Spectol Teclintcul Report 25 p~ 6 ;3 6 FULL-SCALE PATTERN MEASUREMENTS OF SIMPLE HF FIELD ANTENNAS IN A US CONIFER FOREST By: WILLIAM A. RAY GARY E. BARKER SANDRA S. MARTENSEN I Piepared for: U.S, ARMY LU 'E-CTRONICS COMMAND CONTRACT DA-36-039 AMC-00040(E) FORT MONMOJT, NEW JERSEY ORDER NO. 5384-PP.-63--91 D)K DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED
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Spectol Teclintcul Report 25 p~ 6 ;3 6FULL-SCALE PATTERN MEASUREMENTSOF SIMPLE HF FIELD ANTENNAS IN A US CONIFER FOREST
By: WILLIAM A. RAY GARY E. BARKER SANDRA S. MARTENSENI Piepared for:U.S, ARMY LU 'E-CTRONICS COMMAND CONTRACT DA-36-039 AMC-00040(E)FORT MONMOJT, NEW JERSEY ORDER NO. 5384-PP.-63--91
D)KDISTRIBUTION OF THIS DOCUMENT IS UNLIMITED
*SR÷
February 1967
Special Technical Report 25
FULL-SCALE PATTERN MEASUREMENTSOF SIMPLE HF FIELD ANTENNAS IN A US CONIFER FOREST
By: WILLIAM A. RAY GARY E. BARKER * SANDRA S. MARTENSEN
Prepared for:
U.S. ARMY ELECTRONICS COMMANDFORT MONMOUTH, NEW JERSEY -• "
Potential amplitude errors greater than ±3 dB due to VSWR measurement errors. Al: ;inson one frequency normalized to set highest equal to 0.0 dB.
IV IMPEDANCE MEASUREMENTS
Impedance measurements were made of all the antennas as an
aid to patterns analysis and deriving relative gain figures.
They are illuminating in themselves, however, since the grounding
rods or counterpoise wires are clearly shown to be an active part
of the antenna system. They also give an indication of how poor
the ground was during the time of measurement.
A. Measurement Technique
These measurements were taken with an Alford automatic im-
pedance plotter, which provides a rapid and continuous display
of impedance at the antenna feed point over a wide frequency
band. This capability makes it economically feasible to take a
large number of measurements without missing any significant
characteristics [which might be lost if a discrete-point technique
(RX meter) were used]. The price of this convenience and conti-
nuity is the accuracy of any given point. The plotter measured
impedances indirectly by finding the load's reflection coefficient
(compared to 50 Q) and displaying that value en a Smith chart.
The equipment accuracy is expressed as a percentage of the re-
flection coefficient (±5%, ±50); hence, the resistance and reac-
tance numbers near the rim of the chart are not precise. For
this reason, the data is presented on Smith charts, rather than
as tables of resistance and reactance as a function of frequency.
The inaccuracy results from several parts of the plotter
-being frequency-sensitive. The "hybridge" (where the load and
standard are compared) is rated down to only 2.5 Mc/s, and its
performance deteriorates below that figure. The three "phase
splitters" (networks that divide an oscillator signal into
reference and test signals) work well only over limited frequency
bands, overlapping at about 4 and 11 Mc/s.
In order to minimize the errors at the ends of the frequency
band of the phase splitters, the system was calibrated more often
than recommended by the rmstnufacturer. The manufacturer advisesI
that the instrument be calibrated once at the middle of the fre-
quency band of the phase splitter in use. It was found that if
the instrument were calibrated at the middle and both ends of the
frequency band of these phase splitters, there would be less
discrepancy when comparing measurements from the upper frequency
and lower frequency of two consecutive phase splitters. The im-
pedance plotter was also calibrated at each frequency transmitted
by the Xeledop so as to minimize errors when measuring the antenna
VSWR at the frequencies at which data were taken for the radiatio•i
patterns and relative gain figures (see Sec. III-D).
In the previous measurements at Lodi, the unit was calibrated
in the middile of the frequency band of each phase splitter, as
recommended by 4.e manufacturer. Later, the deviation from these
simple calibrations and calibration over the range of specific
frequencies was determined. Then the field data were corrected
and smoothed by calculating these deviations into the data. Thus,
the Lodi data have been smoothed through calculations and the
data in this report have been corrected for major plotter errors
by calibrating the instrumentation over smaller frequency bands.
In some cases, at very high VSWR, the plotter indicated a reflec-
tion coefficient slightly greater than one. Any portion3 of the
curve where this occurred are shown by a dashed line on the Smith
charts.
B. Discussion of Results
Impedance measurements were made on all antennas after they
were erected in their measurement situations. Thus, the impedance
21
plots (Figs. 18 to 26) show the impedance of the antenna as it was
while radiation patterns of the antennas were being measured.
For the cases where match to the antenna is very poor (near
anti-resonance), relatively high currents appear on the o" Z le of
the feeding coaxial line. These currents show up in two ways:
as radiation during pattern measurements and as perturbations in
the impedance curves. The Smith chart for the 23-ft-high dipole
(Fig. 22) shows the presence of these currents very clearly in the
form of small loops between the frequencies of 10 and 15 Mc/s.
Similar loops are also evident on the Smith chart of the 2-ft-high
dipole (Fig. 23) around 4.0 Mc/s and 7.0 Mc/s. These small 1iops
are quite similar to those evident in the measurements at Lodi.
If a further compqrison is made between the impedance
measurement indicated in this report and those made at Lodi, some
information can be deduced about the conductivity of the ground.
The impedance plots of the dipoles and monopole antenna compare
fairly well, while there is a discrete difference between the im-
pedances of the slant-wire and inverted L's. However, the latter
group of antennas are more dependent on ground characteristics,
due to the grounding systems of these antennas (i.e., counter-
poises and grounding rods).
In addition to impedance plots of the antennas at their
pattern measurement heights, impedance measurements were made at
resonant frequency of half-wave dipoles with the height above
ground as a variable. The 6 Mc/s dipole was the 2-ft-high un-
balanced dipole used for pattern measurements and the 3 Mc/s di-
pole was the same antenna but the radiators were lengthened to
77.8 ft. In all cases, the dipoles were unbalanced and the shield
of the RG-58 coaxial line was grounded only at the measurement point
(at the impedance plotter). More detailed information on dipole
impedance as a function of height can be found in other reports. ,4
I=- II
The normalized curves in Figs. 27 and 28 show variations of im-
pedance and re~sonant frequency which are typical of half-wave
dipoles near a lossy ground,
I I0 I22
311
g A,
0 T=
|[0%I220.
Z_--_=9=0,f CO ._0-, I
fo M / 40CI!ISI .0--4 40 99
FIG 18 SMT CHAR RERSNTTO OF ANTNN IMPEDANCE.-- ......
f *8 Mc/s 0-424C-947? fo *8MCA
FIG. 19 SMITH CHART REPRESENTATION OF ANTENNA IMPEDANCE FIG. 20 SMITH CHART REPRESENTATIO)N OF ANTENNA IMPEDANCEFOR 2:1 INVERTED L ANTENNA ~2.6 to 11. 1 Mc/s) FOR 2:1 INVERTED L ANTENNA (IL.1 to 20.0 Mc/s)
23
7I
08
ag 50 a04 z oS0
FIG. 21 SM;TH CHART REPRESENTATION OF ANTENNA IMPEDANCE f-IG. 22 SMITH CHART REPRESENTATION OF ANTENNA IMPEDANCE FORFOR 5:1 INVERT ED L ANTENNA (2.0 to 18.0 Mc/s) 23-FOOT-HIGH UNBALANCED DIPOLE ANTENNA (4.0 to 20.0 Mc/s)
2-1
060 .o 50 A
f*6 Mc/s " 26.. f .5mc/s*
0 4240999 0D-4240-995
FIG. 23 SMITH CHART REPRESENTATION OF ANTENNA IMPEDANCE FOR FIG. 24 SMITH CHART REPRESENTATION OF ANTENNA IMPEDANCE2-FOOT-HIGH UNBALANCED DIPOLE ANTENNA (2.0 io 19.0 Me/s) FOR SLEEVE DIPOLE ANTENNA (2.6 to 11.0 Mc/s)
25 '
0o 1 0.4240 910 0.- t
-'.25 SMITH CHAR~T REPRESENTATION OF ANTENNA IMPEDANCE FIG. 26 SMITH CHART REPRESENTATION OF ANTENNA IMPEDANCEFOR MONOPOLE ANTENNA (2.0 to 21.0 Mc/s) FOR BALANCED DIPOLE ANTENNA (2.0 to 27.0 Ac 's)
26
17-
I 1 A
0IL I00 I
0R
'Iz 9 0
0w
U.
. - IN CLEARING 3-Mc/s DIPOLEz2 80 - IN CLEARING -
FIG. 27 NORMALIZED CURVES OF RESONANT FREQUENCY AS A FUNCTIONOF HEIGHT FOR DIPOLES
iI'
Mir
100IIII
90 IN CLEARING 3-Mc/s DIPOLE
& INCLEAING6-Mci. DIPOLE-0-0- IN FOLIAGE
E so
£
70 -W0 0zW
0
50-
40
0 0.02 0.04 0.06 0.06 0.10
DIPOLE HEIGHT -wavelengths 0-4240-Ions*
FIG. 28 NORMALIZED CURVES OF DIPOLE IMPEDANCE AT RESONANT FREQUENCYAS A FUNCTION OF DIPOLE HEIGHT
27
5
V DISCUSSION OF RESULTS
This section makes some preliminary comparisons between the
results reported here on antennas in a pine forest and the results
reported earlier on essentially similar antennas in open farmland,
since significant changes in both patterns and impedances were
observed.
For many of the antennas, such as the inverted L's, the re-
sistive component of the impedance increased considerably. It is
not clear whether this was entirely or even partly due to the
change from open space to forest because the electrical ground
parameters also changed.
The extent to which these two site differences--trees and
ground--affected the patterns is more apparent. The ground seems
to have affected most the elevation plane patterns of antennas with
major radiating structures very close to the ground (the 30' slant
wire at 6 Mc/s, for example). The 23-ft-high dipole at resonance
(Figs. A-29 and A-30) was relatively unaffected by either ground
or trees in either polarization. No major changes are evident
even at the lower elevation angles; thus, the trees apparently
had little or no effect on the dipole's radiation pattern at 8
Mc/s. Of course, this does not prove whether or not its efficiency
as a vertical-incidence antenna changed due to energy loss in the
dipole's near field; it only shows that the pattern shape did
not change.
The effect of the trees was clearly evident for the monopole
at the higher frequencies. Azimuthal patterns measured on this
antenna at the farmland site and elsewhere have been constant
within a few dB up to 15 Mc/s. This also holds true here, where
the antenna was built in the forest as described in Sec. II-H,
3 F
up to 6 Mc/s (Figs. A-51 through A-54). However, at 8 Mc/l and
above., the azimuthal pattern breaks up dramatically (Figs. A-55
to A-57). This sudden change in pattern for a small change in
frequency was unexpected and hence very significant. Turning
to the 23-ft-high dipole at 15 Mc/s, the E0 pattern (Fig. A-33)
repeats the one measured at the farmland site almost exactly,
while the E0 pattern (Fig. A-32) is similar only at the higher
elevation angles. The response at lower angles seems attenuated
and distorted: The response at all azimuths is lower, but the
sharp null at 2550 azimuth at the farmland site is not evident
here.
28
REFERENCES
1. W. A. Ray, "Full-Scale Patterr Mi rement of Simple HF FieldAntennas, Special Technical Report 10, Contract DA 36-039AMC-00040(E), SRI Project 4240, Stanford Research Institute,Menlo Park, California (May 1966).
2. C. Barnes, "Xeledop Antenna Pattern Measuring Equipment, 2to 50 Mce" Stanford Research Institute, Menlo Park,California (July 1965).
3. G. H. Hagn, J. E. van de Laan, D. J. Lyons, E. M. Kreinberg,"Ionospheric-Sounder Meal.urement of Relative Gains andBandwidths of Selected Field-Expedient Antennas for SkywavePropagation at Near-Vertical Incidence." Special TechnicalReport 18, Contract DA 36-039 AMC-00040(E), SRI Project 4240,Stanford Research Institute, Menlo Park, California(January 1966).
4. T. S. Cory, W. A. Ray4 "Measured Impedances of Some TacticalAntennas Near Ground,' Research Memorandum 7, ContractDA 36-039 AMC-00040(E), SRI Project 4240, Stanford Resear-hInstitute, Menlo Park, California (February 1964).
k
L
B FrK
DISTRIBUTION LIST
No. ofOrganization Copies
Commanding General 1U.S. Army Electronics CommandFort Monmouth, New Jersey 07703
Attn: AMSEL-RD-DO ARMA Coordinator
Commanding General 28U.S. Army El.ectronics CommandFort Monmouth, New Jersey 07703
Attn: AMSEL-NL-R-4R. N. Herring
Marine Corps Liaison Officer 1U.S. Army Electronics CommandFort Monmouth New Jersey 07703
Attn: AMSEL-RD-LNR
U.S. Army Electronics Command Liaison Officer 1Rome Air Development Center EMPLGriffiss Air Force Base, New York 13440
Attn: Capt. A. P. Toth
U.S. Army Electronics Command Liaison Officer 1Rome Air Development Center EMPLGriffiss Air Force Base, New York 13440
Attn: Capt. E. Hee
Commanding General 1U.S. Army Materiel: CommandWashington, D.C. 20315
Attn: ANCRD-DE-C
Director 2Advanced Research Projects AgencyRemote Area ConflictWashington, D.C. 20301
high unbalanced dipole, sleeve dipole, monopole, and balanced
dipole. For each antenna, the two individual polarization plots
and the power plot are given for each measured frequency in order
of increasing frequency. The title block at the lower right-hand
side of each plot gives the antenna name, the polarization, and
the frequency measured for that plot. The polarizations are de-
fined exactly in Sec. III-A; as a reminder, E is horizontal and
E is vertical. The antenna's design frequency, f0 , is indicated
at the lower left corner of each page.
Each contour map shows all the amplitude data taken on one
antenna, for one polarization, at one frequency. The plot can
be visualized in several ways. For instance, one can picture
placing a large hemisphere over the antenna being measured, then
drawing the field-strength contours on its surface. The contour
plots are two-dimensional maps of ._ 3 hemisphere as it appears
from directly above. Hence, the zenith angle is at the center of
the plot, azimuth angles appear as radials, and elevation angles
are concentric circles. The outer rim of the plot is the horizon,
or 0-degree elevation. The azimuth angles numbered around the rim
of the plot are in degrees relative to some principal axis of the
antenna. As an example, for the balanced dipole antenna patterns,
30 azimuth on the plot is actually 1420 from magnetic north. These
angles are indicated on the two site maps (Figs. 3 and 4) by
arrows labeled in degrees magnetic. The relationship of contour
r
V
plot azimuth to each antenna is also shown by the schematic dia-
gram in the center of each E or E pattern plot.
The power plots do not have the antenna diagram, so it is
necessary to refer to the previous voltage plot for the orientation.
Instead of the antenna diagram, a pair of vectors are shown in the
center of each power plot. These indicate the relative signal
voltages (within 2-3 dB) received overhead the antennas from roughly
orthogonal aircraft passes as described in Sec. III-C-2. The"polarization" of the antenna at the zenith can be inferred from
this diagram in the cases where one vector is much larger than the
other; otherwise the test antenna's actual polarization is ambiguous
(see Fig,. 16 and accompanying text).
In examining the plots, the accuracy limits of the measurement
technique should be kept in mind. The details of these limits are
discussed in the previous report, but generally, any features of
the plot which are smaller than ±30 azimuth ±1/2 contour interval
are insignificant due to limited data sampling and processing
errors.
33
0.
330, -1dr so*
300, 60'
27(r 43 its
N 60*
2401 120*
4C*
21
foz 4 Mc/s 210, 150, FIG. A-(
300 SLANT-WIRE
Ee 2 Mc/s
180*
210*
0 30 SLNT-W0R
122M/
0.
0•0
f0 = Mc/sPOWER PATTERN3030 SLANT-WIRE 2 Mc/s
0.04
0.
3oo0
30 0. LNTWR
i . ..1. 2 _ - 15- • . - •
2!
-iss
lea.ý
I0
.~ ~ ~ ~ ~ ~ ~ O E ..
P A.. ..T
T... .... ...R.. .. ..
330* SLN-W0*4M/
0 300 SANT~3IR
218
0..... ......
330* 27 30,
as
300*
2
60*
240* 1200
0.
-to
f z 4 hic/s 210* -27 150, FIG A-80
300 SLANT-WIRE
f 4240.5- o. E 6 M c/s
_06.0-
330!- 30*
/C-'3
POWER PATTERN
0* 3Q0 SLANT-WIRE 6Mc/s
80
I0
030 2: IVETE
E6o 0.c/
0.
30,330*
2733
-- S
.30
60'
300* f
-21
.2 -27
-21 Is I
to is 21
270*
60*
120'
240*
20*
2lo* 150,
fo - 8 Mc /S FIG A-
2 1 INVERTED L
E 8 5 Mc/s180*
0. ........................ ..... .. ....
30,
300, so*
2
60,
IA,4
240* 120*
fo=8 Mc/s 210* ISO* FIG A2 1 INVERTED L
4 E 5 Mc/s180,
00
4,10
2IS0.
2i0.
270
-12Mc/5.1* -1
0.
-- " -- -----330, 30*
300* 2 60*
2M*
12 2
240' 120*0.
210, 150*fo.8 Mc/s FIG A-1521INVERTED L
- 40 -14 Eo 8 Mc/s180*
0.
330* 30*
.,r-J
300, 60,
27(r
60'
240 120*
20-
210, 150, FIG A-16f 0. 8 Mc /S POWER PATTERN
2 1 INvERTED L 8 Mc/s
180*
0*
so*
330, .11
0.
Soo*
21 Is
Is/
60'
_v 120*
240' 0.
-33
210* ISO* FIG A-17
fo.10 Mc/s 51 INVERTED L
ie4C 1ý6
E 9 -1 Mc/s
180*
- 0.
30*
ts
300* 60,
42
12
2?01
12
6 IS
-15
240. 120*
20*
fo--Io k4c/s 210' 150, FIG A-185 1 INVERTED L
-4,4 owl E 4 Mc/s
330
f :IO c/s10*
SooWE PATTERN 60
-.--------- 1 IVERTD L Mc/
300* 0
2I
t0.
I0
270,
fo 0 M:/sPOWER PATTERN5 1 INVERTED L 6 Mc/s
0.
350* 30*
Boo* 60*
Is
270*
-60.
240* 120'
74
2
f
fo 10 1AC/s 210* 150* FIG A-235 1 INVERTED L
0* E a 10 Mc/sISO*
0.
30*
300, 60*
240* 120,
ZY
20*
fo 10 Mc/s 210* - 150* FIG A- 24
51 INVERTED L
E 10 Mc/s
180*
0.
240* 120
180*
0.
330* 30*
Soo / - 7*
I'20/
2' HIG UNAANE1 /8M / I OLF C 5 M // /0
60*
340 As 3
II ISw~ -c/ N1* FGA2
23' HIGH UNBALANCED* ,DIPOLE Ep 5 Mc/s
330
260'
0 ~23' HIGH UNBALANCED
0.
-21n
-21 I
00
23' HIGH UNBALANCEDDIPOLE Ee 8 Mc/s
II
210000
23' HIGH UNBALANCED
.. ........ DIPOLE E4 8 Mc/s
-0*0*
60-60
211* 10*FIG A-3f 8 Mc/s 2O POWER PATTERN0 2ý' HIGH UNBALANCED
44DIPOLE 8 Me/s4'4ieo,
0.
DIOE 8 15M5300.
030
-12
22 -i Mc/s -1.I5 . I A 3
23' HIGH UNBALANCED
DIOE a15M/
240OL 15 Mc/
n
0.
30,
240- , .20*
---o•t.zi-i
300*
fo0 16Mcs *• FIG A-35
2' HIGH UNBALANCED
'?0 " DIPOLE Eq 2 Mc/s180,
-t- - - - - - - -- . ---
33
2 IH NALNE
DIOL7e 0M/--2 1
0.
330. 30*
300, 0
DPOL -1Mc/
0.
330* 30*
300. 60*
2?0' 90,
6
240, 120,
2
FIG A-38
fo 6 Mc/s 210* 150* POWER PATTERN2' HIGH UNBALANCEDDIPOLE 4 Mc/s
4 a,
0.
30 2 IH0NALNE
128
00
DIPOL E3Q 6 Mc/
Soo*'60,
's60.
0.
330, 30*
. ..............
300 60*
-1 15
270
\V1
-45
240* 120*
40'
4
20'
2j0* 150,fo 6 Mc/s FIG A-42
2' HIGH UNBALANCED
0. DIPOLE Ee 10 Mc/sISO*
0.
330* 30,
60*300*
77 -12 2
-2is
2
12
6-ZLrr2l I
-15 21 .30-27 -21 -10 2
240. 120,
-34
fOZ6 Mc/s 210* 150* FIG. A-432' HIGH UNBALANCED
01. DIPOLE Ep 10 Nic/slecr*
330*
V-14
'- '----
- -.
0*0
3330
210*k2
00
.74 .- 0. E05-/
- -- - --- - - - - 80* - - --
II
2709*
60*
2 120*
0.
330* 30*
300* so*
lei
41
120*240'
4
-21
t-IS -is
2
fo - 5 Mc/s 210* 15-)* FIG, A-47POWER PATTERN
SLEEVE DIPOLE 5Mc/s
ISO*
0.
330-
300.
ils
-2j
-18 -15
Vol
fo.
240-
s
40--
120*
0-
fo 2.5 MC/S z1o. .12
4'4, ISO.
FIG A-480'
SLEEVE DIPOLE180. EG a mc/s
D300O4O 0.
letie
I
0.
"20 120*
S-IL •' • -•20-
FIG, A-50
POWER PATTERN0-4240 607 SLEEVE DIPOLE 8 MC/s
IGO*
0.0*0
270*
240*10
0640
ISO*
0.
30*
.........
300*
-3
2 __ u
$0, 2
2401 120,
40*
-15 4 / -19
20'
fo 15 Mc/s W* - 150* FIG A-52MONOPOLE
L.-4240-610 a, E 4 Mc/sl8o*
0.
330* 30*
300* 60*
4
240* 1200
40-
.4
fo 15 MC/S 210, FIG A-53MONOPOLE
0-4240.6it Ee 5 Mc/sleer
180*
-212
2400
0.
330* 30*
300, 60*
12
270'
6
40* 1201
40-
2 ---------
fo 1 15 Mc/s 210* 150, FIG A-56MONOPOLE
D-4240-614 E 9 10 Mc/s
0.
330* so,
As
300, -21
to
1 -12
C12 -12
-IS
-12
2?(r1-5
60*
-12
240' 120*-12
401-
01
2io* ISO-FIG A-57fo 15 M- Is MONOPOLE
Q40 fii- Eq 15 Mc/s
lew
B0
BAACE0*PL330c/
300,ZO-
0*
..... ...
..2 4 -. ." .. .. .. .... .. ...
330o*
Bl.. ...... ........... ..... ... ...........
f-ZO-~ 0~ 15M/ 110 I.A60M/
BAANEDDIOL
3ALNCE 30OL
o00 60,~ M/
ISO.
.3 -32
f0
.U ........ .... .. ....... .....
fOZ15~~~~t Mc/s1*10,FG.A6
2?0*
201
0-4240-623 ---- Eo 15 Mc/s
UNCLASSIFIEDSe'ctlftv Clua.ttflcatton
DOCUMENT CONTROL DATA- R & DSe 'tiefI y CIa" ti cthat Ori nMt ti it-, bliod) oft Ofha trnc- I 4, ided g i O tis an no nte,,n onm *t b•- egIvied when flil t..vtittl report I% r Itl%% I
I OkiGINATING AC IlVIY (Corporate auithor) 2a. REPORST SECURITY C., ASS|IFIA •iOIt
Stanford Research Institute Unilassified333 Ravenswood Avenue 2. r.Roup
Menlo P.rk, California 94025 N/AI REPORT TITLE
FULL-SCALE PATTERN MEASUREMENTS OF SIMPLE HF FIELD ANTE ,.NAS IN A US CONIFER FOREST
4 ODSCRIPTIVE NOTES (Type of report and incluive dates)
Special Technical Report 255 AU TIIORISI (Firal name, middle initial, last name)
Ray A. William; Gary E. Barker; Sandra G. Martensen
F REPORT DATE 70. TOTAL NO OF PAGES 7b. NO OV REFS
February 1967 105 4
8e. CONTkACT OR rRANT NO 9b. ORIGýNATOR*S REPORT NItJMPER($)
DA 36-039 AMC-00040(E) Special Technical Report 25
b. PROJECT NO SRI Project 4240
Order No. 5384-PM-63-91C. S b, OTHER RLPORT NO(S) (Any other numbers that may be assigned
this report)
ARPA Order No. 371d.
10. DISTRIBUTION STATEMENT
Distribution of this document is unlimited.
I11 SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY
Report on communications research in Advanced Research Projects Agencytropical vegetated environments. Washington, D.C.
13 ABSTRACT
"•,During May and June of 1965, measurements of field-expedient antonna impedanceand radiation patterns were conducted in a conifer forest. The antennas measuredincluded dipoles, slant wires, and inverted L's.
The pattern measurements were conducted with an aircraft-towed transmitter. Theresults are presented on contour maps showing individual polarization respollse forelevation angles from 5 to 600 from the horizon and power response from 50 abovethe horizon to the zenith for several frequencies between 2 and 15 Mc/s.
Input impedances are presented on Smith charts for each antenna over the frequencyrange that the above pattern data are presented. In addition, curves of resonantfrequency and input impedance as a function of antenna height are presented forselected dipoles.
The results demonsLrate that the trees surrounding the antennas begin to causeperturbations to the vertical polarization response of antennas at approximately8Mc/s.
DDFORM 47 (FPAGE 1)DD NOV .1473 UNCLASSIFIEDS/N 0101•807.6801 Security Classification