Research and Development Technical Report ECOM-4357

•---"

ROTOR BLADE EFFECTS ON L-BAND S IGNALS RECEIVED BY

[•.: g,"

HELICOPTER ANTENNAS MOUNTED ABOVE THE ROTOR BLADE: CW EXPERIMENTS

0r

M. DeSantis Schwering

°•,!i,•"C. SF. ,-

Communications/Automatic Data Processing Laboratory

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ODISTR IBUTION STATZMENT

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for pubitc release; CoApproves distribution unlimited.."

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US ARMY ELECTRONICS COMMAND FORT MONMOUTH,

NEW JERSEY 07703

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Disclaimers

The findings in this report are not to be construed as an official Department of the Army position, unless so designated by other authoriyed documents. The citation of trade names and names of manufacturers in this report is not to be construed as official Government indorsement or approval of commercial products or services referenced herein.

Disposition Destroy this report when it is no longer rteeded. return it to the originator.

Do not

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REPORT DOCUMENTATION PAGE EPL2.GOVT

___

ACCGSION NO.

3

RLý.

-IECdM-it¶ 30' T

LEwd~bttl.~flOR .AE LFFECTS ON J.-"AM10 /5JGNALS RFCCIVED WBYELUICPER AN4TENNAS M0UNTED1 A8OVE THt ROTOR BLADt: CW EXPERtNENTS._____

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Fort Monmouth, New Jersey 07703

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CONTROLLING OFFICE NAME AND ADDRESS

LZ.ASK

Commiunications/Automatic Data Processing Lab.

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U.S.Army Electronics Cormmand Fort._Monmouth,_N._J._07703 14.

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chwering

11.PERFORMING ORGANIZATION NAý41EAND ADURESS Comnumnications/Automatic Data Proc.,Lab.L AMSEL-NL-RH 11.

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MONITORING AGENCY NAME & AOORESS(il different from Controllfing Office)

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Aproedfor public release; diht4ribution unlimited.....-

1.

DISTRIBUTION STATEMENT

WS SUPPLEMENTARY

19.

K(EY WONr*-

(of the abaitrael entered in Block 20. 111difierent train Report)

NOTES

...

re.verse aide it necensat-

Rotor moduldtion;

and identity by blockt n imber.

L-band navigation system;

Helicopter antennas; Shielding effect of rotor. 20

-

A664ACT (Continue an reverse. aide It neeoaaary end Ident~ity by block number)

Rotor effects on L-Band signals received by helicopter antennas have been examined experimentally. CW data for two receiving-antenna locations the rotor blade, viz, at the turning axis of the blade aid on thie tai ¶ is presented. This data shows the amplitude and phase variations to be exj~--: ted as a function of the direction of the incident signal. The effects of counterpoise size and height above the main rotor are also studied . T n it is shown that the signal variations were typically 85% the data is comparable to that for the 1 •-diameter counterpoise. Peak-to-peak fluctuations in amplitude were even greater for some cases than the attenuation levels shown in Figs. 8 and 9. However, increased receiver sensitivity is more difficult to achieve than dynamic range in current GPS receivers, hence the attenuation data is a better indicator of receiver requirements. C.

Phase Variations

The 3-dimensional plots given in Fig. 10 (for center position) and Fig. 11 (for tail position) show the maximum phase shifts sustained by the received signals as a function of the direction of incidence. The phase variations, of course, are continuous functions of rotor positior; in some cases these variations may be symmetrical about 00 while in others they may occur in one direction only. It is difficult to estimate the effect of these phase variations on receiver performance without additional knowledge of the receiver design. However, in those cases where a 1800 shift occurs, an incorrect bit is introduced into the code and, even for somewhat smaller

1 X at the rotor tips. 'The level received when the rotor was moved to the position of least interference.

3

Table I.

Azimuth and Polar Angles Considered for CW Rotor £2ade Modulation Tests; Antenna at Center Position

Counterpoise D-lamer 2 \ I x

Polarization

Direction of -Incidence

Horizortal

Vertical

Height auove r•otc' ar (in

(in degrees) 45

60

S5

105

x

x

0- 1

x

x

NM

0-1

0.1

x

K

K

x

0-1

0.1

180

x

x

x

NM

0-1

0.2

0

x

x

x

x

0-I

0.1

90

x

x

x

NM

0-1

0.1

180

x

x

x

NM

0-1

0.1

90

x

x

x

NM

0 -1

0.1

0

x

180

x

0

NM: not measured. x 'measured

4

I

-

-

-

&.

Table I&..Azimuth and Polar Angles Considered for CW Rotor Blade Modulatiun Tests; Antenna on Tail DIreto Drection ofPlarizaton of Coun er, PO zajto Height above Rotor Counterpols

Inciim

11 LHorizontal

(Tn degrees) 55

70

0

x

x

45 90

x x

x x

180

x

0 90 180

45

60

85

105

I A,

2~x

t

aa

S

St

("n A,

x

0-1

0.3

t

x

0-1 0-1

0.3 0.3

x

t

x

0-1

0.3

x

x

x

0-1

0.3

x x

x x

t t t

x NM

0-1 NM

0.3 NM

0

x

x

t

x

0-1

0.2

90 180

x x

x x

t t

x x

0-1 0-1

0.2 0.2

0 45 90 135 180

x

x

t

x

0-1

0.2

x x x x

x x x x

t t t t

x x x x

0-1 0-1 0-1 0-1

0.1 0.2 0.1 0.1

-110

x

x

t

NM

NM

NM

- 45 110

x x

x x

t

x

NN NM

NM NM

-110

x

x

t

x

NM

NM

- 45

x

x

t

x

NM

NM

110

x

x

t

x

-1 i 0

x

x

NM NM

NM NM

-4S 110

x x

x x

t

x x

NM NM

NM NM

-110

x

x

t

x

NM

NM

- 45

x

x

x

NM

NM

85

105

eDiamter

Vertical

NM: not measured;

x: measured:

t: only zero position measured.

t

phase deviations, long integration intervals in the receiver could result in the detection of a large number of bits with incorrect coding information. For 0 ',850, nhase variations increase drastically and, in some directiorts, phase • IBO 10eversa's shifts occur. 4.

DATA ANALYSIS It is apparent from Figs. 8 to 11 that the tail position is a better location for the antenna than the center position. Consider in particular the data for = 105c, which simulates a turning and banking maneuver. For this ;ŽuZU, angle, regardless of antenna placement (center or tail position on helicopter), signil degradation is severe. Although this degradation obtains for all zc'; angles at the center location, severe fluctuations at the tail location occur only over an azimuth range of -. 60' around . = 0'. In the former case, the rotor always intercepts the signal at the polar angle 'C••' regardless of the azimuth; for this reason loss of lock in the receiver is a distinct possibility. At the tail location, however, the blade does not intercept the signal directly except over the azimuth range just mentioned. Furthermore, most helicopters normally fly in a pitched-forward attitude, so that the directions of incidence in the tests where large signal perturbations occurred, such as ! =15' and i -', may not occur in practice. Considerably different responses were observed between horizontally and vertically polarized signals. In general, the horizontally polarized signals exhibited greater amplitude and phase fluctuations over all angles of incidence and, in particular, near grazing incidence. The reason for this behavior can be seen from the following argument. The tangential component of the e~ectric fiela in the incident wave must be zero at the metal surface of the rotor blade. It is apparent that the greatest disturbance in the received field will occur when the blade is in the plane of incidence, rather than perpendicular to it. In the latter case, the effective scatter area of the blade, from which significant contributions to the received field strengtrn are made, is considerably reduced, as shown qualitatively in Fig. 12(a). Figure 12(b) shows the increased blade area from which scattering contributes to the receiving antenna when the blade is parallel to the plane of incidence. This is indeed th2 case as shown by the data presented in Appendices II and

I

III. The following description pertains to the parallel orientation of the blade. In this case, for horizontal polarization of the incident signal, the electric field of the incident wave is entirely tangertial to the blade, and trie reflection coefficient at the metal surface is -l, i.e., total re'Ilection with a phase reversal. Thus, near grazinr incidence, 90", vinere the path lengths of the direct and reflected field are appruxii'ately ehua, the tiw, field components tend to cancel at the receiving antenna, producing zero signal. On the other hand, the tangential component of a vertically polarized signal is a function of incidence angle and approaches zero near' grazing incidence. The reflection coefficient at the blade surface is +1, i.e., tota! reflection but no phase reversal, and the equal path lengths occurring at shallow incidence angles result in reinforcement of the received signal. At - = 0', the rotor causes a strong scatter field for both polarizations since there is essentially no difference in the tangential component of the incident wave. Nowever, the counterpoise effectively shields the antenna f:'om this disturbance. For angles of incidence between the t'io limiting cases ( O0 and 0' = 90'),the tanQential component of the 6

L

...

:

horizontally nolari:ed signal will always be greater than that of the vertically polarized signal, and the fluctuations due to scattering will be more severe. This behdvior becon;es more apparent at increasing angles of incide.mce. Circular polarization should minimize some of the fluctuations observed since they are caused by reflections from metal surfaces and will have a polarization sense opposite to that of the incident radiation. The helicopter antennas, of course, should he designed for optimum reception of the latter radiation. Similar phase and amplitude distortions were measured at the two antenna positions for polar angles 470*. Examination of the curves in Appendices II and III also shows that the worst-case conditions depicted in Figs. 8, 9, 10, and 11 artually occur rover, at most, a 40" sector of rotor rotation for the tail position and a 60' sector for the center position. Two such disturbances occur for each complete rotation of a single-bladed helicopter. Since the rotor on the UH-lB turns at v330 rpm, a disturbance of the signal occurs at an 11 Hz rate with a duration of -20 to 30 msec per disturbance, depending on the location of the antenna. This fact coupled with the signal degradation levels given in Figs. 8 to 11 is indicative of the receiver sensitivity required at the present time. 5. CONCLUSIONS The results of this study show that it is more advantageous from an electrical as well as from a mechanical standpoint to locate the antenna on the tail rather than at the center of the helicopter. However, an antenna assembiy which is aerodynamically acceptable must be designed. Two electrical problems still exist for the tail location. Because of the long RF cable from the antenna on the tail to the receiver in the cabin, a low-noise preamplifier may be necessary to maintain an acceptable signal-to-noise ratio. The second problem involves the poor response of planar antennas to signals arriving at or near grazing incidence. In this case, antennas of nonplanar design or conical spirals are strongly recommended. However, such threedimensional designs are subject to somewhat greater influence from the rotor and helicopter. In this regard, the counterpoise having a diameter of one wavelength was found to be sufficient to minimize rotor modulation of the type discussed previously. The larger diameter counterpoise is more effective at the center location. Follow-up studies to determine the proper single antenna configuration, and investigation of multiple antenna configurations using switching and/or phasing techniques should be undertaken as a next step. ACKNOWLEDGMENTS The authors wish to thank Mr. J. R. Wills of the Antenna Research Team of the Communications/Automatic Data Processing Laboratory, ECOM, for his able assistance in performing the numerous and detailed measurements of this study. Thanks are also given Messrs. I. Levine and J. Gray of the Avionics Laboratory, ECOM, for their technical and administrative support, and to the U. S. Army Satellite Communications Agency, the sponsor of the program leading to the results given in this report and those given in reports ECOM-4254 and-4255, September 1974. 7

!

Pn t

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Fig. 1. Wayside test site.

8f~k

X

L

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4al

to P01

0.

cmA

k

tlit

FIG. 3-CW TRANSMITTING, RECEIVING, RECORDING, AND ROTOR POSITIONING EQUIPMENT

10

Receiving Antenna and Counterpo~ise

JA

4

Fig. 4(a).

RECEIVING ANTENNA ABOVE ROTOR

(CENTER

POSITION)

DIPOLE ANTENNA PLEXIGLASS

S-

BUBBLE

COUNTERPOISE TEFLON BEARING

4,-OSUPPORT TUBE

ROTOR

N

I

•

HOLLOW ROTOR SHAFT

100,

i

i -~

Ft4

-

(

II

'

I ISYNCHRO-

I SPOSITIONER

DJUSINGPLATFORM SHEIHT HEIGHT ADJUSTING COLLAR

FIG.

4(b).

STATIONARY

MOUNTED IN THE HELICOPTER ANTENNA AND SUPPORT TUBE 12

p1

Receiving Antenna S

nd Counterpoise

FIG. 5- RECEIVING ANTENNA ABOVE ROTOR

13

(TAIL

POSITION)

tI

114

i-i

l OWI NG SSt T I rIIE n II C ONS T R A I NT iM PO SE D BY

,

14

R

T

AI L R ONTF •

*

DIRECTION 0F INCIDENCE

I

I;I

BLADE

I

"1

HELICOPTER LONG AXIS

FIG. 7-COORDINATE SYSTEM FOR CW ROTOR BLADE MODULATION EXPERIMENTS

15

!* I

A!

I I

NOT MEASURED

INM:

:

'I jI

FIG.

8-

AMPLITUDE REDUCTION DUE TO ROTOR BLADE-

WORST CASE RECEPTION (EXPERIMENTAL) FOR ANTENNA ABOVE ROTOR (CENTER PosITION)

16

-of

FIG.

9.

kMPLITUDE, REDUCTION DUE TO ROTOR BLADEWORST CASE RECEPTION (EXPERIMENTAL) FOR ANTENNA ABOVE R0om (TAIL POSITION).

17

z

*

am0

11Apo

I

NM: NOT MEASURED

I'

I Ip t

FIG.

10.

PHASE DISTORTION DUE TO ROTOR BLADEFOR WORST CASE RECEPTION (EXPERIMENTAL) ANTENNA ABOVE ROTOR (CENTER POSITION)

18

I

A

4ei

FIG. 11,

PHASE DISTORTION DUE TO ROTOR BLADFWORST CASE RECEPTION (EXPERIMENTAL) FOR ANTENNA ABOVE ROTOR (TAIL POSITION)

*19

INCIDENT WAVE

EFECTIVE

0

"- SCATTER AREA

a) ROTOR PERPENDICULAH TO PLANE OF INCIDENCE

INIDN

IIý

:

•mANTENN A

II

II EFFECTIVE

SCATTER AREA

i)

FIG,

12-

ROTOR PARALLEL TO PLANE OF INCIDENCE

EFFECrIVE SCATTER AREA OF THE ROTOR PLADE

20

APPENU;X I TOR--PLADE JFFFCTS UN A.NTENNAS WORST-CASt ANAI.Y!-;,F )r AT THIL TURNINC AXIS THE ROTOR MOUNTHf) AROV!

.c.-,id -'r the ba(ksc(jtLer of th, rutur blade and its effect on a signal receio,', at thf. antennti in the configurtioti illustrated by Fig. 1-1(a). Scatt-rinQ will be q,-eatest when the rotor blade is parallel to the plane of An inciincidence, is depicted in Fig. I-lhb). the worst-cdse configuration. dent plane wave field, in the two-di,,ensional case of Fig. 1-1(b) given by , 0 ex j,-.,)k(jx + .z)

(1)

To some illuminates the antenna and rotor blade. where .i - -sin,,, ..... extent, a counterpuise shields the antenna from the backscattered field of the rotor. This field accordling to rl] is:

E2(xý 7)

a )•ar2 ,o-

2. 2rv

173/l~•..oZep(ju I-u ds, (2)

-ar

a is the rotor blaae half-width, and primed quanwhere r - V(y'-t) 2 + z2 tities denote obsevvation points. What is the resultant field at the antenna? We assume that: Tc simplify this problem, several assumptions will be made. (1) the strongest distortion oF the received field occurs only when the blade is in the plane of incidence (see the Sections "Data Analysis" and "Conclusions"); (2) the rotor blade surface is planar; (3) the blade extends to tin one dimension; (4) the effect of counterpoise shielding on the rotor is negligible [see Fig. 1-1(b)]; and (5) the phase fronts of the scattered field at the location of the counterpoise are planar. Although these assumptions result in a somewhat greater reduction in the total field at the antenna than, ictuafly occurs, they provide an upper bound on the magnitude of the reduction and permit a simplification of Eq. (2):

E2 (x',z) = Eo.A(z).exp(-.jx'

sine),

where

[1]

F. Schwering and c. M. De Santis, "Rotor effects on L-band signals Part I: A theoretical study. received by helicopter antennas. Research effect)," (shielding Amplitude reduction and phase shift Electronics S. Army U. ECOM-4254, Report and Development Technical Command, Fort Monmouth, N. J., September 1974 (AD 787363). 21

(3)

a

A(z)

;

*f .z.ose d 12 coexpL-jW z4_Zs2 cose exPCOS + + 3-n)lTY (z +sds 2)3/444

=+

A(Z) +

All I ,ear dimensions have been normalized by multiplication with k 2w/X. The field expressed by Eq. (3) illuminates the counterpoise from below, When Eq. (3) and the appropriate Green's function for a plane surface are used in Green's Theorem, the field scattered by the counterpoise is 1b

21r

Ee(x'z)

E(x',h) 7re E

_ P,(5r

r2 + . The geometry for this aspect of the problem is shown in Fig. l-2(a). Integration with respect to 0 and partial integration over r may be performed to give:

where R -

t

b-,

E3(z

=

sn•

i•:!•

0O•

E3(z) +EoA(h)';-ýJo(r sine)"T

JR

b + sine- b Jl(r sine)

jR RFdr

(6)

forX' = . Jo and J1 are the first- and second-order Bessel functions of the first kind. A(h) is obtained from Eq. (4) for Z = h. Equations (3) and (6) are added to obtain the total field received at the antenna location when the field produced by the rotor is scattered by the counterpoise, i.e, E2 3 (z)

=

E2 (z) + E3 (z).

(7)

A further contribution to the total field at the antenna sidped: the backscatter of the finite diameter counterpoise the primary field.Using The Green's coordinate systemtheapplicable to this 1-2(b). Theorem, field of in Fig. approximate set of boundary conditions at Z primary = h, -E=(r,h)

Ecounterpoise(rh)

Ecounterpoise(r.h) - 0

for r < b

must be conilluminated by problem is shown Eq. (1) and an

4t. INA

for r > b,

22

4,Af

the backscatter field is: 2Tr

Ecounterpoise()

where R over r yields

E

r

.

Counterpoise

+

b

E +

0

te.jR• El(r,h)

j R

0

r dr do

(8) 4

Integration with respect to o and partial integration

(c)

+ Eo.-.exp(jh cose). {d(r sine) e

0R

-Rb b 0

b

-JR + sine.j Jl(r sine) e p,

(

0 The total field at the antenna due to this contribution is given by: Ecl (z) = E1 (z) + Ecounterpoise(z)

.

(10)

The total field at the antenna from all sources can then be determined by adding Eqs. (7) and (10):

(11)

ET = E2 3 + Ecl.

Equation (11) has been programmed for numerical evaluation,and some results for e = 450 and 850 are shown in Figs. 1-3 tc I-4.* Figure 1-3 also illustrates the effect of counterpoise diameter. The amplitude curves are referenced to the theoretical value of the received field at the 0 position (i.e., l x above the rotor). Comparison of these curves with the appropriate data of Appendix II shows fairly good agreement with regard to the amplitude excursions and the slope of the phase variations. Further detail is lost in the experimental data. The abrupt change in phase shown in Fig. 1-3 (a 3600 phase jump) was caused by the automatic plotting routine and was not a true effect. A more exact theory of rotor modulation for the antenna at both positions above the rotor blade has been attempted, but no results are available at the present time. At or near grazing incidence, this theoretical description of counterpoise In fact, the curves in Fig. 1-4 effects cannot be expected to be accurate. for 0 < h < 1 x, the However, tend to diverge with increasing height. results. measured theory is in fair agreement with the

23

,dr

•

INCIDENT WAVE

A,

ANTENNA

COUNTERPOISE

001,

a) COORDINATE SYSTEM FOR GENERAL PROBLEM

b/

,2

/

/ ANTENNA

//

/

/x#

/

/

"\*

INCIDENT WAVE

N.AI COUNTERPOISE

\

SHADOW REGION (GEOMETRICAL)

/

/

ROTOR PARALLEL TO PLANE OF INCIDENCE

b) WORST CASE CONFIGURATION

FIG.

I-I-

TYPICAL ROTOR SCATTERING PROBLEM 24

ANTENNA COUNTERPOISE.

//

.

INCIDENT WAVE

PLANE_ OFROTOR_ a)

GEOMETRY FOR DETERMINATION OF COUNTERPOISE EFFECT ON FIELD SCATTERED FROM ROTOR

INCIDENT WAVZ

ANTENNA COUNTERPOISE

b)

FIG.

GEOMETRY FOR DETERMINATION OF BACKSCATTER FROM COUNTERPOISE !N PRIMARY FIELD

1-2-

SCATTER EFFECTS CAUSED BY COUNTERPOISE 25 -4

......................

...

.. . .. . .. .

.... .. .. +X

. .... .. ..6

. ..

.~..

.

.

.

.

. . . ..

. . .

.

. . .........

...

.

jý

.

I.

.

. . .

.

.

.

.

.

.

.

...... .

.. . . . . . . . .

27,

.

...

APPENDIX II EXPERIMENTAL DATA CHARACTERIZING THE SIGNAL FLUCTUATIONS AT THE CENTER LOCATION ABOVE THE ROTOR All of the data taken to characterize signal reception at the center location above the rotor blade is shown in the curves of this appendix. In general, eight such curves are required for each set of polar and azimuth angles (o,ý considered. Data for two different sized counterpoises (dia. =1 X , 2x ) is presented for horizontal and vertical polarization. Typically, four odd- and four even-numbered illustrations are presented for each direction of incidence. The odd-numbered figures show the amplitude and phase variations actually measured for the zero position whereas the even-numbered figures are composites generated from the measured data showing the signal variations as a function of height. Only small-counterpoise data for both polarizations is available at ý = 900, 1800 for all e values considered. However, the small counterpoise is less effective as a shield against rotor scatter than the large counterpoise; thus the small-counterpoise data represents worst-case conditions at these azimuth angles. The even-numbered figures for any given (e,f)set consist of multiple curves displaying amplitude and phase changes as a function of neight for several fixed rotor positions. These fixed positions have been selected from the measured data to show the amplitude and phase variations to be expected over the full 3600 rotation of the blade. Two rotor positions, =0' and =900, are shown in each of the even-numbered figures. In addition, a third rotor position, and sometimes a fourth- and a fifth position are shown for clarification of the variations which occurred for the various directions of incidence. The composite amplitude curves show that horizontally polarized incident signals undergo stronger scattering from the rotor than vertically polarized signals, especially at shallower angles of incidence. The composite phase curves shown in the even-numbered figures require some explanation. First of all, some of the curves show an abrupt change of phase with height. These breaks are due to the method of plotting only and do not represent phase reversals of the signal. Since the phase variation measured as a function of height is greater than 3600 for some directions of incidence and since the graph ordinate range is limited to 3600, some of the curves have been broken into two parts in order to show the entire variation. True phase reversals, i.e., Aý a l80*, were observed only for horizontally polarized signals arriving at e = 1050, =900. The slope of the phase curves, which gives an indication of the polar angle of arrival, are as anticipated (i.e., steeper for small polar angles than for near grazing incidence). This behavior agrees with the theoretical curves of Appendix I. *

*

Some comments on the individual figures given in this Appendix are: (1) Figures 11-1 to 11-12 show the set a 450, c~=0, 180'; only two azimuth angles were examined since these directions show helicopter body effects. Note that the larger counterpoise is a more effective shield than the smaller counterpoise. Note also that greater fluctuations result from horizontal polarization than from vertical polarization; 28

(2) Figures 11-13 to 11-24 show the set e - 600 and o = 00, 180*. Differences in the shielding effectiveness of the large and small counterpoise become less significant for this direction of incidence. The general characteristic of all these curves is that there is a I to 2 dB increase in the amplitude variations as compared to those considered in (1) above; (3) Figures 11-25 to 11-40 show the set e = 850 and € = 00 900 1800. Note here that the ordinate for some of the amplitude curves is 10 dB per major division rather than 5 dB and that the slope of the phase curves is decreasing with increasing polar angle. Additional rotor positions have been included to indicate theincreased scatter effects of the rotor at large polar angles; also not3, in contrast to the previous cases of (1) and (2) above, that a change in height did not reduce the scatter effects of the rotor and that there was practically no differench in the shielding effectiveness of the large and the small counterpoise. The azimuth angle 0 = 900 is shown for comparison with € 00 and 1800 in order to indicate multipath eff. .. s of the helicopter body; (4) Figures 11-41 to 11-44 show the set e = 1050 and o- 900. This direction of incidence will occur during turning and banking maneuvers; it is apparent (although no measurements were made) that at e = 1050 and 1800, the antenna will be completely shielded from the direct signal 1= by the te4" boom, the tail fin, and the tail rotor resulting in complete signal d, .- out. True 180' phase reversals in the received signal occurred for this cirection of incidence.

,I

"ii

29

.L-2.>...A

~

a.a2,.

rT

..

A~~aAl

4

-.--.

--3 4

[

-S -

-20-

POLARIZATION AT

72z*

-6

_ _

-

AMPLITUDE AND PHASE VARIATIONS FOR SMALL COUNTERPOISE AND

~HORIZONTAL

_

-

4-

__20

FIG.II-1.

-

081 _

T

_

t

H

t

_

-

,- .-

-

-~-

_

_

_

_

_

_7

-

-

...-

,-----

-

-

-Irv -.

Ki'-30

V

.......-

.

.

.

.

I~

......

..

...... I.

.......

....... ..

1..

................................................ ,

4s,4

*1I

.4..........I

.44

.

FIG.~~~~ PHS

.. . .

AN

,

.

AMLTD

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---- -

--

-

30

1- 1

-~

120----

,--

1 0Leo

1it7 3 120 1777V ~

~

FIG. 11-3.

.

PHASE AND AMPLITUDE VARIATIONS FOR

SMALL

COUNTERPOISE

AND

VERTICAL POLARIZATION AT 60 e-4S,ý

~~-1~~~

--

.

0-

d-±I-f~-k

--

.

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32

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4.

.......

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e

.;: .:1..:

. .

FI.11-4.

.....

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. . . . . . . . .

PHASE AND AMPLITUDE VARIATIONS FOR SMALL COUNTERPOISE AND

VERTICAL POLARIZATION AT

a 04,~

*

a.

A* LD.A

.............

.4.

.

.

. .

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.

.... .: .. ..:.. (.... ............................ 33122

-+~45.

-

-

+1O-0~

t10-

40

I

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FIG. I1-5.

PHASE AND AMPLITUDE VARIATIONS FOR LARGE COUNTERPOISE AND HORIZONTAL POLARIZATION AT

e

*

144'

~

00a

1

j1S_

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FIG. 11-7.

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-

-

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I

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0j1

0-

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PHASE AND AM4PLITUDE VARIATIONS FOR LARGE COUNTFRPOISE AND VERTICAL POLARIZATION AT

~

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1------- u

36

0

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PHASE AND AMPLITUDE VARIATIONS AND FOR LARGE COUNTERPOISE "AT 4 ) IPOLARIZATION VERTICAL0

".... ..

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i'F' ,.A••I • ''

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FIG. 11-9.

I

_i_7

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-------

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PHASE AND AMPLITUDE VARIATIONS FOR SMALL COUNTERPOISE AND HORIZONTAL POLARIZATION AT 645*, *1800

W-

-... _

--

-7

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E 71 ~

A

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....... ...

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110

PHS

AN

AMLTD

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HORIZONTAL POLARIZATION AT o-4S', * 1800

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V

10

II-11.

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*

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2

: ------

1

lO

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--

PHASE AND AMPLITUDE VARIATIONS FOR SMALL COUNTERPOISE AND VERTICAL POLARIZATION AT

72'

-6

'40-

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FIG. 11-13.

e ~

4

-

60*,

0*

m72*

w1

--- -

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--

36'

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-

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8

--

_ T

__

At%-

-7_

_

_

PHASE AND AMPLITUDE VARIATIONS FOR SMALL COUNTERPOISE AND POLARIZATION AT

_____HORIZONTAL

144'

_

_

-30-1i20-_____ ______

}

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_

60

-

----

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4

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t

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HOIONA POLRIZTIO AdT

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... . .114

NLTUEVRAIN PHS.N FIG.~~~~~~~~~~

.412

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FIG. LI-is.

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J-30-120-

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PHASE AND AMPLITUDE VARIATIONS FOR SMALL COUNTERPOISE AND VERT-CAL POLARIZATION AT

4-

--77___7-7

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FIG. 11_27- AMPLITUEAND-HA-E-VA-ATION

_____FO

1440

SMALL_

AND______

2

b-lp..

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d I6

...

COUNTRPOIS

2.

--

.

.

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h..i

.

.

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.

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.

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FIG. 11-28.

. .

.

.

..

,.....I

..

AMPLITUDE AND PHASE VARIATIONS FOR SMALL COUNTERPOISE AND VERTICAL POLARIZATION AT

e

0.

.

00W

850,

..

.

.

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57

.

.

...

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D

.... .

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.

FIG. ~

~ APIUEADPAEVRAIN ~ -4 612, 0 1ONEROS2N

FOR LAG

FIG.1-29

HORPIZOTUEAL

e '36'

--

~~

1:72

8* s,

DPOLARIZ

*

VATIONATIN

= 0

108

____70.oc -

_

....

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1-6-.

J6 -'-4

___

44

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14

__

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. i i~r 7~

-------

58

FIG. 11-30.

AMPLITUDE AND PHASE VARIATIONS

,

FOR LARGE COUNTERPOISE AND

qo.

. ......... .

. . . . .. . . . . . . . . . . . .

. . ..

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................ ?J7:....7

O

.......

$

............. l.......--........ ...................................

59

....

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1

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10- -40

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2

FIG. 11-31.

_ _

.-

108

_

_

_______

_______ ________I ________ _______

-4-.

-.

.....

AMPLITUDE AND PHASE VARIATIONS FOR LARGE COUNTERPOISE AND VERTICAL POLARIZATION AT

2__

*

-

_

2_

__

-Z ------

60

-- -

- - - - --

_

:2..::~2.:..~L.:.I.2.:.:2{2:242..2

;.......

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FIG. 11-32.

AMPLITUDE AND PHASE VARIATIONS FOR LARGE COUNTERPOISE AND VERTICAL POLARIZATION AT....

I..

.

...............................

t .71

.. . . .

.. .~..

.

.

61

4-

FIG. 11-33.

AMPLITUDE AND PHASE VARIATIONS FOR SM4ALL COUNTERPOISE AND HORIZONTAL POLARIZATION AT

-7 5 -----

O

62

.

.*

.,

......

...............

PHRAE SFIG. 11-34.

AMPLITUDE AND PHASE VARIATIONS. FOR SMALL COUNTERPOISE AND

HORIZONTAL POLARIZATION AT

as'

.

.I

90'

........ ..........

ple1

-h.

63

--

4 -~

+45~ +10-

.~ii430-

FIG. I1-3S.

36_

_

__

_

20- 18

so, *

900

72'

wIIO lob4.

4-----4-0 -

---

a

_

j

AMPLITUDE AND PHASE VARIATIONS FOR SM4ALL COUNTERPOISE AND VERTICAL POLARIZATION AT

e

_

I-

120---

---t

---

.

V7T

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...

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FIG. oitFOR

.

. ...

S

(dI

...

....

I1-$6.

4

...........

...

AMPLITUDE AND PHASE VARIATIONS SMALL COUNTIERP•OISE• AND VERTICAL POLARIZATION AT 6 * iS•',% 90* "

..

*

lirO

".

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.,.

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.

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tl*.xi.

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--- 40 i 160-

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FOR SMALL COUNTERPOISE AND HORIZONTAL 0

8S.,

PHLASEIVARIONATION 1800

2:1

-

66

-

-

4.•

-4..

14-

4--

t .

AMPLITUDE AND OHASE VARIATIONS "FOR SMALL COUNTERPOISE AND......... A HORIZONTAL POLARIZATION AT 1800, - sS,*s 0

li) FIG. 11-38.

* .

.4~**

*,-A

&,-

... .....

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,

•.

.

•

,,n . . . ..

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20-4SO-

--

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0-

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VERTICAL POLARIZATION AT 0 85%.~ 180*

72 -'

-

-

-

--

--

--

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0

4-

.-

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kiI

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1800

.. . .

.. .

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AMPLITUDE AND PHASE VARIATIONS FOR SMALL COUNTERPOISE AND VERTICAL POLARIZATION AT.. e - 8s,*

. .

.. .. .

.

...

.

.e

o. FIG. 11-40.

I.

.

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.

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.

.

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.

.

.

.

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VP

0

691

-

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-

-20-

80-t---I___

10

I

____

20

80-

-30.1120-AMPLITUDE AND PHASE VARIATIONS SMALL COUNTERPOISE AND HORIZONTAL POLARIZATION AT e=los0 , *=900

FIG. 11-41. _____FOR

1440__

180,

-

-

_ __

____

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10B

4--

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--

70

316

72'

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L ; ............ . t . ................................... 4-4 "

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~.

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.... ....... . ..........

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RP ISAND + +.• :: .FIG+ 11 +42 : 4i -:+ IT FIGI 42

AMPLITUDE AND PHASE VARIATIONS AND

W. FOR SMALL COUNTERPOISE HORIZONTAL POLARIZATION AT sloSe, 90.

~ 3

•....

......

T

st

*1,,

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,

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.

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.... ~._ .....

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FIG. 11-43.

0..

AMPLITUDE AND PHASE2 VARIATIONS FOR SM4ALL COUNTERPOISE AND VERTICAL POLARIZATION AT g*90 1050,. 6 72'

360

-

oL O....

...

ý>108

ICIE

-4.*

J-7I.77

~

2

-j----6-

77

_

..

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--------------

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P

A

.AL

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T*

.

i, 1

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.

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acSi :9:91'

I.

I.

.-

APPENDIX III SELECTED EXPERIMENTAL DATA CHARACTERIZING THE SIGNAL FLUCTUATIONS AT THE TAIL ABOVE THE ROTOR The first set of curves (Figs. III-11 to 111-7) shows small counterpoise data for both polarizations at zero height. The second set of curves (Figs. 111-8 to 111-38) shows large counterpoise data for both polarizations. Here, however, a selection of curves f'rom the measured data is presented to illustrate the best and worst signal reception as a function of height. Somewhat different polar angle settings were used for the tail position measurements to compensate for the fact that the antenna-to-transmitter distance was changing with azimuth angle. A comparison with the data of Appendix II reveals several features in the curves of Appendix III: (1) There is a decrease in the magnitude and duration of the amplitude variations as a function of rotor position; (2) Differences in response to horizontal and vertical polarizaoccur. However, for some directions of incidence, the vertically still tion polarized signal is received virtually undisturbed; (3) The phase deviations for all directions of incidence were smaller and no 1800 phase reversals occurred. Some curves are also presented to show the effect of tail rotor proximity. In general, the tail rotor does not interfere except at banking angles. However, there may still be other *tirections of incidence not investigated during this study where a strong reflection from this blade can occur. In such a case, the counterpoise should provide adequate shielding. The shielding effectiveness of the different-sized countorpoises is more apparent in the curves of Appendix III due to the narrower range over which the disturbances occur. As expected, the large counterpoise provided better shielding. However, the counterpoise size had little or no effect on vertically polarized signals while notable changes occurred for horizontally polarized signals. This is due to the fact that the tangential electric field must be zero at the surface of the metal disk, and that the electric field component in the horizontally polarized signal is always greater than or equal to that in the vertically polarized signal. Hence the vertically polarized signal is influenced to a lesser degree by the counterpoise. The test results show that the small counterpoise should provide effective shielding at the tail location. The following notes discuss details of the individual curves: 900, 1800 are shown for the 1 X (1) Curves for e = 55' and =00, diameter counterpoise in Figs. II1-1 and 111-2 and for the 2 X counterpoise in Figs. 111-8 to 111-15. This data shows peak-to-peak amplitude variations < 7 dB in the worst case with no sign~ificant phase variations; =0', 900 are shown ,.n Fig. (2) Curves for the set e 700 and 111-3 and in Figs. 111-16 to 111-21 according to counterpoise size. Compared 74

to case (1,somewhat greater amplitude and phase variations occurred for this direction of incidence. Signal reception was not affected by movement of the tail rotor; (3) Curves for the set a 850 and o QO, 450, 900, 1800 are shown in Figs. 111-4 and 111-5 and in Figs. 111-22 to 111-28. In general, significant differences occurred for the two polarizations. However, for some directions of incidence in this set, only one curve is presented since no best/worst case could be distinguished. At * - 900 and horizontal polarizatilon, scattering from the tail rotor occurred; (4) Curves for the set e = l05* and o = 00, 450, 900o 1100 are shown in Figs. 111-6 and 111-7, and in Figs. 111-29 to 111-38. Severe signal distortions can occur during bankipig and turning maneuvers since there is a marked difference between polarizations and there may be some blockage due to the rotor shaft at o a 00. For horizontal polarization, a strong tail rotor effect occurs at o - 450 and h 1.2 x.

75

IE'

FIG. 111-1. -

--

PHASE AND AMPLITUDE VARIATIONS FOR LARGE COUNTERPOISE AND HORIZONTAL POLARIZATION AT e =sso, It 0*O, h OX

.04

76 Al

S50

0%

h

1I

1!JI I

Eli

lvio

4.1~

hi

77

1,

PATTERN NO.

_ii

-

-

PROJECT

1.

ENGRS. ,REMARKS.

._,_

i

FIG.

111-3.

-

_____

I

1

PHASE AND AMPLITUDE VARIATI.4S9" FOR LARGE COUNTERPOISE AND VERTICAL POLARIZATION AT h =0 X ,., e - SS'

*"

IIO

_

___

ii

_

,

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•____

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|

I'

-

. . .

___ ___

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2%7

128

76

IP

FIG. 111-4. _____FOR

I

j

E

PHASE AND AMPL~tUDE VARIATIONS LARGE COUNTERPO ISE AND HORIZONTAL POLARIZATION AT A 0% h *0.8 4 e s* 55

ea--..---

-

1-2

-

a

2W

72-t

79j

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FIG. -

-

-

-

p

~~-

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hl..

1.

X..

-

FOR LARGE COUNTERPOJSE AND

VERTICAL POLARIZATION AT 0 " SS*, * " 90°, h = 1.2k

=-

-

90

PHASE AND AMPLITUDE VARIATIONS

Ill-S.

° -

s.

--

.

-

4 ..

II I -

*

14

--

-

-

-I .

.

.

.

4-.

-72

-

-36'

'

, ,. -

.

-

•

80

. .

-.

-

ENGRS.

...

w .

S.

PROJECT

'

'

-

-

-

-

PATTERN NO.

-

-

,

,

REMARKS

V

.

T

FIG.

...

111-6.

..

.

.-.

.

S,

.

.. .

.

..

..

.

I

..

PHASE AND AMPLITUDE VARIATIONS FOR LARGE COUNTERPOISE AND VERTICAL POLARIZATION AT 00.4 A 6 - SS, 0 - 90', h

.

..

SU

II

I

-

-

-I

-

-

24L 36

7

r---f UO

81

"

A. l' .. .. " r4t4 81

I"

pT

I

I

m FIG. 111-7.

PHASE AND AMPLITUDE VARIATIONS FOA& LARGE COUNTERPOISE AND HORIZONTAL POLARIZATION AT 0 55*, **90% h *0)

14

0

1i1

'4 -

-1 Sl107

'

82

1 1!

'

Ij

ILL

,I

LIl ,II!

•' ,IT.

*4-

. ..

:.

i

' '

il1

IK,

jiI

1

i l

•

il

I

1

fl I

,1

LL

-

-•

I

i

I

::

l

'.

-i-

'

1A II-8.

FIG. '

I

-

PHASE AND AMPLITUDE VARIATIONS FOR LARGE COUNTERPOISE AND HORIZONTAL POLARIZATION AT eSSo, * = 1800, h 0X

.-

•

-

-

-

.

.

..

-...

.

..

toi

-,

V

-i-,

-

,

J

,

I

-

'

..

.

" :1 240

-

-

!. :~

.

-

--

:"1 i

83

-•

- -•---

-

-

-

..- ,-*

_

i

FIG. 111-9.

-r-t+HORIZONTAL

PHASE AND AMPLITUDE VARIATIONS FOR LARGE COUNTERPOISE AND POLARIZATION AT 70*I

10J

0i

h

0

HL

I

84

*II

I

w

FIG. II1-10.

0

85

PHASE AND AMPLITUDE VARIATIONS FOR LARGE COUNTERPOISE AND HORIZONTAL POLARIZATION AT

... ... . .. .... .....

!

S

-

-.-

-,

....

.... .......

-...

,- :i: •-:.,ii , -i:.......e

.

..

.FIG.

-8 .

S......

. .. .. . 14 4-.

-

- b-

0-.-

-

PHASE AND APLITUDE VARIATIONS FOR LARGE COUNTERPOISE AND VERTICAL POLARIZATION ATr -. ?0,• * - 0', b " 0

.

. .

g,

U. "

_

I

_I_

14'"

___

__,,

_

86

"_____

...

36"

-

-

-

. -.-

----

~

A)

-A

P

tf~

4-i

FI.111-12.

PHASE AND AMPLITUDE VARIATIONS

e

-4

-70%

*

0%O h

A~

-0.4

1

-

i441

111 Hz-

N_4

tp -

~

-

a

-

-

-

-

-

-

-

.

..

FOR LARGE COUNTERPOI SE AND

.... -

-

PROJECT

A.1 .IG .1-3 A ..LTDVARIATIONS. . ..

PHS -

~

POLARIZATION AT

-VERTICAL

8 - 70% * 90% h a 1.Z TAIL BLADE: HORIZONTAL -

-

-

-

-

--

. . .

-

-

-. .

.

-m

-. .

..

w -.

-..--

tip..

-.

Z2~

)24

88

-.-.-

)

-.....-

__~~

:

pPATTERN

'T

PROJECT ENGRS.

':.:; -

-

-

....-

~....,..

REMARKS

-

- -

FIG. 111-14. --

-

NO.

-

-

-VERTICAL

PHASE AND AMPLITUDE VARIATIONS FOR LARGE COUNTERPOISE AND POLARIZATION AT

h 6 - 700, *a90% TAIL BLADE: VERTICAL

.

. .. .. .

12

4.

4-

2 A

.

.

.

~-

4-

.

..

-24....~ 41---........

*...........i

-

PATTERN NO. -

-

-

-

PROJECT

ENGRS. --

-

-

-

-

*-

-or

REMARKS

*mm

-rr ______ -

-

...

.~

.. .,

-

- i

---

-

. . .

........2I.111.

44

PAEADAPIUEVRAIN

-

----- 90 I

FIG. 111-16. -

'HORIZONTAL

.....

PHASE AND AMPL1TUDE VARIATIONS FOR LARGE COUNTERPOISE AND POLARIZATION AT 8SO, 00,O" h 0

Ilk

I

IlI

I Flo 7

V9

I4

FIGI. I11-17.

-~~

PHASE AND AMPL ITUDE VARIATIONS FOR LARGE COUNTERPOISE AND HORIZONTAL POI.ARIZATION AT 9

-

TATIL

92

8S*,

BLADE:

-900,

h

-

1.2

IORI ZGNTAL

~

IL

0 II.

[I

4FOR K.......... III

IFIG.

le,

I

LARGE

..A ! ...I

._...__

PHASF. AND AMPLITUDF VARIATIONS COUNTERPOISEL

AND

I

21 ..

1'2

108

72"

93

6.

3

i

PAMl RN NO -~.

MARKc,

4.........Rý

I

--..

~----..~,.-..

f I~.

.

1.

Ii

-~~

1HASI. AND) AMP!. IDT1 ["OR LARGI. (B3UN rRPOI SI ,ND VlERTICAL. PoLARI ZAr IOfN AT h) - 0 . ý - 9O*, ..- 85*, Ir i RIZONTA 1 TAT!. RLA ii:

~~12

-

I24

_

72____

_______94

P

--..---

to

--

PROJECT .

FN(;PRS

L9

--

.

144__

.

"'AT~rRN

I I

NO

PROJECT FNGRS REMARKS

i-

Ln

-

I

I"

-

FIG.

-

.. -

0.

*.. ..

....

IE

VARIATIONS

FOR LARGE COUNTERPOISE AND VERTICAL POLARIZATION AT , h0 - 0 !)o 0 - 8 ,

I

_____

-

-. --

.---- .- .-

jl

1I I

--A

' '

/

-4.-----

,

AND AMPLITUDE

PHASE

111-20.

I,,

__..

.. .. .____. _.. .

-

-

-

-

,

7

95

•5

...... ....

... 7.... F IG 11 -1

W1

.i

AMPLIHIN

VArUDE(N

FRLAR(,I COUNTIRPOI SI AND VIRr(Al, ll(UARI ,A'IION AT h1 - O 18C, 80

I E3 rd

IL'

t*

4

Vt 4

72'

_

96

36

'

-

-

-

.

.

.

.

' -

-t-

----

S..........

----

1'-22.

.FIG.

-

"

1

!

*

--

-

-

.

- 7 -.

-

-

-

PHASE AND AMPLITUDE VARIATIONS FOR LARGE COUNTERPOISE AND

VERTICAL POLARIZATION AT 0 ,x, 0°, h -e - 1 5 ,

I'

______ __

_ _I

-.... - --..

-----

- -... ,--..

. . . .. . .. . ... . . . . .

I

-------V-----

. .•.. . ... 4

.

..

_.

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

F

2

'

.

.

.

.

.

a

j

I--

_,_ _-•

V

________....

241'

-70

)4A98

97

FIG.

111-23.

PHASI: AND AMPLITUDE VARIATIONS FOR IAG OLNTYRPOIS AND fi(RlC)NI'l.POLARI 0

_____

14

k

'0,

ZAT ION A h

-

0

X

--

v_

~~

9P

I_-

AgA

FIG. 111-24. -l8l

99

PHASE AND AMPLITUDE VARTUAHONS FOR LARGE COUNTERPOISE AND VERTICAL POLARIZATION Al 10lS*, * 450, h 0 kX

In' EL~

0

FIG.

111-2S.

IFop I

C.

PHASE AND AMPLITUDIU

VAN1ATIONS

LARG: COtJN'rFRfl) S[: -W) FI~ORIZZONrAL POLAR I:AT ION .T A IO5*, 4'- 4S*. h - I 2 TAIL1 BLADE: HIORI ZONTAL

i

100

FI.112.PHS

N

MLTUEVRAIN

HORIZONTAL POLARI'ATION AT 0 - 10W, s - 45*, h * 1. TAIL BLADE: VERTICAL

150

o90

6

101

KI In

I

FIG. 111-27.

60FOR

PHASE AND AM4PLITUDE VARIATIONS e-O~.ShO , LARGE COUNTERPOISE AND HORIZONTAL POLARIZATION AT

W.

1....

h

0 X

KI

10'

CI

0

90

102

60

39

LA

ni

FIG.

PHASE AND AMPLITUDE VARIATItO)N FOR LARGI COUNTERPOISL AND VERTICAL POLARI:ATION AT h W . 11 f e ,,

111-28.

4

3

I

i

I50

.I

............

°. .

..

_•_.. .

. . . . ..

. ..

.

.

.

103

-..

-

~

-

~~-~-

. -.

'IL

FI.112.

NIMLTUEVRAIN

PHS

FU LAG CUTEPIS

N

HOIONA POAIZTONA

10

At

*

.

104

90

4;

-

,h

-4L~-~-..

...... .,..

FOR7

FIG. I

j8

111-30.

-113

...

-~.-....

..

PHASE AND AMPLITUDE VARIATIONS FORLARGE COUNTERPOISE AND VERTICAL POLARIZATION AT 110% h 0 X 10S',*

10

.

... ...

V~II

105

-IG

11-31

-

HS-

ADAMLTUE-AIT-N

. . . . . . . . .. . . . .. . . . . . . . . . . . . ..

-IO

HOIONA

6!~10I,

VJ

41

I106

POAIZTO

11",h

.

AT

.

.

7

7 7-:--7-.6-7

.

-A

20t80

I.07774h..

FIG. 111-32.

___ki

_

____

PHASE AND AMPLITUDE VARIATIONS FOR SMALL COUNTERPOISE AND HORIZONTAL POLARIZATION AT 8 SS*,*450, h 0OA -t-

-

11 -6

.~~ .

. . ...

---

T-

_7_'-_

7~

-7 7

107

:-107 40-

.

..

30-

. .

FIG.

PHS

10 -

AN

AMLTD

.1-3

VAITIN

FOR SMALL COUNTERPOISE AND VERTICAL POLARIZATION AT

___

:720

-..

-.----.-

-

_______. ....

.

..

..-

--

--

.--

-

.

.. -

--

..

-

r-Iý

4.4

-10Z

108

4

-

--I0 -

1.

---

FIG. 111-34.

--

--6

20- 80--ý-

PHASE AND AMPLITUDE VARIATIONS

FOR SMALL COUNTERPOTSY AND VFRTICAL POLARIZATION AT

e-7O

0

,-77-7-

I-4

2- .--..

4-6-

I. .... .---_------------- -t -

.

-. j.....

109

-- 7 7-'-1

0.

.0"

.

.

.

... . .. .. .

-10- -A0---

,

*FIG.

111-35.

120- 8

-85%

90*,

0

1

0

2

_

- --

PHASE AND AMPLITUDE VARIATIONS FOR SMALL COUNTERPOISE AND VERTICAL POLARIZATION AT 6

--

0 - -

-------

2-

110

h -O0X

72q

-

I

f

~~

I-

--

FIG. -----

71

---

h---

4

111-36.

4-FOR

-

0-480-

PHASE AND AMPLITUDE VARIATIONS SMALL COUNTERPOISE AND HORIZONTAL POLARIZATION AT h *OX e=8S-,

-

*=450,

~

___144'

oec108'

-2

I--4

I

_____

_____

_________________

8 --

-{ 4--.------ --

I ____ _

L _____

------.-

________10__

__-6_

-

-'-~

-___

--

-

-~-30- 19C~

I

-i

r-

*45- 1+Ibu-r---T

-

-

t

36*

-

120-.-t.---. ~~~30

I

-

~

----

---

-

.10- 0

----

4---

------

- _-- -14

- -_

.

-------10 -4 -i

T_

-3-0-T10

. .

.

-

.

.

.

..-

FI.7-4

.

.

.

.

.

....

ARAIN

HSEADAPLTD FOR

VETIALPOAR1

OUNTRPOI7-AN SALL

AIO2A

.

.~.

...

.

4-

60io--

_

-20

_1

F~r.11138.PHASE AND AMPLITUDE VARIATIONS FOR SMALL COUNTERPOISE AND HORIZONTAL POLARIZATION AT 0 0 , h - 0 X~ J1O0Y " 1440

i144.

(.o

.7

2*2.

1

..... ..

v-li-z-

6

6___

~

~

-

HISA-FM-

113

2075-75

.