Network Analyzer Dynamic Range - Understanding and Improving

Application Notes

Table of Contents

  • Introduction
  • Dynamic range defined
  • Nose floor defined
  • Improving dynamic range
  • Averaging
  • IF BW reduction
  • Choosing the best method
  • Dynamic range, segmented sweep, and the configurable test set
  • Summary
  • References

Introduction

Achieving the highest possible network analyzer dynamic range is extremely important when characterizing many types of microwave devices, and in some cases, is the key factor in determining measurement performance. To achieve the greatest dynamic, range from a network measurement system, it is important to understand the essence of dynamic range and the methods that can be employed to increase it. Armed with this knowledge, the designer can choose the method that achieves the best results with the least impact on other instrument parameters such as measurement speed.

Dynamic range defined

Network analyzer dynamic range is essentially the range of power that the system can measure, specifically:

  • Pmax: The highest input power level that the system can measure before unacceptable errors occur in the measurement, usually determined by the network analyzer receiver’s compression specification.
  • Pref: The nominal power available at the test port from the network analyzer’s source.
  • Pmin: The minimum input power level the system can measure (its sensitivity), set by the receiver’s noise floor. Pmin depends on the IF bandwidth, averaging, and the test set configuration.

The two common definitions for dynamic range are:

  • Receiver dynamic range: Pmax - Pmin
  • System dynamic range: Pref - Pmin

Achievable dynamic range depends upon the measurement application.

  • Systemic dynamic range: The dynamic range that can be realized without amplification such as when measuring passive components such as attenuators and filters.
  • Receiver dynamic range: The system’s true dynamic range if it is considered a receiver. An amplifier may be required to realize the receiver’s full dynamic range. This can be the device under test, or an external amplifier added to the measurement system.

Noise floor defined

The receiver's noise floor is an important network analyzer specification that helps determine its dynamic range. Unfortunately, “noise floor” is not a well-defined term and it has been defined in several ways over the years.

The results of an experiment to compare some common noise floor definitions are shown in Figure 2. In this experiment, Gaussian random noise with a noise power of –100 dBm was simulated, and the noise floor was calculated using four definitions:

  • The solid line shows the RMS value of the noise, which is equal to the noise power of –100 dBm.
  • The dashed line (–101 dBm) is the mean value of the linear magnitude of the noise, converted to dBm. – The dotted line (–102.4 dBm) is the mean value of the log magnitude of the noise.
  • The dot-dash line (–92.8 dBm) is the sum of the mean value of the linear magnitude of the noise and three times its standard deviation, converted to dBm.

Keysight Technologies’ vector network analyzers (VNAs), such as the PNA or ENA series, use the RMS value to define the receiver noise floor. This is a commonly used definition and is easy to understand because it is the receiver's equivalent input noise power.

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