Measurements made on the frequency stability of the DSS-13 34-m diameter Beam Waveguide (BWG) antenna showed that at 46.5 and 37 deg elevation angles, the BWG antenna stability at 12.2 GHz was between 1.3 and 2.2 x 10(exp -15) for tau = 1024 sec and good weather conditions. These frequency stability values apply to the portion of the antenna that includes the main reflector, subreflector, tripod legs, and the six BWG mirrors. The test results reported are believed to be the first known successful measurements of the stability of the microwave optics portion of a large antenna to a level of 1 or 2 parts in 10(exp 15)

Franco, M. M.

Otoshi, T. Y.

English

NASA Technical Reports Server

TDA ProgressReport42-110
.b//- 32_.,
August15, 1992
DSS-13 Beam Waveguide Antenna Frequency Stability
T. Y. Otoshi and M. M. Franco
Ground Antennasand FacilitiesEngineeringSection
Measurements made on the frequency stability of the DSS-13 34-m-diameter
Beam Waveguide (BWG) antenna showed that at 46.5- and 37-deg elevation angles,
the BWG antenna stability at 12.2 GHz was between 1.3 and 2.2 x 10 -1_ for v --
1024 see and good weather conditions. These frequency stability values apply to
the portion of the antenna that incIudes the main reflector, subreflector, tripod legs,
and the six BWG mirrors. The test results reported in this article are believed to
be the first known successful measurements of the stability of the microwave optics
portion of a large antenna to a level of 1 or 2 parts in 10zb.
I. Introduction
As was pointed out in a previous article [1], attempts
have been made in past years to measure the frequency
stability of a large antenna using various techniques in-
cluding (1) a probe on the reflector surface method, (2) a
spacecraft Doppler measurement method, (3) a collimation
tower method, and (4) very long baseline interferometry
(VLBI) methods. Most of these methods have been unable
to measure frequency stabilities to better than a few parts
in 1014 or had other disadvantages discussed in [1].
A new method proposed in 1991 [1] involved the recep-
tion of far-field signals from geostationary satellites posi-
tioned at various elevation angles. The proposed method
had the advantages of being simple and inexpensive to im-
plement and could enable stability data to be obtained
in a short time frame. Except for a new fiber-optic sub-
system, most of the components and instruments required
were already available. Since the antenna now remains the
limiting factor that would prevent successful gravitational
wave experiments to be performed in the near future, there
existed an urgency to obtain antenna stability data that
could help establish realistic performance requirements for
new DSN antennas.
In addition to the goal of obtaining data in a short time
frame, another goal of the new method was to demonstrate
that fiber-optic cables could be used to carry microwave
frequencies over long distances with negligible degradation
to amplitude and phase stability. This article presents
data that demonstrates the new method was successfully
employed, and that all of the primary goals have been
met for good weather conditions. BWG antenna stability
data, applicable for inclement weather conditions, are not
yet available.
II. Methodology
Figure 1 shows a block diagram of the test configura-
tion. The method involves the use of far-field signals in
the 11.7-12.2-GHz region from geostationary satellites, a
stable reference antenna, and a phase detector Allan de-
viation measurement instrument. One of the main advan-
tages of the test method is that it does not require refer-
ence signals that are coherent with the station clock. By
receiving the far-field signals simultaneously with a refer-
ence antenna and the 34-m antenna under test, the phase
variations common to both paths tend to cancel at the
151
https://ntrs.nasa.gov/search.jsp?R=19930010235 2020-03-17T08:14:49+00:00Z
output of a mixer contained in the Allan deviation mea-
surement instrument [2].
For the proposed BWG aaltenna stability measurement
method to yield useful and accurate data to the 1 × 10 -15
level, it is required that the 12-GHz reference path have a
fractional frequency stability of better than 1 or 2 xl0 -16
for r = 1000 sec. The fulfillment of this requirement by
the fiber-optic system has been reported in [3].
A Ku-band test package [4] is installed at the pedestal
room focal point F3. For this test configuration, the por-
tions of the BWG antenna being tested are the instabilities
of the main reflector, subreflector, tripod legs, and six mir-
rors of the BWG system.
Specific Satellites selected for this method are posi-
tioned at 47-, 37-, and 12-deg elevation angles. Minor
sec were 2.16 xl0 -15 for the first run and 1.64 x 10 -15
for the second run. These results were about a factor of 3
better than expected.
Also shown in Fig. 3 is the fiber-optic-system-only sta-
bility value of 1.64 x 10 -is for r = 1024 sec. The fiber-
optic-only path is the baseline reference that sets the lower
limit of stability that can be measured for the 34-m BWG
antenna. Descriptions of the fiber-optic-only path and test
procedures were described previously in [3].
Forinterest,Fig. 4 is presented to show the raw phase
data corresponding to the Allan deviation result of the
above 5 a.m.-2 p.m. run. In addition, the outside air tem-
perature and wind conditions that prevailed during the
tests are shown in Figs. 5 and 6, respectively. It can be seen
from Fig. 6 that the air temperature varied from about 6
to 15 deg C and the wind was typically less than 30 km/hr.
antenna-pointing corrections, of about 4-50 mdeg max- A graphic description of the wind data (Fig. 7) shows that
imum during a 24-hr period, are required to keep the tl_e wind was blowing both into the back and into the
antenna beam peak pointed at the satellite. Although front of the main reflector surface at angles of about 16
these antenna pointing changes are small compared with
those involved in an actual spacecraft track, phase change
measurements could uncover problems associated with an-
tenna po_ntlng due tohardware or software. Tile method
is intended primarily to measure instabilities of the BWG
antenna due to outside air temperature and wind condi-
tions.
Even though the measurements are made at Ku-band,
the information can be inferred back to mechanically re-
lated changes and is therefore useful for determining sta-
bility at other frequencies.
I!1. Test Results
Figure 2 shows the block diagram of the test configu-
ration that was used to measure the stability of the BWG
antenna at a 46.5-deg elevation angle. The DSS-13 BWG
antenna was pointed at a 46.5-deg elevation angle and a
156.9-deg azimuth for receiving a 12.2-GHz beacon signal
from the geostationary satellite GSTAR I owned by the
deg (back side) and 52 deg (front side) off the main z-axis
direction.
Figure 8 shows the block diagram of the test configu- --
ration used to measure the stability of the BWG antenna
at a 37-deg elevation angle. The DSS-13 BWG antenna _
was pointed at a 37-deg elevation angle and a 132.9-deg
azimuth so as to receive a 12.2-GtIz beacon signal from
the geostationary satellite Satcom K1 owned by the GE
American Communications Corporation. This test config-
uration differs slightly from that shown in Fig. 2 in that -
one additional 12.198-GHz filter and 20-dB gain amplifier
were used. For these tests and all subsequent tests, a new
calibration procedure was developed for verification of the
test setup. The calibration procedure was to move the =
subreflector in +0.1-in. offset in the z-axis axial direction
from the nominal setting. It is known from previous work
[5], that the effective pathlength change was approximately
1.77 times the z-axis offset subreflection position on a 64-m
Cassegrain antenna. At 12.2 GHz, this pathlength change,
Ap:, corresponds to a phase change in degrees of
GTE Corporation. Tlae signals from the reference a_ntenn a ....... ....
via the fiber-optic_syStem and tile 34:mante:nna under test ...........
360.
are connected to the Allan deviation measurement instru- _iph = --_-(1.77Apt )
m ent, which co_ntains a microwave phase detector. Band-
pass filters (centered at 12.2 GHz) were used to remove
unwanted signals.
Figure 3 shows the Allan deviation plots obtained
March 4 and 5, 1992 for two 9-hour-long runs. The first
was from 4 p.m. to i a.m. PST and the second was from
5 a.m. to 2 p.ml PST. TTie Allan deviations for r - 1024
(1)
where A = free'spacewavelength in centimeters. For
Apt = 0.254 cm (0.1 in.),then _Iph= 65.9 deg. With
tile34-m BWG antenna having shaped main- and subre-
flectorsurfaces,the 1.77 factormight be closerto 1.7so
that 6ph 63 deg. The measured phase changes resulting
from moving the subreflector+0.1 in.was about +60 deg
152
as shown in Fig. 9. This procedure provided a means of
verifying that, for a particular test configuration, phase
changes that occurred in the antenna path above F1 were
actually observed and correctly measured.
Figure 10 shows the Allan deviation plot obtained when
the DSS-13 BWG antenna was pointed at a 37.0-deg ele-
vation angle. The Allan deviations measured for r = 1024
sec was 1.26 xl0 -1S for a 9-hour time period between 4
p.m. to 1 a.m. the next morning.
For interest, the raw phase data for the first run be-
tween 4 p.m.-1 a.m. are shown in Fig: 11 along with out-
side air temperature and wind data in Figs. 12 and 13,
respectively. It can be seen from these figures that the air
temperature varied between 12 and 7 deg C and the wind
was typically less than 24 km/hr. As depicted in Fig. 14,
the wind was blowing into the face of the main reflector
surface, but at a direction between 29 to 53 deg off the
main reflector z-axis.
IV. Future Test Plans
Comparisons of the results showed that for the 4 p.m.-
1i a.m. runs, the Allan deviations were 2.16 xl0 -15 and
1.26 xl0 -15 for r = 1024 sec at a 46.5- and 37-deg ele-
vation angles, respectively. For future tests, it would be
of interest to perform 9-hour runs between 8 p.m. and 5
a.m. when the least amount of air temperature variations
generally occur.
For the future, plans are being made to obtain data at
the 12-deg elevation as well. It is also of interest to obtain
data for the more severe (>32 km/hr) wind conditions that
were shown in Figs. 6 and 13.
V. Conclusions
The initial test results presented in this article show
that the proposed methodology was successfully employed
and the goals were met. Data have been provided to
the gravitational wave experimenters in a relatively short
time frame (about 14 months) from conception of a new
method, followed by the procurement, fabrication, and in-
stallation phases, and then the test phase. More data still
have to be obtained to determine the stability of the BWG
antenna under more severe weather conditions. However,
this article has presented the first known stability data ob-
tained on a large microwave antenna to a level of 1 or 2
parts in x 1015 for r of approximately 1000 sec.
Acknowledgments
D. Bathker of the Ground Antennas and Facilities Engineering Section provided
technical and management support on this project, as well as a needed Ku-band
feed design for the reference antenna. B. Seidel provided technical information on
Ku-band geostationary satellites. Technical discussions with both D. Bathker and
B. Seidel concerning the feasibility of the far-field methodology and test strategies
were helpful.
The authors are grateful to A. Bhanji, B. Conroy, and R. Perez of the Radio
Frequency and Microwave Subsystems Section for the loan of the Allan Deviation
Measurement instrument, as well as the technical information on the use of the
instrument and data reduction software.
The reference antenna and 12-GHz fiber-optic system were key components that
helped to make the measurements successful. :I. Garnica, :I. Ney, and L. Smith of
DSS 13 did most of the work on the fabrication, installation, and checkout of the 10-
ft reference antenna. The successful operation of the 12-GHz fiber-optic system was
primarily due to G. Lutes and R. Logan of the Communications Systems Research
Section.
The support provided by the entire DSS-13 crew during all phases of the testing
at DSS 13 is greatly appreciated. C. Goodson and G. Bury provided the DSS-13
management support needed to work out workforce rescheduling problems. Frequent
periods of rain and bad weather caused some tests to be cancelled, but due to the
excellent station support, the needed test data were ultimately obtained.
153
References
[1] T. Y. Otoshi, "A Proposed Far-Field Method for Frequency-Stability Measure-
ments on the DSS 13 Beam-Waveguide Antenna," TDA Progress Report _2-
107, vol. July-September 1991, Jet Propulsion Laboratory, Pasadena, California,
pp. 81-87, November 15, 1991.
[2] B. L. Conroy eazd D. Le, "Measuren_ent of Allan Variance and Phase Noise at
Fractions of a Millihertz," Rev. Sci. Instruments, vol. 61, no. 6, pp. 1720-1723,
June 1990.
[3] T. Y. Otoshi, M. M. Franco, and G. F. Lutes, "Performance of a 12-GHz Fiber-
Optic System for Be_m-Waveguide Antenna Stability Testing," TDA Progress
Report 42-109, vol. January-March 1992, Jet Propulsion Laboratory, Pasadena,
California, pp. 105-113, May 15, 1992.
[4] T. Y. Otoshi, S. R. Stewart, and M. M. Franco, "A Portable Ku-Band Front-
End Test Package for Beam-Waveguide Antenna Performance Evaluation," TDA
P_'bgress Report _g-i07, vol. July-September i991, Jet Propulsion Laboratory,
Pasadena, California, pp. 73-80, November 15, 1991.
[5] T. Y. Otoshi and L. E. Young, "An Experimental Investigation of the Changes of
VLBI Time Delays Due to Antenna Structural Deformations," TDA Progress Re-
port 42-68, vol. October-December 1981, Jet Propulsion Laboratory, Pasadena,
California, pp. 8-16, April 15, 1982.
_ ÷
154
=
POSSIBLE FUTURE
LOCATIONS OF
REFERENCE
BYPASS
GEOSTATIONARY
SATELLITE
6-MIRROR
BEAM-WAVEG UIDE
AMPLIFIER
FILTER 10-ft DIAMETER
REFERENCE ANTENNA
(FIXED POINTING)
EXISTING
KU-BAND
TEST
R-OPTIC CABLE SYSTEM
(UNDERGROUND PIPING AVAILABLE)
I
I I
I 1
I I
I
ALLAN DEVIATION AND II PEDESTAL PHASE-SPECTRAL
L ROOM DENSITY PLOTS J
! DETECTOR
FREQUENCY STABILITY
MEASURING SYSTEM
Fig. 1. Test conflguratlon for measurement of the frequency stability of the DSS-13 BWG antenna.
155
=156
10-ft DIAMETER
REFERENCE
ANTENNA
54-dB GAIN
160K
(LNR MODEL)
36-dB
GAIN
_7 7-dB
GAIN
BANDPASS RLTER
12,198 GHz
40-MHz BANDWIDTH (BW)
RBER-OPTIC SYSTEM
(TRANSMI'I-rER, 150-ft
RBER-OPTIC CABLE,
AND RECEIVER)
BANDPASS RLTER 50-dB 50-dB BANDPASS FILTER
12.203 GHz GAIN - A-LEANDEV]ATION OAII_ 12,203 GHz
20-MHz BW PHASE DETECTOR 20-MHz BW
MEASUREMENT
INSTRUMENT
34-m DIAMETER
_,....._. J CASSEGRAIN
ANTENNA
i
-_ 6-MIRROR
BWG
SYSTEM
KU-BAND
FEED AND
POLARIZER
54-dB GAIN\ 716oK
(1..NR MODEL)
Fig. 2. The teat configuration involvlng the use of the 12.2-GHz beacon signal from the GSTAR I geostatlonary satellite at a 46.5-deg
elevation angle.
o RUN1 4P.M. MARCH4-
I _ I A.M PST MARCH 5
-13j- _ x RUN2 5A.M.-2PM. PST -
[ _ MARCH 5
FIBER-OPTIC "_,.
'-14 SYSTEM
o
9 -15 _ --_ _
16 _1 _ --
-17 I [ .... 1 i
0 I 2 3 4 5
LOG10 (TAU), sec
Fig: 3. Aiian deviation pl0ts of the DSS'13 BW(_ antenna stability on March 4 and 5, 1992.
The DSS-13 BWG antenna was pointed at a 46.5-deg elevation angle and a 156.9-deg azimuth,
receiving a 12.2-GHz beacon aignal from GSTAR I.
=-
L
F
=90I
45
o
_45 i
-90
i I I I i I t I I
I I I I I J I I I
1 2 3 4 5 6 7 8 9 10
/i TIME, h
Fig. 4. Phase change plot corresponding to the 5 a,m.-2 p.m. run of Fig. 3.
25
2o
td
n-
LUCL
10
I I I ! I I I I I
t J I I I i i I
1 2 3 4 5 6 7 8 9 100
TIME, h
Fig. 5. Outdoor ambient temperature change during the 5 a.m.-2 p.m. run of Figs, 3 and 4.
157
4C
3C
I.
10
0
0
4l__ 38,11kmTn 1 t I I I I } t
__ O WIND SPEED
× WIND DIRECTION
×-_- 284.6 deg AZ
8.2 km/h _=,-
_wrw _ I , l I I 1 I I
1 2 3 4 5 6 7 8 9
A TIME, h
Fig. 6. Outdoor wind date during the S s.m,-2 p.m. run of Figs. 3 end 4.
-3O0
-200
- 100
o
10
(3
Lu
_3
z
W
173 deg AZ
(19.3 kin/h)
\
\
\
\
\
\
\
\
\
\
\
\
285 deg AZ
(< 32.1 km/_)
BORE$1GHT
S
Fig. 7, Wind direction relative to the BWG antenna main axis
during tests with the GSTAR ! geostatlonary satellite.
158
=: :
1o-rt DIAMETER
_..._ REFERENCE
ANTENNA
54-dB GAIN\ 71_K
(LNR MODEL)
GAIN
\7
BANDPASS FILTER
12.198 GHz
40-MHz BW
FIBER-OPTIC SYSTEM
(TRANSMITTER, 150-ft
FIBER-OPTIC CABLE,
AND RECEIVER)
57-dB
GAIN
BANDPASS FILTER
12.198 GHz
40-MHz BW
50-dB
GAIN
",'EATI,
BANDPASS FILTER 20-dB I 50-dB BANDPASS RLTER
12.203 GHz GAIN ALLAN DEVIATION GAIN 12.203 GHz
20-MHz BW PHASE DETECTOR 20-MHz BW
MEASUREMENT
INSTRUMENT
34-m DIAMETER
J _SSEGRAIN
ANTENNA
I I 6-MIRROR
BWG
SYSTEM
-_ KU-BANDFEED AND
POLARIZER
54-dB GAIN
\ 7160K
(LNR MODEL)
Fig. 8. The test configuration Involving the use of the 12.2-GHz beacon signal from the Satcom K1 geostetlonary satellite at a 37-deg
eievatlon angle.
159
9O
60
30
I 1 I I 1 t I I I
...... t I I I., 1 I I I I
200 400 600 800 1000 1200 1400 1600 1800
A TIME, sac
2000
Fig. 9. Subreflector phase change plot ,as part of the precellbratlon procedure to verify test
setup on 1992 day of year 66. The DSS-13 BWG antenna was pointed at • 37-deg elevation
angle and a 132.9-deg azimuth, receiving a 12.2-GHz beacon signal from Satcom KI.
-12 I I t I
n RUN1 4P.M. MARCH5-
1 A.M. PST MARCH 6
-13 -
-14 \ _BER-OPTIC _
GO \ SYSTEM
-17 I I ]
0 1 2 3 4 5
LOGlo (TAU), sec
Fig. 10. Allan deviation plot of the DSS-13 BWG antenna atablllty on March 5 and 6, 1992.
The DSS-13 BWG antenna was pointed at a 37-deg elevation angle and a 132.9-deg azimuth,
recelvlng a 12.2-GHz beacon signal from Satcom K1.
±
=-
=_
160
90 I I I I I I l I I
,41
o.
-90 I I I I.... I I 1 I I
0 I 2 3 4 5 6 7 8 9
,_ TIME, h
Fig. 11. Phase change plot corresponding to the 4 p.m.-1 a.m, run of Fig. 10.
10
(3
g,
"o
uJ-
LU
0_
UJ
i--
25!
20--
15--
10--
5
0
I I I I I I I I I
I I, I I I I I I I
1 2 3 4 5 6 7 8 9
,_ TIME, h
10
Fig. 12. Outdoor arabian! temperature change during the 4 p.m.-1 s.m. run of Figs. 10 and 11.
161
4O
3O
20
10
00
1 I t I t I I I I
r7 WIND SPEED
x WIND DIRECTION
x x-----_-x_ 284.3 deg AZu
AT._X_"A"--'--- X_X26o.3degAZ x-'-.--.-=x_
_-. 15.0 km/h
-300 -o
o
100 z
I I I I 1 1 I I I 0
1 2 3 4 5 6 7 8 9 10
A TIME, h
Fig, 13. Outdoor wind data during the 4 p.m.-1 a.m. run of F|gs. 10 and 11.
W
N
260 deg AZ
(< 24.1 krn/h)
E
S
Fig. 14. Wind direction relative to the BWG antenna main axis
during tests wlth the Satcom K1 geostatlonary satellite.
162


DSS-13 beam waveguide antenna frequency stability

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