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NASA Technical Memorandum 83195

TM 8319519810022875NASA- -

MLS Antenna IDeations For The de Havilland

DASH 7 Aircraft

Melvin C. Gilreath, Henry S. Earl, Jr.,am Berkley A. Langford, Jr.

July 1981

NI\SI\National Aeronautics andSpace Administration

Langley Research CenterHampton, Virginia 23665

https://ntrs.nasa.gov/search.jsp?R=19810022875 2018-07-13T17:23:29+00:00Z

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MLS ANTENNA LOCATIONS FOR THEde HAVILLAND DASH 7 AIRCRAFT

by

Melvin C. Gilreath, Henry S. Earl, Jr.and

Berkley A. Langford, Jr.NASA Langley Research Center

Hampton, VA 23665

SUMMARY

The first commuter airline to utilize the new Microwave Landing System

(MLS) will be Ransom Airlines operating between the Washington and Philadelphia

areas. The airline will use de Havilland DASH 7 aircraft. Several proposed

aircraft antenna locations were investigated to determine their potential

for satisfying the MLS antenna coverage requirements. The results of this

investigation are presented and antenna locations are recommended for the

de Havilland DASH 7 aircraft.

INTRODUCTION

The first commuter airline to be used in the Federal Aviation Administra-

tion's MLS flight test program, STEP (Service, Test and Evaluation Program)

is scheduled to start operating with the MLS in the late summer of 1981. To

insure that the required antenna pattern coverage is provided by the airborne

antennas, scale model measurements or calculations must be done to determine

the antenna performance. The antenna location has a very significant affect

on1the pattern coverage, therefore, the location must be optimized when it's

necessary to satisfy a certain set of pattern coverage requirements. Typical

airborne antenna coverage requirements (References 1, 2) for large commercial

aircraft range from 25 to 30 degrees above the horizon to 30 to 40 degrees

below the horizon with complete 360 degree coverage in azimuth. It is assumed

that the commuter aircraft requirements are similar.

2

The objective of this work was to investigate the antenna locations

available for MLS applications and, based on antenna performance, recommend

the antenna locations that would better satisfy the MLS antenna coverage

requirements. A scale model of the front section of the de Havilland

DASH 7 was constructed for evaluating those antenna locations on the

forward nose and top fuselage. Calculations were performed for other

locations under consideration.

ANTENNA LOCATIONS

Several proposed antenna locations on the de Havilland DASH 7 were

investigated and these are shown in Figure 1. Locations 3 and 4 were

selected, prior to any antenna measurements or calculations, because of

their proximity to the MLS electronics and available mounting fixtures.

These locations; however, do not provide the optimum antenna pattern

coverage. The antenna at location 3 (station 97~75) is mounted on a 20.3 cm

(8 in.) square ground plane which is attached to the fiberglass nose

section. Top forward fuselage locations are desirable because adequate

elevation plane coverage can be obtained and normally better azimuth

coverage is provided than for a bottom fuselage location that is influenced

by the landing gear. Two top forward fuselage locations were investigated.

Location 1 is at station 231.7 and location 2at station 189.5. Location

1 was chosen for evaluation because of an existing mounting fixture.

This location appears to be too far back on the fuselage to provide the

required down coverage in the forward sector.

•

•

3

To provide coverage in the rear sector for MLS approaches and missed­

approaches an antenna must be located on the bottom rear fuselage. The

bottom fuselage locations investigated were at stations 354.0 (location 4)

and 714.50 (location 5) •

ANTENNA RADIATION PATTERNS

Radiation patterns were measured for some of the proposed antenna

locations and calculated for the others. A one-seventh scale model of the

front portion of the de Havilland DASH 7 aircraft was constructed for

evaluating the forward antenna locations. The test model is shown in

Figure 2. Radiation patterns were measured for the two top forward

fuselage locations and the nose location. The antennas measured were one­

quarter wavelength monopoles and one-quarter wavelength monopoles with

reflectors. The monopoles with reflectors were used to simulate the actual

flight antennas. The measurements were conducted at 35 GHz since a one­

seventh scale model was used. The nose section of the test model (i.e.,

between stations 74 and 147.0) was constructed from thin fiberglass

material to simulate the test aircraft. Measurements were also conducted

with the nose avionics compartment, between body stations 97.75 and 147.0,

covered with a conducting metal foil. The foil simulates the production

aircraft which will have an aluminum acreen on the outer surface of this

compartment to prevent structural damage from lightning strikes and to

shield the avionics from the indirect effects of a lightning strike.

Radiation patterns measured for a centerline mounted monopole at

location 1 are presented in Figure 3. Results for a dielectric nose

compartment only are given since the nose compartment has a very small

effect on the antenna performance at this location.

4

The conducting nose should provide essentially the same results. As

indicated by the elevation pattern shown in Figure 3(a), this location is

not suitable because the required down coverage in the forward region is

not provided. A more forward location on the down sloping part of the

fuselage is required to improve the down coverage; therefore, location Z

was chosen for evaluation. Measurements were performed for several different

test conditions at location Z. For the final flight configuration a back-up

system will be used requiring an additional antenna located at the same

station location and separated by at least-ZO.3 em (8 in.). Measurements

were conducted simulating this condition with two antennas to determine

the influence of a second antenna on the radiation patterns of the primary

antenna. The primary antenna was fed and the secondary antenna was terminated

in a SO ohm matched load during the measurements. Both monopoles and monopoles

with reflectors were used. The results are given in Figure 4 for two mono­

poles spaced 3.0 em (l.Z in.) apart at location Z with a fiberglass nose

compartment. The fiberglass nose compartment was covered with a conducting

metal foil and the measurements were repeated. These results are shown in

Figure 5. By comparing the elevation patterns in Figures 4(a) and Sea) one

can see the effect of the conducting nose compartment. The radiation shown

in Figure 4(a) in the region from theta equals lZO to 140 degrees has been

reduced considerably by the conducting nose compartment as shown in Figure

Sea). The pattern fluctuations above the nose in the forward direction

increased slightly due to reflections off the conducting nose. The effects

of the secondary antenna appear to be limited primarily to small pattern

fluctuations visible in the azimuth patterns of Figures 4(c) and S(c) in the

phi = 180 to 300 degrees region.

•

5

A reflector was added behind the monopoles to direct the radiation

forward and simulate the actual fligh~ antennas.' The patterns measured

for a single monopole with reflector at location 2 are shown in Figure 6

for the fiberglass nose. Figure 7 shows the results obtained for the

same test conditions except now the nose compartment is conducting.

Essentially the same effects are observed on the forward portions of the

elevation patterns as those observed for the monopole case. The down

coverage is reduced in the theta equals 120 to 140 degree range and the

pattern fluctuations above the nose increase for the conducting nose

compartment condition. When the secondary antenna is installed the azimuth

pattern fluctuations in the phi range of approximately 180 to 300 degrees

increase slightly as shown in Figure 8(c).

The antennas measured at location 3 were mounted on a 3.0 em (1.2 in)

square ground plane simulating the 20.3 em (3 in.) ground plane used on the

actual aircraft. The ground plane was bonded directly to the fiberglass

nose section as shown in Figure 2{h}, The antennas evaluated at this location

were mounted on the centerline of the scale model. The radiation patterns

measured for a monopole at location 3 for a fiberglass nose are presented

in Figure 9. Large fluctuations are present in all the patterns caused

by the small ground plane size and scattering off the metal bulkhead at

station 147.0 and the nose landing gear. A reflector was added behind

the monopole and the results obtained for that antenna are given in Figure 10.

The forward portion of the pattern improved considerably; however, there is

still to much radiation on the bottom of the aircraft. Only the elevation

and azimuth patterns are presented for this series of measurements. The

roll plane patterns are not presented; however, the azimuth patterns can be

6

used to obtain an indication of the roll plane levels. The ground plane

size was increased in the forward direction in an effort to improve the

patterns and these results are presented in Figures 11-13. Figure 11

shows the results obtained for an increase in the ground plane size in

front of the antenna of 2.2 cm (0.875 in.) providing a total ground plane

length in the forward direction of 3.75 cm (1.475 in.) while maintaining

the same ground plane size 1.5 cm (0.60 in.) in the rear direction. This

improved the forward coverage somewhat and lowered the radiation below the

aircraft. The ground plane was increased again in the forward direction by

2.2 em (0.875 in.) and the results obtained for this case are shown in

Figure 12. Further improvement can be seen in the elevation pattern, Figure

l2(a). Figure l3(a) shows more improvement in the elevation pattern when

the ground plane is increased to a total length of 8.2 em (3.2 in.) in the

forward direction. Most of the pattern fluctuations in the forward direction

and the radiation below the aircraft were caused by strong illumination of

the ground plane edges and possibly surface wave effects. The patterns can

be improved to provide very good forward region courage by using a larger

ground plane; however, the ground plane size required may be to large to be

used at this location.

The radiation patterns of antennas at locations 4 and 5 were calculated

since it was not possible to perform measurements for those locations with

the scale model available. These calculations were done at NASA Langley

Research Center using computer programs developed at the Ohio State University.

The calculations were performed by Timothy J. Kneer, a Graduate Research

Assistant from the Old Dominion University, working at NASA LaRC on NASA

Research Grant NSG 1655. Calculations of the elevation and roll plane

patterns were done for monopole antennas; however, the results should indicate

the type of coverage that can be obtained in the rear direction of the

.. -

7

elevation plane at the different locations. The results obtained for

locations 4 and 5 are presented in Figures 14 and 15 respectively.

Location 4 doesn't provide enough up coverage in the tail region plus

blockage and scattering off the landing gear can degrade the coverage.'

The up coverage is improved at location 5 and the landing gear effects are

reduced; however, additional improvement can be achieved by moving farther

back on the aircraft. Station locations as far back as 793.4 could be used;

however, a bulkhead at this station would make locations beyond that point

less desirable because the installation becomes more difficult and the

cable loss increases.

CONCLUDING REMARKS

Several proposed MLS antenna locations on the de Havilland DASH 7

aircraft were investigated. The antenna pattern measurements and calculations

show that at least two MLS antennas are required to provide the necessary

coverage. The top forward fuselage locations provide adequate coverage

for the front sector, and the bottom rear fuselage location gives good

coverage in the rear sector. The coverage provided by the two antennas

together should satisfy the MLS requirements.

The MLS antenna locations recommended, based on the results of this

study, for the de Havilland DASH 7 are location 2 (station 189.5) for

providing the front sector coverage and a location on the bottom rear fuse­

lage as near station 793.4 as possible to provide good rear sector coverage.

8

REFERENCES

1. Gilreath, Melvin C., and White, William F.: "Flight Test Evaluationof Microwave Landing System Airborne Antennas," IEEE AP-S Inter­national Symposium Digest, May 1978.

2. Thompson, A. D., Stapleton, B. P., Walen, D. B., Reider, P.F., andMoss, D. G.: "MLS-Airplane System Modeling" Boeing CommercialAirplane Company, NASA Contractor Report 165700, NASl-14880,April 1981.

Location Station

1 231. 702 189.503 97. 754 354.005 714.50

Antenna locations~

2 f

J ~/O""""",,-- _

Station 74 J 4

Station 147

5\... Station 793.4

Figure I. Antenna locations on deHavilland DASH 7.

(a) MlS antennas on scate model

Figure 2. One-seventh scale model of forward sectionof deHavHfand DASH 7aircraft.

Figure 2. Concluded.

Theta 0 ° 260°

\

\ 10o •t 250°

,_Phi= 90°

_"-- I Phi = 0e240 Phi = 180° Theta = 90°1200 I

I= !

I230€ I

131J° I

!220° .... 1

1. (a) Elevationpattern Theta= 180° .i

21oo Principal plane patterns -:

2L_ o 160 °1605 200 °

190_ 170_1,o° 180 190°

Bottom

Figure3. Measuredprincipalplanepatternsofamonopoleat locationno. !.o

oTop

; "!"~.::::.J~~:£c:::j:::::~17;;C:-:·1/0' 180 190

0

--------

Bottom

Theta....35Cl.l

iO'

I

rj1

;,

I'!1

II:1:1'II

I)

":1'II

Figure 3. Continued.

Phi NoselO'.

lO° 350_3400 200

340°

330o 30_330"

40o°32O

260°

,10°250o

,20=240= 240°120°

(c) Azimuthpattern_=

1300 230°

220" 140"1400 2200

210° 50* ,_15

=-_0o 160°11 200°

190o 170=,,o° 180 ,,o°

Tail

Figure3. Concluded.

Figure 4.

Theta Top...-:::;;- 0 10"lU,-·__,,-__ ~!:,"","_....,.__ ,3~u,;,

180Bottom

Measured principal plane patterns of twomonopoles spaced 3 em (1,.'2 in) apart atlocation no. 2 with a fiberglass nose.

-.-{2.

90 !"'

Theta

190· 18017J'

Bottom

\0'350"

I

IIiI

Figure 4. Continued.

/ ..........

310c 50°050' 310

300¢

290=l

260°I100=

II0°25C 250=llO'

20°240' 240°

120o

140°2205140° _, 220o

- (c) Azimuthplane210= 150°

150' 210_

. _'_0_ 160°=_C_O© 20n=

190_ 170_'

Figure4. Concluded.

,+

Theta TopO ,o°

I0+ 350°340= 20_340

330° 30_N 330 -

310' 500o310

280=

240 20°1_o 240°

230= 30=130= 230+

140°

220 (a) Elevationpattern 22oo210° tSO°

150 210=

060;= 150=200°190° }.70__'°0 180 _+o°

Bottom

Figure5. Measuredprincipalplanepatternsof twomonopolesspaced3cm(I.2 in) apartatlocationno.2with aconductingnose.

i'

~:

,.r

.. '

~ i

,;.p...

"L'

"Irl,,

.,ij-;

'.

i•i·rr

~Ce.-

~3=-.r::.'t

.~e:::90 l

!'I.I"i:I.

t

I: !I

Topo-

; I i

190" 170·170" 180 190"

Bottom

Theta

90

c".-3=

Ii

Figure 5. Continued.

• , • . • .... •.,

Phi Nose+

0 1o°i0+ 350°

340° 20_,340

...-30° 30°3300

4o_320"

310' 50°o310

10°250+

240120°

30°230o 230_

130°

140= 220°

(c) Azimuthpattern2100 150°

150° 210°

^,, o 160°_uO160°

19_° i7G°

Nil

Figure5. Concluded.

m

Theta Top350o 10°10_ k 350o

340o 20.=20 340

_30° 30o330°

e

40o320o

50o310°

300:60

290:

110°2500 250°

30°230c 230°

1300

2-.0_ 140°1,oo (a) Elevationplane 22o0

2i0_' 150°i 210 °

) 2%° 20o,6o:" 190" ".... 170_

; 170° 180 t90° '

Bottom

Figure6. Measuredprincipalplan_e_.patternsfor asinglemonopolewith reflector spacedI.5 cm(0.5 in) offcenterline with afiberglassnose.

'r

5000310

290=70°

100°260°

250° LIO°110° 250°

L20•1200 240°

130o 230_

Figure6. Continued.

'i ........ ?..... " " " ' ........................

50 °

50 310°

290_

260'100°

L20°240 240°

1200

2200 !40=

,,o (c) Azimuthplane =o.210o tSO°

15 210°

^ o 160°,_ ,_63__ 2000

1_° 180 1,0°170° 190°

Tail

Figure5. Concluded.

............. ". . ,!.i "i.'"" i-...'.i.';'; ......" . ............_,." i

--6

Topo

Theta----;;-

lUi'"~__~__+ _

180Bottom

IiO·190·

­.-90

iII

JII

Figure 7. Measured principal plane patterns of asingle monopole with reflector spacedI. 5 cm (0.6 in) off centerline with aconducting nose.

Topo

1C"·1 ....17Uo __ 180_

Bottom

Theta~

lu"'__--~--.,_._...:.~

I

I

III

Figure 7. Continued.

9081

Phi

190"170·

Figure 7.

Nose

o'80Tail

Concluded.

......

.J::~.-

0:::.~:::::::C:::l

270

50050 310°

280;

2601000

: 250110=

120o 240=

30*230° 230=130°

22°-0 (a) Elevationpattern =o.I 210° 150°i 210°

200_'o 160°160 200°190 ° ....... 170€

1,o° 180 1,o°Bottom

Figure8. Measuredprincipalplanepatternsof twomonopoleswith reflectorsspaced3cm(I.2 in)

; _, apartat locationno.2withaconductingnose.-\

0')s::::: J'j ,Q

13:

I \t:: 11111iiiiii'(1)I....J

190

1

I

Theta

!--+--O"--+-­190;'-......--.:;:.-'---''---,

170' 180

Bottom

III

I

I

..

Figure 8. Continued.

Nose

oPhi~("OJJIe' "+"""'_....__~v

tII

0')s:::

i.-!==..- !.s::. I

.2' .,0::: I

i,fI!

90!~

iII ,

I

!;

II

II

i

I

!Ii!I

Figure 8. Concluded.

300'

290=

80°2_0°

140=220° 220=I40=

_50o

2,o° (a) Elevationpattern 2,0._vO

160' 200190= !70j

Bottom

k.

Figure9. Measuredprincipal planepatternsof arnonopoleat locationno. 3with afiberglassnose.

Theta~

,"".;'~'

IV

Top

o

ISOBotto m-

17CO

190°

Figure 9. Continued.

40 320

300

130o 23(_

220° 140°220=

'40= (c) Azimuthpattern150o

210° 210_

° 160°l_O ZOO= "

it._,Oo _70_

rail

Figure9. Concluded.

. . . . ,.. _..

Theta Top

IG+ 350°340c 20°

340_

. 330_ 30°30 330°

4O

290°70o

220° !40°14{ 220°

; 150o

, :'%°+ (a) Elevationpattern _oo200_ 160°200°

,_°+ 180+ ,,°°170_ 190°

Bottom......

FigureI0. Measuredprincipal planepatternsof amonopolewith reflectorat locationno. 3

i with a fiberglassnose.+....... ........ :i. ..... i,. i+ " i . _i _+,i/+_i "

o

180Tail

Nose

190"170'>

Phi~

:0' ~:;;.._

'.

Figure 10. Concluded.

I0°250 250°ii0=

FigureI1. Measuredprincipalplanepatternsofamonopolewith reflectorat locationno. 3with a fiberglassnose.i i

i

iI

I:~'e:!.-I;:Jtt=l~

190

I!

I

Theta~

Iv"

Nose

o

180Tail

I

..I

..

Figure II. Concluded.

Topo

Theta

-.-C1>

~

en0Z

9090

..

..190 0

170' f80Bottom

Figure 12. Measured principal plane patterns of amonopole with reflector at location no. 3with a fiberglass nose.

c:::n ,0.!::: 0l=:::;:::~&:-.:::.:~3:

Phi Nose

Y.

I"II

I

i

II

III,iiIII

c:::nc::.-

,;:.......c:

..

Figure 12. Concluded.

,.

90

Figure 13.

Theta

180Bottom

Measured principal plane patterns of a monopolewith reflector at Jocat ion no. 3 with a fiberglass nose.

­.-

Phi Noseo

i0_ 350°

2L 3 o

330°

320° 40_a2o

5003100

300'

29U'

I00°260o

250o

_20°240< 240°1200

230 230,-J130°

140 _

220o (b) Azin [h 22°°210° 150_

210_

200° 160°200o

!60_ 190° 170_ 4 ;

170_ 18O i90°

Tail

Figure13. Concluded.

Topo

..

J..i

Figure 14.

Theta~

l0r:-°=::l==::O:==+=:?r:-

180Bottom

Calcul~ted principal plane patterns of amonopole at location no. 4.

­.-90

(80Bottom

Top-

190";o;---..........""..,i;:....,--'---;:1700

Theta"'---350' 0 10"

~IO~0__r"--''''7;-'_.,.._-':350"

0')c:.-3:

3: ..-;:t:: .c:(1) .2'

....J ~

90--

90

Figure 14. Concluded.

310' 500310e

290=70°

260°100_

llO°250 250=.II0°

20•240 2400

120°

130o 230°

220° 140"

1+o (a) Elevationplane _oo• 210° 150"

150 = 210"

200=0 160°• 160 200°

ic_3_ - 170°

1,o° 180 ,9°°Bottom

Figure15. Calculatedprincipalplanepatternsofamonopoleat locationno. 5.

. . .... • • •

Theta Top350_ 10°10° 350_

340 _ 20 _340*

330o 30°330°

3g:

300'

230 30°130° 230°

220° 140"220"

21oo (b) Rollplane 15o. •210"

200°o 150°

160 190o L70o 200° ill

Bottom

Figure15. Concluded.