Effects of a tapered pitch helix on traveling wave amplifier performance

137 Pages·2015·3 MB·English

by  Glenn T. Eksaa

Lehigh University
Lehigh Preserve
Theses and Dissertations
1991
Effects of a tapered pitch helix on traveling wave
amplifier performance
Glenn T. Eksaa
Lehigh University
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Recommended Citation
Eksaa, Glenn T., "Effects of a tapered pitch helix on traveling wave amplifier performance" (1991).Theses and Dissertations.Paper 13.
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Effects of a Tapered pitch Helix
on
Traveling Wave Amplifier Performance
by
Glenn T. Eksaa
A Thesis
Presented to the Graduate Committee
of Lehigh University
in Candidacy for the Degree of
Master of Science
in
Electrical Engineering

ACKNOWLEDGEMENTS
The author wishes to express his gratitude to the staff of
ITT Electron Technology Division for encouragement, guidance
and for making their facilities available to complete this
project.
• • •
1//
TABLE OF CONTENTS
i. Abstract 1
1•0 Introduction 3
2.0 Operation of a Traveling Wave Tube 6
2 •1 General Characteristics 6
2.2 Theory of Operation of a Traveling Wave 13
Tube
2.2.1 The slow Wave Structure 15
2.2.2 The Linear Theory 16
2.3 Linear versus Non-linear Systems 23
2.4 The Non-linear Model 30
2.5 Improved Non-linear Model 36
3.0 Computer Programs for Large Signal Analysis 43
3.1 Rowe One-dimensional Large Signal 44
Analysis Program
3.2 Modifications to the Rowe Program 57
3.2.1 possible solutions to Enhance 58
Interaction
3.2.2 Automatic Computer Selection of 59
Helix pitch
3.2.3 Results of the Modified Program 63
3•3 Sununary 70
4.0 Theoretical Results for an Actual Traveling 71
Wave Tube
4.1 Introduction 71
4.2 Traveling Wave Tube Description 71
4.3 The F-2205 Tube with a Uniform pitch 74
Helix
•
IV
4.4 A Computer Selected Velocity Taper 81
4.5 A Second Method of Selecting a Velocity 87
Profile
4.6 Third Helix Design 92
4.7 Converting the Profile of b(y) Into a 92
Helix pitch Profile
4. 8 Additional Data Collected 95
4.9 Conclusion 97
5.0 Experimental Results on a Ku-Band Traveling 99
Wave Tube
5. 1 Introduction 99
5.2 Incorporating Helix Design Changes in the 99
F-2205
5.3 Actual Tube Performance 101
5.3.1 Comparison of Small Signal Gain 101
Data
5.3.2 Comparison of rf output Data 104
5.3.3 Comparison of Efficiency Data 106
5.4 Discussion 109
5.5 Summary 112
6.0 Summary of a Helix Taper Design 115
6.1 Introduction 115
6.2 Steps in Designing a Helix Taper 115
6.3 Discussion 118
7.0 Conclusion 119
Vita 125
v
LIST OF TABLES
TABLE
4.1 Values of band C for the Single pitch Helix 77
.
VI
TABLE OF FIGURES
FIGURE
2.1 Traveling Wave Tube Cross Section 7
2.2 Slow Wave Structure Cross Section 11
2.3 Electron Bunching Illustration 17
2.4 Slow Wave Structure Model 18
2 . 5 Transfer Curve 24
2.6 Eulerian Flight-Line Diagram J..n z, t coordinates 26
2.7 Eulerian Flight-Line Diagram in y, 0 coordinates 26
2.8 Lagrangian Flight-Line Diagram 29
2.9 Maximum Efficiency versus Injection versus 35
Injection Speed
2.10 A(y) versus 'y' with Second Hump After 35
Saturation
3.1 Electron Phase Diagram for Single pitch Helix 46
3.2a A(y) versus y', Iteration = 0.2 Inches 48
=
3.2b A(y) versus 'y', Iteration 0.4 Inches 48
3.3 Rf Power Level versus Distance 'y' 50
3.4 Phase Lag of rf Wave to Electron Stream 54
versus 'y'
3.5 Electron Phase Diagram for Single pitch Helix 56
3.6 Flowchart of Rowe Program with Added Subroutine 64
3.7 Electron Phase Diagram for Single Pitch Helix 68
3.8 Electron Phase Diagram for Computer Selected 68
Taper
3.9 b(y) versus 'y' for the Computer Selected Taper 69
3.10 A(y) versus 'y' for the Computer Selected Taper 69
4.1 F-220S Traveling Nave Tube 72
-r
VI(
FIGURE
4.2 Saturated rf Output Power for Single pitch Helix 75
4.3 Small Signal Gain for Single pitch Helix 75
4.4 A(y) versus 'y' for Single pitch Helix 79
4.5 Electron Phase Diagram for Single pitch Helix 79
4.6 Electron Phase versus Axial Distance 80
4.7 A(y) versus 'y' for Computer Selected Taper 83
4.8 Electron Phase Diagram for Computer Selected 83
Taper
4.9 b(y) versus 'y' for the Computer Selected 85
TaPer
,
4.10 b(y) versus y for several Scaled Tapers 86
,
4.11 A(y) versus y for Scaled Tapers 86
4.12 b(y) versus 'y' for Constant Impedance Case 90
4.13 b(y) versus 'y' for Realistic Impedance Case 90
4.14 New Reduced Height TaPer Diagram 93
4.15 Electron Phase Diagram for Reduced Height 93
TaPer
4.16 A(y) versus 'y' for All Three Helix Designs 94
4.17 Electron Velocity Spread versus 'b' for 96
All Three Helices
4.18 Predicted small Signal Gain 96
5.1 Slow Wave structure Cross Section 100
5.2 Helix Turns per Inch 102
5.3a Predicted Small Signal Gain 103
5.3b Actual Small Signal Gain Performance 103
5.4 Actual rf Saturated Output Power 105
5.5 Overall Tube Efficiency ve.r.s.us Frequency 107
VIII