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
- 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. - Connect RF output to RF input of spectrum analyzer.
- Setup for Signal Generator:
Pout = -10dBm
RF = CW @ 1GHz
ALC = auto - Allow at least 30 minutes or longer for warm-up time.
- Set up spectrum analyzer:
- Freq = 1GHz
Freq step size = 10Hz (repeat with 100Hz & 1kHz step size for RBW/VBW settings that follow). - Span = 0Hz
Trigger = free run
Points = 751, not adjustable - RBW/VBW = 100Hz (repeat for 1kHz and 10kHz)
- Attenuator = auto
- Pre-amp = off
- Ref level = 0dBm
- Scale/Div = 5dB
- Detector = Pos Peak
- Sweep Mode → sweep rule → accuracy
- Sweep time = auto
- Marker = center of sweep
Measuring shape factor:
- Turn the signal generator ON
adjust RF output amplitude for a -10dBm reading on the spectrum analyzer - Increase/decrease the frequency of the spectrum analyzer by 10Hz steps and record values.
- 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