Extend the Keysight N8975A Noise Figure Meter to Millimeterwave

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The industry widely used Keysight Noise Figure Analyzer (NFA) N8975A can provide accurate measurement of both gain and noise figure up to 26.5 GHz. SAGE Millimeter’s STG series Noise Figure and Gain Analyzer Extenders can extend the measurement up to 170 GHz while preserving the functionality and features that Keysight standard models offer. The model STG includes two critical assemblies: down converter (STC) and noise source (STZ). The system interface drawing is shown in below.

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This Blog is to give the detailed step by step instructions for how to use the STG series product with N8975A to perform the system calibration. All commands appearing in bold squared brackets relate to hard key presses e.g., [Hard Key]. All commands appearing in bold curly brackets relate to soft key presses e.g. {Soft Key}. All other statements appearing in bold relate to display settings or values, e.g., Bold Text.

Calibration:

  1. Make the connection per above block diagram.
  2. Turn on the N8975A, STG and STZ. Allow half an hour warm up time so that stable system status is reached.
  3. Ensure the preset on the NFA is set to factory settings, press [System], {More}, {Power On/Preset} make sure {Power On} is set to Preset and {Preset} is set to Factory.
  4. Press the [Preset] button of the N8975A and wait for the routine to finish.
  5. Input or Load (if it was preloaded and saved) the ENR table of the noise source (STZ) being used.
  6. Press the [System] button, set {Remote Port} to GPIB. Press {GPIB}, then set Noise Figure Analyzer Address to 8, External LO Address to 5, and LO GPIB Address to 5 using keypad.
  7. Press the [System] button, then {External LO}, then set the {Max Freq} to 110 GHz using the keypad.
  8. Press {LO Commands}, set Power Prefix to L1, Power Suffix to DM, Frequency Prefix to F1, Frequency Suffix to Hz using the keypad and leave Auxiliary Command blank.
  9. Press [Meas Mode], set Device Under Test to Amplifier, System Downconverter to On, and LO Mode to Variable.
  10. Press [LO Mode], set IF Frequency to 1 GHz, Sideband to DSB, LO Control to On, External LO Power Level to 5 dBm.
  11. Press [Frequency/Points], then {Freq Mode} and select the frequency mode to Sweep. To set the frequency range, press {Start Freq}, key in 75 GHz, and press {Stop Freq}, key in 110 GHz for W Band operation for instance.
  12. Press [Averaging/Bandwidth], and then set {Averaging} to On, {Averages} to 16, {Average Mode} to Point, and {Bandwidth} to 4 MHz.

The following screenshot shown the W band calibration results. After the calibration, the noise figure uncertainty should be within ±0.2 dB typically.

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Measurement:

After calibration disconnect the noise source from the RF INPUT of the STC Down Converter. Connect the noise source STZ output to the input of the device under test (DUT) and the output of the DUT to the Down Converter RF INPUT. Press [Restart] and wait for the measurement sweep to complete. The gain and noise figure are displayed on screen in tabulate format is shown below.

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