l reflector antenna system with a multimode · pdf file a two-channel monopulse reflector...

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A TWO-CHANNEL MONOPULSE REFLECTOR ANTENNA SYSTEM -

WITH A MULTIMODE LOGARITHMIC SPIRAL FEED /

GPO PRICE $ 1

1 CFSTI PRICE(S) $ 1 I .

Hard copy (HC) 2/50 ~

ff 663 July 66

' JUNE 1966

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https://ntrs.nasa.gov/search.jsp?R=19670002033 2020-03-21T00:41:08+00:00Z

- b X-525-66-262

A TWO-CHANNEL MONOPULSE REFLECTOR ANTENNA SYSTEM

WITH A MULTIMODE LOGARITHMIC SPIRAL FEED

Paul A. Lantz Advanced Development Division

June 1966

GODDARD SPACE FLIGHT CENTER Greenbelt, Maryland

A TWO-CHANNEL MONOPULSE REFLECTOR ANTENNA SYSTEM

WITH A MULTIMODE LOGARITHMIC SPIRAL FEED

Paul A. Lantz Advanced Development Division

ABSTRACT

It is possible to excite multiarm planar logarithmic spiral an- tennas in various modes. These antennas can be used to feed re- flectors for monopulse tracking and space data acquisition. This report reviews the basic theory of operation of these antennas, ex- pands i t , and describes a two-channel monopulse antenna system usinga feed of this type. It also describes performance of an oper- ational 85-foot diameter reflector antenna and discusses limitations of performance capability. Feeds of this type a re shown to provide increased efficiency for paraboloidal reflector antennas, improved tracking capability, and simplicity of design.

iii

CONTENTS

Page

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PLANAR LOG SPIRAL ANTENNA . . . . . . . . . . . . . . . . . . . . . . . . 2 MODAL EXCITATION OF MULTIARM LOG SPIRALS . . . . . . . . . . . 4 TIROS OPERATIONAL SATELLITE (TOS) ANTENNA REQUIREMENTS 6

REFLECTOR FEED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Choice of Feed Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spiral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cavity Reflector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Theoretical Phase Center . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impedance Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 11 11 13 14

15 TWO-CHANNEL MONOPULSE SYSTEM . . . . . . . . . . . . . . . . . . . . .

RFSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excitation Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15 18

ANTENNA PERFORMANCE RESULTS . . . . . . . . . . . . . . . . . . . . . . 23 23 28 42 42 42 45 47

Primary Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Secondary Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gain and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impedance Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . Wave Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Boresight Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tracking Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49 FUTURE PLANS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . c

49 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

V

CONTENTS (con't)

Page

ACKNOWLEDGMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 APPENDIX - Performance Capability Limitations of Crossed Dipole Fed

Reflectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

c

vi

ILLUSTRATIONS

Figure

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1 7

Page

Log Spiral Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Stylized Sketch of Dual Four-Arm Planar Log Spiral Showing Defining Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Typical Reactive Near-Field Modal Excitation Across a Four- 5 Arm Log Spiral, a = 86" . . . . . . . . . . . . . . . . . . . . . . . . 7 Excitation Network for Four-Arm Log Spiral . . . . . . . . . . .

Typical Radiation Patterns of a Four-Arm Log-Spiral Antenna for Each Excitation Mode . . . . . . . . . . . . . . . . . . . . . . . . 8 Comparison of Reflector Illumination Contours Assuming Equal Difference Patterns for Dipole and Log-Spiral Feeds . . . . . 10 Distribution of Modal Excitation Across Spiral . . . . . . . . . . 12

13 Cavity Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . TOS-Wallops Antenna R F System ......................... 16 Phase Relationships Between First (x) Mode and Second ( A ) Mode for Right-Circular Wound Spiral . . . . . . . . . . . . . . . 18 Typical Excitation Matrix, Block Diagram . . . . . . . . . . . . . 19 Performance of Printed-Circuit Hybrid Junctions . . . . . . . . 20 Performance of 90-Degree Phase Shifter . . . . . . . . . . . . . 20

Printed- Circuit Diplexers . Schematic . . . . . . . . . . . . . . . . 21 Performance of Printed-Circuit Diplexers . . . . . . . . . . . . . 22 2.5:l-Scale Model of Feed . . . . . . . . . . . . . . . . . . . . . . . 23 Full-scale Feed with Al l RF Printed-Circuit Boards . . . . . . 24

vii

ILLUSTRATIONS (con't)

Figure

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Page

Primary Pattern-136.5 Mc ...................... 24 Primary Pattern-235 Mc ........................ 25

25 Primary Pattern-406 Mc . . . . . . . . . . . . . . . . . . . . . . . . Primary Pattern Gain .......................... 26 Feed Being Installed into Reflector . . . . . . . . . . . . . . . . . 29 Closeup of Feed Installed at Focus of Reflector . . . . . . . . 29

Theoretical Secondary Pattern-136.5 Mc . . . . . . . . . . . . . . 31 Theoretical Secondary Pattern-235 Mc . . . . . . . . . . . . . . . 32 Theoretical Secondary Pattern-406 Mc . . . . . . . . . . . . . . . 33 Measured Secondary Pattern-136.5 Mc . X-Cut . LHC Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Measured Secondary Pattern-136.5 Mc . Y.Cut. LHC Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Measured Secondary Pattern-136.5 Mc . X.Cut. RHC Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

30 Measured Secondary Pattern-136.5 Mc . Y-Cut . RHC Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

31 Measured Secondary Pattern-235 Mc. X-Cut . LHC Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

32 Measured Secondary Pattern-235 Mc. Y.Cut. LHC Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

33 Measured Secondary Pattern-235 Mc . X-Cut . RHC Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

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Figure

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A- 1

A-2

A- 3

ILLUSTRATIONS (con't)

Page

Measured Secondary Pattern-235 Mc, Y-Cut, RHC Polarization . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . Sum Channel Input Impedance . . . . . . . . . . . . . . . . . . . . . Difference Channel Input Impedance . . . . . . . . . . . . . . . . . Comparison of RF and Optical Boresight Axes . . . . . . . . . .

Primary Feed Tracking Records-136.5 Mc . . . . . . . . . . . . Primary Difference Pattern Illumination, Four-Dipole Mono- pulse Feed . . . . . . . . . . . , , . . . . . . . . . . . . . . . . . . . . . Primary Sum Pattern Illumination, Four-Dipole Monopulse Feed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparison of Primary Patterns and Classic Aperture Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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48

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ix

TABLES

Table

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9

A- 1

A-2

Page

Anticipated Antenna Temperature for Log-Spiral Reflector Pointed at Quiet Sky at 1700 Mc . . . . . . . . . . . . . . . . . . . . . 9 Performance Characteristics of Printed-Circuit RF Matrix . . 21 Reflector Edge Illumination . . . . . . . . . . . , . . . . . . . . . . . 26 Primary Pattern Polarization Ellipticity . . . . . . . . . . . . . . . 27 Primary Difference Pattern RF Boresight Er ror . . . . . . . . . 27 Computed Secondary Pattern Boresight Er ror . . . . . . . . . . . 28 Axial Ratio of Sum Pattern Polarization Ellipse . . . . . . . . . 45 Measured Shift of RF Boresight