Network analyzer

Network analyzers characterize radio frequency (RF) devices and is an instrument that measures the network parameters of electrical networks.

Introduction

A network analyzer is an instrument that measures the network parameters of electrical networks. Today, network analyzers commonly measure s–parameters because reflection and transmission of electrical networks are easy to measure at high frequencies, but there are other network parameter sets such as y-parameters, z-parameters, and h-parameters. Network analyzers are often used to characterize two-port networks such as amplifiers and filters, but they can be used on networks with an arbitrary number of ports.

The network analyzer is a instrument used for transmission measurements and reflection measurements. There are two types of network analyzer viz. Scalar and Vector.

Transmission measurements include transmission coefficient, insertion loss, gain etc. Reflection measurements include reflection coefficient, return loss, impedance etc.

Network analyzers are used mostly at high frequencies; operating frequencies can range from 1 Hz to 1.5 THz. Special types of network analyzers can also cover lower frequency ranges down to 1 Hz. These network analyzers can be used for example for the stability analysis of open loops or for the measurement of audio and ultrasonic components.

What Is A Network Analyzer?

Network analyzers characterize radio frequency (RF) devices. Although they started out just measuring S-parameters, network analyzers have become highly integrated and advanced to stay ahead of the devices they test.

RF circuits require unique testing methods. Voltage and current are difficult to measure directly at high frequencies, so components must be characterized by their response to RF signals. Network analyzers make these characterizations by sending known signals into a device and taking ratioed measurements between the input and output signals.

Early network analyzers only measure magnitude. These scalar network analyzers will measure return loss, gain, standing wave ratio, and other magnitude-based measurements.

Today, most network analyzers are vector network analyzers — measuring both magnitude and phase. Vector network analyzers are extremely versatile instruments that can characterize S-parameters, match complex impedances, make time-domain measurements, and more.

This high-level block diagram of a measurement shows a signal being sent forward through the device under test (DUT) from the input to the output. Measurements that go through a device’s input to the output are called forward measurements.

The network analyzer’s receivers measure the incident, reflected, and transmitted signals to calculate the forward S-parameters.

The two basic types of network analyzers are

scalar network analyzer (SNA)—measures amplitude properties only.
vector network analyzer (VNA)—measures both amplitude and phase properties

scalar network analyzer (SNA)

The Scalar Network Analyzer, SNA, can be used for measuring the scalar response of a network to an input signal.

The scalar network analyzer, SNA is considerably less common in RF design circles than the VNA, but it can provide some useful insights.

As the name indicates a scalar networj analyzer, SNA, measures only the amplitude response of an RF network to an applied stimulus.

Scalar network analyzers can be very useful in measuring aspects like the amplitude response of a filter or other network. In this way a good insight can be obtained into a number of the aspects of the operation of the network.

Effectively, a scalar network analyzer, SNA, works just as a spectrum analyzer in combination with a tracking generator. When a tracking generator and spectrum analyser are used together, their operation is electrically closely linked.

The tracking generator generators a swept signal on exactly the same frequency that the spectrum analyser is receiving. Thus if the output from the tracking generator was connected directly to the input of the spectrum analyzer, then a constant line would be seen across the screen of the analyzer indicating the amplitude of the tracking generator output.

If a device is placed between the two items, then the spectrum analyser will note any amplitude variations. In this way for example, the response of a filter can be plotted. The constant output of the tracking generator will pass into the filter, where the response of the filter will change it according to the frequency and the response of the filter at that frequency, and in this way the spectrum analyzer will be able to display the response of the filter. From this it can be seen that scalar network analyzers, SNA, are very useful for measuring the amplitude response of a variety of components.

What is a Scalar Network Analyzer?

A Scalar Network Analyzer is a type of RF network analyzer that is used to measure only the amplitude properties of a DUT (Device Under Test). Unlike a Vector network Analyzer, it does not measure both amplitude and phase of the DUT. They can be used to measure parameters like VSWR and Return loss, which only requires the measurement of the magnitude of a signal at a particular frequency or frequency range.

A Scalar Network Analyzer can also be developed using a Spectrum Analyzer with a Tracking Generator. If both the Spectrum Analyzer and Tracking generator are operated at the same frequency and the output of the tracking generator is connected to the input of the spectrum analyzer, the spectrum analyzer will show a flat line on its screen to represent the output level of the tracking generator. Now if we place a device (DUT) between the tracking generator and the spectrum analyzer, the signal level we get at the spectrum analyzer will be a function of the DUT. Thus, we can calculate the amplitude properties of a device using a combination of a spectrum analyzer and tracking generator. This response can be calculated over a range of frequencies.

Benefits or advantages of Network Analyzer

Hardware required for down conversion and power detection is relatively simple.
Due to above SNAs are cheaper.
It peforms sweep faster compare to VNA type.

Drawbacks or disadvantages of Network Analyzer

They can not be used for phase related measurements.

What is a Vector Network Analyzer

VNA is a test instrument that measures the response of a network as vector. real & imaginary parameters so that its performance can be characterised.

Vector Network Analyzers are used to test component specifications and verify design simulations to make sure systems and their components work properly together.

Today, the term “network analyzer”, is used to describe tools for a variety of “networks”. For instance, most people today have a cellular or mobile phone that runs on a 3G or 4G network. In addition, most of our homes, offices and commercial venues all have Wi-Fi, or wireless LAN “networks”. Furthermore, many computers and servers are setup in “networks” that are all linked together to the cloud. For each of these “networks”, there exists a certain network analyzer tool used to verify performance, map coverage zones and identify problem areas.

From mobile phone networks, to Wi-Fi networks, to computer networks and the to the cloud, all of the most common technological networks of today were made possible using the Vector Network Analyzer that was first invented over 60 years ago.

R&D engineers and manufacturing test engineers commonly use VNAs at various stages of product development. Component designers need to verify the performance of their components such as amplifiers, filters, antennas, cables, mixers, etc.

The system designer needs to verify their component specs to ensure that the system performance they're counting on meets their subsystem and system specifications.

Manufacturing lines use Vector Network Analyzers to make sure that all products meet specifications before they're shipped out for use by their customers. In some cases, Vector Network Analyzers are even used in field operations to verify and troubleshoot deployed RF and microwave systems.

How does a Vector Network Analyzer (VNA) work?

A Vector Network Analyzer contains both a source, used to generate a known stimulus signal, and a set of receivers, used to determine changes to this stimulus caused by the device-under-test or DUT.

The stimulus signal is injected into the DUT and the Vector Network Analyzer measures both the signal that's reflected from the input side, as well as the signal that passes through to the output side of the DUT. The Vector Network Analyzer receivers measure the resulting signals and compare them to the known stimulus signal. The measured results are then processed by either an internal or external PC and sent to a display.

Benefits or advantages of Network Analyzer

They can be used for both magnitude and phase measurements unlike SNA counterpart.

Drawbacks or disadvantages of Network Analyzer

It performs sweep slower compare to SNA type.
They are very complex compare to SNAs. This is due to use of full heterodyne architecture used in the receiver part of it. This is required to measure both magnitude and phase parts of the signals.
Due to above VNAs are costly compare to SNAs.