Vector Network Analyzers 1

8/22/2019 Vector Network Analyzers 1

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K7RXV [email protected]

Vector Network analyzers


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Introduction

What are they?

What do they tell you?

How do they work?


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First What is a Network

A network is simply any combination of

components through which you pass asignal.

It can be a simple as a resistive voltage

divider, Or as complex as an filter oramplifier.

DC circuit can be analyzed with nothing

more than a High impedance voltmeter.


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Circuits with AC signals are morecomplex to analyze.

The phase between the current andvoltage must be taken into account.

We are interested in the bandpass,amplitude of both the current andvoltage, the phase angle between thecurrent and voltage, and the change in

any of these caused by passing the signalthrough the network.


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The simplest form of analyzer just givesrelative amplitude results with no phase

information. (scalar network analyzer)

This can be done with a dedicatedinstrument or with other equipment suchas a signal source and a signal leveldetector (ie RF voltmeter).

The advantage of a dedicated instrumentis graphic output which is easier tointerpret.

You can manually graph the outputhowever this takes time and effort.


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A vector network analyzer measures

scalar values and phase information.

A vector analyzer displays its output ineasy to understand form.

Smith Chart output is provided as well asphase and amplitude information.

This enables the instrument to alsocalculate and display impedanceinformation.


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S parameters are also a very useful wayto present this information (Scattering

parameters)

S21= Insertion Loss (IL) in the Forwarddirection

S11= Return Loss (RL) in the Forwarddirection

S12= IL in the Reverse direction S22= RL in the reverse direction


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The picture on this Slide is in a separate file

in the same folder as these slides.


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Return Loss

What is Return Loss?

Hams are used to VSWR to represent

how good the impedance match is.See the ARRl 2010 handbook for a

discussion of the relationship between

RL and VSWR.Return loss is easier to manipulate

mathematically and is directly measured by

most instruments


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What can we measure with this instrument

Single port measurements such as antennaor feedline input impedance.

Multi port measurements such as LCR filterpassband or amplifier gain passband etc,

crystal filter pasband, group delay, or phase

change across the passband.Crystal or other component characteristics


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With the software enhancements the VNWA

can also be used as a spectrum analyzer.

The secret to the power of this simple

implementation of a network analyzer is in

very good software implementation.

If you recognize the accuracy limitations of

simplified approach makes these

measurements within the reach of the

hobbiest


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During the brakes between talks

we can demo some of these

measurements.

Vector Network Analyzers 1

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