What is Network Analyzer : Working & Its Applications

In RF & microwave industries, the key measurement technology is the network analyzer. The former products of a network analyzer have been introduced a few years back, which has a large influence on the design & testing of active and passive electronic components. So, these analyzers were mainly focused on the measurements of transmission & reflection. After that, they became the basis of s-parameter characterization. When time passed, extra capabilities & measurements have been included. And also includes some features to deal with the growing market requirements like noise, error-corrected power, converter, etc. So this article discusses an introduction to the network analyzer and its working with applications.

What is Network Analyzer?

Network analyzer definition: It is an instrument that is used to measure an electrical network’s network parameters. Currently, these instruments are normally used to measure S-parameters because transmission & reflection of electrical networks are very simple to calculate at high frequencies, although there are other types of network parameter sets like Y, Z & H-parameters. These analyzers are frequently used to differentiate two-port networks like filters & amplifiers and filters.

The basic working principle of a network analyzer is to measure the phase & amplitude of both the waves like reflected & incident at the different ports of the Device Under Test (DUT). This analyzer includes both a source & set of receivers. A source is used to produce a known stimulus signal whereas receivers are used to decide changes in stimulus signal which is caused by the DUT.

Why do we Need Network Analyzer?

A network analyzer provides information regarding what is happening on a network by letting you observe the actual data that supplies packet by packet over it. Generally, a network analyzer has the capacity to understand different protocols, which allows it to show conversations occurring between hosts over a network.

A network analyzer characterizes & measures the device or network response. So that the operator can monitor how the network or device functions in an RF circuit. Generally, these devices are used for different parts measurements like filters, mixers, frequency sensitive networks, transistors & other RF-based devices.

It is used in transmission & reflection measurements. Transmission measurements comprise gain, insertion loss, transmission coefficient whereas reflection measurements comprise return loss, reflection coefficient, impedance, etc. The operating frequencies of these analyzers range from 1 Hz – 1.5 THz. These analyzers can also be used for the analysis of stability for the measurement of ultrasonic, audio components, and open loops.

Measurements

Network analyzer measurements are three types transmission, reflection, and scattering parameter.

• Transmission measurements are used to measure insertion loss, gain, and transmission coefficient.
• Reflection measurements are used to measure VSWR, reflection coefficient, impedance & return loss.
• Scattering parameter measurements are used to measure s-parameters like S11, S12, S21 & S22.

Network Analyzer Block Diagram

The block diagram of this analyzer is shown below. This block diagram mainly includes four essential components like signal source, signal separation, receiver or detector, and processor or display.

Signal Source

The main function of the signal source in the network analyzer is to provide the incident signal which excites the device under test which is also known as DUT. This test device simply responds by reflecting elements of the incident signal & transmitting the leftover part. The response of the DUT can be simply determined through frequency sweeping of the frequency response of the source. The sources are available in two types sweep oscillator & synthesized signal generator.

Signal Separation

The next part in this block diagram is a signal separation that is used to divide different signals like incident, reflected & transmitted. When these three signals are divided then their phase & amplitude measurement can be simply carried out & their variations can be identified. So this can be done by using power splitters, high impedance probes or bridges, and directional couplers.

Receiver/Detector

The receiver or detector in this block diagram is used to change RF voltage to lower intermediate frequency or direct current signal to permit more precise measurement.  There are three major receiver methods are used to achieve this diode, fundamental mixing & harmonic mixing.

A diode is one type of broadband detector used to change RF signal to the relative DC voltage. This method is most frequently used in SNA or scalar network analyzers.

The remaining two are broadband tuned receiver methods which are used for changing RF signal into the low-frequency intermediate frequency signal. These two signals will have BPF at IF frequencies to refuse the false frequencies & expand the noise floor.

Processor/Display

The display is the final part of this analyzer that generates the results as preferred by the operator. The signal processor or display processes the intermediate frequency signal & displays the information on the cathode ray tube screen.

Working

The above network analyzer block diagram working is, fist the signal source generates an incident signal to DUT. After that, the signal separation device divides incident, reflected & transmitted signals. The receiver or detector changes the frequency from microwave to lower IF to make it simple for further processing. Finally, the processor or display processes the IF signal & displays the data on the CRT display.

Types of Network Analyzer

Network analyzers are classified into three types SNA, VNA & large signal network analyzer which helps in measuring both phase & magnitude-based measurements.

Scalar Network Analyzer

The term SNA stands for scalar network analyzer is an RF type network analyzer, used to measure simply the amplitude properties of a DUT. Not like a VNA, SNA does not measure both phase & amplitude of the DUT. A scalar type analyzer is mainly used to measure different parameters like return loss, VSWR which simply need the signal’s magnitude measurement at a specific frequency.

The development of this analyzer can be done with a spectrum analyzer and a tracking generator. When these two are operated at a similar frequency & the tracking generator’s output is given to the spectrum analyzer’s input, this analyzer will illustrate a plane line on its display to signify the tracking generator’s output level.

If we situate a DUT in between the spectrum analyzer & tracking generator, then the level of signal we obtain at the spectrum analyzer will be a DUT function. So, we can measure the device amplitude properties with a blend of a spectrum analyzer as well as a tracking generator. So this response can be simply measured over a range of frequencies.

Scalar analyzers are used to measure the gain of amplifiers, responses of filter, mixer conversion & return loss.

Vector Network Analyzer

VNAs are mainly used for testing the specifications of components and also verifying design simulations to confirm the systems and their components together work properly or not. The VNA is a more practical form of RF network analyzer as compared to the SNA because it is capable to determine additional parameters regarding the DUT (device under test).

These analyzers not only measure the response of amplitude and also measures phase. So this is the reason to call this analyzer an automatic network analyzer otherwise gain-phase meter.

Large Scale Network Analyzer

The term LSNA stands for Large Signal Network Analyzer. It is extremely specialized for RF network analyzers because it is capable of investigating the device characteristics in large-signal conditions.
This analyzer is also capable to look at the non-linearities & harmonics of a network in different conditions like providing a complete operation analysis. The previous version of the LSNA is called the MTA or Microwave Transition Analyzer.

S Parameters in Network Analyzer

The S parameters are also known as scattering parameters which describe the main relationships between input and output ports within an electrical system. At maximum frequency, it becomes particularly essential to explain a specified network in terms of waves instead of current or voltage. So in scattering parameters, we utilize power waves. For a 2- port network, scattering-parameters can be simply defined as;

• S11 is the reflection coefficient of i/p port voltage.
• S12 is the gain of reverse voltage gain.
• S21 is the gain of forward voltage gain.
• S22 is the reflection coefficient of o/p port voltage.

The matrix of Scattering-parameter is simply used to conclude transmission gains & reflection coefficients from both faces of a 2- port network. Further, this concept is used to decide the scattering parameters of a multi-port network. These concepts can be used further in determining Return loss, Gain, Insertion Loss & VSWR.

Network Analyzer Vs Spectrum Analyzer

The difference between network analyzer and spectrum analyzer includes the following.

Network Analyzer Specifications

The specifications of the network analyzer include the following.

• Frequency ranges from 100 kHz to 20 GHz.
• Measured parameters are S11, S21, S2, and S22.
• The noise level is 133dB.
• The dynamic range is 1MHz to 20 GHz.
• The adjustment range of output power is -60 dBm to +10 dBm.
• Time taken for measurement for each point is <12us.
• Full CW frequency accuracy is + or – 2×10^-6.
• Setting resolution of frequency is 1Hz.

Advantages

The advantages of a network analyzer include the following.

• Scalar network analyzers are cheaper.
• As compared to VNA type, SNA performs sweep faster.
• In SNA, the hardware necessary for power detection & down conversion is fairly simple.
• VNA is used for phase as well as magnitude measurements not like SNA.

Disadvantages

The disadvantages of a network analyzer include the following.

• SNA type is not applicable for phase-related measurements.
• As compared to the SNA type, VNA performs sweep slower.
• VNAs are very complex because of the full heterodyne architecture utilized within the receiver of it.
• VNAs are expensive as compared to SNAs.

Applications

The applications of network analyzers include the following.

• VNAs are used to check the specifications of components & also design simulations.
• RF Network type analyzers are simply used to measure circuits, devices, components, etc.
• These are used in a range of industries to check different equipment, measure materials & observe the integrity of the signal.
• VNAs are essential for the devices & components characterization used within microwave & RF systems.
• These are used to measure the S parameters, insertion loss, reflection, transmission & return loss.
• These are mainly used do research & development purposes.
• These instruments are used in linear networks to measures transfer & impedance functions through sine-wave testing.
• These analyzers are used to measures the network parameters within electrical networks.

Thus, this is an overview of a network analyzer that normally measures S-parameters because, in electrical networks, the transmission & reflection are simple to measure at maximum frequencies. These are frequently used for differentiating two-port-based active & passive devices, although they can also be utilized on networks including an arbitrary no. of ports. Here is a question for you, please mention some of the manufacturers of network analyzers?