Unveiling the Power of Network Analyzers: A Comprehensive Guide

In the realm of electrical engineering, understanding the behavior of electrical networks is crucial. A network analyzer is an indispensable tool used to measure the network parameters of these networks, providing insights into their performance and characteristics. This article delves into the world of network analyzers, exploring their types, architecture, calibration, and applications.

What is a Network Analyzer?

A network analyzer is an instrument which measures the behavior of electrical networks. It does this by injecting a signal into the network and measuring the reflected and transmitted signals. These measurements are then used to characterize the network's properties, such as impedance, scattering parameters (S-parameters), and frequency response.

Network analyzers are most commonly employed at high frequencies, ranging from 1 Hz to 1.5 THz, and provide detailed analysis for components such as amplifiers and filters. They can also be used at lower frequencies, covering down to 1 Hz, allowing analysis of open loops or measurement of audio and ultrasonic components.

Scalar vs. Vector Network Analyzers: Choosing the Right Tool

There are two primary types of network analyzers, each offering unique capabilities:

• Scalar Network Analyzer (SNA): Measures only the amplitude properties of a network.
• Vector Network Analyzer (VNA): Measures both the amplitude and phase properties of a network, providing a more comprehensive characterization. VNAs are sometimes called gain-phase meters or automatic network analyzers.

While an SNA is similar to a spectrum analyzer combined with a tracking generator, VNAs have become the more prevalent type due to their superior analytical capabilities. Today, some prominent VNA manufacturers are Keysight, Anritsu, Rohde & Schwarz, and Copper Mountain Technologies.

For hobbyists and educational purposes, entry-level and DIY network analyzers are available, offering limited functionality at a lower cost.

Also, a microwave transition analyzer (MTA) or large-signal network analyzer (LSNA) is another type, measuring both amplitude and phase of the fundamental and harmonics.

Decoding the Architecture of a Network Analyzer

A typical network analyzer consists of four main components:

• Signal Generator: Provides the test signal for analyzing the network. Modern network analyzers typically have a built-in signal generator, with high-performance models featuring two sources for applications like mixer and amplifier testing.
• Test Set: Routes the signal generator output to the device under test (DUT) and directs the measured signal to the receivers. It also includes a reference channel for the incident wave.
• Receiver: Measures the signal characteristics. SNAs measure only the magnitude, while VNAs measure both magnitude and phase. VNAs require at least two receivers: one for the test signal and one for the reference channel.
• Processor and Display: Processes the received signals and presents the data in a user-friendly format, including linear and logarithmic sweeps, polar plots, and Smith charts.

S-Parameter Measurement with a Vector Network Analyzer

A VNA characterizes the RF performance of devices by measuring their S-parameters. S-parameters define the input and output relationships of a network when subjected to different signals. A typical 2-port VNA setup involves connecting the DUT to the VNA's ports and measuring the signals transmitted and reflected through the device. These measurements are then used to calculate parameters, which provide a complete understanding of the DUT's behavior. For example, a VNA is able to measure S11 and S21 when switch SW1 is at position 1, enabling it to measure the test signal’s amplitude and phase at the test frequency.

Calibration and Error Correction: Ensuring Accuracy

To achieve accurate measurements, network analyzers require periodic calibration and error correction.

• Calibration: This is typically performed annually by the manufacturer or a specialized calibration laboratory.

• Error Correction: Also known as user-calibration addresses the systematic errors introduced by the instrument, cables, adapters, and test fixtures. Several calibration methods exist, including:

  • SOLT (Short, Open, Load, Through): A common method suitable for coaxial measurements.
  • TRL (Through-Reflect-Line): Useful for non-coaxial environments like waveguide.

Before calibration, it's crucial to inspect and clean the connectors, gauge them for mechanical problems and tighten them to the specified torque.

Verification Kits: Ensuring Reliable Performance

Verification kits are available to confirm the accuracy of network analyzer measurements. Some kits, such as the Keysight 85055A verification kit, include transmission lines, attenuators, and data to verify the analyzer's performance.

Expanding Capabilities: Noise Figure Measurements

High-end VNAs from manufacturers like Keysight, Anritsu, and Rohde & Schwarz offer noise figure measurement capabilities. Vector error correction enables higher accuracy than traditional noise figure meters. Learn more on how to measure electrical signals on the Keysight website.

Conclusion: Network Analyzers as Essential Tools

Network analyzers are powerful instruments that provide invaluable insights into the behavior of electrical networks. Whether you're designing amplifiers, testing filters, or analyzing complex systems network analyzer, understanding the capabilities and operation of network analyzers is essential for success.