Urn 100730

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Antenna

Text of Urn 100730

  • Antenna tuning for WCDMA RF front end

    Reema Sidhwani

    School of Electrical Engineering

    Thesis submitted for examination for the degree of Master ofScience in Technology.

    Espoo 20.11.2012

    Thesis supervisor:

    Prof. Olav Tirkkonen

    Thesis instructor:

    MSc. Janne Peltonen

    A Aalto UniversitySchool of ElectricalEngineering

  • aalto universityschool of electrical engineering

    abstract of themasters thesis

    Author: Reema Sidhwani

    Title: Antenna tuning for WCDMA RF front end

    Date: 20.11.2012 Language: English Number of pages:6+64

    Department of Radio Communications

    Professorship: Communication Theory Code: S-72

    Supervisor: Prof. Olav Tirkkonen

    Instructor: MSc. Janne Peltonen

    Modern mobile handsets or so called Smart-phones are not just capable of commu-nicating over a wide range of radio frequencies and of supporting various wirelesstechnologies. They also include a range of peripheral devices like camera, key-board, larger display, flashlight etc. The provision to support such a large featureset in a limited size, constraints the designers of RF front ends to make compro-mises in the design and placement of the antenna which deteriorates its perfor-mance. The surroundings of the antenna especially when it comes in contact withhuman body, adds to the degradation in its performance. The main reason forthe degraded performance is the mismatch of impedance between the antenna andthe radio transceiver which causes part of the transmitted power to be reflectedback. The loss of power reduces the power amplifier efficiency and leads to shorterbattery life. Moreover the reflected power increases the noise floor of the receiverand reduces its sensitivity. Hence the over performance of the radio module interms of Total Radiated Power and Total Isotropic Sensitivity, gets substantiallydegraded in the face of these losses.This thesis attempts to solve the issue of impedance mismatch in RF front-ends byintroducing an adaptive antenna tuning system between the radio module and theantenna. Using tunable reactive components and by intelligently controlling themthrough a tuning algorithm, this system is able to compensate the impedance mis-match to a large extent. The improvement in the output power and the reductionin the Return Loss observed in the measurements carried out for WCDMA, aspart of this thesis work, confirm this. However, the antenna tuner introduces aninsertion loss and hence degrades the performance in perfect match conditions.The overall conclusion is that the adaptive antenna tuner system improves theperformance much more than it degrades it. Hence it is an attractive solution tobe included in mobile terminals on a commercial scale.

    Keywords: front end, impedance mismatch, antenna tuner, measurement re-ceiver, adaptive tuning, reflection coefficient

  • iii

    Preface

    Now that the daunting task of developing an antenna tuner system in ST-Ericssonhas come to a conclusive point, I cant help but wonder how I would have managedto come this far without the help, encouragement and guidance of my colleagues inTurku, Lund and Nuremberg offices. Most of all I would like to thank my instruc-tor Janne Peltonen for his useful insights and for sharing his knowledge with me.Also, my sincere thanks to Jean-Louis Mendes, Michael Hirschmann, Joerg Meiss-ner, Christina Grapsa, Bjorn Gustavsson and Jari Horkko. Next, I would like tothank my supervisor Prof. Olav Tirkkonen. His suggestions and corrections madea tremendous difference to the shape this thesis has taken.

    I would like to express my heart felt gratitude to my friends in Finland, not justfor their friendship but also for encouraging me to explore the unknown. Withoutyou I would not have made it. Thanks for making my life here filled with fun andhappiness.

    Last but not the least, I want to thank my family for their love and trust andfor constantly supporting me in all my decisions.

    Otaniemi, 20.11.2012

    Reema Sidhwani

  • iv

    Contents

    Abstract ii

    Preface iii

    Contents iv

    Abbreviations vi

    1 Introduction 11.1 Motivation for the research . . . . . . . . . . . . . . . . . . . . . . . . 1

    1.1.1 Impedance mismatch . . . . . . . . . . . . . . . . . . . . . . . 11.1.2 Antenna tuning . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1.3 Impedance Tuner . . . . . . . . . . . . . . . . . . . . . . . . . 5

    1.2 Objective and goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.3 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

    2 Background 82.1 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

    2.1.1 Impedance matching . . . . . . . . . . . . . . . . . . . . . . . 82.1.2 LC Impedance Matching Networks . . . . . . . . . . . . . . . 92.1.3 Binary capacitance array . . . . . . . . . . . . . . . . . . . . . 122.1.4 Measuring parameters . . . . . . . . . . . . . . . . . . . . . . 13

    2.2 Antenna Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . 152.2.1 Antenna Characteristics . . . . . . . . . . . . . . . . . . . . . 162.2.2 Antenna types . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.2.3 Design issues . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

    2.3 Building Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182.3.1 Adaptive Antenna Tuner . . . . . . . . . . . . . . . . . . . . . 192.3.2 Bidirectional Coupler . . . . . . . . . . . . . . . . . . . . . . . 192.3.3 Measurement Receiver . . . . . . . . . . . . . . . . . . . . . . 212.3.4 MIPI RFFE interface . . . . . . . . . . . . . . . . . . . . . . . 212.3.5 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222.3.6 Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

    3 Design and implementation concept 243.1 Reflection coefficient tracking . . . . . . . . . . . . . . . . . . . . . . 24

    3.1.1 Coexistence with other control algorithms . . . . . . . . . . . 263.2 Impedance calculation . . . . . . . . . . . . . . . . . . . . . . . . . . 28

    3.2.1 Equation based algorithm . . . . . . . . . . . . . . . . . . . . 283.2.2 Gradient Search algorithm . . . . . . . . . . . . . . . . . . . . 313.2.3 Hill Climbing algorithm . . . . . . . . . . . . . . . . . . . . . 33

    3.3 Common algorithm control . . . . . . . . . . . . . . . . . . . . . . . . 353.3.1 Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . 353.3.2 Antenna tuner state machine . . . . . . . . . . . . . . . . . . 36

  • v3.4 Timing considerations . . . . . . . . . . . . . . . . . . . . . . . . . . 413.4.1 RAT specific timings . . . . . . . . . . . . . . . . . . . . . . . 423.4.2 MIPI RFFE timings . . . . . . . . . . . . . . . . . . . . . . . 44

    3.5 Performance degradation considerations . . . . . . . . . . . . . . . . . 453.5.1 Error Vector Magnitude . . . . . . . . . . . . . . . . . . . . . 453.5.2 Linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.5.3 Insertion loss . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.5.4 Reflection coefficient accuracy . . . . . . . . . . . . . . . . . . 46

    4 Performance and measurements 484.1 Implementation and measurement set-up . . . . . . . . . . . . . . . . 48

    4.1.1 Chosen control algorithm . . . . . . . . . . . . . . . . . . . . . 484.1.2 Chosen antenna parameters . . . . . . . . . . . . . . . . . . . 494.1.3 Chosen frequencies . . . . . . . . . . . . . . . . . . . . . . . . 49

    4.2 Lab set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504.2.1 Radio module and antenna tuner . . . . . . . . . . . . . . . . 504.2.2 Load-pull tuner . . . . . . . . . . . . . . . . . . . . . . . . . . 504.2.3 Network Analyzer . . . . . . . . . . . . . . . . . . . . . . . . . 514.2.4 Radio Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

    4.3 Measurement results . . . . . . . . . . . . . . . . . . . . . . . . . . . 514.3.1 VSWR and S11 . . . . . . . . . . . . . . . . . . . . . . . . . . 514.3.2 Output power . . . . . . . . . . . . . . . . . . . . . . . . . . . 524.3.3 EVM and ACLR . . . . . . . . . . . . . . . . . . . . . . . . . 52

    4.4 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

    5 Conclusion 575.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605.3 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

    References 62

  • vi

    Abbreviations

    RF Radio FrequencyRAT Radio Access TechnologyMIPI Mobile Industry Processor InterfaceGSM Global System for Mobile CommunicationsWCDMA Wideband Code Division Multiple AccessLTE Long Term EvolutionFDD Frequency Division DuplexingTDD Time Division DuplexingSMA SubMiniature version ALO Local OscillatorPA Power AmplifierLB Low BandHB High BandBB BasebandADC Analog to Digital Converter3GPP Third Generation Partnership Project

  • 1 Introduction

    The fastest growing segment in consumer electronics is that of Smart-phones andTablet PCs. Key features of these devices are ubiquitous communication, contin-uous access and small size without compromising on the battery life. Consumersdemand faster and uninterrupted internet connection as the need to be connectedanytime and anywhere continues unabated. While the thirst of higher transmissionrates driven by the high resolution images, videos and sound data remains unquench-able, another trend that has been growing at equal pace in the telecom industry isto include more and more functionality in the mobile handsets. Todays wirelesshandsets are not just expected to communicate over a wide range of frequencies andmodulation schemes with