Figura De Ruido

Agilent
Fundamentals of RF and Microwave Noise Figure Measurements
Application Note 57-1

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Table of Contents
1. What is Noise Figure?
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 The Importance of Noise in Communication Systems . . . . . . . . .. . . . .5 Sources of Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 The Concept of Noise Figure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Noise Figure and Noise Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

2. Noise Characteristics of Two-Port Networks

. . . . . . . . . . . .9 The NoiseFigure of Multi-stage Systems . . . . . . . . . . . . . . . . . . . . . . . .9 Gain and Mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 Noise Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 The Effect of Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 . . . . . .. . . . . . . . . . . . . . . . . .12 Noise Power Linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 Noise Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 The Y-Factor Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 The Signal Generator Twice-Power Method . .. . . . . . . . . . . . . . . . . . . .14 The Direct Noise Measurement Method . . . . . . . . . . . . . . . . . . . . . . . . .14 Corrected Noise Figure and Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Jitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Frequency Converters . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .16 Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 LO Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 LO Leakage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 Unwanted Responses . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .16 Noise Figure Measuring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Noise Figure Analyzers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Spectrum Analyzers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Network Analyzers . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . .18 Noise Parameter Test Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 Power Meters and True-RMS Voltmeters . . . . . . . . . . . . . . . . . . . .18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .29 . . . . . .31

3. The Measurement of Noise Figure

4. Glossary

5. References

6. Additional Agilent Resources, Literature and Tools

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Chapter 1. What is Noise Figure?
Introduction
Modern receiving systems must often process very weak signals, but the noise added by the system components tends to obscure those very weak signals. Sensitivity, bit error ratio (BER) andnoise figure are system parameters that characterize the ability to process low-level signals. Of these parameters, noise figure is unique in that it is suitable not only for characterizing the entire system but also the system components such as the pre-amplifier, mixer, and IF amplifier that make up the system. By controlling the noise figure and gain of system components, the designer...