NASA-CR- 178099 19880014547 NASA Contractor Report 178099 MANUAL FOR OBSCURATION CODE WITH SPACE STATION APPLICATIONS , -.1. --- MOT TO BC TAKEN FHOM MIS noon R. J. Marhefka and L. Takacs UNGLEY RESEARCH CENTER THE OHIO STATE UNIVERSITY LIBRARY, NASA l-!A?.!PTOtj, VIRGINIA ElectroScience Laboratory Col urnbus, Ohio Grant NSG- 1498 May 1986 information to other Foreign reley&&ay be made only with prior izwap- gppropriate export licenses. This legend sh I any reproduction of this information in whole% Date for general release 31 9 1988 National Aeronautics and Space Administration Langley Research Center Hampton,Virginia 23665 Contents I Ueer'e Manual 1 Introduction 1 2 Method 4 3 Principle of Operation 13 3.1 Overview . 13 3.2 Modeling the Structures. 14 3.3 Running the Code . 14 3.4 Non-Interactive Commands . 15 3.5 Interactive Commands . 18 3.6 Keypad Use . 19 4 Non-Interactive Commands 22 4.1 Command CC: Cone Frustum Geometry . 24 4.2 Command CG: Cylinder Geometry . 27 4.3 Command CM: and CE: Comments. 30 4.4 Command EN: End Program . 30 4.5 Command GP: Ground Plane . 31 4.6 Command NC: Next Set of Cylinders . 32 4.7 Command NG: No Ground Plane . 32 4.8 Command NP: Next Set of Plates . 32 4.9 Command NS: Next Set of Sources . 32 4.10 Command NX: Next Problem . 32 , 4.11 Command PG: Plate Geometry . 33 4.12 Command RT: Rotate-Ranslate Geometry . 36 4.13 Command SG: Source Geometry . .. 38 4.14 Command UF: Scale Factor . 42 4.15 Command UN: Units of Geometry . 42 4.16 Command US: Units of Source . 42 4.17 Command VF: Far Zone Volumetric Pattern . 44 4.18 Command XQ: Execute Code . 47 5 Interactive Commands 48 5.1 Overview . .. , . 48 5.2 Command Descriptions . , . 48 5.2.1 EXIT ................................... 5.2.2 HELP ................................... 5.2.3 SHADOW ................................. 5.2.4 SPAWN .................................. 5.2.5 SET ANTENNALOCATION .................1. .... 5.2.6 SET COORDINATES .......................... 5.2.7 SET FILL-CHARACTER ........................ 5.2.8 SET INPUTSET ............................ 5.2.9 SET KEYPAD-MODE .......................... 5.2.10 SET OUTPUT ............................... 5.2.11 SET PATTERN-CUT .......................... 5.2.12. SET SCALE-FACTOR ......................... 5.2.13 SET UNITS ................................ 5.2.14 SET WINDOW .............................. 5.2.15 SHOW ANTENNA-LOCATION .................... 5.2.16 SHOW COORDINATES ........................ 5.2.17 SHOW FILL-CHARACTER ....................... 5.2.18 SHOW INPUTSET ........................... 5.2.19 SHOW KEYPADMODE ........................ 5.2.20 SHOW OUTPUT ............................ 5.2.21 SHOW PATTERN-CUT ......................... 5.2.22 SHOW SCALE-FACTOR ........................ 5.2.23 SHOW UNITS .............................. 5.2.24 SHOW WINDOW ............................ 6 Interpretation of the Output 7 Examples 7.1 Example 1: A Plate ............................... 7.2 Example 2: A Different Plate .......................... 7.3 Example 3: The First Plate Revisited ..................... 7.4 Example 4: A Non-Interactive Version of Example 1 ............. 7.5 Example 5: An Elliptic Cylinder ........................ 7.6 Example 6: Two Elliptic Cylinders ....................... 7.7 Example 7: A Space Station Model ...................... 7.8 Example 8: Another Look at the Space Station ............... References I1 Code Manual 8 Introduction 9 Code Organization 10 Lietinga of the Code 126 10.1 VAX/VMS Subroutines ............................. 126 10.1.1 MAIN PROGRAM ............................ 126 10.1.2 SUBROUTINE INIT ........................... 128 10.1.3 SUBROUTINE INTRAC ......................... 130 10.1.4 Interactive Service Routines ....................... 133 10.2 Non-VAX/VMS Subroutines .......................... 146 10.2.1 MAIN PROGRAM (non-interactive) .................. 146 10.3 Subroutines common to both modes ...................... 148 10.3.1 SUBROUTINE ABSCIN ........................ 148 10.3.2 FUNCTION BABS ............................ 187 10.3.3 BLOCK DATA .............................. 188 10.3.4 FUNCTION BTAN2 ........................... 189 10.3.5 SUBROUTINE CAPINT ........................ 190 10.3.6 SUBROUTINECYLINT ........................ 192 10.3.7 SUBROUTINE CYLROT ........................ 194 10.3.8 SUBROUTINE DOCYLS ........................ 195 10.3.9 SUBROUTINE DOCYL ......................... 196 10.3.10SUBROUTINE DOPLAS ........................ 200 10.3.11SUBROUTINE DOPLA ......................... 201 10.3.12SUBROUTINE GEOM ......................... 203 10.3.13SUBROUTINE INITGF ...............; ......... 205 10.3.14SUBROUTINE PLAINT ........................ 206 10.3.15SUBROUTINE SCAN .......................... 208 10.3.16FUNCTION SCANC/SPANC ...................... 210 ~O.~.~~SUBROUTI.NEWRTOUT ................; ..... 211 10.3.181nclude file ................................ 213 10.4 Non-FORTRAN VAX/VMS source files .................... 216 10.4.1 CDU Source file ............................. 216 10.4.2 Keypad initialization file ......................... 219 11 VAX Implementation 221 11.1 Assembling the Code ............................... 221 11.2 Running the Code ................................. 222 11.3 Modifying the code ................................. 223 12 Non-VAX Implementation 13 NCAR Plot Program iii List of Tables 3.1 Table of non-interactive commands. ...................; .. 16 3.2 Table of interactive commands. ......................... 20 3.3 VTlOO keypad for SHADOW interactive commands. ............. 21 List of Figures Geometry showing the projection of the plate edge onto the far zone sphere. 5 Geometry showing the projection of a cone frustum onto the far zone sphere. 7 Intersection of observation direction vector with plate. ............ 8 The geometry for deciding whether a ray does or does not hit the plate. .. 10 Geometry illustrating the hit point on a cone frustum segment. ....... 11 Definition of finite cylinder geometry composed of cone frustum segments with elliptic cross section. ............................. 26 Definition of finite elliptic cylinder geometry. ................. 29 Definition of flat plate geometry. ........................ 35 Definition of rotate-translate coordinate system geometry. .......... 37 Definition of source geometry for dipole antennas. .............. 40 Definition of source geometry for aperture antennas. ............. 41 Definition of volumetric pattern coordinate system. .............. 46 Illustration of the Space Station ......................... 115 Three-axis view of the Space Station as modeled by the input set. ..... 116 NCAR plot showing the shadow map of the space stat:?n model. ...... 118 Part I User's Manual Chapter 1 Introduction When siting antennas on large structures, it is desirable to be able to quickly determine the clear line of sight transmission or reception paths for the antennas. If the structure under consideration is a space station, there will be many antennas to consider in an environment composed of a very large and complex array of living and working module, solar panels, and support structures. The antennas will potentially need to communicate with systems anywhere around the near zone of the structure and the complete far zone sphere. In short, a challenging problem. In order to aid the antenna design engineer in the prediction of the near and far zone antenna patterns, antenna to antenna coupling, and radiation hazard considerations, for high frequency antennas in a complex environment, a couple of user oriented computer codes have been developed: the NEC - Basic Scattering Code (NEC-BSC) [1,2] and the Aircraft Code (NEWAIR) [3]. Both codes are based on the Uniform Geometrical Theory of Diffraction (UTD) (41, which is a high frequency ray optical method with corrections at shadow boundaries. The UTD is ideal for construction of efficient computer codes, such as these, for modeling the scattering from large structures. The NEGBSC and NEWAIR are complementary codes, that is, the NEGBSC is used when the antennas are not mounted on a curved surface, and the NEWAIR is used when the antennas are mounted on a curved surface. Both codes use plates to model flat structures, the NEGBSC presently uses finite elliptic cylinders to model curved surfaces, and the NEWAIR presently uses ellipsoids. Although the two UTD codes are presently very useful for predicting the performance of antennas in a complex environment, such as a space station, there are a few important consideration that should be taken into account. First, the present versions of these codes were not specifically developed for a space station application. The NEGBSC was developed for ships and the NEWAIR for aircraft. Second and most importantly, even though they run fast for large size structures in terms of a wavelength, as compared with computer codes using other theories, such as method of moments; a probIem with as many structural pieces as a space station can take a very long time to calculate a volumetric pattern. This means that the problem of antenna siting in a large structural environment should be viewed as a multiple stepped procedure to optimize results for minimum time and cost. The design procedure for antenna siting can be viewed as a three step process, as far as the computer codes are concerned. First, it can generally be assumed that a good antenna location will provide a clear line of sight path between transmitter and receiver over the desired range of operation. This can best be accomplished