RF Noise Figure Measurements using Spectrum Analyzer Siglent SVA1032X (9kHz – 3.2GHz)

May 22, 2023

Introduction

The noise figure is a major measurement parameter in the process of microwave product development and production, and its measurement test is an important element of noise measurement test. This manual describes in detail how to use a spectrum analyzer to measure noise coefficients by using the Siglent SVA 1032X (9kHZ – 3.2GHz), including spectrum analyzer filter response, derivation of noise coefficients, calculation of cascaded output noise floor, etc.

Spectrum Analyzer filter response – RBW

The following procedure is used to measure the filter response or resolution bandwidth shape factor.  Knowing the shape factor is useful when measuring noise figure.  The procedure will cover measuring the shape factor of 100, 1kHz, and 10kHZ RBW; however, this procedure can be used for other RBW and frequency settings.

Setup for SA and Signal Generator

  1. Tie the 10MHz clocks together, does not matter which is primary or secondary.
    For Siglent equipment, the external clock is automatically detected and displayed in use.
    Ensure connectors are clean and properly torqued.
  2. Connect RF output to RF input of spectrum analyzer.
  3. Setup for Signal Generator:
    Pout = -10dBm
    RF = CW @ 1GHz
    ALC = auto
  4. Allow at least 30 minutes or longer for warm-up time.
  5. Set up spectrum analyzer:
  6. Freq = 1GHz
    Freq step size = 10Hz (repeat with 100Hz & 1kHz step size for RBW/VBW settings that follow).
  7. Span = 0Hz
    Trigger = free run
    Points = 751, not adjustable
  8. RBW/VBW = 100Hz (repeat for 1kHz and 10kHz)
  9. Attenuator = auto
  10. Pre-amp = off
  11. Ref level = 0dBm
  12. Scale/Div = 5dB
  13. Detector = Pos Peak
  14. Sweep Mode → sweep rule → accuracy
  15. Sweep time = auto
  16. Marker = center of sweep

Measuring shape factor:

  1. Turn the signal generator ON
    adjust RF output amplitude for a -10dBm reading on the spectrum analyzer
  2. Increase/decrease the frequency of the spectrum analyzer by 10Hz steps and record values.
  3. Repeat for other RBW/VBW settings and other frequency step sizes.
Fc Frequency Delta (dB) RBW/VBW
1GHz +/- 50Hz 100Hz
  Fc – 50 Hz -2.95
  Fc – 40 Hz -1.87
  Fc – 30 Hz -1.07
  Fc – 20 Hz -0.44
  Fc –  0Hz 0
  Fc + 20 Hz -0.44
  Fc + 30 Hz -1.08
  Fc + 40 Hz -1.87
  Fc + 50 Hz -2.94

 

Fc Frequency Delta (dB) RBW/VBW
1GHz +/- 500Hz 1kHz
  Fc – 500 Hz -3.0
  Fc – 400 Hz -1.92
  Fc – 300 Hz -1.08
  Fc – 200 Hz -0.47
  Fc –  0Hz 0
  Fc + 200 Hz -0.49
  Fc + 300 Hz -1.07
  Fc + 400 Hz -1.91
  Fc + 500 Hz -3.0

 

Fc Frequency Delta (dB) RBW/VBW
1GHz +/- 5kHz 10kHz
  Fc – 5000 Hz -3.02
  Fc – 4000 Hz -1.94
  Fc – 3500 Hz -1.51
  Fc – 3000 Hz -1.08
  Fc – 2000 Hz -0.48
  Fc –  0Hz 0
  Fc + 2000 Hz -0.48
  Fc + 3000 Hz -1.09
  Fc + 3500 Hz -1.5
  Fc + 4000 Hz -1.94
  Fc + 5000 Hz -3.03

Conclusion:  The shape factor for +/- 2.0dB is approximately 0.80 of the RBW

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