NAVAL POSTGRADUATE SCHOOL Monterey, California

TIIESIS \} 0'2xo5

DEEP 1\ULL A~TEi\~AS Al\D Tl-IEIR J\PPLICATlO?\S TO TJ\CTICJ\L

VHF RADIO CO~L\IU?\ICJ\ TIO:\S

Co-Advisor Co-Advisor

by

Kenneth A. Vincent , ' 0

i\Iarch 1989

Richard \V. Adler James K. Breakall

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I Title Unclude securiry classification) DEEP :\"CLL A:\"TE:\":\"AS A'D THEIR APPLICATIO:\"S TO TACTICAL VHF RA­~ 1 0 C0\1\ 1C~ICATIO~S ~ Personal Author(s) Kenneth A. Vincent ~a T}pe of Report 1 !3b T1me Covered !4 D;,te of Report (year, monrh, day) 115 Page Count ·laster's Thesis From To \larch 1989 99

5 Supplementary .'\ otat10n The views expressed in this thesis are those of the :1uthor and do not refl ect the oflicial poDcy or po ­tion of the Dep;.:u1ment of Defeme or the C.S Gowmment. i Cosat1 Codes I :-< Subject Terms r con rinz,e on re\'erse !f necPss,v}' and idelliifv by block number) -~e-ld---.-u---ro-u-, "---,.--S-u-· '.,-,:-ro- ... -. ;,- -l thesis , ant e1111:1, card io id:1l r:1d ia t ion pattern .

; Ah:r;!ct c O>llim~t: C"2 rer.:rsc if nne55,; ry and UenrU:·.·-[ly bf,•ck nwnber i This study e.xJ.Inine~ antcm1as with a char:lcteri,tic cardioid radiation pattern. their app}jcations to \'1 If radio conununi ­

ations and their desi~n. comtruction and perfonnance. Structures are im·estigated usmg both the \Iilli ~umerical :lectromagnctics Code (\11:\1:\"EC) and the :\"umerical Electromagnetics Code (~EC). A test structure i~ built. test dat:1 bt:1ined. and a comparison of te ~t result s \·ersus predicted result s i~ made.

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Deep :\"ull Antennas and their 1\pplications to Tactical

\.HF Radio Communications

by

Kenneth A. Fincent ?'

\;lajor. Lnited States \1arine Corps B.S., Oregon State Cniversity. 1972

Submitted in partial fulfillment of the requirements for the degree of

\lASTER OF SCIE:\"CE I~ ELECTRICAL E~GI"EERI:\"G

from the

~A VAL POSTGRADCATE SCI IOOL \1 arch 19 89

ABSTRACT

This study examines antennas with a characteristic cardioid radiation pattern, their

applications to VHF radio communications and their design, construction and perform­

ance. Structures are investigated using both the \1ini ~umerical Electromagnetics Code

(\11::\I::\EC) and the ::\umerical Elcctromagnetics Code (::\EC). A test structure is built,

test data obtained, and a comparison of test results versus predicted results is made.

ill

I

y / /l

TABLE OF CONTENTS

I. I:\TRODCCTIO:\ ............................... .. ............. l

A. PCRPOSE OF STCDY ..................... ...... ............ I

B. :VIETHODOLOGY ........................................... I

II . SCRVEY OF PREVIOCS \\'ORK ................................. 5

A. EARLY FI:\DI~·Gs ......................................... 5

B. FA:VliLIARIZATIO:\ \VITH THE PROBLE:vt ..................... 5

C. I~'ITIAL PERSPECTIVES ................................... IO

D. LI.\liTATIO:\S OF .\11~- I~·Ec ................................ 10

III. I:\YESTIGATIO:\ ........................................... 12

A. fOR.\ILLATI:\G THE PROBLE.\1 CSI:\G :\EC .................. I2

B. fEED SYSTE.\1 Co~·siOERATIO~·s ........................... I2

C. EfFECTS OF SCPPORT .\lAST 0:\ RADIATIO:\ PATTER:\ ....... 13

D. EFFECTS OF VARYI~·G STRCCTCRE HEIGHT ................. 13

E. EFFECTS Of \'ARYI:\G GROL~'<D CHARACTERISTICS .......... I3

F. EfFECTS OF VARYI:\G GROL:\D PLA:\E STRLCTLRE GEO\lETRY 1-4

G. EfFECTS OF SLRFACE \\'AVES ............................. 29

IV. A~·TE~·:\A D ESIG:\ ......................................... 32

:-\. BASIS FOR DESIG:\ ....................................... 32

B. DESIG~· CO:\SIDERA. TIO:\S ................................ 32

C. PROTOTYPE DESIG:\ ...................................... 32

D. FEED HAR:\ESS VARIA TI 0:\S .............................. 33

E. A~·TE:\:\A TESTI~·G ....................................... 3-4

F. TEST SETCP .............................................. 39

V. PROTOTYPE A:\TE:\:\A EVALCATIO:\ .......................... 42

A. LABORATORY TESTS ...................................... 42

B. FI ELD TESTI~·G PROCEDCRE ............................... 42

1. Field Test at 100 .\Ictcr Range .............................. 42

iv

'"' Tests at 1000 \I eter Range ................................. 46

C. TEST RESCL TS ........................................... -46

1. Results at 100 .Vleter Range ................................ -46

2. Results ofTests at 1000 \leter Range ......................... -47

VI. A:\AL YSIS A:\0 CO:\CLCSIO:\S .............................. 54

A. C0\1PARISO:\ OF RESCLTS TO PREOICTIO:\S ................ 54

1. Bandwidth and Standing \Vave Ratio (S\VR) Characteristics ........ 54

2. Radiation Pattern Comparisons ............................. 54

B. REC0\'1 \1E:\OA TI 0:\S ..................................... 55

APPE:\DIX A. Cl'RRE:\T CALCCLATIO:\ PROCEOCRE .............. 56

1'\. Pl'I{.POSE ................................................ 56

B. T\YO PORT :\ET\\'ORK APPROACH .......................... 56

C. A SHORTCCT \IETHOO .................................... 58

D. \lATRIX I:\VERSIO:\ ROCTI:\E ............................. 60

APPE:\DIX B. fEEOLI:\E LE:\GTH CALCCLATIO:\ \IETHOD ......... 61

A. Pl.I{.POSE ................................................ 61

B. BASIC PROGRA\1 LISTI:\G ................................. 61

APPE:\OIX C. AOOITIO:\AL TEST DATA .......................... 63

A. GROL.:\0 PLA:\E STRCCTL:RE VARIATIO:\ PLOTS ............. 63

B. AOOITIO:\AL LABORATORY PLOTS ......................... 66

1. 55 .\I H z Feed IIarness .................................... 66

2. 60 \1H z Feed Harness .................................... 70

3. 66 \1Hz feed Harness .................................... 75

APPE:\OIX D. :\EC OATASETS ................................... 81

A. ELE.\lE:\T AO\'IITTA:\CE A:\D \ICTCAL AD\1ITTA:\CE ........ Sl

B. GROC:\D R.A.OIALS AT 120 DEGREE A:\GLE TO \10:\0POLES ... 81

C. GROC:\D RADIALS AT 135 DEGREE A:\GLE TO \10:\0POLES ... 82

D. GROC:\0 RADIALS AT 150 DEGREE A:\GLE TO \10:\0POLES ... 83

E. TEST STRL'CTCRE SI\'ICLATIO:\ OVER I:\IPERFECT GROC:\D ... 83

F. SLRFACE \\'AVE \IODEL OF PROTOTYPE A:\TE:\:\A ........... 84

LIST Of REfERE:\CES ........................................... 86

I:\ITIAL DISTRIBCTIO:\ LIST ................... . ................ 87

\"!

LIST OF TABLES

Table 1. PHASED \10:\0POLES CHARACTERISTICS, ELE\1E~T

RADICS = .001 \1ETER ........................... ......... 9

Table 2. PHASED \110:\0POLES CHARACTERISTICS, ELE\1E:\T

RADICS = .01 :VIETER ..................................... 9

Table 3. PHASED :VIO:\OPOLES I\1PEDA-:\CE VARIATIO:\S ........... 10

Table 4. FEED HAR:\ESS PHYSICAL LE:\GTHS ..................... 34

LIST OF FIGURES

Figure 1. Typical \llutual Interference Situation .... ...................... 2

Figure ") ~. Typical Electronic \Varfare Threat Situation ..................... 3

Figure .., .). Far Field Pattern of Phased 60 \1Hz Monopoles at Resonance ....... 6

Figure 4. Far Field Pattern of Phased 60 MHz :\1onopoles Excited at 59 \1Hz ... 7

Figure 5. Far Field Pattern of Phased 60 \1Hz Monopoles Excited at 61 \1Hz ... 8

Figure 6. Initial Test Structure Geometry ............ ..... ............. 14

Figure 7. Initial Test Structure Radiation Pattern at Design Frequency ........ 15

Figure s. Test Structure Elevated by \!Ietailic \last ...................... 16

Figure 9. Radiation Pattern Distortion Caused by \1 etallic \last ............ 17

Figure 10. Insulating Section Inserted in \Ieta llic Support \;last .............. 18

rigure 11. Radiation Pa ttern with Insulating Section l nserted ............... 19

Figure 1 ~- Radiation Pattern with Test Antenna 2.5 \ 'leters Above Ground 20

rigure 13. Radiation Pattern with Test Antenna 5 \II eters Above Ground ....... 21

figure 1-L Radiation Pattern with Test Antenna 10 \Ieters Above Ground ...... 22

Figure 15. Pattern of Test Antenna Over Rice Paddy (Theta = SO Degrees) ..... 23

Figure 16. Pattern Over Average Ground (Theta = SO Degrees) ... ........... 2--l

figure 17. Pattern Over Poor Ground (Theta = SO Degrees) ................ 25

Figure 1 S. Pattern Over Rice Paddy (Theta = 89 Degrees) .................. 26

Figure 19. Pattern Over Average Ground (Theta = 89 Degrees) .............. 27

Figure ~0. Pattern Over Poor Ground (Theta = 89 Degrees) ................ 28

Figure 21. Surface \Vave Included. F=60 \ ·IHz, H= 10\1, Average Ground 30

Figure 2~. Surface \Vavc Included. F = 60 \I liz, H = 2.5 \11. A vcrage Ground 31

Figure ")"I .... .) . Structure Geometry of Prototype Deep -:'\ull Antenna ..,., . . . . . . . . . . . . . ... ) .)

Figure 2-L Prototype Antenna Details. Construction ...................... 35

Figure 25. Fecdpoint Details ........................................ 36

Figure 26. Photograph. Completed Prototype Deep :\ull Antenna ............ 37

Figure 27. Photograph, Prototype Antenna F eedpoint Details ............... 38

Figure 28. Test Setup for \ 'leasuring Radiation Pattern at 100 Meters ......... 40

Figure 29. Test Setup for \Ieasuring Radiation Pattern at 1000 \ 'leters ......... 41

Figure 30. Laboratory Plot. F= 60.00 \IlHz. 60 \1Hz Feed Harness ........... 43

Figure 31. Laboratory Plot, F= 59.50 \!l-I z. 60 .\1Hz Feed Harness ........... 4--l

viii

figure "'") J ...

Figure .., ... Jj,

Figure 34.

Figure 35.

Figure 36.

Figure 37.

Figure 38.

Laboratory Plot. F = 59.25 \11-lz, GO \H-Iz Feed I Iarness ........... 45

Radiation Pattern at 100 \1. F= 59.25 \1Hz. 60 \1Hz Feed Harness .. 48

Radiation Pattern at 100 \L F= 53.00 :VI Hz, 55 .VIHz feed Harness .. 49

Radiation Pattern at 100 \1, F= 65.75 \1Hz, 66 \1Hz Feed Harness .. 50

Radiation Pattern at 1 Km, F = 59.25 .VI Hz, 60 \1Hz Feed Harness ... 51

Radiation Pattern at 1 Km. F= 54.00 Y1Hz, 55 \1Hz Feed Harness ... 52

Radiation Pattern at 1 Km, F= 66.00 Y1Hz, 66 Y1Hz Feed Harness ... 53

Figure 39. T\\'0 Port :\etwork. . ...................................... 57

Figure 40. Radials Drooped at 120 Degrees from :\1 onopoles ................ 63

Figure 41. Radials Drooped at 135 Degrees from Y1 onopoles ................ 64

Figure 42. Radials Drooped at 150 Degrees from Y1 onopoles ................ 65

Figure 43. 55 \1Hz IIarness, F= 53.75 \1Hz, Laboratory Plot ............... 66

Figure 44. 55 .\II Iz Harness, F= 54.00 \I Hz. Laboratory Plot ............... 67

Figure 45. 55 \!l-I z Harness, F= 54.50 \1Hz. Laboratory Plot ............... GS

Figure 46. 55 \1Hz I larness, F= 55.00 .\'i!Iz. Laboratory Plot ............... 69

Figure 47. GO \I l-Iz I Iarness , F= 58.50 \1Hz. Labora tory Plot ............... 70

Figure 4S. 60 \I li z Ilarne~s. F= 59.00 \I l-I z. Laboratory Plot ............... 71

Figure 49. GO \1Hz !I arness. F= 59.35 \1H z. Laboratory Plot ............... 72

Figure 50. GO \'lll z Ilarness. F= 60.00 \11-Iz. Laboratory Plot ............... 73

Figure 51. 60 \I Hz Harness, F = 60.50 \I liz, Laboratory Plot ............... 74

Figure 52. 66 \'1Hz Ilarness, F=64.00 .\1Hz, Laboratory Plot ............... 75

Figure 53. 66 \1Hz IIarness. F= 64.50 \III z. Laboratory Plot ............... 76

figure 54. 66 \I Hz I Iarncss. F = 65.00 \1H z, Laboratory Plot ............... 77

Figure 55. 66 \1Hz I Iarness. F = 65.50 \1Hz, Laboratory Plot ............... /S

Figure 56. 66 \ [Hz Harness, F = 66.00 \1 I Iz. Laboratory Plot ............... 79

Figure 57. <56 \I Hz I Iarness, F = 66.50 \1 li z. La bora tory Plot ............... SO

lX

ACKNO\VLEDGEl\IENTS

Completion of this thesis would not have been possible without the guidance and

encouragement rendered by Professors Richard \V. Adler and James K. Breakall, and the

patience of my \Vife Kay. Additionally, the author wishes to acknowledge the assistance

provided by E\Vl John Alexakos CS:\, E\VC .:viax CorneliUS:\, ETCS Mark Delagasse

CS:\, \'Irs . Janeen Grohsmeyer, and :'vir. Joe Vitale during testing of the prototype an­

tenna, to Cpt .\1cCoy, Communication-Electronics Staff Officer of the 3d Brigade, 9th

Regiment, 7th Infantry Division (Light) for loan of equipment used in testing, and to

.\llr. Steve Blankschein who helped with fabrication of the prototype antenna.

X

I. INTRODUCTION

A. PURPOSE OF STUDY

In tactical military communications systems it is often advantageous for a radio to

transmit and receive v:ell in most directions but poorly or not at all in a fe\v directions,

or in one sector. :Vlutual interference from co-sited transmitters operating on adjacent

frequencies and januning by enemy electronic warfare acti,·ities are typical examples.

Figures 1 and 2 illustrate these situations. \\'bile modern signal processing techniques

and equipment can do much to reduce or eliminate such interference, t\\'0 or three deci­

bels of improvement is often prohibitively expensi\·e, impractical, or in the worst case,

impossible to produce. The use of antenna characteristics to get additional inurmnity

to jamming and interference is thu s a ttractive from the standpoints of both cost and

practicality.

B. I\IETHODOlOGY

This study examines a class of antenna<; having a characteristic cardioidal radiation

pattern. Such antennas offer the prospect of putting sources of interference in the null

portion of the radiation pattern, thereby reducing or eliminating the unwanted signals.

Since it is usually desirable not to radiate transmitted signals in the direction of the en­

emy, reciprocity of receiving and transmitting characteri stics is an advantage in thi s ca se.

The most common configuration in a tactical conununications network is that of

se\·eral stations. all within normal transmission range and located in relative directions

covering up to about '270 degrees of horizontal coverage. This configuration is usually

dictated by the operational situation. and is seldom based on conmmnications consider­

ations.

C se of directional antennas is often a means of coping with marginal or inadequate

signal strength, but frequently using such antennas creates ne\\· problems. since they do

not radiate well in all directions, and are in some cases nearly unidirectional. \\-bile such

antennas are usually available to conm1Unicators, their often complex or unpredictable

patterns of gain and loss (lobes and nulls ) frequently makes them impractical to usc on

any but point-to-point circuits. Development of practical antennas with a single well­

defined null covering a 45 to 90 degree sector and having as much gain as possible in all

other directions is attracti\·e. since it offers the possibility of getting a significant im­

provement in inmmnity to januning anc..l co\·erage range in most directions. at rebtively

t: ~-S

~ Q).E

~~ a ~

0 :;J

~ ~I; ~

'""1

:Uo § CQ ~~ ~ ~~ a a ~ -..J8 g: Q)

tl) IJ

0 '""1 'ti

t3 ~ II

~ D

~ ~0 ~ h

~ ~

:§ h ~ ~

Figure 1. Typicall\tutual Interference Situation

2

Enemy Territory Jam

------II = Radio fa &:" Jammer

.-----1---'" = CommUtJlca tlons lJnk

Figure 2. Typical Electronic \Yarfare Threat Situation

3

low cost. This thesis examines the po ssibilities for such antennas, develops a design for

a prototype ante nna having a characteristic cardioidal radi ation pattern, models the

prototype design over several combinations of grounJ and structure height, and evalu­

ates ac tual performance of the implemented prototype versus predicted performance

obtained through modeling.

The perfo rmance criteria of interest in this study are the radiation pattern, input

impedance. and usable frequency range for a single structure. The shape and depth of

the null in the radiation pattern are of special interest. since that single characteristic is

unique to the category of antennas under study. Specific measure s for these character­

istics arc developed when needed.

II. SURVEY OF PREVIOUS 'YORK

A. EARLY FINDINGS

Antennas with characteristic deep nulls have been known since the early days of

radio, and are \\·ell documented in most texts on basic antenna theory. Review of some

classic and current texts [Refs. 1, 2] reveals that the desired cardioidal deep null radiation

pattern may be obtained by correct phasing of currents in the elements of an array of

elements. Further research of the literature produced several practical structures having

the desired radiation pattern, along with useful insight on productive lines of research

[Refs. 3, 4].

B. FAl\IILIARIZATION \VITH THE PROBLE!\1

Initial simplified studies of two \·ertical monopoles o\·er perfect ground were con­

ducted using the .\tlini :\umerical Electromagnetics Code ( .\tl I:\ l :\EC) antenna m odeling

program [Ref. 5] running on a personal computer. This prelirninary work immediately

revealed the need to knmv the characteristic impedance of each monopole and the mu­

tual impedance between monopoles in order to provide the input arguments required by

the .\l 1:\I:\EC program. Appendix A addresses this problem and presents two methods

which can be used to find the necessary information. A few runs of the .\1 1:'\T\TC

program provided initial insight into the scope and nature or the des ign ta sk at hand.

Figures 3. 4. and 5, each produced using a .\11:\I:\EC simulation of a structure similar

to one used in Christman's study [Ref. 4] indicate that while a well defined cardioida l fa r

field radiation pattern can be obtained using an array ofproper dimensions with prop­

erly phased currents of equal magnitude f1owing in the elements. the desired pattern is

essentially a n;.urowband phenomenon and deteriorates quite rapidly as the frequency

varies from that for \Vhich the structure was designed. In addition to deterioration of

the desired radiation pattern. the input impedance of the structure varies over a wide

range as the frequency ,·aries from the design frequency of the array.

In order to characterize the results of this study in quatntiati\·e terms, the null depth

in decibels relati\·e to the front-lobe, the angle over which various null depths were ex­

hibited, and the input impedance variations that occurred in each of several simulations

are summarized in tables which follow. \:Vhile null depth relati\·e to an isotropic radiator

is of interest from an analytical standpoint, the null depth relati\·e to the gain from the

5

Figure 3. Far Field Pattern of Phased 60 .!\1Hz I\lonopoles at Resonance

6

~--__ ......

,./·-------+---

Figure 4. Far Field Pattern of Phased 60 J\IHz l\lonopoles Excited at 59 l\'lHz

7

\ \ \ \ -, i

-, --..................... , __ --+--~

............... ___ _

figure 5. Far Field Pattern of Phased 60 l'YIHz l\1onopoles Excited at 61 l\1Hz

8

front lobe of the antenna is a more practical and useful measure of deep null effect and

is therefore included in the tables.

Table 1. PHASED l\lONOPOLES CHARACTERISTICS, ELEI\1ENT RADIUS=.OOil\IETER

Frcq 0 dBi -10 dBi -20 dBi 20 dB F B :\ull (\1Hz) An~:de Angle An£dc (degrees) Depth

(degr-ees) (degrees) (deg1:-ees) (dB)

5S 156 62 32':: 38':: -26.2

59 138 90 14':: 60':. -24.8

60 120 64 36 56 -49.6

61 112 42 26 -14.0 (1 )_ 102 -9.4

... T\\'O null~ ... =

Table .2. PHASED l\10~0POLES CHARACTERISTICS~ £LEl\1ENT RADIUS= .01 l\IETER

frcq U dBi -10 dBi -20 dl3i 20 dB F B :\ull (\I Hz) Angle Ansdc An2le (degrees) Depth

(degrees) ( dcg1:-ces) (dcgr~ccs) (dB)

.5 8 1 ()0 I 8':' .56 ':: 98 -2/.()

59 1::;~ ~4::: 6U 136 -27.0

60 14() 64 36 58 -47.4

61 1 ... ., j_ 43 42 -1 9.2

62 1~ 6 34 )) -13.5 ...

= T\\·o nulls

Examination of the foregoing tables shows that clement radius has an effect on the

shape of the radiation pattern, and also afTects the bandwidth oYer which appreciable

nulls are exhibited. The input impedance \·ariations predicted by these simulations are

sununarizcd below:

9

Table 3. PHASED l\lONOPOLES 11\'lPEDANCE VARIATIONS

Freq :vi onopole 1 \;l onopole 2 :\1 onopole 1 :\1 onopole 2 (:\1Hz) Input Z Input Z Input Z Input Z

(radius= .001 :\1) (radius= .001 :\1) (radius= .OL\1) (radius= .01 :\1)

58 I-tS -l-l.O 17.2 56.6

59 IS. S 60.0 20.2 66.6

60 23.0 70.6 23.2 62.5

61 27.-l 7S.l 26.2 80.5

6~ "') I _)_,_ 85. 1 29.5 86. 1

From this stmunary of monopole impedance characteristics it can be seen that the

impedance of both monopoles increases as the frequency of excitation increa~es and

drops as the excitation frequency decreases below the structure design frequency. Fig­

ures 3. -l. and 5 illustrate the deep null performance of the t\\'0 monopoles. :\ ote that

these three plots show the narrowband behavior of the structure when the magnitude

and phase of the excitation voltages are not changed to compensate for changing ele­

ment and mutual impedances as the excitation frequency varies. The cDccts of opti­

nlizing these cxcit<.Hions is explored in later chapters.

C. I;'\ITIAL PERSPECTIVES

This prclinlinary in\·estigation indicated that there arc many ways to implement an

array of clements that ha,·e the desired characteristics, but also revealed that all the

methods found ha\·c the common disadvantage that their cardioidal patterns arc not

exhibited over a ,,·ide band of frequencies and that input impedances vary over a wide

range. lm·estigati on of dipole arrays and folded dipole arrays did not produce a struc­

ture of substantially better characteristics. These structures were therefore discarded in

order to linlit the investigation to a manageable scope.

D. LIJ\liTATIO NS OF 1\liNINEC

\\'hile a :\11:\1:\[C simulation of monopoles over perfect ground is useful in a pre­

liminary investigation. simulation of a phased monopole array over real ground using a

realistic support structure and a practical feed system is beyond the capabilities of the

10

\1 I ~I ~EC program. This dictates that the remainder of the ~imulation \\'ork be carried

out using the );"umerical Electromagnetics Code ();"EC).

ll

III. INYESTIGA TION

A. FORl\lULA TING THE PROBLEl\1 USING NEC

Having narrowed the investigation to a specific monopole array using the :\EC

simulation system, a \Vhole nev; set of requirements arises. First, since this study is ori­

ented toward study of practical antenna systems, the simulations must be carried out

over less than perfect grounds. Reviev; of the Antenna Engineering Handbook. Vol. I

[Ref. 6] provided the needed dielectric and conductivity values for good. average and

poor grounds.

Since the structure must be elevated above the (imperfect) ground in order to pro­

,·ide sa tisfactory line-of-sight coverage. a support structure must be used. Since practical

antennas must often be erected at varying heights above ground, it is necessary to sim­

ulate the st ructure s investigated at varying heights above the terrain. The :\EC program

can easily handle thi s requirement if the coordinates describing the test structure are

translated along the "Z" axis (chosen as the vertical axis).

B. FEED SYST£01 CONSIDERATIONS

Rea l antennas must hav e some feed system. and. in the case of the family of a rrays

chosen for study using :\EC. the feed system is a key consideration. This is due to the

critical effects of current magnitude and phase in the elements upon the radiation pattern

produced. This current phasing can be accomplished in a variety of \\·ays. as inJicated

by Christman and \l clody [Refs. 7. 8]. Cnfonunately, a simple and practical means of

getting the desired phase and magnitude relationships was not found, and as mentioned

in the ARRL Antenna Book [Ret: 3: pp. 8-l-l], a number of designers are still looking

for a simple and practical means of accomplishing a constant phase equal current iced

over a v:ide bandv:idth. As a means of further exploration of this problem, the antenna

feed method of Christman [Ref. 7] \\·as chosen since it provides a computer program

which in most cases provides at least one solution v:hich is physically realizable. and

since it provides a rigorous (but difTicult) derivation of the theory behind the published

program. This program. written by Roy Lewallen, is listed in Appendix B since it was

central to the \rork done.

Finally, each time the test structure is changed, or the frequency used to excite the

structure changes. the characteristic impedance of the monopoles and their mutual

impedance changes. A mechanized \\'ay of manipulating the complex impedance matrix

12

describing the antenna's characteristics is almost mandatory since it is necessary to in­

vert the characteristic admittance matrix to get the antenna's impedance matrix. Once

the impedance matrix is found, the element impedances and mutual impedances are

knov;n. and the entry arguments of Lewallen's feed harness length calculation program

[Ref. 7] can be supplied. A simple routine to do the required matrix manipulations was

written using the :\1A THCAD co [Ref. 9] program running on a personal computer. This

routine is included at the end of Appendix A.

At this point, all the necessary tools and information elements were at hand to

proceed with a ~EC-based simulation of phased monopoles over imperfect ground,

employing a practical feed system.

C. EFFECTS OF SUPPORT l\1AST ON RADIATION PATTERN

A ~EC dataset describing the model to be studied was constructed and initial test

runs were made. During this sequence of tests it became clear that something was

wrong. in that the radiation patterns obtained from the test structure ele\·ated abo\·e

ground by means of a metallic mast were not the same as those obtained earlier at the

same height without the metallic support structure. Since the support structure \\·as the

only difference bet\\·een the two cases, a one meter long insulating section \\·as inserted

between the metallic mast and the antenna. This immediately cured the problem. and

the model then performed as expected. Figures 6 through 11 illustrate the problem, its

remedy. and the resultant radiation pattern.

D. EFFECTS OF YARYJNG STRUCTURE HEIGHT

In order to explore the effects of raising and lowering the test antenna. the ~EC

dataset was modified by adding the vertical height to be used to all the \\·ire Z­

coordinates. Test heights of 2.5. 5 and 10 meters were chosen as those most likely to

be used in practice. The efTects of running the program at these heights can be seen in

figures 12 through 14. The structure and operating frequency ( 60 \H-Iz) are unchanged

and only the antenna height is varied. The deterioration of the deep null is e\·ident when

the structure is close to the ground.

E. EFFECTS OF VARYING GROUND CHARACTERISTICS

The effects of varying the ground over \vhich the te st antenna is used can be simu­

lated by \'<.Hying the relati\·e dielectric constant and the conductivity (epsilon and sigma

values) in the G-:\ card of the -:\EC dataset describing the antenna and its environment.

In order to simulate the full range of conditions that might be encountered in practice,

13

Figure 6. Initial Test Structure Geometry

three cases were chosen: rice paddy (epsilon = 3--l, sigma = 0.15), average ground

(epsilon = I 0, sigma = 0.003) and poor ground such as Jescrt or rocky areas (epsilon

= 2.5, sigma = 0.00022). The efTects of changing ground characteristics can easily be

misinterpreted if the angle from the zenith is not considered. To illustrate this hazard,

Figures 15 through 17 show the patterns obtained over average ground at a zenith angle

of SO Jegrccs. The same antenna at the same frequency, but viewed at an angle from

the zenith of 89 Jegrecs proJuced the radiation patterns shown in Figures 18 through

20. The efTect of imperfect ground is clearly evident at very low angles.

From these plots it is evident that the poorer the ground is, the less the available

signal strength at very low radiation angles (i.e., theta angles close to 90 degrees). This

phenomenon holLis in general for all antennas over imperfect ground. Its efTccts on the

test antenna's radiation pattern arc as expecteJ.

F. EFFECTS OF VARYING GROUND PLANE STRUCTURE GEOI\1ETRY

Since the input impedance of the test antenna is of interest, the efTects of varying the

angle of the grounJ plane radials \Vith respect to the radiating elements was explored.

The l\EC datasets useJ to conJuct this stuJy are included in Appendix D, and the plots

14

2 MONOPOLES OVER GROUND PLANE IN FREE SPACE F=60 MHZ, (STRUCTURE 1H), FED VIA TWO TL LENGTHS

0

PATTERN GAIN IN OBI 180 •• •• • • •• ••HORIZONTAL

-•-VERTIC.ll

----TOTAL

AIICLES IN DECREES TRUE

figure 7. Initial Test Structure Radiation Pattern at Design Frequency

15

figure 8. Test Structure Elerated by I\letallic !\last

16

2 MONOPOLES, BOTH DRIVEN AT 60 MHZ VIA TL SECTIONS FULL 10M METAL SUPPORT MAST, EPS=lO, SIG=.003

0

PATTERN GAIN IN OBI 180 • • • • • • • • •• HORIZONTAL

-·-VERTICAL

----TOTAL

ANGLES IN DEGREES TRUE

Figure 9. Radiation Pattern Distortion Caused by l\1etallic !\last

17

lllSULATING SECTION

MET.ALL!C SECTION --~

figure I 0. Insulating Section Inserted in 1\letallic Support l\last

18

INITIAL TEST STRUCTURE DRIVEN AT 60 MHZ WITH 1M INSULATING SECTION, EPS=10, SIG=.003, 1ST SOLN

0

PATTERN GAIN IN OB I 180 ••••••• •••HORIZONTAL

-·-VERTICA-l

----TOTAL

ANGLES IN DEGREES TRUE

Figure 11. Radiation Pattern '\ ith Insulating Section Inserted

19

2 MONOPOLES, BOTH DRIVEN AT 60 MHZ VIA TL SECTIONS AVG GND: EPS=10, SIG=.003, 2.5M HIGH 1.5M METAL MAST

0

PATT[FIN GAIN IN OBI 180 • • • • • • • • ••HORIZONTAL

-·-VERTICAL

----TOTAL

ANGL[S IN 0[GRE[S TRU[

figure 12. Radiation Pattern "ith Test Antenna 2.5 1\leters Abore Ground

20

INITIAL TEST STRUCTURE, F=60 MHZ, EPS-10, SIG=.003 4M METAL MAST WITH 1M INSULATING SECTION

0

PATTERN GAIH ltl OBI 180 • • • • • • • • ••HORIZONTAL

-·-VERTICAL

----TOTAL

AIIGLES IN DEGREES TRUE

Figure 13. Radiation Pattern "ith Test Antenna 5 1\leters A bore Ground

2 l

2 MONOPOLES, BOTH DRIVEN AT 60 MHZ VIA TL SECTIONS AVG GND: EPS=10, SIG=.003, 10M HIGH, 1M INSUL SECT

0

PATTERN GAIN IN OBI 180 ••••••••••HORIZONTAL

-·-VERTIC.LL

----TOTAL

AtiGLES IN DEGREES TRUE

figure l..t. Radiatiou Pattern H ith Test Antenna 10 I\leters AhoYe Ground

22

INITIAL TEST STRUCTURE, F=60 MHZ, EPS=34, SIG=.15 9M METAL MAST WITH 1M INSULATING SECTION

PATTERN GAIN IN OBI

••••••••••HORIZONTAL

-·-VERTICAL

----TOTAL

ANGLES IN DEGREES TRUE

0

180

figure 15. Pattern of Test Antenna Orer Rice Paddy (Theta = 80 Degrees)

23

2 MONOPOLES, BOTH DRIVEN AT 60 MHZ VIA TL SECTIONS

0

I'AlltiiH CAlM IH Dll 1!0 • •• •••• •••HOIIIZOHTAL

~·-V[IITICAL

----TOTAL

ANOLU IN DICII[[S TfiUI

figure 16. Pattern OYer Average Ground (Theta = 80 Degrees)

24

INITIAL TEST STRUCTURE, F=60 MHZ, EPS=2.5, SIG=.00022 9M METAL MAST WITH 1M INSULATING SECTION

0

PATHRH GAIN IN OBI 180 ••••••••••HORIZONTAL

-·-VERTIC.~l

----TOTAL

ANGLES IN DEGREES TRUE

Figure 17. Pattern OYer Poor Grouud (Theta 80 Degrees)

25

2 MONOPOLES, BOTH DRIVEN AT 60 MHZ VIA TL SECTIONS 10M UP, 9M METAL MAST, EPS=34, SIG=.15, THETA=89 DEG

0

PATTERN GAIN IN OBI 180 • • • • • • • • • o HORIZONTAL

- o- VERTI CAL

----TOTAL

AUGLES IN DEGREES TRUE

Fi gure IR. Pattern OYer Rice Paddy (Theta = 89 Degrees)

26

INITIAL TEST STRUCTURE, F=60 MHZ, EPS=10, SIG=.003 9M METAL MAST WITH 1M INSULATING SECTION, THETA=89 DEG

0

PATTERN GAIN IN OBI 180 • • • •• • •• ••HORIZONTAL

-•-V[RTICJ.L

----TOTAL

ANGL[S IN O[GRHS TRU[

Figure 19. Pattern Orer An~rage Ground (Theta = 89 Degrees)

27

INITIAL TEST STRUCTURE, F=60 MHZ, EPS=2.5, SIG=.00022 9M METAL MAST WITH 1M INSULATING SECTION, THETA=89 DEG

0

PATTERN GAIN IN OBI 180 • •• • ••• • ••HORIZONTAL

-·--VERTICAL

----TOTAL

ANGLES IN DEGREES TRUE

Figure 20. Pattern Orer Poor Ground (Theta = 89 Degrees)

28

used are included in Appendix C. \Vith each \·ariation of the geometry. it was necessary

to recompute the impedance matrix for the structure, in order to adjust the transmission

line feed harness lengths. The conclusion drawn from this study was that while feedpoint

impedances can indeed be varied by changing the angle of the ground plane radials with

respect to the dri\·cn clements, deep null characteristics disappear as the ground plane

elements are varied from a perpendicular orientation to the driven elements.

In order to investigate the effect of removing ground plane elements on the structure

radiation pattern. clements \\'ere removed, characteristic impedances found, and

excitations recalculated and applied to the modified structure. It was found through

modeling that the ground radials on the ends of the structure could be removed \\'hile

maintaining good deep null performance. yet simplifying the test structure. Figure 23

shows this configuration. Subsequent modeling rc\·calcd that this structure has deeper

nulls in most cases than did the initial test structure. Subsequent work was therefore

done using this structure vice that of the initial test structure.

G. EFfECTS OF SURF ACE \VA \'ES

In order to investigate the effects of surface waYes on the radiation patterns

produced by the test structure. the ::\[C dataset was modified to include surface wave

cfTects. This required using the Sonm1erfcld ground option of ::\EC. Before running a

simulation using this option. it is necessary to create a ground characteristics lookup

table for u se by ::\EC Juring calculation. The table is created by S0\1::\EC \vhich u ses

a data card containing the frequency. dielectric constant. and conductivity value' char­

acteristic of the ground over \vhich the simulation is to be done. The -:'\EC input dataset

and S0.\1::\EC data card used are included in Appendix D.

The results of the surface \\·ave-included study were surprising in that the nulls pre­

dicted \\·ere deeper than th osc obtained over similar ground \\'ithout surface wave effects

included. This result ofTers the hope that \·cry deep nulls may be encountered during

field testing of a prototype antenna.

The efTccts of varying the test structure height above ground were quite noticeable,

as can be seen from comparing Figures 21 and 22. \\'hile from a visual standpoint the

difTcrcnce is obvious. from the standpoint of a practical system, the case of Figure 22

represents a null of o\·er 20 dB. \\·hich is still useful in practice.

29

GP10M7SA E SUB THETA, PHI, RHO, TOTAL, 10M HIGH F=60 MHZ - SW RP PLOT AT 100M, EPS=lO, SIG=.003

FIE:LD STRENGTH IH 08/V/U

• • • • • • • • • • HORIZONTAL

-·- VERTICAL

''"'"''"'"'""R~DlAL ----TOTAL

AHGLES IN DEGREES TRUE

0

180

Figure 21. SurfaLe " 'aYe Included, F= 60 1\lHz, H = 10 l\'1, AYerage Ground

30

GP2 SSA E SUB THETA, PHI, RHO, TOTAL F=60 MHZ, AVG GND, SW RP PLOT AT 100M

FIELD STRENGTH IH DB/V/I.A

• • • • • • • • ••HORIZONTAL

-·-VERTICA.L

'""'''''''"'"''RADIAL

----TOTAL

.AHCLES IN DE:GREES TRUE:

0

180

Figure 22. Surface \Yare Included, F = 60 1\IHz, H = 2.5 l\1, Are rage Ground

31

IV. ANTENNA DESIGN

A. BASIS FOR DESIGN

The work presented to this point is based on computer simulation of various struc­

tures under varying conditions and explores certain structures that are likely candidates

for further development. The structure geometry shown in Figure 23 was chosen for

construction and further eYaluation because of its relative simplicity and predicted null

characteristics.

B. DESIGN CONSIDERATIONS

In order to keep the mechanical work of constructing the prototype antenna to a

minimum, the follo\\'ing assumptions and decisions \Vere made:

• A frequency of 60 \1Hz is used as the design operating frequency

• Half inch copper pipe is used for antenna elements due to its lov:: cost, availability. and aYailability of fittings at nominal cost

• Belden 8219 type coaxial cable is used for the matching harnesses due to its low cost and aYailability

• An aluminum mast kit \\'ith two inch diameter and including a three foot dielectric section is used to eleYate the prototype antenna as necessary

• Insulating plates are used to support the radiating elements

• LT:I F type coaxial connectors are used in building the prototype due to ease of as­sembly. a\·ailability and low cost

C. PROTOTYPE DESIGN

Having defined the essential characteristics of the prototype deep null antenna, the

structure detailed by Figures 23 through 27 was constructed, keeping clements as close

to a quarter waYelength at the 60 \1Hz design frequency as possible. A feed harness for

60 \I Hz was also constructed. Since the "Tee" connector at the junction of the two

transmission line sections and the wire from the connectors at the antenna bases added

about 3.5 em to the length, that amount was subtracted from the length of each cable.

The velocity factor of Belden 8219 cable is 0. 78, and was also included in calculating

physical fecdline lengths for the 60 :VIHz feed harness.

In order to facilitate transporting the prototype antenna, hose clamps were used to

hold elements in place, rather than solder. A wooden mounting bracket was made to

32

Figure 23. Structure Geometry of Prototype Deep Null Antenna

allo\V connection to the support structure, and an azimuth indicator was made for at­

tachment to the support mast during field testing.

D. FEED HARNESS VARIATIONS

In order to get more usable bandwidth from the prototype antenna a way of main­

taining the proper current relationships in the two driven elements at frequencies other

than the structure design frequency was needed. It was noted that, as the frequency of

excitation varies from the structure design frequency, the spacing between the dri\'en

elements departs from the ideal 90 electrical degrees. This effect can be compensated

by varying the phase angle between excitation currents when calculating feed harness

lengths using Christman's feed method. ~Iinor adjustments to the current magnitude

33

ratio resulted in feed harness lengths that produced clean cardioidal deep null patterns

when modeled using -:'\EC. It was noted during this iterative process that the first sol­

ution from the feed harness length calculation program [Ref. 7] produced feed harness

lengths that provided clean patterns, while the second solution from the program did not

produce the desired deep null patterns. Due to the need to keep this work within a

manageable scope, the cause of this effect was not pursued.

In order to test the validity of results obtained from ~EC modeling, three feed har­

nesses were constructed for field testing. The 60 MHz harness length was obtained by

direct application of Christman's feed method [Ref. 7], taking into account a 0.78

transmission line velocity factor and a 3.5 em correction for the length of connectors and

wires in the prototype antenna structure. The 55 and 66 :VI Hz harness lengths were

obtained by applying the compensation method described above, again using a 0. 78 Ye­

locity factor and a 3.5 em correction for connector and \\·ire lengths. The results of these

calculations and adjustments are sunm1arized in Table 4 below.

Table ..J. FEED HARi"ESS PHYSICAL LENGTHS

Harness Desi2n L 1 Len2th L2 Len2th Freq uency (\llfz) ( \1 ete1:-s) (:'vlete(s)

55 0.715 2.57S

('() 1.577 1.R59

66 1.-459 2.795

E. ANTENNA TESTING

The objecti\·e of this phase of the study was to see if the results predicted through

computer modeling agree with measurements. To check the predicted results, it was

necessary to measure the far field radiation pattern and the input impedance of the

prototype structure over a range of frequencies. In order to evaluate potential useful­

ness of this class of antennas for reduction of either mutual interference due to nearby

transmitters on adjacent frequencies or reduction of jamming from a transmitter some

distance a\\·ay, two cases were tested, one where the prototype antenna's far field pattern

was measured 100 meters a\\·ay, and a second case where the antenna's pattern was

measured 1000 meters away. Test data is then compared with predictions and conclu­

sions drt.1\\·n.

3-+

INSULATING SECTION

METALLIC SECTION --~

figure 2-J. Prototype Antenna Details, Construction

35

~- RADIATING ELEMENT

figure 25. Feedpoint Details

36

Figure .26. Photogr3ph. Completed Prototype Deep Null Antenna

37

figure 17. Photograph. Prototype Antenna Feedpoint Details

38

F. TEST SETUP

The setup to be used in the two tests is shown graphically in Figures 28 and 29.

Volunteer ~ssisw.nts rotated the proto ~ype antenna anJ collected data as necessary. A

hilltop site was chosen to aYoid reflections ofT nearby objects. anJ a line of sight path

to the 1000 meter reception site was identified. The ground at the test site was moist

sandy soil.

39

PROTOTYPE ANTENNA{r

/~ COORDINATION

UNK

100 METERS

AZIMUTH INDICATOR

DIPOLE ANTE..."'lliA CUT FOR 60 MHz

~ !COM R7000 RECEIVER

figure 28. Test Setup for 1\leasuring Radiation Pattern at 100 I\leters

40

VOICE COORDL~ATION

UNK AZIMUTH INDICATOR

1000 .METERS

VALLEY

VERTICAL DIPOLE ANTENNA CUT FOR 60 MHz

... ?11Caa.--- !COM R7000 RECEIVER

HILLTOP

figure 29. Tc~t Setup for J\leasuring Radiation Pattern at 1000 l\leters

41

V. PROTOTYPE ANTENNA EVALUATION

Testing of the prototype deep null antenna was conducted both in the laboratory

and in the field as outlined in the previous chapter. Field tests were done to include the

effects of real ground in the evaluation.

A. LABORATORY TESTS

Prior to conducting field tests of the prototype antenna, it was considered as prudent

to conduct some preliminary tests under controlled conditions to see if the structure and

feed scheme worked as predicted. This test was accomplished by raising the prototype

~mtenna on a mast (\\·ith an insulating section), exciting a vertical monopole about 80

meters ~m·ay \\'ith a signal generator, and using a receiver and rotator-turntable ar­

rangement to produce a logarithmic pob.r plot of the received signal strength versus

azimuth. Figures 30. 31 and 32 show the results of this test. It \\·as discovered during

the course of this test that the prototype antenna's actual resonant frequency was 59.25

\!Hz vice the 60.00 \;1 liz design frequency. This 1.2Y~ o departure from the design fre­

quency \\·as ,·in,·ed as minor, and the structure was not modified to correct this due to

test schedule considerations.

From Figures 30-32 it is evident that the deep null performance of the structure is

rclati\·ely na rrO\rband. and that it deteriorates rather quickly as the frequency of

excitation departs fr om the actual resonant frequency of the structure. During this se­

quence of tests it was noted that tuning in a television sound carrier at 59.7 5 \1Hz and

then running a signa l strength plot produced patterns that were neither cardioidal nor

deep null. Since this signal \\'as circularly polarized. the performance of the prototype

deep null antenna on signals other than vertical linear polarization is suspect. Tactical

Yl I r radio systems nearly always use vertical linear polarization, however. so the pro­

totype antenna's response to other types of polarization was not of immediate concern.

B. FIELD TESTING PROCEDURE

I. Field Test at 100 l\leter Range

The next stage of the testing procedure was to set up the prototype antenna in

the field. excite it with an A:\ , PRC-77 tactical VHF F\1 radio set, and measure the

signal strength at a range of I 00 meters. The test antenna was then rotated and another

measurement taken. This process was repeated at regular increments of azimuth until

~2

Figure 30. Laboratory Plot, f = 60.00 1\IHz! 60 1\'!Hz feed Harness

4.3

Figure 31. Laboratory Plot, F = 59.50 I\ 1Hz, 60 I\ 1Hz Feed Harness

44

Figure 32. Laboratory Plot, F= 59.25 1\11-Iz, 60 1\IHz Feed Harness

45

sufficient data to construct a polar plot of the antenna radiation pattern was obtained.

Signal strength readings were taken from the S-mcter of an I CO ~vi-R 7000 receiver, and

recorded on data collection forms. Additional passes through nulls were made as nec­

essary to get accurate strength readings at the null azimuths. Since the characteristics

of the recei\·er S-meter were not known, the recei\·er was connected to a signal generator,

and input signal strength versus S-meter reading data was taken. This allo\\'ed all signal

strength readings to be translated into microrolts, and the micro,·olt readings of signal

strength at many azimuths were obtained. In order to plot these readings on polar log­

arithmic graph paper the voltage ratios had to be converted to decibels using the re­

lationship:

v 2 dB=20logy

1

where: V2 = Reading for azimuth being plotted

V, = Maxi mum reading for any azimuth

(I)

The initial test run was done using the 60 :vi liz feed harness in order to make

an early comparison \Vith laboratory results. In order to test the validity of the feed

harness compensation method outlined earlier, the test structure was next excited using

the 55 and 66 :\I I Iz harnesses. Signal strength measurements were made for \·a rio us

I'requencies while again varying the azimuth to the recei\'ing antenna in increments.

Tests at 1000 l\leter Range

In order to test the prototype antenna's potential usefulness in eliminating

signals from jammers located in enemy controlled areas, the receiving setup \\'as relo­

cated to a hilltop about 1000 meters away, and another series of tests made. Since ra-

diation pattern data and bandwidth measurements were made in detail at 100 meters,

frequencies were chosen at which good null performance was expected. Feed harnesses

for 55, 60, and 66 :\II Iz were used, and data taken.

C. TEST RESULTS

1. Results at 100 l\ lcter Range

In each of the cases tested radiation patterns with substantial nulls were ob­

tained as shown by figures 33, 34 and 35. The results obtained during this sequence of

tests are in general agreement with the predictions obtained using 1\EC, and they show

46

that the predicted deep null behaYior can be obtained in practical structures. Further­

more. the test sequence demonstrated the behavior of the structure and feed harness at

frequencies abo\·e and below the structure and feed harness design frequencies. \Vhile

the figures sho\\·n above are indicative of the results obtained, additional test data is in­

cluded in Appendi:'\ C.

2. Results of Tests at 1000 l\1eter Range

Figures 36-38 show the prototype antenna's deep null characteristics at 1000

meters, and are in good agreement with plots taken at the 100 meter range. Since the

radiation patterns obtained agree ,,·ith those obtained for the same configuration at 100

meters. testing at close range can be done with some confidence that similar results

would be obtained at greater di~tances.

-+7

Figure 33. Radiation Pattern at 100 l\1, F= 59.25 1\IHz, 60 1\IHz Feed Harness

48

1 0

figure 34. Radiation Pattern at 100 l\1, f= 53.00 .IVIHz, 55 1\H-Iz feed Harness

49

Figure 35. Radiation Pattern at 100 1\1, F= 65.75 1\'IHz, 66 1\IHz Feed Harness

50

1 0

figure 36. Radiation Pattern at I Km, F= 59.25 I\lHz, 60 I\IHz feed Harness

51

figure 37. Radiation Pattern at 1 Km, F = 54.00 1\IHz, 55 .I\ 1Hz Feed Harness

52

figure 38. Radiation Pattern at 1 Km, f= 66.00 1\lHz, 66 1\IHz feed Harness

53

VI. ANALYSIS AND CONCLUSIONS

A. COl\'IPARISON OF RESULTS TO PREDICTIONS

HaYing predicted the performance of the prototype antenna under various config­

urations, excitations, and environments, and having field tested the antenna under some

(but not all) of the conditions simulated during computer modeling, some useful con­

clusions can be drawn and some observations made.

1. Bandwidth and Standing \Vave Ratio (S\VR) Characteristics

The bandwidth characteristics of the prototype antenna are such that current

military radios can operate into the antenna over a substantial range of frequencies. A

usable ba ;1 d\Yidth of over 20<% of the design frequency was predicted, and field testing

confirmed that prediction. At the resonant frequency of the structure, the S\VR ·was

computed (based on fonYard and ref1ected power readings) as 1.75 : 1. This is an ac­

ceptable S\\'R for a practical antenna system, but could probably be improYed by

"pruning" the antenna structure for resonance at exactly GO \1Hz. At the edges of the

usable bandwidth. S\\.R 's of 3.4 : 1 were calculated (again from fonv ard and reflected

power measurements). \Vhile these values are substantially higher than that obtained

at the structure resonant frequency. they are still within the usable range. as demon­

strateJ by the ability of the A:\ PRC-77 radio to work. into the prototype antenna dur­

ing testing. C se of low lo ss coaxial cable would be advisable in this situation. but even

\\'ith standard RG-8 type cable, transmission line losses at the S\\'R's encountered are

acceptable. AdJition or a simple matching network. between the transmitter and trans­

mission line would be advisable in high power systems, or ·where the transmitter in use

is not designed to couple into high S\YR loads. Location of a matching device at the

feed harness "Tee" is another possible means of reducing S\YR losses and improving

transmitter matching.

2. Radiation Pattern Comparisons

The radiation patterns obtained during field and laboratory testing agreed

closely with those predicted by :\EC modeling. The laboratory plots were much more

precise than those derived from field data, but overall agreement was remarkably close,

considering the limitations imposed by construction techniques, measurement equip­

ment. and normal experimental error. The prototype deep-null antenna appears to have

considerable potential for de\·clopment into a militarized antenna for tactical use. Fur-

54

ther testing to better define its performance on signals other than vertical linear

polarization is advisable. however.

B. REC01\L\IENDATIONS

\Vhilc this stuJy has resulted in confirmation of several predictions, it has also raised

numerous questions that, due to their nature and the need to limit the scope of this

study. ,,·ere not pursued beyond noting their existence and immediate impact on the

goals of the study as previously defined. These questions include:

• Can Christman's feed method be replaced with a network optimized for various frequencies throughout a desired operational bandwidth? If so, this would offer greater control o\·er radiation pattern shape. and might also allow reJuction of the standing wave ratio seen by the radio attached to the antenna.

• How far can the bandwidth of the prototype structure be stretched using Christman's feed method?

• Can the prototype structure be modeled at a higher frequency in order to ease the burden of further laboratory testing?

• Can the Yertical plane radiation pattern of the prototype structure be modified to impro\'e lo\\' angle radiation \\·hile presen·ing deep null performance?

• \Yhat are the performance characteristics of the prototype structure on signals of polarization other than \"Crticallinear?

• \Vhat other structures c\.hibit deep null characteristics, and arc they better or worse candiJates for de\·clopmcnt than the structure i1wcstigatcd herein?

These questions arc the basis for further work in this area, and proYide an indicator

of the scope of the subject.

55

APPENDIX A. CURRENT CALCULATION PROCEDURE

A. PURPOSE

Both :VII::\1::\EC and ::\EC require that the specified structure be excited by a volt­

age of magnitude and phase specified by the user. Since the antenna radiation charac­

teristics of interest derive from equal magnitude currents of specific phase relationships

f1owing in the structure elements. a procedure for calculating these excitation voltages

is needed.

This Appendix describes two procedures by V·:hich the required excitation voltages

may be found. Since both magnitude and phase are involved, and since the structure

impedance im·olves both real and imaginary components, it is advantageous to do all

such calculations on a computer. Improved accuracy and less time expended are the

b~ncfits of this approach.

B. T\\'0 PORT NEnVORK APPROACH

In order to find the excitation voltage that will produce equal magnitude currents

of the proper phase relationship. it is necessary to know the admittance of each element

to be driven. and the mutual admittance bet\\·ccn driven elements. This is accomplished

by exciting one element with one volt at a phase angle of zero degrees while shorting the

other clement to the ground structure. This produces a current value for the driven el­

ement and a current \·alue at the base of the element shorted to ground.

56

11 I2 + +

V1 V2

Figure 39. Tn o Port Netn ark.

Starting with the equation set for a two port network,

(J)

It can be seen that when the other monopole of the structure (the one that is not

excited) is connected to the ground plane elements, 1'2 = 0. Thus:

I I y __ 1

11- J" J·' =0 1 2 .

Since the monopoles arc identical, it follows that

57

(5)

The mutual admittance can be found by following the same line of reasoning:

y __ 1 I I

12- v2 vl = o (6)

(7)

~ate that 1~ 1 = 12 when V1 = 0 Yolt at a phase angle of zero. Since in this case the

current magnitudes in the t\\'O monopoles arc equal. it can be seen that the admittance

matrix is symmetric. i.e .. rll = }.22 and 1.12 = r21'

\\'hilc it is com·enient to deYclop the abo\·e argument in terms of admittances, cle­

ment impedances and mutual impedances arc needed when working with Christman's

feed line matching arrangement [Ref. 7]. By inYcrting the admittance matrix the

impcdJnce matrix can be obtained:

(8)

A \IA TI JCAD \0 routine [Ref 9] was \Hittcn to accomplish this matrix inversion in

order to a\·oid tedium and errors. The impedance values are then accessible for further

usc. The :'vi:\ THCAD co routine used is listed at the end of this appendix. \Vhcn the

impedance ,·alues are found, the feed system described in [Ref. 7] can be calculated using

the B:\S I C program presented therein. These transmission line lengths can then be

modeled using ~EC TL "cards."

C. A SHORTCUT l\IETHOD

\\'hile the abo\'e method is more general, it is possible to avoid much of the work

by placing a large resistance in the structure. then exciting it with a known voltage. The

resulting clement current is then essentially constant, so the impedance can be calculated

58

directly and then the loading resistance subtracted out. If the loading resistance is high

enough. the remainder after the subtraction is then:

(9)

(10)

These voltages can then be used to excite the two monopoles of the structure under

study. The correctness of this approach can be easily checked by looking at the currents

in the segments of the two monopoles nearest the ground plane structure. The currents

should be equal in magni~ude and difTer in phase by 90 degrees.

59

D. 1\IATRIX INVERSION ROUTINE

- USE THIS ROUTINE TO FIND MUTUAL IMPEDANCE BETWEEN ANTENNA ELEMENTS THEN USE THE MUTUAL IMPEDANCE WITH LEWALLEN'S PROGRAM TO FIND TRANSMISSION LINE LENGTHS TO GET DESIRED CURRENT RELATIONSHIPS. CF=58 MHz HERE)

28.892 i 811 .- --··---·---···2·TT angle of I1 current

360

i . 0 l 1 y 11 .04443·e complex form of Il = Yll

-150.784 812 --------·-- . 2 . TT angle of I2 current

360

i. 812 Yl2 .02206·e complex form of I2 Yl2

Y22 y 11 Y21 : = Y 12

from symmetry, Yll = Y22 and Yl2 thus the admittance matrix is

Y21,

y

2

2 =

[y ll Y2l

- l y

y 12-J Y22

by applying Ohm's law to the admittance matrix

~6.206 - l4.335i L 13.052 - 7.044i

13.052 - 7.044i] 26.206 - l4.335i_

the element impedance for use with Lewallen's program is thus 211 or 212, and the mutual impedance is 212 or 221

60

APPENDIX B. FEEDLINE LENGTH CALCULATION l\1ETHOD

A. PURPOSE

The experimental approach used in this study makes extensive use of Christman 's

feed [Ref. 7]. In order to provide better documentation of the methods used in this work,

the program is listed here. The theoretical work that provides the basis for this program

is presented in Christman's paper [Ref. 7] and is not repeated due to its length and

complexity.

B. BASIC PROGRAl\1 LISTING

100 RErl 110 REH SIMPLIFIED FEED SYSTEM FOR TWO-ELEHENT ARRAYS 120 REM ROY W. LEWALLEN, W7EL 130 REM 7 JAN. 1985 140 RH1 150 REM ANGULAR CALCULATIO~S ARE DONE IN RADIANS; 160 RE~l INPUTS AND OUTPUTS ARE IN DEGREES. 170 RH1 180 PRINT 190 PRINT 200 PRINT "R, X OF LEADI~G ELErlENT (OHMS)" 210 INPUT R1,X1 220 PRINT "R,X OF LAGGING ELErlENT (OHMS)" 230 IKPUT R2,X2 240 PRI~T "~1UTUAL R, X ( OHNS)" 250 INPUT R3,X3 260 PRINT "EL.2:EL. 1 CURRENT MAGNITUDE, PHASE" 270 PRINT "--PHASE !'lUST BE ZERO OR NEGAT IVE (DEGREES)" 280 I NPUT M,P 290 IF P<=O THEN 340 300 PRINT "PHASE MUST BE NON -POSITI VE, SINCE EL.2 IS" 310 PRI NT "DEFINED AS BEING THE LAGGING ELEl'lENT" 320 PRINT 330 GO TO 260 340 PRINT "FEEDLINE 1,2 IMPEDANCE (OHHS)" 350 INPUT F1,F2 360 LET P1=3. 14159 370 LET J=O 380 LET C1=COS(P*P1/180)/M 390 LET S1=SI N( P*P1/180)/M 400 LET H=R2+C1*R3+S1*X3 410 LET A=(R3+C1*R1+S1*X1)/H 420 LET B=S1*F1/H 430 LET C=((X3+C1*X1-S1*R1)*H-(X2+C1*X3-S1*R3)*(R3+C1*R1+S1*X1))/F2/H 440 LET D=F1 ~·:( C 1 ~·:H- S 1~':( X2+C 1~':X3- S 1 ~·:R3)) /F2/H 500 LET Q=2-(A*A+B*B+C*C+D*D) 510 LET E=(A*A+C*C-B*B-D*D)/Q

61

520 LET F=2*( A*B+C*D) / Q 530 LET R=E 540 LET I=F 55 0 GOSUB 810 560 LET G1=V 57 0 IF U<1 THEN 910 580 LET X=ATN( SQR(U*U-1)) 590 LET T1=(X+G1)/2 600 IF T1=>0 THEN 620 610 LET T1=T1+2*P1 620 IF T1<P1 THEN 640 630 LET T1=T1-P1 640 LET I=C*COS(T1)+D*SIN(T1) 650 LET R=A*COS(T1)+B*SIN(T1) 660 GOSUB 810 670 IF V=> THEN 690 68 0 LET V=V+2•'•P 1 690 IF J=1 THEN 790 700 PRINT 710 PRI NT II "," ZO=";F1;" OHMS","ZO=";F2;" OHNS" 720 PRI NT II ","TO LEAD. EL. ","TO LAG. EL. II

730 PRit\T II ","ELE CT L. (DEG. )","ELECT. L. (DEG. ) 11

740 PRI NT 75 0 PRINT "FIRST SOLN. II ,T1•'•180/P1,V•'•180/P1 760 LET J=1 770 LET X=2•'•P1-X 780 GO TO 590 790 PR I NT "SECOND SOLN. II' T1'"•180/P1 'V•'t-180/P1 800 GO TO 970 810 REN RECTANGULAR-POLAR SUBROUTINE 820 LET U=SQR( R*R+I*I) 830 IF u=O THEt\ 870 840 IF ABS(U+R)<1. OE-7 THEN 890 850 LET V=2*ATN( I /(U+R ) ) 860 RETURN 870 LET V=O 880 RE TURN 890 LET V=P1 900 RETURN 910 PRIKT 920 PRit\T "NO SOLUTION FOR THE SPECIFIED PARANETERS." 930 PRINT 11 WOULD YOU LIKE TO TRY DIFFERENT 11

940 PRINT "FEEDLINE ZO'S (Y/ N)?" 950 INPUT A$ 960 IF A$=11 Y11 THEN 340 970 PRINT 980 PRINT 990 END

62

APPENDIX C. ADDITIONAL TEST DATA

A. GROUND PLANE STRUCTURE VARIATION PLOTS

2 MONOPOLES, F=60 MHZ, THETA=120 DEG, 6 GROUND RADIALS DROOPED AT 120 DEG (STRUCTURE 28)

0

PATTERN GAIN ltl OBI 180 ••••••••••HORIZONTAL

-·-VERTICAL

----TOTAL

AtiGLES IN DEGRHS TRUE

figure 40. Radials Drooped at 120 Degrees from l\lonopoles

63

2 MONOPOLES, F=60 MHZ, 6 RADIALS DROOPED AT 135 DEG FREE SPACE, (STRUCTURE 38)

0

PATTERN GAIN IN OBI 180 • • • • • •• • ••HORIZONTAL

-·--VERTICAL

----TOTAL

AHG LES IN DEGREES TRUE

figure 41. Radials Drooped at 135 Degrees from 1\lonopoles

64

2 MONOPOLES, F=60 MHZ, 6 RADIALS AT THETA=150 DEG (STRUCTURE 48)

0

PATTERN GAIN IN OBI 180 • •• • • • •• ••HORIZONTAL

-·-VERTICAL

----TOTAL

ANGLES IN DEGREES TRUE:

Figure 42. Radials Drooped at ISO Degrees from I\lonopoles

65

B. ADDITIONAL LAllORATORY PLOTS

1. 55 l\11-Iz Feed Harness

Figure 43. 55 l\lHz Harness, F= 53.75 l\11-lz, Laboratory Plot

66

Figure 4..J. 55 I\ 1Hz Harness, F = S..J.OO 1\IHz, Laboratory Plot

67

figure 45. 55 I\ 1Hz Harness, F = 5-tSO 1\IHz, Laboratory Plot

68

Figure 46. 55 1\lHz Harness, F = 55.00 1\lHz, Laboratory Plot

69

2. 60 1\lHz Feed Harness

Figure 47. 60 l\11 Iz Harness, F = 58.50 l\11-Iz, Laboratory Plot

70

figure -tS. 60 1\IHz Harness, f = 59.00 1\IHz, Laboratory Plot

71

Figure 49. 60 1\IHz Harness, F = 59.35 1\IHz, Laboratory Plot

72

Figure 50. 60 I\ 1Hz Harness, F = 60.00 I\ 1Hz, Laboratory Plot

73

figure 51. 60 I\ 1Hz Harness, f = 60.50 I\ 1Hz, Laboratory Plot

74

3. 66 1\IHz Feed Harness

Figure 52. 66 l\11--Iz Harness, F= 6-tOO !\1Hz, Laborator)' Plot

75

figure 53. 66 l\IHz Harness, f = 64.50 I\ 1Hz, Laboratory Plot

76

figure 5-t. 66 I\ 1Hz Harness, F = 65.00 I\ 1Hz, Laboratory Plot

77

figure 55. 66 1\lHz Harness, f = 65.50 1\lHz, Laboratory Plot

78

Figure 56. 66 I\ I Hz Harness, f = 66.00 I\ 1Hz, Laboratory Plot

79

Figure 57. 66 1\IHz Harness, F = 66.50 1\IHz, Laboratory Plot

80

APPENDIX D. NEC DATASETS

A. ELEI\IENT AD I\ lilT ANCE AND I\'IUTUAL ADI\IITT ANCE

The dataset below was used to find the currents at the bases of the two monopoles

of the test structures investigated. The current in segment one of tag one is the element

admittance, and the current in segment one of tag two (the base of the other monopole)

is the mutual admittance. These admittance values are used as shown in Appendix A

to find the impedance matrix for the te st structure.

CM TEST STRUCTURE n1. TWO QTR WAVE MONOPOLES ABOVE AN ARTIFICIAL CM GROUND PLANE WITH RADIALS AT 90 DEGREES TO DRIVEN MONOPOLES. CM ONLY ONE MONOPOLE DRIVEN CM ENTIRE STRUCTCRE ELEVATED 10 METERS ABOVE GROUND. CE mv- 1,5,o,o. 625,1o,o,o. 625,11. 25,0. oo6 G\v 2,5,o,-o. 625,10,o,-o. 625,11. 25,0. oo6 GW 3 , 5 , 0 , 0. 6 2 5 , 10 , - 1. 2 5 , 0. 6 2 5 , 1 0 , 0. 0 0 6 G\v 4 , 5 , o , o. 6 2 5 , 1 o , o , 1. 8 7 5 , 1 o , o. o o 6 GW 5 , 5 , 0 , 0. 6 2 5 , 1 0 , 1. 2 5 , 0. 6 2 5 , 1 0 , 0. 0 0 6 GW 6,5,0,. 625,10,0,-. 625,10,0. 006 GW 7,5,0,-0. 625,10,1. 25,-0. 625,10,0. 006 G\v 8 , 5 , o , - o. 6 2 5 , 1 o , o , - 1. 8 7 5 , 1 o , o. o o 6 GW 9,5,0,-0. 625,10,-1.25,-0. 625,10,0. 006 GE FR 0,0,0,0,60 EX 0 , 1, 1 , 0 , 1 , 0 PL 3,2,0,4 RP 0,1,361,1501,80,0,0,1 XQ E~

B. GROUND RADIALS AT 120 DEGREE ANGLE TO l\10NOPOLES

This dataset \\·as used to inYestigate the effects of putting the ground radials at an

angle of 120 degrees to the monopoles. The corresponding radiation pattern plot is in

Appendix C.

CM TEST STRUCTURE f/2. TWO QTR \vAVE MO~OPOLES IN FREE SPACE CM WITH RADIALS AT 120 DEGREES TO DRIVEN MONOPOLES CM MONOPOLES DRIVEN VIA TL SECTIONS TO GET PROPER CURRENTS CE GW 1,5,0,0. 625,0,0,0. 625,1. 25,0. 006 GW 2 , 5 , 0 , - 0. 6 2 5 , 0 , 0 , - 0 . 6 2 5 , 1. 2 5 , 0 . 0 0 6 GW 3,5,0,0. 625,0,-1. 083,0.625,-0. 625,0.006 G\v 4 , 5 , o , o . 6 2 s , o , o , 1. 7 o 8 , - o . 6 2 5 , o . o o 6

81

GW 5,5,0,0. 625,0,1. 083,0. 625,-0. 625,0. 006 GW 6 , 5 , 0 , . 6 2 5 , 0 , 0 , -. 6 2 5 , 0 , 0. 0 0 6 GW 7,5,0,-0.625,0,1.083,-0.625,-0.625,0.006 GW 8,5,0,-0. 625,0,0,-1. 708,-0. 625,0. 006 m.,r 9,5,o,-o. 625,0,-1. 083,-o. 625,-o. 625,o. oo6 G\v 99,1,10000,10000,10000,10000,10000.05,10000,5E-4 GE FR 0,0,0,0,60 TL 1 , 1 , 9 9 , 1 , 50 , 1. 3 3 6 , 0 , 0 , 0 , 0 TL 2,1,99,1,50,1. 865,0,0,0,0 EX 0,99,1,0,1,0 PL 3,2,0,4 RP 0,1,361,1501,90,0,0,1 XQ EN

C. GROUND RADIALS AT 135 DEGREE ANGLE TO I\10NOPOLES

The dataset below \"ras used to find the effects of drooping the ground radials at an

angle of 13.5 degrees from the radiating monopoles. The radiation pattern plot for this

dataset is in Appendix C.

CH TEST STRUCTURE #3. TWO QTR WAVE ~10NOPOLES IN FREE SPACE CM ~ITH RAD IALS AT 135 DEGREES TO DRIVEN HONOPOLES. CM MONOPOLES EXCITED VIA TL SECTIONS CE mv 1,5,o,o. 625,o,o,o. 625,1. 25,o. oo6 G\<,7 2,5,0,-0. 625,0,0,-0. 625,1. 25,0. 006 GW 3, 5, 0,0. 625,0,-0. 884,0.625,-0.884,0.006 GW 4,5,0,0. 625,0,0,1.509,-0.884,0.006 GW 5,5,0,0. 625,0,0 .884,0. 625,-0. 884,0. 006 GW 6,5,0,. 625,0,0,-. 625,0,0. 006 GW 7 ,5,0,-0. 625,0,0. 884,-0. 625,-0. 884,0. 006 m.,r 8, 5, o, -o. 625, o , o, -1. 509, -o. 884, o. oo6 Gw· 9,5,o,-o. 625,o,-o. 884,-o. 625,-o. 884,o. oo6 GW 99,1,10000,10000,10000,10000,10000.05,10000,5E-4 GE FR 0,0,0,0,60 TL 1, 1, 9 9, 1, 50, 1. 25 6, 0, 0, 0, 0 TL 2, 1, 9 9, 1, 50, 1. 7 3 7, 0, 0, 0, 0 EX 0,99,1,0,1,0 PL 3,2,0,4 RP 0,1,361,1501,90,0,0,1 XQ EN

82

D. GROUND RADIALS AT 150 DEGREE ANGLE TO l\10NOPOLES

The following dataset was used to inYestigate the effects of drooping the ground

radials at an angle of 150 degrees from the radiating monopoles. The radiation pattern

plot for this dataset is in Appendix C.

CM TEST STRUCTURE U4. TWO QTR WAVE MONOPOLES IN FREE SPACE CM WITH RADIALS AT 150 DEGREES TO DRIVEN MONOPOLES CM BOTH MONOPOLES EXCITED VIA TL SECTIONS CE G\v 1 , 5 , o , o . 6 2 5 , o , o , o . 6 2 5 , 1. 2 5 , o . o o 6 GW 2 , 5 , 0 , - 0. 6 2 5 , 0 , 0 , - 0. 6 2 5 , 1. 2 5 , 0. 0 0 6 G\v 3,5,o,o. 625,o,-o. 625,o. 625,-1. o83,o. oo6 GW 4 , 5 , 0 , 0. 6 2 5 , 0 , 0 , 1. 2 50 , - 1. 0 8 3 , 0. 0 0 6 GW 5,5,0,0. 625,0,0. 625,0. 625,-1. 083,0. 006 GW 6, 5, 0,. 625, 0, 0,-. 625,0, 0. 006 G\v 7, 5, o, -o. 625, o, o. 625, -o. 625,-1. o83, o. oo6 GW 8,5,0,-0. 625,0,0,-1. 250,-1. 083,0. 006 GW 9 , 5 , 0 , - 0. 6 2 5 , 0 , - 0. 6 2 5 , - 0. 6 2 5 , - 1. 0 8 3 , 0. 0 0 6 GW 99,1,10000,10000,1000 0 ,10000,10000.05,10000,5E-4 GE TL 1,1,99, 1,50,1. 214,0,0,0,0 TL 2,1,99,1,50,1.662,0,0,0,0 FR 0,0,0,0,60 EX 0,1,1,0,1,0 PL 3,2,0,4 RP 0,1,361,1501,90,0,0,1 XQ EN

E. TEST STRUCTURE Sll\IULATION OYER Il\IPERFECT GROUND

The :\.'EC dataset belo\\' was used to add the effects of imperfect ground to the test

structure model.

C ~l TEST STRUCTURE # 1. TWO QTR \\'AVE ~101'-iOPOLES ABOVE AN ARTIFICIAL Cf1 GROUND PLANE WITH RADIALS AT 90 DEGREES TO DRIVEN MONOPOLES. C ~l CURRE~T FEED ACCOflPLISHED USING TWO TL SECTIONS. CM E~TIRE STRUCTURE ELEVATED 10 METERS ABOVE GROUND. CM 9M MAST WITH 1M INSULATING SECTION SUPPORT USED. CM GOOD GROUND: EPSILON=34, SIGMA=. 15 CE GW 1,5,0,0. 625,10,0,0. 625,11. 25,0. 006 G\v 2 , 5 , o , - o. 6 2 5 , 1 o , o , - o. 6 2 5 , 11. 2 5 , o. o o 6 G\V 3 , 5 , 0 , 0 . 6 2 5 , 1 0 , - 1. 2 5 , 0. 6 2 5 , 1 0 , 0. 0 0 6 GW 4 , 5 , 0 , 0. 6 2 5 , 10 , 0 , 1. 8 7 5 , 1 0 , 0. 0 0 6 G\V 5 , 5 , 0 , 0. 6 2 5 , 10 , 1. 2 5 , 0. 6 2 5 , 1 0 , 0. 0 0 6 G\v 6 , 5 , o , . 6 2 5 , 1 o , o , - . 6 2 5 , 1 o , o. o o 6 G\v 7 , 5 , o , - o. 6 2 5 , 1 o , 1. 2 5 , - o. 6 2 5 , 1 o , o. o o 6 GW 8 , 5 , 0 , - 0. 6 2 5 , 1 0 , 0 , - 1. 8 7 5 , 10 , 0. 0 0 6 GW 9 , 5 , 0 , - 0. 6 2 5 , 1 0 , - 1. 2 5 , - 0. 6 2 5 , 1 0 , 0. 0 0 6 GW 1 0 , 5 , 0 , 0 , 0 , 0 , 0 , 9 , . 0 2

83

GW 99,1,10000,10000,10000,10000,10000.05,10000,5E-4 GE FR 0,0,0,0,60 GN 0,0,0,34,.15 TL 1,1,99,1,50,2.067,0,0,0,0 TL 2,1,99,1,50,2.428,0,0,0,0 EX 0,99,1,0,1,0 PL 3,2,0,4 RP 0,1,361,1501,80,0,0,1 XQ EN

F. SURFACE \VAVE l\IODEL OF PROTOTYPE ANTENNA

The :\EC dataset bela\,. was used to model the prototype antenna over imperfect

ground with the effects of the surface wave included. -:\"ate that prior to using this list­

ing. it was necess<lry to create the required lookup ta ble of ground characteristics using

SO\J:\EC. The SO\r,:EC card required to get a lookup table for poor ground is sh0\n1

bela \\·.

2. 5 '. 000 22' 60.

-:\" ote that the epsilon . sigma and frequency values (2.5. 0.000.22. 60). must match those

in the :\EC dataset being used.

C~1 SURFACE \vAVE STUDY-- TWO QTR WAVE HOt\OPOLES ABOVE AN ARTIFICIAL CM GROUND PLANE WITH RADIALS AT 90 DEGREES TO DRIVEN HO NO POLES. Cf1 CURRENT FEED ACC OHPLISHE D USING T\-lO TL SECTIONS. CH EKTIRE STRUCTURE ELEVATED 10 ~IETERS ABOVE GROUND. CM 9M METALLI C HAST WITH 1M INSULATING SECTION USED. CM SURFACE WAVE I NCLUDED VERSION OF GP10M3B STRUCTURE CM GROUKD CHARACTERISTICS: EPSILON=2.5, SIGHA=.00022 CE G\v 1, 5, 0, 0. 625, 10,0, 0. 625, 11. 25, 0. 006 GW 2, 5, 0 , -0. 625, 10, 0, -0. 625, 11. 25, 0. 006 G\v 3,5, o ,o. 625,10,-1. 25,o. 625,1o,o. oo6 GW 5 , 5 , 0 , 0. 6 2 5 , 1 0 , 1. 2 5 , 0. 6 2 5 , 1 0 , 0. 0 0 6 G\v 6 , 5 , 0 , . 6 2 5 , 1 0 , 0 , -. 6 2 5 , 1 0 , 0. 0 0 6 GW 7 , 5 , 0 , - 0. 6 2 5 , 1 0 , 1. 2 5 , - 0. 6 2 5 , 1 0 , 0. 0 0 6 G\-J 9 , 5 , 0 , - 0. 6 2 5 , 1 0 , - 1. 2 5 , - 0. 6 2 5 , 1 0 , 0. 0 0 6 G\{ 1 0 ' 5 ' 0 ' 0 ) 0 ' 0 ' 0 ' 9 ' . 0 2 GW 99,1,10000,10000 ,10000,10000,10000.05,10000,5E-4 GE FR 0,0,0,0,60 GN 2,0,0,0,2.5,.00022 TL 1 , 1 , 9 9 , 1 , 50 , 2. 0 6 7 , 0 , 0 , 0 , 0 TL 2,1,99,1,50,2. 428,0,0,0,0 EX 0 ,99,1,0,165.567,0 PL 3 ,2,1,0

S-+

RP 1,1,361,1000,10,0,0,1,1000 PL 3,2,2,0 RP 1,1,361,1000,10,0,0,1,1000 PL 3,2,3,0 RP 1,1,361,1000,10,0,0,1,1000 XQ EN

This dataset produces all data needed to plot the vertical, horizontal and radial compo­

nents of the total field at the specified observation points, 1000 meters from the test

antenna in this case.

85

LIST OF REFERENCES

I. Kraus, John D., Anrennas. \t1cGra\v-Hill Book Co., ~ew York, 1950.

2. Jordan, Edward C. and Balmain, Keith G., Electromagnetic TV aves and Radiating

~):stems, Prentice-Hall, Inc., Englewood Cliffs, ::\J, 1968.

3. American Radio Relay League, The ARRL Antenna Book, 15th ed., American Ra­

dio Relay League, ~e,Yington, CT, 1988.

4. Christman. Al. "Ele,·ated Vertical Antenna Systems." QST. v. 72. pp. 35--12, Amer­

ican Radio Relay League, :\e\\·ington, CT, August 1988.

5. Logan. J. C. and Rock\\·ay, J. \V., The Sew "\!ISISEC f Version 3; : A .\!ini­

.Ywnerical Elecrromagnetics Code, ~aval Ocean Systems Center, San Diego. C--\,

September 1986.

6. Breakall. J. K. and others, Anrenna Engineering Handbook., v. 1. p. 19. La\nence

Livermore :\ational Laboratory. Livermore. CA, 1987.

7. Christman, Al. "A Voltage-matching \lethod for Feeding Two-tower Arrays,"

IEEE Transaczions on Broadcasting, v. BC-33, ::\o. 2. pp. 33--12. June 1987.

8. \lelody. James V .. "An HF Phased Array C sing Twisted-\\·ire Hybrid Directional

Couplers." ARRL Amenna Compendium, v. I , pp. 67-71, American Radio Relay

League. :\ewington, CT, 1985.

9. \lathsoft Inc., JIATHCAD [jsers .\fanual, \1athsoft, Inc., Cambridge, \tlA. 1988.

86

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4. Cormnunication Oflicers School :\Iarine Corps Combat De\·elopment Center Quantico. VA 2213-l

5. Professor R. \V. Adler Code 62Ab :-\aval Post£raduate School :\Ionterey. CA 939-43

6. Professor J. K. Breakall Code 62l3k :-\aval Postgraduate School \Ionterey. CA 939-43

7. Commandant of the :Vlarine Corps Code TE 06 Headquarters C. S. :\Iarine Corps \Vashington. D.C. 203SO-OOOI

8. :\Iajor K. A. Vincent CS:\·IC ASST P:\/1 (Terminal Systems) CO:Vl:\1 :\AV Code C2C :\ICRDAC Quantico, VA 2213-l

9. Professor Al Christman Electrical Engineering Department Grove CitY Colleee Grove Cit~·. PA ( 6 127

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87

:\o. Copies

2

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88

IT I v~ Thesis c. V6865

c.l Vincent

Deep null antennas and their applications to tactical VHF radio communications.

~II~ ----~~-~~_~·r_Y_l ______ ~_-7_~ ~-7_~_

Thesis V6865 c.l

Vincent Deep null a ntenna s a nd

their applica tions to tactical VHF radio communications.

Deep null antennas and their application

1111111 1111111111111111111111111 11111 11111 1111111111111111111 11111111111 11111 111