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Network Analyser

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This is a report on Network Analyser. This will give us a basic idea regarding what exactly is required to build such an instrument.

Text of Network Analyser

  • Low Cost Narrowband

    Network Analyzer

    Bachelor Degree Project Report

    Submitted by:

    Kaja Ameeruddin Mohammad (09007035)

    Under the guidance of

    Prof. Girish Kumar

    Department of Electrical Engineering

    Indian Institute of Technology Bombay

    November 2012

  • i

    Abstract

    Network analyzers have become one of the most important measurement tools for

    characterizing the performance of high-frequency components and devices. They can

    provide a wealth of knowledge about a device under test (DUT), including its magnitude,

    phase and group-delay response etc. But high costs of such instruments makes them

    unaffordable, especially in engineering institutes, where the use will only be limited to

    testing of devices for a specific application range. This project aims to design a low cost

    computer interfaced network analyzer to make it more affordable and portable, operating in

    the frequency range 800MHz 1000MHz.

    The design has been started with the idea of keeping the cost low without significantly

    affecting the performance of the system as a whole. Since laptops, computer desktops are

    extremely common nowadays, their computation power can be used for analysis. A

    microcontroller is used for system control and the laptop/computer desktop is used for

    computation and display purposes. The performance of both hardware and software has

    been followed very closely so as to keep the performance optimal. The following report

    covers not only the logic involved but also the detailed working, results and prototype

    hardware and software used.

  • ii

    Table of Contents

    Abstract .. i

    List of Figures .... iii

    List of Tables iv

    Nomenclature . iv

    Chapter 1 Introduction 1

    1.1 Networks and their Properties 1

    1.2 Scattering Parameters .. 2

    1.3 Measurement of S-parameters .. 3

    1.4 Network Analyzers Background and Cost Survey .. 5

    1.5 Motivation . 6

    1.6 Outline of Report .. 6

    Chapter 2 Network Analyzer Overview . 7

    2.1 Network Analyzer Architecture .. 7

    2.1.1 Transmission/Reflection (T/R) Test Set .. 8

    2.1.2 S-parameter Test Set 9

    2.2 Proposed Design Technique . 10

    Chapter 3 Hardware Specifications of SNA 12

    3.1 Computer Microcontroller Interface 12

    3.1.1 Microcontroller Unit .. 12

    3.2 Voltage Controlled Oscillator (VCO) . 14

    3.3 Power Divider .. 15

    3.3.1 Wilkinson Power Divider . 15

    3.4 Directional Coupler . 17

    3.5 Power Detectors 19

    Chapter 4 Software Specifications of SNA 21

    4.1 PC Software and Graphical User Interface (GUI) . 21

    Chapter 5 Conclusions and Future Work .. 23

    Bibliography . 24

  • iii

    List of Figures

    Figure 1.1 Two port network showing incident and reflected waves . 2

    Figure 2.1 Transmission/Reflection (T/R) Test Set Network Analyzer . 8

    Figure 2.2 S-parameter Test Set Network Analyzer . 9

    Figure 2.3 Proposed PC-based Network Analyzer Architecture .. 11

    Figure 3.1 PIC18F4550 pin Configuration . 13

    Figure 3.2 Functional Block Diagram of ADF4350 . 14

    Figure 3.3 T-junction Power Divider 15

    Figure 3.4 Wilkinson Power Divider 16

    Figure 3.5 Directional Coupler 18

    Figure 3.6 Power Detector - MAX4003 pin configuration 19

    Figure 3.7 MAX4003 Output Voltage vs Input Power . 20

  • iv

    List of Tables

    Table 1.1 Cost Survey of Network Analyzers 5

    Table 4.1 Advantages and disadvantages of different Coding Platforms .. 21

    Nomenclature

    VSWR Voltage Standing Wave Ratio

    Vmax, Vmin Maximum and Minimum Voltage Values

    Reflection Coefficient

    T Transmission Coefficient

    ZL Impedance of Load

    ZO Impedance of the Transmission Medium

    IL Insertion Loss

    RL Return Loss

    Efficiency

    S11 Input port Voltage Reflection Coefficient

    S12 Reverse Voltage Gain

    S21 Forward Voltage Gain

    S22 Output port Voltage Reflection Coefficient

  • 1

    Chapter 1

    Introduction

    Microwave and RF Networks are used in a large variety of applications today, and their uses

    will keep increasing in the future with the coming of next generation of networks. It is

    important to understand the properties of these networks as well as the transmission and

    receiving devices. Each of these would have parameters we can theoretically calculate, but

    their practical applications can only be understood once their parameters are measured.

    1.1 Networks and their properties

    The main properties of a network you would capture is the power at any point along with its

    reflection coefficient, transmission coefficient, insertion loss, gain which are best described

    by finding its scattering parameters. As for a high frequency network, there is no proper

    definition for current voltage in the circuit. (They can even be used at lower frequencies

    but since we are dealing with microwave frequency range we limit our calculations to the

    S-parameters)

    Power at a given point is a measurable quantity. The other parameters are described in the

    equations below.

    Reflection coefficient is given by

    =

    +

    Transmission Coefficient T

    T = 1 +

    Efficiency

    =

    =

    |2|

    1| |2

    Return Loss

    RL = -20log | |

  • 2

    Insertion Loss

    IL = 20log |T|

    Voltage Standing Wave Ration: Measures the level of mismatch

    VSWR =

    =

    1+| |

    1| |

    The above equations exhaustively describe the quantities of a given network we would want

    to analyse. In order to simplify the calculation and measurement of these quantities we use

    the two-port method calculating the scattering parameters for the signal. We use matched

    and unmatched loads unlike a normal electric circuit. Quantities are measured in terms of

    power of voltage or travelling waves.

    1.2 Scattering Parameters

    Two port method

    Figure 1.1: Two Port network showing incident and reflected waves

    For a case like the above two-port, the relations between the input and the output ports can

    be shown as the following equation

    Scalar linear gain

    |G| = |S21|

  • 3

    Scalar logarithmic gain

    g = 20 log|S21| dB

    Insertion Loss

    IL = -20 log |S21| dB

    Input Return Loss

    RLin = |20 log|S11|| dB

    Output Return Loss

    RLout = |20 log|S22|| dB

    Reverse Gain (for when we invert the circuit)

    grev = 20 log|S12| dB

    VSWR

    VSWRin = 1+|11|

    1|11|

    1.3 Measurement of S-parameters

    The measurement in case of a given network circuit is the power given by source, power

    reflected and power transmitted of a two-port device. The Device Under Test (DUT) is

    considered a two-port black box and by obtaining its scattering parameters, we can

    characterize it.

    In order to connect the scattering parameters with the power measurements, we can

    observe the following

    From Figure 1.1 of the two-port network we can see

    a1, a2 are normalized incident waves on port 1 and 2 respectively

    b1, b2 are normalized reflected waves on port 1 and 2 respectively

  • 4

    Hence,

    |a1|2 = Power incident on input of the network; Power available from the source

    |a2|2 = Power incident on the output of the network; Power reflected from load

    |b1|2 = Power reflected from the input port of the network; Power available from source

    minus the power delivered to the network

    |b2|2 = Power reflected from the output port of the network; Power incident on the load

    |S11|2 =

    S11 = 1

    1 (if a2 = 0)

    |S22|2 =

    S22 = 2

    2 (if a1 = 0)

    |S21|2 =

    S21 = 2

    1 (if a2 = 0)

    |S12|2 = Reverse Transducer power gain

    S12 = 1

    2 (given a1 = 0)

    Considering we have found the modulus of the S-parameters, we know the values of most of

    the properties of the given device under test (DUT).

    Since we are working on a scalar network analyzer, we plot only the magnitudes of the

    reflection and transmission coefficients and VSWR.

  • 5

    1.4 Network Analyzers Background and Cost Survey

    A network analyzer is an instrument that measure the network parameters of electrical

    networks. It commonly measure S-parameters because reflection and transmission of

    electrical networks are easy to measure at high frequencies. A modern vector network

    analyzer can measure a components magnitude, phase, and group delay, show port

    impedances on a Smith chart, and, with time-domain capability, show the distance from a

    test port to an impedance mismatch or circuit fault.

    Network analyzers commonly measure S-parameters because reflection and transmission of

    electrical networks are easy to measure at high frequencies. Understanding a network

    analyzers capabilities and operation can help an operator derive optimum performance

    from the instrument.

    There are two kinds of network analyzers, depending on the measured s-parameters

    1. Scalar network analyzer (SNA): Measures only the magnitude of the S-parame

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