,"

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SINGLE-PHASE UNIDIRECTIONAL TRANSDUCERS FOR

"LOW-LOSS SURfACE ACOUSTIC WAVE DEVICES

by

~ C.B. SAW. B.Eng .• H.Eng.

A ThesIs

Submftted to the School of Graduate StudIes

In PartIal FulfIlment of the RequIrements

for the Degree

<0' Doctor of' Ph I losophy

July 1988

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SINGLE-PHASE UNIDIRECTIONAL

SURFACE ACOUSTIC WAVE TRANSDUCERS

----_!_---.-DOCTOR OF PHILOSOPHY (1988)

(Electrical Engineering)

McHaster University

HamI , ton. Ont.. canada

TITLE: Single-phase ~Idfrectlonal Transcb:ers for Low-loss

Surface Acoust I c Wave DevI ces

AUTHOR: Choo Beng Saw. B.Eng. (HcKaster)

H.Eng. (HcHaster)

SUPERVISOR: Prof~ C.K. Campbell. Ph.D •• D.Se •• FRSC. FIEEE. FEle. FRSA,

NUHaER OF PAGES: xv. 267

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ABSTRACT

There ha~. been an up~urg~ fn Interest recently' fn lower~'loss

surface acoustfc wave

app J I c\t Jon~ •

,(,SAW) dev f ces for' new signa I . process I ng. ' , ,

(

In this thesis; a·'dew generation of.. unIdirectional

transducers (UDT~) for the realization of low-loss SAW devices has been'.' I

stud I ed I In wh I ch un i direct fona I i ty I s~ effected~. by· exploft fng cohe'rimt. . .

'Internal reflectfons within a transducer.\I

These sf ng.l'e-phase UDTs'

(SPUDTs) offer many' aavantages 'and attract Ions that are unava II ab lei n•

1,\1tc'!Y prev I ous UOT des fgns. Coup I ed-mode 'theory is extens i ~e1Y used to

analyze and characterIze these structures. A general theory Is proposed,'whlch wi 11 guide design' and construction of all SPUDT devices.' This

, .JIncludes specificatIons of the optimum conditions for achieving maximum

directIvIty. An accurate and detailed model is also developed for SPUDTs

wIth Inter-lOT ref1ectors. The mode I accounts for a I I major electrode4'

InteractIon ~fects and Involves the cascade of transfer matrices of~ p

reflectors. transmission I fnes and transducers,. to realize the avera I 1I

response. Experimental verIfications have consistently shown that thl~

model Is very accurate in the analysIs of SPUDTs. I....

Based on a better understanding of the SPUDT concept. several new

SPUDT designs have been developed. SpecIal efforts are expended towar-ds

scqu Iring key propert f es never before obta Ined with SPUOTs. such a\

Improved sidelobe suppression. ,wider bandwIdths and higher oPtr~tlng

,frequencIes. In these respects. the new designs represent a sfgnificant

Ifl

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Improvement over the earlier SPUDT designs.

;.

The final part of the the3ls'

•

. - describes the theory and Qpet:8t..lon of a novel SPUOT-based multlmode

osclUator for frequency.agfle radar. An InnovatIve Injection-locking.'!"'. " .

,scheme Involving FH chlrp-mlxl~g Is. also disclosed. PrelimInary tests

have Indicated very encouraging results including .low phase noise levels

(120 dBc/Hz -@ 10 kHz) t. wide tuning bandwidth (50'1) and fast switching

speeds « 2 us) •

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• CKNOVlEDGE"ENTS.

Th's research wou'ld not have succeeded without Dr.:. C.K.

Can1Jbel 1'5 actIve help, guIdance and encouragement; It fs dIfficult for. ..me to express my thanks adequately:' HIs sUPpOrt and conc~rn are deepl~

:.apprecfated. I am also grateful for the gufdance and counsel received. .

from the other membef"S of my .supervlsory conmfttee, namely, Drs. B.K.# •

Garside, J.P. Ref Ily and D.P. Taylor\' Dr. Campbell and Dr. P.M. Smith/

took time to p~oof-read this thesIs and I than~hem for their helpful

suggestions and crIticisms (mostly kInd and constructIve).

\

P.J.

I Wou I d a 150 I fke to thank my co II eagues, I1r. C. G. Ba f 1ey, Hr., CEcinonson and "s. S. F. Yuen for" the many discuss Ions on the finer

)

thIngs In lIfe, not the least of whIch were noise measurements and other

topIcs of general electrIcal Interest.

The f Inanc I a I support prov I ded by the Goverrvnent of Ontar 10 and

the Department of EI ectr I~I and CQITl)uter Eng I neer I ng I n the fonn of

scho I arsh I ps, teachsJ ng ass I stantsh Ips ctnd bursar I es Is gratefu 11 y

acknowledged.

a I so wIsh to acknowI edge the years of he I p and encouragement

given to me by my parents. In additIon, I wish to thank my fiancee for;

all her encouragement, love and sacrifIces.

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TABLE OF CONTENTS

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CHAPTER I - INTRODUCnON

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I . I Mot Ivat I on for Low- Joss Transducer Study

1.2...

Unidirectional Transducers (UDTs)..,...

5

1.3 Objectives

PART I

.THEORY OF SINGLE-PHASE UNIQIRECTIONAL TRANSDUCERS•

10

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CHAPTER 2 - UNIDIRECTIONAL SAW TR~SDUCTION EXPLOITING

( COHERENT INTERNAL REFLECTIONS

2.1 . Introduct~n

2.2 Theory of Coupled ~des

2.3 Coupled-mode Equations of ~ Periodically

Perturbed Piezoelectric Surface

2.4 Coupled-mode Analysis of lOTs with Enhanced

Internal Reflections"

2.5 The SPUDT Criterion•I ~

2.6 Practical SPUDT Design, (1982-1~85)

2.7 Standing Wave Patterns In SPUDTs

CHAPTER 3~- MODELLING AND SIMULATIONS

3.1 Introduction

vi

) 13 ,

13

14

19

27

37

41

47

50

50

.I/ •

'. ' .. ,.',~ ., ~

~

3.2., ..

interactIon EffectsEYeluatlon of Electr~e 52, .

3.2.1 '~Yer8ge"VelocIty Shfft 53' ,.. :. e ,

"- 3.2.2 ' AcoustJc "Ismatch 56.. ',- .. ' , \',,.' , 3.2.3 Summery of Results ,,58

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3.3 AcoustIc Reflector Gratfn~

t:'-60

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V· 4 Acoustfc Transmlssfon Lfnes - 77..a."5 Interdlgftal Transducers 78

3.5.1 Scatterfng Parameters.of Electrfcallyt.ooded lOTs J 79

• (a) Acoustft Reflection Coefficient 80/ " Acoustfc T,ransmfsslon Coefficient(b) 88

q(c) Acousto-electrlc ConYers~on 88

3.5.2 Scattering Transfer Parameters 89-.'. 3.6 Experimental Verifications ,

101 I

- 3.6. I SPUDT with SplIt-electrode lOTs 10J.>

3.6.2 SPUDT wfth Single-electrode JOTs 102

3.6.3, SPUDT with Bloomfng Reflectors 105

Passband-shifted SPUDT~

3.6.4 107

"3.6.5 Two-port SAW Resonator 110

PART II

NEW SPUDT DESIGNS

PREFACE

CHAPTER 4 - SPUDT TECHNIQUES FOR SPECIALISED FILTERS

113

115

4. 1,

Low-loss Comb FIlters

4.1.1 Theory of SAW Ladder Transducers

4.1.2 Sampled DIstrIbuted Reflector Arrays I

115

116

123

4.2 Low-loss Wfde-band DesIgn

4.2.1 Slanted Reflector Arrays"

4.2.2 Slanted SPUDTs

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130

131

135

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4.3. Low-loss Harmonic-mode Excftatfons

. \ 4~3·.1 The SPUOT Crftetfon~at Harmonlc..Frequencles, ~

4~3.2 Efflcfency of Reflectors at Harmonic'. Frequencf es .

41.3.3 Stepped-electrode SPUDTs for Mode Selectlon

4.4 Passband-sh Ifted F1'1 ters

146

150

153 ."-

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CHAPTER'5 - LOW SIDELOBE DESIGNS '.~. 168

5.1 Wfthdrawal Weighted SPUDT

5.1.1 Time DomaIn CharacterizatIon

5.2 Aperture WeIghted SPUDT

5.2.1 Lfnear Array Hodel

5.2.2 Dolph-Chebyshev Array' Synthesis'

5.2.3 IllustratIve Designs

5.3 Electrically-coupled SPUDTr.

PART III~.

SPUDT-BASED APPLICATIONS

•PR~FACE

CHAPTER 6 - FREQUENCY AGILE SPUDT OSCILLATOR USING FH

< CHIRP-HIXING SIGNAL INJECTION •

168

175

17&

nrl-·181

190

198

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204

201

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6.1 Introduction 201

6.2 Oscillator StabilIty as a Funttlon of InsertIon Loss

of Feedback Element 20e

6.3 Frequency AgIlity UsIng Hultlmode OscIllators 210

6.4 DesIgn of Prototype Oscll18tor

6.4.1 Phase CondItions for Oscfllatlons

6.4.2 Gain Condftlons for Frequency HoppIng

6.4.3 Chlrp-mfxlng Network

vIII

215

215

219

220

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240

223.

229

229233' .~

;/ . ~235 ..

237

237

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Frequency Swftchfng Speed

Short Term Stabf 1Ity

. (8)\ Phase Noise Spectral Density\ .

(b) Time Domain StabI 1fty.,

"e~fum T~rm Stability

Beat-frequency Spectra I~ Dr f yenUn locked State

6.5.4

6.5.5

.,.6.5 Osc" lator Perfo~mance

6.5.1 Locking Bandwidth

6.5.2.. 6..-5.3

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"CONCLUSION AND APPENDICES

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CHAPTER 7 - CONCLUDING REMARKS .

APPENOIX A - EQUIVALENT FORMS OF SAW COUPLED-HODE EQUATIONS

246

251

APPENg IX B - DOLPH-CHEBY~HEV ARRAY SYNTH~S 1-5 PROCEDURE 254

APPENDIX C - REFERENCES 260

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SAW reflector grating 66

Reflection magnitude for 200 AI strips on ST-X Quartz 72

Single reflector 6(Equivalent circuit

Reflection coefficient Vs. Number of strl~s

on ~T-X Quartz 73

54,

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2

4

9- -

16

17 ...21

26.~.' ,.,30

33

36

38

43

49

. .LisT QF FIGURES.

Hechanism of acoustic mismatchSimple equivalent circuit representation

Varlatlon of directivity in a SPUDT

Expanded view of SPUDT section

Group-type SPUDT with unshorted reflectorsGroup-type SPUDT with shorted reflectorsGeneral SPUDT with unshorted reflectors

General SPUDT using split-finger lOT

Some practical SPUDT designs

First order SAW grating dispersion diagram

General SPUDT structure

Periodically pertur~ed substrate

Basic SAW. device

Plot10f minimum TTl level Vs. inser\lon loss

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"Some low-loss techniques

~llcatfons of OFBs

General DFB structure

1 .'. ,.~

Figure,;.

1• I_.. - .1.2 ~

1.3I\

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

2.10(a)(b)(c)

3.I(a)(b)

3.2(q)(b)

3.3

3.4

3.5(a)

x

. .3.SCb

3.6(8) .(b)

(c)•. Cd} •

•3.7(8)

Jb}(c)

3.S 7

3.9(a) .

(b)

•.:-: .. '... :'.

Reflec~lon coefficient Vs. Number of str(p~on 128 YX-LINb0

3

Grating resonator.~lltude responses ef grating fl Iter comput~ usfnq.·the coupled-mode~ndmodified equivalent circuIt models

,CorrespondIng e)(per Imenta I response '.Refrectlvlty responses of gratings using 2 models

EV8J~atfon of regeneration effectsEqul~lent circuit Of lOT'Eva luat Ion of edge ref I ect Ions .

3-port lOT

Computed. short-cIrcuit reflectivity responses 'ofsingle-electrode and ::plit-electrode lOTsCorresponding experimental results from [54]

73

75

76

82

90

96

97

99

3.10(a)

(b),

3.1I(a)

( 0)

3.12(a)

(b)

. 3. J3

Computed open-circuit reflectivity responses ofsingle-electrode and split-electrode lOTsCorresponding experimental results from '[54]

Amplftude-f,requency responses of SAW filter usingsIngle-electrode and splft-electrode lOTsFInger reflections between two lOTs

A~I ftude response of SAW ff Iter on 1280 YX-L INb03using single-electrode lOTs 100

Same fIlter on ST-X Quartz

Responses of low-loss SAW device usIng group-type SPUDTs 103(a) Experimental responses reported by Lewfs[IO](b) Corresponding theoretical amplitude response

3.14

3.15(a)(b)(c)

3.16

AmplItude responses of SAW filter using SPUDTs withsIngle-electrode lOTs(a) ExperImental response(b) Correpondfng theoretical response

SPUDT wfth blooming reflectors.,Experlmental response of spuor filter on ST-X Quartz

TheoretIcal response

Amplitude responses of passband-shifted filters usingmodIfied SPUOTs(a) TheoretIcal response computed using latest

SPUDI model(b) ExperImental response(c) Theoretical response computed using "old"

SPUDT model

xl

104

106

108

fIlter

, ,3.17

3.18(a) .(b)

.4.1

4.2

4.3

4.4(a}(b) ,

4.5

4.6

4.7 :,..4.8{a}

(b)

4.9

4. 10

4. II

4.12

4.13

4.14

4. 15

Phas~ respOnses of passband-shffted filter(a) Exper fmenta I respOnse(b) Theoretfcal respOnse ~

Amplftbde and phase resPonses of 2-pOrt SAW resonatorCorrespOnding experfmental respOnses

Basfc M-rung ladder transducer.

Phasor analysfs of 3-rung comb

Sampl'ed ~eflector array

Reflectlvfty respOnse of sampled reflector arrayReflectivity response of conventional grating

Amplitude responses of low-loss comb filter(a) Theoretical response(b) Experimental response

Wide-band sweep of the low-loss comb filter response

Slanted reflector array

Overall reflectfvlty response of a 9-channel slantedreflector gratingRe~lectfvity response of a conventional grating fora IO~ reflectivfty ban~ldth

•Section of slanted SPUDT

Responses of 6~ 'bandwldth low-loss SAW filter usingslanted SPUOTs{a} Theoretfcal response(b) Experfmental responses

Computed amplitude response of IO~ bandwIdth low­loss fflter

Measured responses of IO~ bandwfdth 10W~OSS(a) Amplftude and group-delay responses(b) Expanded dfsplay of amplftude ·response

Hodiffed floatlng-electrpde SPUDT

Amplitudes of spatial harmonics as a function ofmetallization ratio In a single-electrode IOT{?7)

3rd and 7th harmonic responses of fEUDT-baseo filter(a) 3rd harmonic response(b) 7th 'harmonic response

109

112

118

IZZ

124

125

127

129

132

134

136

141

143

144

147

149

152

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f xII

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4.16 •

4.17(a)

(b)

4.16

, 4. 19

4.20

5. I

5.2(a)(b)(c)

5.3(a)

(b)

5.4

5.5(a)(b)

5.6(a)(b)

5.7

5.8

5.9

. Var·fatlon of arpplltude dfrectlvftfeswfth electrodewIdths for sl,ngle metal strip on YZ-L~Nb03

Measured,amplltude response of FEUDT-based filter.showIng the Ist~ 3rd and 5th harmonfcMeasured response of stepped-e' ectrode SPUDT f_. Iter

Stepped-e Iectrode SPUDT'•

5th harmonIc and 1st harmonic responses of stepped­-e1ectrode SPUDT f II ter 1\(a) 5th harmonIc response(b) 1st harmonIc (fundamental) response

.Design chart showing variation of normalized frequencyshift wIth SPUDT spacing d

1-

Amplitude responses of passband-shifted SPUDT filter'(al TheoretIcal response(b) ExperImental response

Schematic of withdrawal weighted SPUDT

Amplitude respo~se of a SAW filterWIthdrawal weightIng by selective removal electrodesAmplftude response of withdrawal weIghted SPUDT filter

Measured amplitude response of withdrawal weightedSPUOT filterMeasured amplItude response of filter using conven­tional groupe-type SPUOTs

Test set-up for time domaln,studles of SPUOTs

Impulse response of withdrawal weighted SPUOT filterCorrected frequency response after time-gating

~

Antenna array of H ~ubarrays

The acoustic analogue

AmplItude responses of a SPUOT comb filter(a) Experimental response(b) Computed response us:ng lInear array model

Computed frequency responses of weighted andunwelghted element factors

Amplitude responses of SPUOT comb filter with flatwide-band envelopes(a) Theoretical response(b) Experimental response

xffl

154

156,

)

158....,

160 \

164

167

169

171

173

176

177

180

183

186

5.10(a),.­(b)

5. II

5.12(a)(b)

Computed values of aperture weights for 35 ,dB side lobesComputed.amplltuijeresponse of a SAW Dolph-Chebyshev'ladder transducer wfth, 35 dB sfdelObe 'suppresslon .

Amplitude responses of aperture weighted SPUOT fflt~

(a) Theoretical response C-(b) ExperImental response

Impulse response of aperture wefghted SPUOT·fllterCorrected frequency response after time gating

188

189

191

193

5.13 Artwork of prototype's mask showing aperture weightedInput SPUOT and'unfform output SPUOT 194

'5. 14 Amp I Itude responses of aperture we f ghted comb f I Iter 191(a) TheoretIcal response(b) ExperImental response

5.15 Impulse response of aperture weighted SPUDT comb filter 197

5. 16 EIectr Ica I Iy-coup Ied SPUOT 199

5.17 Amplitude responses of electrically-coupled SPUDT filter ,202(a) Theoretical response(b) Experimental response

5.18

P.ICa)(b)

P.2

6. I

6.2(a)(b)

6.3

6.4

6.5(a)(b)

6.6(a)(b)

6.7

6.8

Impulse response of electrically-coupled SPUDT filter

Descrambler blodK diagramChannel 3 audio SPUDT filter

Frequency agile radar sys~em

theoretical and experimental phase noise spectra ofa SAW oscillator

. Varactor-tuned coot:> osc·11 IatorInJection-locked comb oscillator

Prototype frequency agile SPUDT oscillator

Measured amplitude response of SPUDT comb fl Iter

Basic chirp-mixing networkTypical chirp mixer output spectrum

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Measured oscillator output spectrum for 80 "Hz modeMeasured oscillator output spectrum for 100 MHz mode

Measured oscillator output spectrum for 70 MHz mode

Convex parabo I Ie enve Iope for clean modes

xlv

203

206

206

211

214

216

218

221

225

226

227

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