surrounding frequencies.

In the following image, Narrowband Compensation combines DUT measurements with characteristics of the noise receiver, which accommodates changes in DUT gain over the receiver bandwidth. The result is a better gain-bandwidth value of the system. Notice how the peaks and valleys of the NF measurement disappear when narrowband compensation is applied.

Notes on using Narrowband Compensation:

  • Can be used with either option 028 (Noise figure measurements using standard receivers) or 029 (Fully Corrected Noise Figure).

    • With option 029 (NF receiver) Narrowband Compensation is available only for the 800 kHz, 2 MHz, and 4 MHz noise bandwidths.

    • With option 028 (Standard VNA receivers) you MUST re-configure the front panel loops. Learn how.

  • Can be used with both Scalar and Vector NF calibrations, on either NF or NFX channels.

  • The ON / Off state has no effect on calibration. In other words, it does not matter if Narrowband Compensation is On or Off while a noise calibration is being performed.

  • Is applied only when corrected DUT measurements are made. If correction is turned off, it has no effect.

  • Can be ON or Off while the NF channel is in Hold mode, and it will modify the NF trace appropriately. There is no need to re-sweep.

Noise Receiver

NA (Network Analyzer) Receiver (Opt 028) - Use a standard VNA receiver to measure noise figure.

  • Connect the DUT to any VNA ports. For vector noise figure measurements, connect the noise tuner to the source port.

  • The gain plus noise figure of the DUT minus cable loss must be at least 40 dB (G+ NF - Loss > 40 dB). This ensures that there is sufficient DUT noise power for the VNA to measure. Learn more.

  • Additional filtering may be required. Learn more.

Noise Receiver (Opt 029) - Use internal low-noise receivers to measure noise figure.

  • Opt 029 measures devices with noise figure values ranging from about 0 to 50 dB and devices with GAIN ranging from about -40 to +60 dB. Learn more.

  • Amplifiers with higher gain can be measured by adding an attenuator to the output of DUT and using fixture de-embedding to remove the attenuator loss. An alternative for measuring high-gain devices is to use the standard receivers (Opt 028) as they have a higher compression level.

Receiver Gain  

This setting is NOT available when Noise Receiver is set to NA (Network Analyzer) Receiver (Opt 028).

With knowledge of your DUT gain, set the appropriate amount of receiver gain in order to optimize the power level at the noise receiver.

The following values reflect the SUM of the DUT gain (dB) PLUS NF (dB). For example: DUT gain = 20 dB; NF = 10 dB; SUM = 30 dB.

  • Select High if the SUM is relatively low (<30 dB).

  • Select Medium if the SUM is about average (20 dB to 45 dB).

  • Select Low if the SUM is relatively high (>35 dB).

There is considerable overlap in these settings. Because all three gain settings are calibrated with each Noise Calibration, this setting can be changed after calibration to achieve the least amount of jitter without overpowering the noise receiver.

One of following messages appears when too much power is detected at the noise receiver:

  • Compression in noise receiver: excess signal - The noise receiver is likely compressing.  NF results are possibly not accurate. Select a lower gain setting.

  • Compression in noise receiver: gain has been limited - The gain has been limited to avoid damage to the receiver. NF results are NOT accurate. Select a lower gain setting.

  • ADC over-range in noise receiver: excess signal - Often caused by a CW signal, an oscillation, or LO feedthru during an NF measurement. Find and correct the cause, or try a lower gain setting.

Only ONE gain setting can be used for the entire frequency range of your noise measurement.  Therefore, it may be necessary to use two noise channels with different frequency ranges and gain settings to achieve the very highest noise figure accuracy.

Source Temperature

Note: This setting is only used for calibrated noise figure measurements, but has no effect in an uncalibrated noise figure channel. The default value is used for uncalibrated measurements.

Note: The 302 K value is based on the internal temperature of an ECal (304 K) and assumes 1.5 dB of cable loss and a room temperature of 297 K. The ambient-temperature field can still be set by the user, but the user-entered value is ignored when using VNC with an ECal or the internal tuner (but not ignored for SNC). Starting with firmware release A.15.55.08 (Jan 2022), the ambient temperature field was renamed Source Temperature, and a check box labeled “Use 302 K for Vector Noise Cal with internal/ECal tuner” was added. When checked (the default behavior), the ambient temperature field is ignored as before when using VNC with either an external ECal module or the built-in tuner available on higher-frequency models. Note that if the box is checked when using an electromechanical tuner for measuring noise parameters, the default or user-entered value in the field is used. When the box is cleared, the default or user-entered value in the field is used. This allows the user to enter a value for test setups that have higher cable loss or when the testing environment is significantly hotter or colder than 297 K.

Enter the equivalent port 1 temperature at the time of the measurement, in Kelvin (K). One can use a thermometer to measure the temperature of the input cable.

In the case of full vector correction, it is the temperature of the Ecal Tuner (31 °C or 304.15K) minus the loss effect of the cable from the tuner to the DUT; both internal and external Ecals used as tuners have the same internal heater to heat to 31 °C.

For scalar it is the temperature of the internal load (such as the internal step attenuator) minus the loss of the cable, typically around 297K.

The cable loss compensation is computed from Tambient_setting=Tvna_source*|S21|^2+(1-|S21|^2)*Tcable  where S21 is the loss of the port 1 cable, Tcable is the temperature of the cable, and Tvna_source is the temperature of the either the Ecal used as a tuner, for full vector, or the temperature of the internal load for scalar calibration. Tecal is typically 304.15K; the internal load is typically around 297K (if the attenuator internally is set to 10 dB or more) or 303K if the internal source attenuator is set to 0. The attenuator is physically located near the input of the air flow and so it is very close to the external ambient temperature, but with 0 dB setting, the temperature of the internal source becomes the effective input temperature and it is a little warmer at about 6 degrees rise above ambient.

This temperature number has an inverse relationship to the noise figure. When using the effective noise temperature (Te) format, a 3 degree increase in the ambient temperature will make the calibration measurement result drop 3 degrees, which will then have an effect on subsequent noise figure measurements. One can directly measure the port 1 equivalent temperature by connecting port 1 to port 2 with a low loss through, and measuring the mean value directly. Because the noise value is quite low, averaging or using trace statistics should be used to find this value.

Use 302K for Vector Noise Cal with internal/ECal tuner  When checked will use 302K as the source temperature when vector correction is applied and the tuner is an ECal or internal tuner. When unchecked, the specified source temperature will be used.

Impedance States

Noise Tuner  Displays the ECal module to be used as a noise tuner. Select the Noise Tuner during calibration on the Select Cal Method dialog.

Max Acquired Impedance States  Select the number of impedance states in which to make noise measurements. At least FOUR impedance states are required. Learn more.

Frequency Tab - Noise Figure dialog box help

These settings can also be made from the normal VNA setting locations. Click links below to learn how.

Sweep Type

Choose a sweep type. Learn more.

Segment Sweep Notes:

Sweep Settings

Click each to learn more about these settings.

Power Tab - Noise Figure dialog box help

Note: S-parameter power settings are critical for accurate noise figure measurements. See Noise Figure Measurement Tips.

Configures RF power settings for the S-parameter measurements that occur before noise measurements. Input power to the DUT is turned OFF during noise measurements.

These settings can also be made from the normal Power setting locations.

Power ON (All channels)  Check to turn RF Power ON for all channels.

DUT Input Port

Opt 028 - Select a VNA port to be connected to the DUT input.

Opt 029 Scalar Noise Figure - Select a VNA port other than port 2.

Opt 029 Vector Noise Figure - The DUT input CAN be connected to any VNA port other than port 2. However, without a noise tuner bypass switch, measurements on other channels that use the same source port will always go through the noise tuner. The noise tuner must be connected to the source loop of the selected port.

Note: Input power levels are critical for accurate noise figure measurements. Learn more.

Power Level  The input power to the DUT during S-parameter measurements.

Source Attenuator Auto  Check to automatically select the correct attenuation to achieve the specified input power. Clear, then select attenuator setting that is used achieve the specified Power Level. Learn more about Source Attenuation.

All VNA channels in continuous sweep must have the same attenuation value. Learn more.

Receiver Attenuator  Specifies the receiver attenuator setting for input port.  (M938xA)

Source Leveling Mode   Specifies the leveling mode. Choose Internal.  Open Loop should only be used when doing Wideband Pulse measurements (not available with Noise figure measurements).

DUT Output Port

Opt 028 - Select a VNA port to be connected to the DUT output.

Opt 029 - Connect the DUT output to VNA port 2.

Output Power  Sets power level in to the output port for reverse sweeps. Port power is automatically uncoupled. Reverse sweeps are always applied to the DUT when Full 2-port correction is applied.  Enhanced Response Cal is NOT available for noise figure measurements.

Source Attenuator  Specifies the source attenuator setting for reverse power.

Receiver Attenuator  Specifies the receiver attenuator setting for the output port. (M938xA: Receiver Configuration)

Source Leveling   Specifies the leveling mode. Choose Internal.

Path Configuration  Launches the path configuration dialog. Learn More.

Noise Path Configurator - dialog box help

26.5 GHz Models

50 GHz Models (Opt. 029)

Port 1 Noise Tuner Switch (Opt 029)

26.5 GHz

The orange line between CPLR THRU and SRC OUT represents the Noise Tuner.  

  • External selects the external Noise Tuner for making noise figure measurements.

  • Internal bypasses the external Noise Tuner

See Important Notes about managing this switch.

50 GHz Models

  • Tuner - Represents the built-in Noise tuner.

  • Bypass - Bypasses the built-in tuner

Port 2 Noise Receiver Switch (Opt 029 All models) allows you to make Noise Receiver measurements.  

To prevent premature wear on the above two Noise switches, the VNA does not allow these switches to be thrown when sweeping a Noise channel and non-Noise channel. To make noise figure measurements and non-noise figure measurements in different channels and continuously trigger both, set these switches to the same state as the Noise channel:

  • With the non-noise figure channel active, go to Noise Path Configurator.

  • Set Noise Tuner switch to External.  This routes source power to the front-panel loops, and to the Noise Tuner when connected. Use CONT:ECAL:MOD:PATH:STATE to set the internal state of the Noise Tuner to THRU, which creates a small amount of additional loss in the source path.

  • Set Noise Receiver Switch to Noise Receiver.

Noise Figure Measurement Tips

Note: In this topic, the term Jitter is used to describe the trace-to-trace fluctuations in a measurement. In other topics, this is called 'trace noise'.

Option 029

See Opt 028 (NF with Standard Receiver)

Power level at the DUT Output - Opt 029

S-parameters are used to measure the gain of the DUT before each series of noise measurements. Jitter in the S-parameter measurements corresponds directly to jitter in the noise measurements.

For best noise figure accuracy, the power level out of the DUT should be between 15 dB and 20 dB below the compression point of the DUT during the S-parameter portion of the noise figure measurement.

To reduce jitter, the power level at the B receiver (port 2) should be above approximately -20 dBm. Much below this level, S-parameter measurements have more jitter. Power must be below +10 dBm as the B receiver starts to compress at this point, although there is no warning or annotation that shows this condition is occurring in S-parameter measurements.

The best way to monitor power at the B receiver is to display a B,1 measurement. With your DUT in place and powered ON, change the input power to the device and note the power at the B receiver.

Attaining the optimum power level during calibration can also be challenging since calibration is performed without the DUT in place. Because of this, it is often necessary to set source power higher during the calibration than during the measurement. This will cause the 'CD' annotation on the status bar. Measurement results are accurate as long as the step attenuators and other configuration switches are in the same position and all receivers remain in their linear range (below +10 dBm).

It is best to find the optimum power and attenuation settings for both the calibration and subsequent noise measurements before performing a calibration.

IF Bandwidth

Jitter is further reduced by narrowing the IF bandwidth. If the calibration needs to be performed at a low source power, or with receiver attenuation due to high DUT gain, the IF bandwidth should be reduced during the calibration to reduce jitter. The IF bandwidth can then be increased to improve measurement speed.  The CD annotation can be ignored when changing IFBW after calibration.

Noise Settings

See Noise Figure dialog box help for a complete description of these important settings.

Temperature

Noise Figure measurements are extremely sensitive to temperature. As such, there are two settings that require an accurate temperature measurement: At the DUT input, and at the Noise Source connector.

Interference

When measuring the noise figure of an unshielded device, like an amplifier on a printed-circuit board, it is very common to pick up interference from external signals such as cellular phones, wireless LAN, or mobile radios. This interference shows up as non-repeatable spikes in the measurement, as shown below.

Usually, the interference adversely affects the noise figure measurement only at the frequency where it occurs. However, if the interference is large enough and present all of the time, it can cause the noise receivers to compress, which results in inaccurate measurements at many frequencies. In this case, the noise figure measurements should be done in a shielded environment like a screen room.

Option 028

Noise Figure of VNA receiver - Option 028 gives you the flexibility to measure noise figure using a standard VNA receiver. For best measurement accuracy, the DUT excess noise power, which is gain plus noise figure minus cable loss in dB (G + NF - Loss), should meet or exceed the noise figure of the receiver. This is generally not a problem with very high-gain devices such as converters with approximately 60 dB of gain.

If your DUT is NOT a very high-gain device, you can re-configure the VNA front panel loops to increase receiver sensitivity.

Re-configuring the front panel loops - This configuration reverses the main arm and coupled arm of the test-port coupler (see following images). This increases the signal to the receiver port by about 15 dB, while lowering the available port power by the same amount. This is a good tradeoff for noise figure measurements.

Block diagram showing port 2 thru coupler main arm to B receiver.

Configure the receiver port front-panel loops to a vertical orientation as shown here.

The following table shows the excess noise that is required at various frequencies. These values assume the front-panel loops have been re-configured as shown above:

Frequency range

Required Excess Noise Power

Up to 20 GHz:

30 dB

Up to 50 GHz:

40 dB

Up to 67 GHz:

45 dB

For devices that do NOT meet this requirement, a low-noise amplifier (LNA) must be added to the receiver loop (see following image). This boosts the noise power at the receiver by the gain of the LNA. The disadvantage is the possibility of measurement drift and receiver compression. Any change in the gain of the LNA will have an impact on measurements that use the receiver with the LNA, so frequent calibration may be required. Care should also be taken when setting the channel power (used during the S-parameter portion of the calibration, and the gain portion of the DUT measurement) to ensure that the added gain of the LNA does not cause receiver damage or compression. A filter is also required on the output of the LNA. Learn more.

(Option 028)

Option  029  includes noise receivers with filtering to keep mixing-product noise out of the low-noise receivers

Using Noise Figure Traces in Equation Editor

In a Noise Power trace, the underlying unit is noise temperature.  

10*log10( temperature * 1000mw/w * 1.38e-23)

(1.38e-23 is Boltzmanns constant)

Any time you use Equation Editor on a Noise Power trace, the LogMag formatting will apply the above equation.  Therefore, first select REAL format and then generate the equation.

The following screen is an example showing three traces: DUTNPD (DUT Noise Power Density), NF (Noise Figure), and S11 with the equation set to "***=10". Note that formatting for noise figure measurements is different than noise power measurements or temperature measurements. For regular receiver power measurements, the conversion from linear magnitude to log magnitude uses 20*log10 (linear magnitude).

Radio-Frequency Electromagnetic Field Immunity

When a 3Vm-1 radio-frequency electromagnetic field is applied to an PNA with Opt 029 according to IEC 61000-4-3:1995, degradation of performance may be observed. When the frequency of the incident field matches the frequency of a measured noise figure or gain, the values displayed will deviate from those expected. This phenomenon will only affect that specific frequency, and the analyzer will continue to perform to the specification at all other frequency sample points.

The VNA with Opt 029 may be unable to calibrate a chosen frequency sample point if the frequency matches that of an incident electromagnetic field.