Computer Modeling of Tactical HF Antennas

8/3/2019 Computer Modeling of Tactical HF Antennas

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6a. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION(If appliceble)Naval P ostgraduate School Naval Postgraduate School6c. ADDRESS (City, State, and ZIP Code) 7b. ADDRESS (City, State, and ZIP Code)Monterey, CA 93943-5000 Monterey, CA 93943-50008a. NAME OF FUNDING/SPONSORING 8b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER

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8c. ADDRESS (City. State, and ZIP Code) 10. SOURCE OF FUNDING NUMBERSPROGRAM PROJECT TASK WORK UNITELEMENT NO . NO . NO. ACCESSION NO .

11 . TITLE (Include Security Classification)COMPUTER MODELING OF TACTICAL HIGH FREQUENCY ANTENNAS12. PERSONAL AUTHOR(S)GREGORY. Bobb G. Jr.

13a. TYPE OF REPORT 13b. TIME COVERED 14. DATE OF REPORT (Year.MonthDay) 15. PAGE CfJTlMaster's Thesis FROM TO June 199216. SUPPLEMENTARY NOTATIONThe views expressed in this thesis are those of the author and do not reflect the official policy or position ofthe Department of Defense or the U.S. Government.17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number)

FIELD GROUP SUB-GROUP NEC-3, PAT7, HT-20T, ELPA-302, Horizontal Dipole19. ABSTRACT (Continue on reverse if necessary and identify by block number)The purpose of this thesis was to compare the performance of three tactical high frequency antennas to be used

as possible replacement for the Tactical Data Comm unications Central (TDCC) antennas. The antennas weremodeled using the Numerical Electromagnetics Code, Version 3 (NEC3), and the Eyring Low Profile andBuried Antenna Modeling Program (PAT7) for several different frequencies and ground conditions. Theperformance w as evaluated by comparing gain at the desired takeoff angles, the voltage standing wave ratio ofeach antenna, and its omni-directional capability. The buried antenna models, the ELPA-302 and horizontaldipole, were most effective when employed over poor ground conditions. The best performance under allconditions tested w as demonstrated by the HT-20T. Each of these antennas have tactical advantages anddisadvantages and can optimize communications under certain conditions. The selection of the best antenna issituation dependent. An experimental test of these models is recommended to verify the modeling results.

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Approved for public release; distribution is unlimited.COMPUTER MODELING

OF TACTICAL HIGH FREQUENCYANTENNAS

byBobby G. Gregory, Jr.

Captain, United States Marine CorpsB.S.E.E., University of Colorado, 1985

Submitted in partial fulfi l lmentof th e requirements for th e degree of

MASTER OF SCIENCE IN ELECTRICAL ENGINEERINGfrom th e

NAVAL POSTGRADUATE SCHOOLJune 1992

Author: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _Bob'4 G. ref r

Approved by: __ R. W. Adler, Thesis Advisor-a,.,jC.-

D. C. Jenn, 1esis Co-Advisor

M. A. Morgan, CharmanDepartment of Electrical and Computer Engineering

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ABSTRRCT

The purpose of this thesis was to compare the performanceof three tactical high frequency (HF) antennas to be used aspossible replacement for the antenna system of the TacticalData Communications Central (TDCC). The antennas were modeledusing the Numerical Electromagnetics Code, Version 3 (NEC-3),and the Eyring Low Profile and Buried Antenna Modeling Program(PAT7) fo r several different frequencies and groundconditions. The performance was evaluated by comparing gainat the desired takeoff angles, the voltage standing wave ratio(VSWR) of each antenna and its omni-directional capability.The buried antenna models, the ELPA-302 and horizontal dipole,were most effective when employed over poor ground conditions.The best performance under all conditions tested wasdemonstrated by the HT-20T. Each of these antennas havetactical advantages and disadvantages and can optimizecommunications under certain conditions. The selection of thebest antenna is situation dependent. An experimental test ofthese models is recommended to verify the modeling results.

Accesion ForNT;3 CRA&,&DTIC IAA3

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TABLE OF CONTENTS

I. INTRODUCTION .................. ................... 1A. OVERVIEW .................. ................... 1B. BACKGROUND ................. .................. 1

II. PROBLEM DISCUSSION ............... ................ 3A. PROBLEM STATEMENT .............. ............... 3B. ANTENNAS .................. ................... 3

III. MODELING SOFTWARE ............... ................ 8A. NUMERICAL ELECTROMAGNETICS CODE-3 ......... 8

1. STRUCTURE MODELING ............ ............. 92. WIRE MODELING .............. ............... 10

B. PAT7 PROGRAM ............. ................. 12C. TAKEOFF ANGLE CALCULATION .... ........... 14

IV. MODELING RESULTS ............ ................. 17A. GENERAL .............. .................... 17B. HT-20T MODEL ........... ................ .. 18C. ELPA-302 MODEL ........... ................ 33D. HORIZONTAL DIPOLE MODEL ...... ............ 63

V. EXPERIMENTAL VERIFICATION ....... ............. 92

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VI. CONCLUSIONS .................... 94A. MODEL COMPARISON ......... ............... 94B. RECOMMENDATIONS ........... ................ 94

APPENDIX A. SAMPLE NEC-3 DATA SET ..... .......... 96

APPENDIX B. SAMPLE PAT7 PROGRAM DATA SET ......... .. 97

LIST OF REFERENCES ............. .................. 98

INITIAL DISTRIBUTION LIST ........ ............... 99

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LIST OF FIGURESFigure 1. The hub-spoke deployment of th e TDCC ... 4Figure 2a. HT-20T Antenna........... ............... 6Figure 2b. ELPA-302 Antenna ........... .............. 6Figure 2c. Horizontal Dipole Antenna ....... ........ 6Figure 3. Skywave Transmission chart developed by Prof.

R.A. Helliwell, Stanford University, 1964 .... 16Figure 4. HT-20T Antenna ....... ............... .. 19Figure 5. VSWR fo r HT-20T over good ground ........ .. 20Figure 6. Elevation pattern fo r HT-20T over good ground

for f=2, 4, and 8 MHz ....... .............. .. 21Figure 7. Elevation pattern fo r HT-20T over good ground

for f=12, 20, and 30 MHz ..... .............. ... 22Figure 8. Elevation pattern for HT-20T over fair ground

for f=2,4, and 8 MHz ....... ................ .. 23Figure 9. Elevation pattern fo r HT-20T over fair ground

for f=12, 20, and 30 MHz ..... .............. ... 24Figure 10. Elevation pattern fo r HT-20T over poor ground

for f=2, 4, and 8 MHz ..... ............... ... 25Figure 11. Elevation pattern for HT-20T over poor ground

for f=12, 20, and 30 MHz ..... .............. ... 26Figure 12 . Azimuth pattern for HT-20T fo r f=2 MHz over

good ground, varying takeoff angle(theta) ..... 27

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Figure 13. Azimuth pattern for HT-20T for f=4 MHz overgood ground, varying takeoff angle(theta) .... 28

Figure 14. Azimuth pattern fo r HT-20T fo r f=8 MHz overgood ground, varying takeoff angle (theta) ..... .. 29

Figure 15. Azimuth pattern fo r HT-20T for f=12 MHz overgood ground, varying takeoff angle (theta). . .. 30

Figure 16. Azimuth pattern fo r HT-20T for f=20 MHz overgood ground, varying takeoff angle(theta) .... 31

Figure 17. Azimuth pattern fo r HT-20T for f=30 MHz overgood ground, varying takeoff angle (theta) ..... .. 32

Figure 18 . ELPA-302 Antenna ....... ............. .. 34Figure 19. VSWR fo r ELPA-302 over good ground, varying

heights ............... ...................... .. 36Figure 20. VSWR for ELPA-302 over poor ground, varying

heights ............... ...................... .. 37Figure 21. Elevation pattern for ELPA-302 fo r f=2 MHz

over good ground ......... .................. .. 38Figure 22. Elevation pattern for ELPA-302 fo r f=2 MHz

over fair ground ......... .................. .. 39Figure 23 . Elevation pattern for ELPA-302 fo r f=2 MHz

over poor ground ......... .................. .. 40Figure 24. Elevation pattern for ELPA-302 fo r f=4 MHz

over good ground ......... .................. .. 41Figure 25. Elevation pattern for ELPA-302 fo r f=4 MHz

over fair ground ......... .................. .. 42

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Figure 26. Elevation pattern for ELPA-302 fo r f=4 MHzover poor ground ......... .................. .. 43

Figure 27. Elevation pattern fo r ELPA-302 fo r f=8 MHzover good ground ......... .................. .. 44

Figure 28. Elevation pattern for ELPA-302 for f=8 MHzover fair ground ......... .................. .. 45

Figure 29. Elevation pattern fo r ELPA-302 fo r f=8 MHzover poor ground ......... .................. .. 46


Figure 31. Elevation pattern for ELPA-302 for f=12 MHzover fair ground ......... .................. .. 48

Figure 32. Elevation pattern for ELPA-302 for f=12 MHzover poor ground ......... .................. .. 49

Figure 33. Elevation pattern fo r ELPA-302 for f=20 MHzover good ground ......... .................. .. 50

Figure 34. Elevation pattern fo r ELPA-302 fo r f=20 MHzover fair ground ......... .................. .. 51

Figure 35. Elevation pattern for ELPA-302 fo r f=20 MHzover poor ground ......... .................. .. 52


Figure 37. Elevation pattern fo r ELPA-302 fo r f=30 MHzover fair ground ......... .................. .. 54

Figure 38. Elevation pattern for ELPA-302 for f=30 Mhzover poor ground ......... .................. .. 55

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Figure 39. Azimuth pattern for ELPA-302 fo r f=4 MHz,h=0.5m, varying takeoff angle (theta) ......... .. 56

Figure 40. Azimuth pattern fo r ELPA-302 fo r f=12 MHz,h=0.5m, varying takeoff angle (theta) ......... .. 57

Figure 41. Azimuth pattern fo r ELPA-302 fo r f=30 MHz,h=-.5m, varying takeoff angle (theta) ......... .. 58

Figure 42. Azimuth pattern fo r ELPA-302 fo r f=4 MHz,constant takeoff angle (theta), varying heights. . 59

Figure 43. Azimuth pattern for ELPA-302 fo r f=12 MHz,constant takeoff angle (theta), varying heights. . 60

Figure 44. Azimuth pattern for ELPA-302 fo r f=30 MHz,constant takeoff angle (theta), varying heights. . 61

Figure 45. Horizontal Dipole .... ............. ... 64Figure 46. VSWR fo r horizontal dipole fo r varying heights

over good ground ......... .................. .. 65Figure 47. VSWR for horizontal dipole fo r varying heights

over poor ground ......... .................. .. 66Figure 48. Elevation pattern for horizontal dipole for

f=2 MHz over good ground ..... .............. ... 67Figure 49. Elevation pattern fo r horizontal dipole for

f=2 MHz over fair ground ..... .............. ... 68Figure 50. Elevation pattern for horizontal dipole for

f=2 MHz over poor ground ..... .............. ... 69Figure 51. Elevation pattern for horizontal dipole for

f=4 MHz over good ground ..... .............. ... 70Figure 52. Elevation pattern for horizontal dipole for

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Figure 65. Elevation pattern for horizontal dipole forf=30 MHz over poor ground ...... ............. .. 84

Figure 66. Azimuth pattern for horizontal dipole for f=4MHz, h= 0.5m, varying takeoff angle (theta). . . . 85

Figure 67. Azimuth pattern for horizontal dipole fo r f=12MHz, h= 0.5m, varying takeoff angle (theta) .... 86

Figure 68. Azimuth pattern for horizontal dipole fo r f=30Mhz, h= 0.5m, varying takeoff angle (theta). . .. 87

Figure 69. Azimuth pattern for horizontal dipole for f=..MHz, constant takeoff angle (theta), varyingheights ............... ..................... .. 88

Figure 70. Azimuth pattern fo r horizontal dipole for f=12MHz, constant takeoff angle (theta), varyingheights ............... ...................... .. 89

Figure 71. Azimuth pattern for horizontal dipole for f=30MHz, constant takeoff angle (theta), varyingheights ............... ...................... .. 90

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I. INTRODUCTIONA. OVERVIEW

Computer modeling of wire antennas provides an inexpensiveand efficient means for predicting the performance ofantennas. There are several software packages available whichuse various numerical methods to predict antennacharacteristics. The Numerical Electromagnetics Code, Version3 - Method of Moments (NEC-3) uses the method of moments foranalysis of the electromagnetic response of antennas and othermetal structures. NEC-3 is capable of modeling antennaslocated above ground and buried or near the earth. The EyringLow Profile and Buried Antenna Modeling Program (PAT7) isbased on equations developed in Reference 1 which also usesthe method of moments and field integral equation techniques.PAT7 is used primarily to model near-earth or buried antennas.Each program has its advantages and limitations forapplications based on antenna geometry and location.B. BACKGROUND

The Marine Corps Tactical Systems Support Activity(MCTSSA) at Camp Pendleton, California is exploring thepossibility of replacing an existing antenna system. Twoantennas have been proposed as possible replacements. MCTSSAhas requested that a computer model of both antennas be

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generated so that a theoretical comparison of characteristicsand capabilities can be accomplished. This thesis discussesthe computer models used for the comparison, analyzes th eresults of the models and proposes an additional model forconsideration.

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II. PROBLEM DISCUSSIONA. PROBLEM STATEMENT

The antenna to be investigated is used fo r the TacticalData Communication Central (TDCC) which provides an HF radiocommunications hub for the centralized computer processing ofdata for the tactical command and control of Marine Air Wingassets. Operational employment of the TDCC normally dictatesthat the distant stations are within a 600 mile radius of ti.ehub as illustrated in Figure 1, so the antenna must be omni-directional. The transmitters operate with one kilowatt ofpower output. The current system uses an antenna whichrequires a coupler that has a poor maintenance history. It isdesired that the new antenna not require a coupling device toeliminate this problem. The antenna must also be fieldexpedient and require no more than two men to erect it. Itmust be broadband so that trimming antenna dimensions fo r eachfrequency is not required.B. ANTENNAS

Tw o antennas which fit the criteria above were chosen forfurther analysis. The HT-20T, designed by the AntennaProducts Corporation, and the ELPA-302, designed by the EyringCorporation, were decided upon by MCTSSA as antennas that metthe requirements above. The HT-20T is a back-to-back sloping,

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c00 C:

U-U

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C

Figure 1. The hub-spoke deployment of the TDCC.

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horizontal dipole configuration as shown in Figure 2a. TheELPA-302 is a buried or near-earth horizontal dipole arrayantenna as shown in Figure 2b.

Additionally, a simple horizontal dipole antenna (Figure2c) was proposed as a result of this thesis which wouldsatisfy these requirements as well as requirements for manpackradios in the Marine Corps inventory. The reason ahorizontal dipole was chosen is that it is a common, fieldexpedient antenna that is familiar to Marine Corpscommunicators. Its advantages are that it can be erectedabove ground, as it is now most commonly used, or it can beburied or employed near earth, which has not been a commonpractice, but is practical. The horizontal dipole is ideallysuited for Marine Corps type missions since buried or nearearth antennas are more easily concealed, easy to employ, andlightweight.

The length of the horizontal dipole was chosen afterconsidering test results from Eyring, Inc. on the ELPA-302antenna design. These results showed that when operating atthe lowest desirable frequency, 2 MHz, the electrical lengthof a 91.5 meter buried antenna is approximately 0.75wavelengths. Above ground, this antenna would be 0.6wavelengths long. The difference in length is due to theconductivity and permittivity of the soil conditions, whichare frequency dependent, that change the electrical length ofthe buried antenna. The desired power gain for an antenna in

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25 9m

Figure 2a. HT-20T Antenna.

1.5m __ _ __ _

6.2m$ IZFigure 2b. ELPA-302 Antenna.

___ __ _ 91.5m __ _ _ _ _p........................... y i zFigure 2c. Horizontal Dipole Antenna.

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contact with the soil occurs at an electrical length of onewavelength. As the operating frequency of th e antennaincreases and additional wavelengths are formed on th eelement, a higher antenna gain results and produces a highersignal-to-noise ratio. Considering this information and thepractical aspects of carrying and burying an antenna, a lengthof 91.5 meters was chosen as optimum. The input impedance ofa buried antenna will be discussed later. (Ref. 2]

Comparisons between normalized radiation power output overgood, fair and poorly conducting ground conditions at severalheights of employment, required takeoff angles for propagationpaths, and a discussion of the results and recommendations arediscussed in this thesis.

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III. MODELING SOFTWAREA. NUMERICAL ELECTROMAGNETICS CODE-3

The Numerical Electromagnetics Code-Version 3 (NEC-3) wasdeveloped by the Lawerence Livermore National Laboratorylocated in Livermore, California. NEC-3 is a user-orientedcomputer code for the analysis of the electromagnetic responseof antennas and other metal structures using the numericalsolution of integral equations for the currents induced on thestructure by sources or incident fields [Ref. 3). Thisapproach avoids many of the simplifying assumptions requiredby other solution methods and provides a highly accurate andversatile tool for electromagnetic field analysis.

The code combines an integral equation for smooth surfacesto provide convenient and accurate modeling of a wide range ofstructures. A model may include nonradiating networks andtransmission lines connecting parts of the structure, perfector imperfect conductors, and lumped element loading. Astructure may also be modeled over a ground plane that may beeither a perfect or imperfect conductor. NEC-3 also has thecapability to model antennas with elements that touch or areburied in the ground using the Sommerfeld method.

The excitation may be either voltage sources on thestructures or an incident plane wave of various polarizations.

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The output may include induced currents and charges , nearelectric or magnetic fields, and radiated fields. Hence, theprogram is suited to either antenna analysis or scattering andElectro-Magnetic Pulse (EMP) studies.

The integral equation approach is best suited tostructures with dimensions up to several wavelengths.Although there is no theoretical size limit, the numericalsolution requires a matrix equation as the structure size isincreased relative to one wavelength. Hence, the modeling ofvery large structures may require more computer time and filestorage than is practical on a specific machine. In suchcases, standard high-frequency approximations such asgeometrical optics, physical optics, or the geometrical theoryof diffraction may be more suitable than the integral equationapproach used in NEC.

1. STRUCTURE MODELINGThe basic elements for modeling structures in NEC are

short straight segments for thin wires and flat patches forsurfaces. An antenna and any conducting object in itsvicinity that affect its performance must be modeled withstrings of segments following the paths of wires and withpatches covering closed surfaces. Proper choice of th esegments and patches fo r a model is the most critical step inobtaining accurate results. In this thesis, thin wiremodeling by NEC is used.

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2. WIRE MODELINGA wire segment is defined by the coordinates of its two

end points and its radius. Modeling a wire structure withsegments involves both geometrical and electrical factors.Geometrically, the segments should follow the paths ofconductors as closely as possible, using a piecewise linearfit on curves. The following are electrical considerationsfor wire segment modeling:

- The segment length A relative to the wavelength ):- Should be less than about 0.11 in order to getaccurate results in most cases.- May be somewhat longer than 0.11 on long wires with noabrupt changes while a shorter segment, 0.051 or less,may be needed in modeling critical regions of th eantenna, such as feed points and connections ofmultiple segments.- For A less than 0.0011 should be avoided since th esimilarity of the constant and cosine components ofthe current expansion can lead to numerical inaccuracy.

- The wire radius, r, relative to I is limited by th eapproximation used in the kernel of the electric fieldintegration equation. The segment radius a relative toboth segment length A and wavelength A requires that:- a should be less than 0.11.- a should be less than 0.125A.- a can be less than 0.5A, but this requires theextended thin-wire kernel option by placing the EKcard in the input data set. The limits on an EK cardare straight-line segments and no multiple connectionpoints.

Connected segments must have identical coordinates forconnected ends. NEC-3 connects two end segmentsif the separation between the end of the segments isless than 0.001 times the length of the shortestsegment.

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Segment intersections other than at their ends do notallow currents to flow from one segment to another.Large wire radius changes should be avoidedparticularly for adjacent segments. If the segment hasa large radius, then sharp bends should be avoided aswell.When modeling a solid structure with a wire grid, alarge number of segments should be used.A segment is needed at the point where a networkconnection , a voltage or a current source, is going tobe located. Current sources are limited to isolated,very short constant current sources located at th eorigin. (i.e., excitation of tiny constant currentdipole).

- Base fed wires connected to ground should be vertical.- The segments on either side of the excitation sourceshould be parallel and have the same length and radii.- Parallel wires should be several radii apart.- Before modeling a structure , th e l im it of the numberof segments and the number of connection points shouldbe checked for the particular version of NEC.

Once the antenna geometry and ground plane are specified,the type of excitation must be declared. The excitation canbe either a voltage source or an incident plane wave ofvarious polarizations.

The wire radius, a, relative to A, is limited byapproximations used in the kernel of the electric fieldintegral equation. The thin-wire kernel and the extended-wirekernel approximations are used to approximate the currentdistribution fo r each wire segment. From these currentdistributions, far-field radiation patterns are calculated.

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NEC-3 requires that fo r the thin-wire kernelapproximation, the segment length to wire radius ratio, A/a,must be greater than 8 fo r errors less than 1% and A/a for theextended-wire kernel approximation must be greater than 2 forthe same accuracy. Segments with bends in the wire shouldavoid using small values fo r A/a. The angle of intersectionof wires is not restricted in any manner. Segments cannotoverlap since the division of current between two overlappingsegments is indeterminate. A large radius change betweenconnected segments should be avoided since this will introduceerrors in calculations. A segment is required at each pointwhere a network connection or voltage source will be located.B. PAT7 PROGRAM

The PAT7 program is specifically designed to model thepeformance of buried or near earth antennas and traveling-wave antennas in the 1 kH z to 100 MHz frequency range. Themodel is based on the theory developed in Reference 1 whichuses the formal solution of Maxwell's equations to calculatethe electromagnetic fields and associated distributions ofcurrent and charge in bounded regions. The electricalproperties and characteristics of the material media in whichthe antenna is located and its effects on fields and currentsare the focus of the analysis. [Ref. 4]

PAT7 tabulates and plots both pattern and feedpointcharacteristics for models in real earth environments. Ground

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conductivity and dielectric constants as a function offrequency are used to characterize the burial or underlyingenvironment of the antenna. Radiation patterns are describedas a function of elevation, azimuth, and polarization.Groundwave patterns are described in terms of field strengthat a specific far field distance over real ground conditions.

PAT7 possesses an NxM multi-element array modelingcapability. The assumed geometry of the model consists offrom 1 to N parallel, linear elements arranged in a subarray.From 1 to M of these subarrays can be combined in-line to forman array.

The program very accurately describes the performance ofreal antennas when the input model uses measured data indescribing the various input parameters used in makingcalculations. Buried antennas are most effective when they areinsulated from their environment. The following are electricalconsiderations, characteristics, and capabilities the usermust be concerned with when modeling with PAT7:

- Desirea elevation and azimuth angle of view, in degrees,to obtain desired antenna radiation pattern.- Transmit frequency- Soil conductivity and perm itt ivi ty- Antenna wire insulation conductivity and permittivity.The complex permittivity of the wire insulation shouldbe 1.2 times less than that of the surrounding ground.- Antenna element length and height (negative values areused for buried antennas) Height must be less than0.1) and cannot be zero because PAT7 does not calculateelements touching the air-ground interface.

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- Wire radius must be small compared to antenna length.(Same conditions as NEC-2)- Conductor radius and insulation radius. (The insulationradius must obviously be larger than the conductorradius.)- Number and spacing of elements used in array modeling aswell as number of and distance between subarrays.Subarrays cannot overlap.- Main beam steering. (The user can steer the main beam ina desired direction. This is done in practice bycontrolling the feed signal and using phase sensitivebaluns.)- The actual impedance of the feed element may be used,otherwise a matched, perfect feed element is assumed.- The desired wave type (ground or skywave) to becomputed.- E-field polarization(vertical, horizontal or mixed).- Designation whether element is end or center fed.- Antenna may be either terminated by a user given loadimpedance or open termination.

A graph of the antenna radiation pattern is then produced. Asample input screen is shown in Appendix B.C. TAKEOFF ANGLE CALCULATION

The takeoff angle for High Frequency communications is animportant characteristic in antenna design. In order toobtain the desired signal strength at the receive station, themaximum power radiated at a specific azimuth and elevation, ortakeoff angle, must be calculated so that the signalreflected off the ionosphere to the receive station isoptimal. The takeoff angle fo r the problem discussed in this

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thesis was determined using Reference 5 and the skywavetransmission chart as shown in Figure 3. The takeoff anglewas calculated fo r two ranges, 300 and 600 miles. A one hoppath is considered optimum since signal attenuation and pathlosses are minimized. For daytime communications, a one hoppropagation path was used with a reflection off the 'E' layerat an altitude of 110 km. For nighttime communications, a onehop path reflected off the F2 layer at an altitude of 300 kmwas used. Using Figure 3 and the conditions above, fordaytime communications, a one hop path requires a t;keoffangle of 39 and 20 degrees fo r the ranges of 300 and 600 P.lesrespectively. For nighttime communications, again using a onehop path, the takeoff angles are determined to be 49 and 28degrees fo r the ranges of 300 ard 6u0 miles respectively.These takeoff angles will be osed to compare the results ofthe computer models. (Ref. 51

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4C-

* --- _--.--

Figure 3. Skywave Transmission chart developed by Prof.R.A. Helliwell, Stanford University, 1964.

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IV. MODELING RESULTS

A. GENERALIn order to make an accurate comparison of the antennas,

some common conditions were imposed. Each antenna was modeledover the three types of grounds with different conductivities,a, and relative permittivities, er. The values used for th evarious ground conditions were: fo r "good" ground, a = 0.01S/m and er = 30; for "fair" ground, a = 0.005 S/m and Er = 12;and for "poor" ground, a= 0.001 S/m and er = 6 [Ref. 1]. TheHT-20T was modeled at the fixed height and dimensions asdescribed in Reference 6. The ELPA-302 and horizontal dipolewere modeled for dimensions given in Reference 2 at fourdifferent heights to allow for comparisons of non-traditionalemployment. Radiation patterns were computed fo r each of theantennas under the various height and ground conditions.Antenna performance was analyzed using the maximum gainachieved at the desired takeoff angles and direction, and eachantenna's voltage standing wave ratio (VSWR) over the 2 to 30MHz frequency spectrum. The transmission line impedance wastaken as 50 ohms, a standard value for most radio frequency(RF) applications. The frequencies chosen to make comparisonswere 2, 4, 8, 12 , 20 and 30 MHz. These frequencies werechosen after analysis showed that these frequencies most

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accurately represented the antenna's characteristics over thefrequency spectrum.B. HT-20T MODEL

The HT-20T is a omni-directional, "sloping vee-like",orthogonal dipole antenna designed primarily fo r HighFrequency (HF) skywave propagation. It consists of two dipoleantennas mounted mutually perpendicular in azimuth asillustrated in Figure 4. Each element is terminated with a400 ohm resistor. The center of the antenna is 27 feet abovethe ground.

The VSWR varies between 1.02 and 1.78 over good groundconditions as illustrated in Figure 5. The VSWR of fair andpoor ground is also within these limits but not illustratedbecause the change in ground conditions had little effect onVSWR in this case. The antenna radiation patterns areillustrated in Figures 6 through 17. Each figure shows th epattern for a fixed ground condition fo r frequencies underconsideration. The antenna is oriented fo r transmission ofthe main beam along the positive and negative x-axis. Thereference plane from which plots were taken was from the xz-plane and azimuthal plane through the origin. Fromexamination of these antenna radiation patterns, it is evidentthat the HT-20T is omni-directional and demonstrates goodskywave propagation gains at 39 and 49 degree takeoff angles.The radiation patterns show a maximum gain of -2 db at 20 Mhz

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Figure 4. HT-20T Antenna.

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Figure S. VSWR for HT-20T over good ground.

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2CCo

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Figure 7. Elevation pattern fo r HT-20T over good ground forf=12, 20, and 30 MHz.

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Figure 8. Elevation pattern for HT-20T over fair ground forf=2,4, and 8 MHz.

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Figure 10. Elevation pattern for HT-20T over poor groundfor f=2, 4, and 8 MHz.

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Figr 11. Elvaio patr o H 0;vr or gonfo fE2, 2 , nd 3 ,M

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-o =. (i~i.

or*

Figure 12. Azimuth pattern for HT-20T for f=2 MHz over goodground, varying takeoff angle(theta).

27


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C-=0

"0

caaComo

M 0000)00

-

0;cc~J

Figure 13 . Azimuth pattern fo r HT-20T fo r f=4 MHz over ggoodgr.ound, varying takeoff angle(theta).

28

I II I"


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CO-=0

cu)

F-0

00))MM0)0N (1) (a, )mc >c 03E

Figure 14. Azimuth pattern for HT-20T for f=8 M4Hz over goodground, varying takeoff angle (theta).

29


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2cmJ~-0

(00cu)

4-J .00 0)M--0 .

ca McJc (a

4-0 4-A 4-aO

Figure 15. Azimuth pattern for HT-20T for f=12 MHz overgood ground, varying takeoff angle (theta).

30


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0if 0

.I%-0

C\IDF"7

0~)O5?: R ~NC

0~ (D 0' 0

Figure 16. Azimuth pattern for HT-20T for f=2.0 MHz overgood ground, varying takeoff angle(theta).

31


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CD,0


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over good ground.A change in ground conditions does have some effect on th e

radiation pattern. As the ground conditions vary from good topoor, peak gain varies 2 to 3 dB at takeoff angles greaterthan 30 degrees, depending upon frequency. For takeoff anglesbelow 30 degrees, however, there is virtually no change.These results are expected because, although the ground hassome effect, the antenna as designed is high enough tominimize ground interactions. The antenna radiation patternsalso match those predicted in Reference 6, which validatesthis model.C. ELPA-302 MODEL

The ELPA-302 antenna is a broadband HF skywave antenna andis illustrated in Figure 18. It does not require tuningeither electronically or by trimming the antenna length. Theantenna is fed by an Element Feed Unit (EFU) which acts as abalun and phase controller. By using the EFU, the mainantenna beam can be steered in elevation and azimuth. TheELPA-302 can also be terminated so reflections on th eradiating elements are reduced or eliminated. The ELPA-302was modeled in PAT7 using a matched termination to minimizereflections on the antenna and an elevation steering at 34degrees, the median takeoff angle, to achieve the bestpossible results. [Ref. 2)

The VSWR fo r the ELPA-302 was calculated fo r good and poor

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20OfL

Figure 18. ELPA-302 Antenna

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ground conditions at each height as illustrated in Figures 19and 20. For good ground, the VSWR is somewhat higher forheights above ground. For poor ground, the VSWR issignificantly lower for heights below ground. This can beexplained by examining the electrical characteristics of thevarious types of ground. Ground conductivity and permittivityare functions of frequency. The electrical characteristics ofpoor ground effectively reduce the input impedance of th eantenna to a value closer to the 50 ohm transmission lineimpedance. This results in a reduction in VSWR fo r poorground. Good ground does not have this effect because theconductivity and permittivity are higher and do notsignificantly help the antenna to match the transmission lineimpedance. Although the VSWR is reduced fo r the antennaburied in poor ground, the negative consequences are that th egain is also reduced by burying the antenna. [Ref. 3]

The antenna radiation patterns fo r the ELPA-302 areillustrated in Figures 21 through 44. Each figure shows th epattern for a fixed ground condition fo r the heights of 0.5meters, 0.006 meters, -0.5 meters, and -1.0 meters. Theseheights were chosen because they are the most practical whenusing the ELPA-302 for the TDCC mission. The patterns areoriented with the main beam along the positive and negativex-axis. The reference plane from which plots were taken wasfrom the xz-plane through the origin. The radiation patterns

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E

HI H II II

ca

4-aCN0 0

'mrj co

_Jw

Figure 19. VSWR for ELPA-302 over good ground, varyingheights.

36


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E8

6OuiIt B II ,

0 0i

13) 0 I -.o

UMSA

Figure 20. VSWR for ELPA-302 over poor ground, varyingheights.

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O2 c

Mom

aa

0cy)4-jw

"0C 0)n1 ..... Ln>J -J 0w ii I I

Figure 21. Elevation pattern fo r ELPA-302 for f=2 MHz overgood ground.

38


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SC

caJC:

Cj0CY)-J

M E EE E>0

- W I11111 IIJCC *13

Figure 22. Elevation pattern for ELPA-302 fo r f=2 MHz overfair ground.

39


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-o%CO0

CU')-- N [] , iiI

40

Co-

c'J4-jw

EE~EE00,

Figure 23. Elevation pattern for ELPA-302 for f=2 MHz overpoor ground.

40


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C2 cC

-0


54/111

N Co~

co

cC\1

...J

EC- gE EEE0 U)C', -t5._> > o

Figure 25. Elevation pattern for ELPA-302 for f=4 MHz overfair nround.

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N) "0

L-CC'Ca).e--

0cu)

cN

4-J

"..........E

C " I-Cf

Figure 26. Elevation pattern for ELPA-302 fo r f=4 M4Hz overpoor ground.

43


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2CD

Cc-10

C'Cccy

0c E EESVo,

Figure 27 . Elevation pattern fo r ELPA-302 fo r f=8 MHz overgood ground.

44


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NCq

ccco)Cy

0

\IlT)

=1E EEECO 0)

~ooj

Figure 28. Elevation pattern for ELPA-302 for f=8 MHz overfair ground.

45


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II 0D-5-o

=~oc

00

C\440C'Y)

EE0 '10 > 0 0 ci


46


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L-co

00ca,-Jw:

(DE

E~E

cuoFigure 30 . Elevation pattern for ELPA-302 for f=12 MHz overgood ground.

47


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a)D.I-JOC:

c=

C:CY)

EE0

U--


48


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"0

CLl4

cu

c'Jm00

cc ! w 0


49


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0 C:CC

c)cc

E E E0 U~

cc I 11 11111CD

Figure 33. Elevation pattern for ELPA-302 for f=20 MHz overgood ground.

50


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2 I

co,-J7

Ec E SE E

CO 0

00

Figure 34. Elevation pattern for ELPA-302 for f=20 M4Hz overfair ground.

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co

co5C)

C\1

0CY,wc

ES0 UE EE> > 0 0 q

coo


52


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L- cNC

cuJ0Cl,

wwE" EE

-0 0C D

Figure 36. Elevation pattern for ELPA-302 for f=30 M4Hz overgood ground.

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a)3"0

cyC)" ..

-u

wC~j0

E"E E ESIIi II IIII


54


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|0 a

Ca0

No

00COOV

c ., ......4-j,

i ~II II I I

C\1'

Figure 38. Elevation pattern for ELPA-302 for f=30 Mhz overpoor ground.

55


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NE

00

0C:)W

4-Ju~j

vvvv~~0)J)M0

a !9 11 1111 11

Figure 39. Azimuth pattern for ELPA-302 for f=4 MHz,h=0.5m, varying takeoff angle (theta).

56


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70/111

N

ci))C)I

cu

CY)

wM0) )0)M

,C) r C\I C~jMV> E ~11 1111 11COa Mcucacto

Figure 41 . Azimuth pattern for ELPA-302 for f=30 MHz,h=Q.5m, varying takeoff angle (theta).

58


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C0Cr00

0

C-

SII II II I

CD)

_E E

Figure 42. Azimuth pattern for ELPA-302 fo r f=4 MHz,constant takeoff angle (theta), varying heights.

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q. 2MCC

00

C.E b 0 C5

Figure 43 . Azimuth pattern for ELPA-302 for f=12 Mz,constant takeoff angle (theta), varying heights.

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(D CDO0il

c5_'JCl)

CLwE

"-- E EE-o to0

Figure 44. Azimuth pattern fo r ELPA-302 for f=30 MHz,constant takeoff angle (theta), varying heights.

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show a maximum gain of -16 dB at 2 Mhz fo r h= 0.5 meters overpoor ground. The patterns illustrate that changes in heightand ground condition have a great effect on antenna gain.

For all ground conditions, a height of 0.5 meters providesoptimal gain at the desired takeoff angles while the buriedantennas have approximately 12 dB less gain. The buriedantennas, however, have an increase in gain as groundconditions degrade. One explanation for this can be relatedto image theory. As the ground becomes more lossy, thedistance between the image plane and the antennaincreases.This allows fo r more constructive addition of thetransmitted and reflected wave. If the image plane was exactly1/4 distance from the antenna, then constructive interferencewould be at a maximum. In poor ground, the image plane toantenna distance is closer to 1/4 than in good ground. (Ref. 1]A height of 0.5 meters provides optimal gain at the desiredtakeoff angles.

Azimuth patterns fo r the ELPA-302, shown in Figures 35through 41, were modeled in two ways. First, the height waskept constant at 0.5 m (the height which provided the highestgain) and the takeoff angle was varied to illustrate thechange in azimuthal gain versus takeoff angle. Next, thetakeoff angle was held constant at 34 degrees, a median value,and the height above ground was varied to illustrate th echange in azimuthal gain versus height.

The VSWR and various radiation patterns agree with those

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in Reference 2, which lends validity to the results obtainedhere.

D. HORIZONTAL DIPOLE MODELThe horizontal dipole is an omni-directional antenna

designed primarily for HF skywave propagation. It consists oftwo wires of equal length connected via a balun to atransmission line as illustrated in Figure 45. The horizontaldipole modeled is not terminated because, in some tacticalenvironments, trimming and terminating antennas is not alwayspractical. The overall characteristics of the horizontaldipole are similar to those of the ELPA-302, but with someexceptions that will be discussed later. PAT7 was used tomodel this antenna.

The VSWR for the horizontal dipole was taken fo r good andpoor ground conditions at each height and is illustrated inFigures 46 and 47. For good ground, the VSWR is notsignificantly affected by changes in height. For poor ground,the VSWR is relatively constant for heights above ground butsignificantly lower for heights below ground. The comments onthe ELPA-302 also apply to the horizontal dipole with respectto electrical effects of the ground.

Antenna radiation patterns fo r the horizontal dipole areillustrated in Figures 48 through 71. Each figure shows thepattern fo r fixed ground conditions fo r heights of 0.5 meters,0.006 meters, -0.5 meters, and -1.0 meters. The patterns are

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Figure 45. Horizontal Dipole.

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E

toEo

U)S

0

0mI 0

04

m' U) cm W)

UMSA

Figure 46. VSWR for horizontal dipole for varying heightsover good ground.

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E

I I I

0-N.o. C CoC"

N V.-c "" 0

UIMSA

Figure 47. VSWR for horizontal dipole fo r varying heightsover poor ground.

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"Co

U-)aa-O-

00

N s

,

SgE ECi 0w 11

Figure 48. Elevation pattern fo r horizontal dipole for f=2MHz over good ground.

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2-T Ca

00

0CC0NE

icm

N g E EE

C

SII i II II

Figure 49 . Elevation pattern fo r horizontal dipole fro f=2Mz over fair ground.

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CD

a-CV""0

aa

CU2N

ECO 0 E EEc m

Figure 50. Elevation pattern for horizontal dipole for f=2MHz over poor ground.

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CO

ca

EE E EE0

c n m

07


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C ccQ

U-CO

ONCY.

EE E E00 Lf,.,,T

6 IIUII

Figure 52 . Elevation pattern fo r horizontal dipole fo r f=4MHz over fair ground.

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(DZca

00

4 -J

0

0 ~EE_ o-2cU')oCIOa

Figure 53. Elevation pattern for horizontal dipole for f=4MfHz over poor ground.

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T3

CC:C

ci))50

N

E EO O

. E ~EE

C!, I

Figure 54. Elevation pattern fo r horizontal dipole for f=8MHz over good ground.

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0C

4'-a

.........,

E_" E EE>""o U'j -)

Figure 55. Elevation pattern for horizontal dipole fo r f=8MHz over fair ground.

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2 aoDo

Z0

NII

Figure 56. Elevation pattern for horizontal dipole for f=8MHz over poor ground.

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U))

-r"

ooNO

EC E EEE0o 0

Sw

Figure 57. Elevation pattern for horizontal dipole fo r f=12MHz over good ground.

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2 o

"1-)

" g E EE

( ~~II I I I0n

Figure 58. Elevat ion pattern for horizontal dipole for f=12Mz over fair ground.

77

5 nu uu,


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-DCmJ

INLin.

0 E EE

C. ZO9-

Figure 59. Elevation pattern fo r horizontal dipole fo r f=12MHz over poor ground.

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P4

"0

- " "........... "\-

" g E EE

.c__oo>0 d 0Cn

Sw II1II I II

Figure 60. Elevation pattern for horizontal dipole for f=20MHz over good ground.

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NC

CC:C\1I I.

ca0,N

0 0w.J1II 1I1I II

Figure 61. Elevation pattern for horizontal dipole fo r f=20MHz over fair ground.

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N f-

UC) 0

0 0aa

00

.c_ mSEEE

SII II II II

Figure 62 . Elevation pattern fo r horizontal dipole for f=20MHz over poor ground.

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0CO

40

a)

Coc-

-...........

Figre 3.evtio pater fo hoizotaldiple or =kMHZ~ ovrgoErud

E82


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C))a

0Nt

EE E ECO 0 O Ln

Figure 64. Elevation pattern for horizontal dipole for f=30MHz over fair ground.

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NC

CL

0

cm EE EEw 1nn111IIICO-

Figure 65. Elevation pattern fo r horizontal dipole for f=30MHz over poor ground.

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*0

0

CLC

cci

CO~4 000)

0

Figure 66. Azimuth pattern for horizontal dipole fo r f=4MHz, h= 0.5m, varying takeoff angle (theta).

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L -o

"-CO%all 0

co)

4N

D)0)0)C

'0 *000a0

Figure 67. Azimuth pattern for horizontal dipole for f=12MHz, h= 0.5m, varying takeoff angle (theta).

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-cLO C.

0C-

OCV3 )D

-ox 7JCVN . .... .,tI N

0 0

Figure 68. Azimuth pattern for horizontal dipole for f=30Mhz, h= O.5m, varying takeoff angle (theta).

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QQ)010

4-- II.~

or

m-.

E EE

C 4 IIII II II.C: .Z .IZ.I

Figure 69. Azimuth pattern for horizontal dipole for f=4MHz, constant takeoff angle (theta), varying heights.

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NCD

CC

0

1a)

N ......Iw4-0-r-

E EELOqLnOVb C

Figure 70. Azimuth pattern fo r horizontal dipole for f=12MHz, constant takeoff angle (theta), varying heights.

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zo~

00........

55090


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oriented for transmission of the main beam along the positiveand negative x-axis. The reference plane was from the xz-planethrough the origin. The radiation patterns show a maximumgain of -5 dB at 2 MHz for h= 0.5 meters over poor ground.The patterns illustrate that change in height and groundconditions have a great effect on the radiation pattern. Asground conditions vary from good to poor, the peak gainactually increases a maximum of approximately 7 dB at 2 MHz.

When the antenna is buried, there is an increase in peakgain as ground conditions degrade. This can be explainedusing image theory as discussed fo r the ELPA-302. Also, as inthe case of th e ELPA-302, the height at 0.5 meters providesoptimal gain at the desired takeoff angles fo r all groundconditions. The buried antenna's gain in the direction of th etakeoff angle is 15 dB less than the gain of the antenna aboveground.

Azimuth patterns for th e horizontal dipole are shown inFigures 55 through 65 and were modeled to illustrate thechange in azimuthal gain versus takeoff angle and the changein azimuthal gain versus height.

The results the various radiation patterns obtained aresimilar in shape but not in gain to what would be expected ofa dipole in free space. This allows a rough check of themodel used here and suggests the results are within reason.

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V. EXPERIMENTAL VERIFICATION

The results of this thesis should be verified byexperiment before a final decision to procure a specificantenna is made. A proposed experiment is included forcontinuation of this thesis by another party. The experimentshould contain five sites in the hub-spoke configurationdiscussed earlier to test the performance of the antennas.Each of the three antennas would be operated at the hub sitewith the four spoke sites located from 300 to 600 milesincrementally away in radius from the hub and 90 degreesapart. This will test the omni-directional capabilities andth e short to medium skywave range of the antennas. Groundconstants at the sites should be measured accurately andcompared with model results. The antennas should operate for24 hours per day to test frequency response fo r day and nightcommunications. The test should continue from several days toa week to ensure that a fairly normal ionosphere activityperiod was used. The VSWR for each antenna should be measuredover the entire spectrum. The antenna elevation and azimuthradiation patterns should be measured via a helicopterflyover.

The importance of accurate measurements under th eidentical conditions used for the models is paramount fo r a

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valid comparison of results.

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VI. CONCLUSIONS

A. MODEL COMPARISONA direct comparison between the models discussed is

dependent upon th e user's criteria. All of th e antennasdemonstrate broadband characteristics and omni-directionalazimuthal capability. The HT-20T has the highest gain at eachof the required takeoff angles and the lowest VSWR whencompared to the ELPA-302 and horizontal dipole. The ELPA-302and horizontal dipole provide adequate gain at th e requiredtakeoff angles at heights above ground and fo r buried antennasunder certain conditions. The VSWR for th e ELPA-302 ispractical fo r use with transmitters that require a VSWR of 2.5or less. The VSWR for the horizontal dipole is too high formost frequencies below 7.0 MHz. The ELPA-302 and horizontaldipole are much easier to construct and erect than th e HT-20T,and provide a much less visible battlefield target.B. RECOMMENDATIONS

From th e results of this thesis, the HT-20T antenna isrecommended for use whenever there is adequate space, time, aminimum requirement on displacement, and when concealment isnot a priority. An example of this type of employment wouldbe for physically large communications systems, like th e TDCC,that do not displace frequently. The ELPA-302 is recommended

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when concealment is a priority, ground conditions are poor,and when deploying vehicle-mounted radios which move morefrequently than the TDCC type systems, but are sometimes ableto stay in position long enough so that burying the antennawould be practical. The horizontal dipole is recommended forlimited use for manpack, mobile employment, and where mobilityand ease of construction and concealment are a priority. Itis important that, in this method of employment, the limitedfrequency range of the antenna is considered for frequencyallocation and mission planning. A typical application wouldbe a reconnaissance unit or an infantry unit which movesconstantly but could stop in order to employ a simple, fieldexpedient tactical antenna in a desert environment where poorground prevails.

Each of these antennas have advantages and disadvantagesas outlined in this thesis. Each antenna can optimizecommunications under certain conditions. The user must makethe final decision on which antenna to use in order tomaximize communications.

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APPENDIX A. SAMPLE NEC-3 DATA SE T

**COMMJENT CARDS**CM THIS IS AN HT-20T ANTENNA, f=2 MHz OVER GOOD GROUNDCE**GEOMETRY CARDS**GW1O, 15,.5, 0.25, 9.2, 26.4, 12 ,95, 1,.001GW2O,1,26.4,12.95,1.,26.4,12.95,0.,.001GW3O,6,26.4,12.95,0.,26.4,12.95,-2.,.01GW5,10,-.5,0.25,9.2,-26.4,12.95,1,.001GW15,1,-26.4,12.95,0.,26.4,12.95,0.,.001GW25,6,-26.4,12.95,1.,-?6.4,12.95,-2.,.001GW2,1,-.5,0,9.2,-.5,0.25),9.2, .001GW1, 1, 5, 0,9.2, .5, 0.25, 9.2, .001GXO, 010GE-1,0, 0**PROGRAM CONTROL CARDS**EXO,1,1,O0, 1.0,0,0EXO,1,2,00,-1.0,0,0EXO,2, 1,00,1.0,0,0EXO,2,2,00,-1.0,0,0FRO,1,0,0,2.0,1GN,2,0,0,0,30.O, .01LD4 ,20, 0,0,400, 0.LD4, 15,0,0,400,0.RPO,91,9, 1501,0,0, 1,10,0,0PL3 ,2 ,0, 4RPO, 4, 181, 1000, 20., 0., 0. 2., 0., 0.PL3 ,2 ,0, 4RPO,4,181,1000,28.,0. 0. ,2. ,0.,0.PL3 ,2,0,4RPO,4,181,1000,39. ,0.,0.,2.,0. ,0.PL3, 1,0,4RPO,181,1,1000,-90,0,1,0,0,0

This is a sample data set for NEC-3 input to obtain data forelevation and azimuth patterns and input impedance.

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APPENDIX B. SAMPLE PAT7 PROGRAM DATA SET

ELPA-302 ANTENNAT Elevation (deg), Theta [0-180] 0P Azimuth (deg), Phi [0-360] 0F Frequency (MHz) 30C Conductivity of Soil (Siemens/m) 0.01H Permittivity of Soil (relative) 30E Permittivity of Insulation (relative) 5X Conductivity of Insulation (Siemens/m) 0L Length of Element (m) 46Z Height of Element (m) 0.5A Radius of Conductor (m) 0.001B Radius of Insulation (m) 0.005N Number of Elemencs 2S Spacing of Elements (m) 6.2J Azimuth Steering (deg) 0K Elevation Steering (deg) 90M Number of Subarrays 1D Distance between Subarrays (m) 0I Matching Impedance (ohms) [0=ignore] 0W Wave/Polarization/Symmetry/Termination SVBOG Graph Gain (dBi) vs T = 0 to 180 by 5Enter symbol of variable to change, or;O=Options, Q=Quit, R=Run:

This is a sample data set for the antenna radiation patternsused in the PAT7 program for the ELPA-302 antenna using goodground.

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LIST OF REFERENCES

1. King, R.W.P. and Smith, G.S., Antennas in Matter, The MITPress, 1981.2. Eyring Inc., Operations Manual fo r the 302A Evring LowProfile Antenna, 1990.3. The Numerical Electromagnetic Engineering Design System,Version 3.0, The Applied Computational ElectromagneticsSociety, 1989.4. King, M.B., Gilchrist, R.B., and Faust, D.L., Eyring Lo wProfile and Buried Antenna Modeling Program, Eyring Inc.,1991.5. Boithias, L., Radio Wave Propagation, McGraw-Hill BookCompany, 1987.6. Antenna Products Corp., HT-20T Transportable HF Antenna,1988.

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INITIAL DISTRIBUTION LISTNo. Copies

1. Commandant of the Marine Corps 1Code TE 06Washington, D.C. 20380-00012. Defense Technical Information Center 2Cameron StationAlexandria, VA 22304-61453. Library, Code 52 2Naval Pcstgraduate SchoolMonterey, CA 93943-50024. Chairman, Code EC 1Department of Electrical and Computer EngineeringNaval Postgraduate SchoolMonterey, CA 93943-50005. Director, Research Administration 1Naval Postgraduate SchoolMonterey, CA 93943-50006. Dr. Richard W. Adler, Code EC/Ab 5Department of Electrical and Computer EngineeringNaval Postgraduate SchoolMonterey, CA 93943-50007. Dr. David C. Jenn, Code EC/Jn 1Department of Electrical and Computer EngineeringNaval Postgraduate SchoolMonterey, CA 93943-5000

Computer Modeling of Tactical HF Antennas

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