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AND I^-BAND TRACKING FEED for a TORS REFLECTOR ANTENNA Tradeoff Study JC Pullara, CW Bales, GP Kefalas and M. Uyeh

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AND I^-BAND TRACKING FEED for a TORS REFLECTOR ANTENNA Tradeoff Study JC Pullara, CW Bales, GP Kefalas and M. Uyeh https://ntrs.nasa.gov/search.jsp?R=19750002240 2020-03-23T03:25:59+00:00Z DUAL S- AND I^-BAND TRACKING FEED FOR A TORS REFLECTOR ANTENNA Tradeoff Study J.C. Pullara, C.W. Bales, G.P. Kefalas and M. Uyehara Martin Marietta Aerospace Corporation P.O. Box 5837 Prlando, Florida 32805 August 1974 Final Report (Phase I) for Period-August 1973 - June 1974 Prepared for NASA GODDARD SPACE FLIGHT CENTER Greenbelt, Maryland 20771 •"«!*W•i • Report No. 2. Government Accession No. 3. Recipient's Catalog No. Final (Phase I) j Title and Subtitle 5. Report Date l DUAL S- AND Ky-BAND TRACKING FEED FOR A TORS August 1974 I REFLECTOR ANTENNA 6. Performing Organization Code Author(s) Joseph C. Pullara, C. William Bales, 8. Performing Organization Report George P. Kefalas, and Masao Uyehara No. OR 13,225 Performing Organization Name and Address 10. Work Unit No. Martin Marietta Aerospace Corporation P.O. Box 5837 Orlando, Florida 32805 11. Contract or Grant No. NAS5-20415 13. Type of Report and Period Covered Sponsoring Agency Name and Address Phase I Final Report NASA, L.R. Dod (Project Manager) August 1973 - June 1974 GODDARD SPACE FLIGHT CENTER 14. Sponsoring Agency Code Greenbelt, Maryland 20771 Supplementary Notes Abstract This report presents the results of a trade study designed to identify a synchronous satellite antenna system suitable for receiving and trans- mitting data from lower orbiting satellites at both S- and Ku-bands simul- taneously as part of the Tracking and Data Relay Satellite System (TDRSS). The study addresses all related problems associated with maintaining a data link between two satellites with a Ku-band half-power beamwidth of 0.4 dB. Specifically, the study addresses data link maintenance techniques, beam pointing accuracies, gimbal and servo errors, solar heating, angle tracking schemes, acquisition problems and aids, tracking accuracies versus SNR, antenna feed designs, equipment designs, weight and power budgets, and detailed candidate antenna system designs. Key Words (Selected By Author(s) 18. Distribution Statement Satellite antenna Auto tracking Dual frequency '' Acquisition Erectable reflectors Monopulse feed Beam steering Security Classif. (of this report 20. Security Class.(of this page) 21. No. of 22. Price* Unclassified Unclassified Pages 350 PREFACE The purpose of this task is to define the optimum antenna system for the synchronous altitude Tracking and Data Relay Satellite (TDRS) Antenna for communication with lower orbit user spacecraft, and to demonstrate its performance through evaluation of a breadboard model of the antenna. The antenna system shall include the reflector, feeds, pointing mechanism, and tracking subsystems. This effort is divided into two phases. Phase I (reported herein) is a tradeoff study of con- ceptual antenna systems to determine one or more preferred designs for optimization of communication capability consistent with minimizing the equipment and complexity of TDRS. Phase II is the detailed hardware design, fabrication, test, and delivery of the preferred design for a reflector with minimum diameter of 12.5 feet. The S- and Ku-band beams simultaneously generated in the 12.5 foot reflector antenna must be steered throughout a 30-degree cone centered on the local radius. Four S-band options were addressed relating to the capability to independently steer the S-band beam relation to the Ku-band beam and the auto tracking capability of the S-band feed system. The tradeoff study involved detailed analysis on beam pointing via ground commands, auto tracking, acquisition, SNR impact, angle sensing feed systems, mechanical designs, weight, and power consumption. The preferred candidate recommended for Phase II breadboard design and testing is a 12.5 foot erectable reflector system of the cassegrain design. The Ku-band feed is located at the secondary focal point and is comprised of a five- horn array. The center horn is optimized to achieve the required gain and is used only for data reception and transmission. The other four horns are configured as a monopulse array for angle sens- ing and auto tracking. The tracking array is defocused in order to generate a wider field of view -required for acquisition of the user satellites. The S-band feed is a simple cupped helix antenna located at the primary focal point of the reflector. Both feeds can operate simultaneously due to the dual frequency characteristics of the dichroic subreflector. Both S- and Ku-band beams are fixed with respect to the reflector and are steered by gimballed movement of the complete reflector relative to the satellite. 11 CONTENTS 1.0' Introduction 1 2.0 Summary 7 3.0 Preferred Antenna System Candidates 11 3.1 Option I Candidate 11 3.2 Option II Candidate '. • 32 3.3 Option III Candidate 44 3.4 Option IV Candidate 56 3.5 Weight Budget - All Options 61 3.6 Performance Summary for Preferred Candidates 61 4.0 Supporting Analysis . 68 4.1 Basic S-Band Antenna Options and Implementation Require- ments 68 4.2 Data Link Maintenance . 79 4.3 Designation and Aided Designation 82 4.4 Methods for Determining Data Channel Gain Reduction Due to Data Beam Pointing Errors 95 4.5 Main Reflector and Feed Configurations 123" 4.6 Angle Tracking Receivers - Evaluation and Selection. ... 171 4.7 Data Signal Loss Resulting from Beam Pointing Errors . 203 4.8 Characterization of Designation and Aided Designation Methods ....... 212 5.0 Recommendations for Additional Effort 243 5.1 Defocused K -Band Feed Effort 244 u 5.2 Field-of-View of Auto Tracking System 244 5;3 Off-Axis S-Band Operation 245 or Appendixes A. The Effects of Pre/Post-Comparator Phase/Amplitude Unbalance in a Sum and Difference Monopulse System . >-.. ...... 251 B. Servo Design Concept and Characteristics . 263 C. Tracking Velocity and Acceleration . _• • • .T" . 269 ill .D. Angular Beam Pointing Error which Results from S-Band Feed Positioning Error .................. 277 E. A Survey of Reflector Antennas ........ 281 F. Summary and Critique of Radiation, Inc.'s, Report on a 12.5-Foot Deployable Reflector ......... 287 G. S-Band Beam Steering in a Parabolic Reflector 291 H. Optimum Design of Large Cassegrain Antennas for Spacecraft Applications ; 299 The Use of Coherent Detection for Angle Tracking 303 J. Analysis of Angle Sensor Characteristics for Non-Coherent Processing 317 K. Formulation of Correlation Function of Angle Sensor Output: Non-Coherent Detection 331 L. Analysis of Angle Sensor Characteristics for Coherent Processing . 337 **<IJM VAJ* ^.^jcss******. ^ai^Ksi^^^ifiMiSim^A^^mmm^f,^ t * I i ILLUSTRATIONS 1. 12 2. 13 3. Variation of Beamwidths Versus Cavity Sizo ..... 26 4. Deployable Antenna Systems — Option I 27 5. ' Detail Drawing of S- and Ku-Band Feed System 29 6. Block Diagram of S-Band Angle Tracking System with Shared Data Channel (TDRS Equipment Only) .... 33 7. Ground Station Equipment for S-Band Angle Tracking . 8. 42 9. Detail Drawing ot S-Band Feed System 43 10. Preferred Candidate for Option III ........ 45 11. Deployable Antenna System - Option III 51 12. Detail Drawing of S- and Ku-Band Feed System - Option III 53 13. Deployable Antenna System — Option IV 66 14. Detail Drawing of S-Band Feed System - 67 15. Simplified Block Diagram of S-^and Ku-Band 70 16. 71 17. 72 18. Interconnecting Keys to Preliminary Block Diagram 74 1 19. Notes on Preliminary Block Diagram of S- and Ku-Band 74 20. S-Band Feed System - Option I - Beam Fixed and Coincides 75 21. S-Band Feed System - Option II - Beam Fixed and *"* : Coincides with Reflector Axis (with Autotrack) .... 76 ' :; 22. S-Band Feed System - Option III - Beam Steered 77 23. S-Band Feed System - Option IV - Beam Steered 78 24. Main Reflector Pointing Via Ku-Band Auto Tracking 83 «9l 25. Main Reflector Pointing Via Ku-Band Auto Tracking 84 26. Main Reflector Pointing Via S-Band Auto Tracking 85 27. Main Reflector Pointing Via Ground Command 86 28. Main Reflector Pointing Via Ground Command ..^ • (RP/GC (.*) ) .'" . 87 29. S-Band Feed Positioning Via Ground Command . JL8- ILLUSTRATIONS (Continued) 30. Basic Functions Associated with Designation 91 31. Summary of Methods for Designation, Aided Designation, and Data Link Maintenance 93 32. Basic Operations Associated with Designation, Aided Designation, and Data Link Maintenance 94 33. Data Link Maintenance Via Auto Tracking 100 34. Data Link Maintenance Via Reflector Pointing . 114 35. Data Link Maintenance Via Feed Positioning 120 36. Actual/Desired Feed Location Geometry 122 37. Dual Reflector Cassegrain 128 38. Dual Reflector Gregorian 128 39. Dual Reflector Gregorian Feed Blockage Problem ..... 130 40. Potter's Concept 137 41. Cramer's Concept 137 42. Transverse.Feed Correction ... 139 43. Line Feed Correction 139 44. TDRS Constraints on Spherical Relfector Design 141 45. Compromise Design of a Spherical Dual Reflector ^Antenna 141 46. Loss in Gain for Spherical Reflectors 142 47. Increase in Total Spherical Reflector Diameter to Maintain Constant Effective Diameter 144 48. Relative Gain as a Function of Scan Angle 145 49. Relative Aperture Efficiency Versus Scan Angle for a Spherical Reflector 146 50. Array Geometry 148 51. Bandwidth Versus Incidence Angle 148 52. Measured Radiation Patterns . ; . 150 53. Aperture Efficiency as a Function of Sidelobe Ratio . .152 54. Diamond Shaped Monopulse Comparator 152 55. Square Shaped Monopulse Comparator 153 56. Performance Characteristics of Square Four Horn Monopulse Cluster 154 57. Relative Phase Velocity As a Function of Diameter .... 155 58. Half Power Beamwidth Versus the Length of the Polyrod . 157 59. Crossover Level as a Function of Offset Angle 157 60. Single Aperture Horn 157 61. Modal Radiation Pattern 159 62. Feed Network for Beam Broadening by Under-Illumination . .160 63. Aperture Illumination Assumed for Computations 162 64. Pattern Gain Versus Defocus or MPD 163 65. Slope of Relative Difference Signal as a Function of Defocus or MPD • ..__ .
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