The efficiency and noise temperature characteristics of the DSN 64 m antenna network prior to its upgrading to 70 m configuration are documented. The DSS 14 (Goldstone, California) is the last of the three large antennas to be upgraded, and the test results presented document its performance just prior to its downtime during the end of 1987. Antenna area efficiency was found to be somewhat higher at DSS 14 than at DSS 43 (Australia) and DSS 63 (Spain). The peak X-band efficiency was determined to be 49.8 percent (without atmosphere), compared with 45.4 and 45.1 percent for DSS 43 and DSS 63, respectively. The X-band zenith system noise temperature was found to be 1 to 3 Kelvins higher than at the other two stations, depending on which maser was chosen for the measurements. Ascribing efficiency differences to small-scale antenna surface roughness, DSS 14 may be regarded as having a 1.5 to 1.6 mm rms surface as compared to the other two antennas with 1.7 to 1.8 mm rms surfaces

Slobin, S. D.

English

NASA Technical Reports Server

-f/d -.3 2----
/23 _ "_
TDA Progress Report 42-92
i
J :i
N88-18790
October-December 1987
DSS 14 64-Meter Antenna S- and X-Band Efficiency and
System Noise Temperature Calibrations,
September 1987
S. D. Slobin
Radio Frequency and Microwave SubsystemsSection
This article is the third in a series documenting the efficiency and noise temperature
characteristics of the DSN 64-meter antenna network prior to its upgrading to 70-meter
configuration./DSS 14 (Goldstone, California) is the last of the three large antennas to be
upgraded, and the test results presented here document its performance just prior to its
downtime during the end of 1987. Antenna area efficiency was found to be somewhat
higher at DSS 14 than at DSS 43 [Australia) and DSS 63 (Spain). The peak X-band effi-
ciency was determined to be 49.8 percent (without atmosphere), compared with 45.4per-
cent and 45.1 percent for DSS 43 and DSS 63, respectively. The X-band zenith system
noise temperature was found to be I to 3 kelvins higher than at the other two stations,
depending on which maser was chosen for the measurements. Ascribing efficiency differ-
ences to small-scale antenna surface roughness, DSS 14 may be regarded as having a 1..5-
to 1.6-ram rms surface as compared to the other two antennas with 1. 7- to 1.8-mm rms
surfaces.
I. Introduction
This article is the third in a series documenting the perfor-
mance of the DSN 64-meter network prior to its upgrading to
70-meter configuration. DSS 14 is the third of the three large
antennas to be modified; DSS 63 was upgraded in May 1987,
and DSS 43 in September 1987. DSS 14 will achieve its final
configuration by early 1988. The S- and X-band performance
of the overseas 64-meter antennas is documented in [1] and
[21.
Antenna calibration measurements were taken during the
months of August and September 1987. Because of a change
in radiometer calibration technique in the middle of the cali-
bration project (hourly noise diode calibration instead of ap-
proximately once every 6 hours), only those data from days
258,267, and 270 were used in the final data reduction. The
radio sources used on those days as standard efficiency cali-
brators were 3C123, 3C274, and 3C286. Subsequent to the
DSS 14 tests, modifications were made in the DSN radio source
list 1 which affected these sources. The changes involved
both flux and source size corrections, and it was necessary to
1M. Klein, A. Freiley, and P. Richter, DSN Radio Source List for An-
tenna Calibration, JPL Report D-3801, Rev. B (internal document),
Jet Propulsion Laboratory, Pasadena, California.
138
https://ntrs.nasa.gov/search.jsp?R=19880009406 2020-03-20T08:22:13+00:00Z
apply these corrections to the measured efficiency values
after the fact. Since 3C274 is one of the strongest DSN cali-
brators visible from both the northern and southern hemi-
spheres (and is also used in both the DSS 43 and DSS 63 cali-
brations), it must be accepted that the efficiency calibrations
based on this source, as published in [1] and [2], are slightly
in error. The source size correction for 3C274 increased
0.369 percent. This would have the effect of increasing the
apparent antenna efficiency by approximately half this amount
(for a 50 percent efficient antenna). The effect of these changes
on the published DSS 43 and DSS 63 performance values will
be discussed later.
The DSS 63 calibration article [1] contains a great amount
of detail regarding calibration methods used and techniques
involved in data reduction and analysis. That reference should
be used if any uncertainty of meaning arises in the reading of
this article.
Data taken on the three listed days appear to be generally
well-behaved, and the weather was noted as clear with wind
not exceeding 15 mph. Psychrometric data were taken hourly
during the measurements, and this proved to be extremely
useful in determining adjustments for the "no-atmosphere"
antenna calibration values. Based on the temperature and rela-
tive humidity values given in the calibration report, an average
weather model for DSS 14 was developed for the 13-day span
of measurements. Total atmospheric attenuation was deter-
mined to be surprisingly constant over this time period, even
though the temperature and relative humidity values varied
greatly (e.g., the temperature ranged from 58°F to 103°F,
and the relative humidity varied, almost inversely, from
89 percent down to 7 percent). For the purposes of this arti-
cle, the S-band zenith attenuation was determined to be 0.025
dB, and the X-band zenith attenuation was determined to be
0.033 dB. These may be contrasted with the DSS 43/63 model
of 0.03 dB and 0.04 dB, respectively, for S- and X-band, for
year-average attenuation at those temperate locales.
After the data were corrected for flux and source size as
given in [3], it became clear that the efficiency values deter-
mined using 3C123 were about 3 percent high (about 1-1/2
efficiency percent) when compared to the efficiency values
determined using sources 3C274 and 3C286. This difference
was the same at S- and X-bands, and did not seem to be a
function of elevation angle (which would rule out a weather
model error for data taken on different days). After consulta-
tion (M. J. Klein, private communication), it was decided to
adjust the S- and X-band efficiency values by the factor 0.97
for those antenna efficiencies determined using radio source
calibrator 3C123. This radio source calibrator is about one-
fourth as strong as the strongest DSN standard calibrator
(3C274), and since 3C274 and 3C286 give results agreeing very
well with one another, 3C123 efficiency determinations were
changed. It is possible that 3C123 flux has changed; however,
at this time, the source of the discrepancy has not been deter-
mined. The problem will be examined in the future, and
3C274/3C123 comparisons using other antennas at Goldstone
may help resolve it. Although both 3C274 and 3C123 were
used in the DSS 63 calibration [1], the 3 percent difference
was not apparent in those data.
II. Antenna Area Efficiency
Figures 1 and 2 show the S-band antenna area efficiencies
both with and without the atmospheric attenuation included.
Note that area efficiency is referenced to a uniformly illumi-
nated aperture, 64 meters in diameter, at the given frequen-
cies. For S-band (2295 MHz), the 100 percent efficient antenna
gain is 63.75 dBi; for X-band (8420 MHz) it is 75.04 dBi.
It should be noted that data taken at the low elevation an-
gles (less than 10 degrees) show much scatter. This is possibly
due to atmospheric attenuation changes from point to point or
scintillations that affect the noise temperature measurement in
the on-source position. Also shown in the figures are second-
order curve fits to the data. Note that the curve fit in Fig. 2
(S-band efficiency without atmosphere) actually curves slightly
upward! This is obviously a curve-fitting anomaly, with a pos-
sible contribution from a slight atmospheric model error. It
would seem reasonable to assume that the S-band efficiency is
nearly a constant 59.4 percent at all elevation angles. The data
do not warrant a more complex description.
Figures 3 and 4 show the X-band area efficiencies both with
and without atmosphere. Note again the extreme spread of
measured values at elevation angles below 30 degrees. This
undoubtedly contributes to the large uncertainties in the shape
of the curve, even though the tight clustering of points in the
40- to 70-degree elevation region appears to determine the
peak value fairly well.
Table 1 gives the coefficients of the second-order curve fits
in Figs. 1 through 4. Also given in the table are peak values of
efficiency and the elevation angles at which they occur.
III. System Noise Temperature
Figures 5 and 6 show the S-band system noise temperature
both with and without atmospheric contribution. The two sets
of data represent data taken with two different masers. The
upper curve shows data taken with the Block V maser; the
lower curve is that taken with the SPD maser in a low noise
path. Because of the limited elevation angle range of the lower
data set, it was not curve-fitted to represent system noise tern-
139
perature as a function of elevation angle. The upper data set
in Figs. 5 and 6 was fitted with a fourth-order curve, the coef-
ficients of which are given in Table 2. Note that in Fig. 5 (above
65 degrees) and in Fig. 6 (above 70 degrees) the extrapolated
values of the curve fit are created to be constant, as the actual
fourth-order curve varies radically from what would be consid-
ered a reasonable extrapolation.
Figures 7 and 8 present the X-band system noise tempera-
tures both with and without atmospheric contribution. Note
again two sets of data. The upper data set was taken with the
TWM-1 maser, while the lower data set was taken with the
TWM-2 maser. Only the upper data set was curve-fitted, owing
to the limited elevation angle range of the lower set. It appears
that a constant difference (approximately 3 kelvins) separates
the two sets. For the X-band curve fit in Fig. 7, the extrapo-
lation is constant above 75 degrees; for Fig. 8 it is constant
above 85 degrees.
IV. Error Analysis
A comprehensive review of error sources in this antenna cal-
ibration scheme is given in [1] and [2]. It bears repeating that
the major contributor to the error in determination of antenna
efficiency is the uncertainty regarding radio source flux density.
It is estimated that this uncertainty at S-band is -+0.3 dB (3o)
(-+3 percent, la); at X-band it is -+0.5 dB (3o) (-+4 percent,
lo). Indeed, the 3 percent efficiency adjustments at S- and
X-band are perhaps indicative of this problem. The absolute
accuracy in the determination of antenna efficiency for the
DSS 14 antenna (as determined similarly for DSS 43 and DSS
63) is thus stated as:
S-band: -+0.4 dB (30)
X-band: +0.6 dB (3o)
V. Comparison of Measured and Expected
Antenna Efficiencies
As described in [1] and [2], a comparison was made among
the 64-m X-band antenna performance expectations as given
by the physical optics (PO) and geometrical theory of diffrac-
tion (GTD) programs. The PO analysis was described in great
detail in those references and will not be repeated here. Of
interest here are the GTD calculations of antenna efficiency as
a function of elevation angle, taking into account the long-
period (_1 to 30 meters) gravitational deformation of the
main reflector surface, The GTD-generated efficiency curve is
modified by known or postulated hardware loss (0.821 dB;
cf. Table 3, items 8-11 in [1]), and this curve is then further
modified by various amounts of so-called Ruze loss, the loss
of antenna efficiency due to small-scale (_1- to lO0-centi-
meter) surface roughness.
Figure 9 shows the GTD curves with three levels of surface
roughness: 1.06 mm (the design expectation of rms panel and
subreflector tolerance), 1.5 mm, and 1.6 mm. It is seen that
the DSS 14 antenna efficiency curve corresponds over the
entire elevation angle range to an rms surface tolerance of
1.55 ram. Also shown on this curve are the DSS 43 and
DSS 63 efficiencies, which, as stated in previous articles, cor-
respond to surface tolerances of 1.7 to 1.8 mm. Note that the
DSS 63 antenna differed structurally from the DSS 14 and
DSS 43 antennas, and thus the greater efficiency falloff of
that antenna is not surprising.
VI. Future Updates for DSS 14, 43, and
63 64-Meter Efficiencies
Due to a recent change in the source size correction factor
for radio source 3C274 (see footnote 1), there exists a very
small discrepancy in the efficiency values determined for DSS
14 as compared with those determined for DSS 43 and DSS
63. For example, it is possible that the 0.369 percent increase
in X-band source size correction might increase the efficiencies
of the overseas antennas by as much as 0.2 percent (e.g., from
50.0 percent to 50.2 percent). This increase is small compared
to the scatter of data points (cf. Figs. 3 and 4 and Table 1),
and thus may be judged as not significant in a statistical sense.
Consultation with one of the authors of JPL Report D-3801
(see footnote 1) revealed that the present source size correc-
tion value should be considered interim only, and that an
updated and highly improved document will be published
within the next several months. 2 His advice in the matter of
efficiency adjustment was to make no changes at this time.
This article and its two precursors used radio source flux and
size corrections which were the latest available at the time.
Updated values of efficiency for the three stations can be
computed when the future DSN radio source list becomes
available, although values of tenths of an efficiency percent
are not judged significant in view of the absolute accuracy
levels presently attainable.
2M. J. Klein, private communication, Jet Propulsion Laboratory,
Pasadena, California.
140
Acknowledgments
The author wishes to thank the engineers at the Goldstone DSCC, in particular Bill Wood
and Tim Gregor, for their efforts in obtaining the data needed for this article. The M&I
Group members Jim McCoy and Jerry Crook assisted with much-needed equipment
maintenance.
References
[1] S. D. Slobin, "DSS-63 64-Meter S- and X-Band Efficiency and System Noise Tem-
perature Calibrations," TDA Progress Report 42-90, vol. April-June 1987, Jet Pro-
pulsion Laboratory, Pasadena, California, pp. 103-115, August 15, 1987.
[2] S. D. Slobin. "DSS-43 64-Meter S- and X-Band Efficiency and System Noise Tem-
perature Calibrations," TDA Progress Report 42-90, vol. April-June 1987, Jet Pro-
pulsion Laboratory, Pasadena, California, pp. 116-126, August 15, 1987.
141
Table 1. Coefficients of second order curve fits for antenna area efficiencies
efficiency = a 0 + alO + a202
where 0 = elevation angle, degrees
Coefficient/parameter S-band (2295 MHz) X-band (8420 MHz)
With atmosphere With atmosphere
(cf. Fig. 1) (cf. Fig. 3)
a 0 0.567571 0.434121
a 1 7.446475 E-04 2.234165E-03
a 2 -5.887066E-06 -2.082133E-05
Peak efficiency, % 0.59112 0.49405
Peak angle, deg 63.244 53.651
Standard deviation, % 0.00354 0.00853
Without atmosphere Without atmosphere
(cf. Fig. 2) (cf. Fig. 4)
a o 0.592390 0.457946
a 1 1.936510E-06 1.572380E-03
a 2 4.675295 E-07 -1.541394E-05
Peak efficiency, % 0.594 (see text 0.49805
Peak angle, deg (see text) 51.005
Standard deviation, % (see text) 0.00859
142
Table2.Coefficientsoffourth-ordercu vefitsfor S- and X-band system noise temperatures
Tsystem =a O +alO +a202+a303+a404
where 0 = elevation angle, degrees
Coefficient/parameter S-band (2295 MHz) a X-band (8420 MHz) b
a 0
a 1
a 2
a 3
a4
Zenith noise temperature, K
Standard deviation, K
a 0
a 1
a 2
a 3
a 4
Zenith noise temperature, K
Standard deviation, K
With atmosphere With atmosphere
(cf. Fig. 5) (cf. Fig. 7)
4.919551E+01 5.836215E+01
-2.040157E+00 -2.234962E÷00
6.445888E-02 6.128831E-02
-9.468854E-04 -7.517988E-04
5.169310E-06 3.378224E-06
Note: If0 /> 65 deg, Note: If0 _ 75 deg,
T = 21.161 K T = 25.211 K
21.161 25.211
0.334 0.358
Without atmosphere Without atmosphere
(cf. Fig. 6) (cf. Fig. 8)
2.727111E+01 3.355993E+01
-2.675004E-01 -5.586415E-01
2.027795E-03 1.278769E-02
2.917834E-05 -1.356839E-04
-3.911682E-07 5.376014E-07
Note: If0 _ 70 deg, Note: If0 _ 85 deg,
T = 19.098 K T = 23.203 K
19.098 23.203
0.239 0.284
aS-band (2295 MHz) specs: Maser SPD Blk IV, S/N 4002, 1.83 K; Maser Blk V, S/N 5002, 4.48 K.
bX-band (8420 MHz) specs: Maser Blk II, TWM-2, S/N 2007, 3.46 K; Maser Blk IIA, TWM-1,
S/N 2011, 3.82 K.
143
0.65
0.64
0.63
0.62
0.61
z
G 0.60
0.5B _,=._ d
oq
0.57 _ _:P
0.56
0.55
0 20 40 60 80
ELEVATION ANGLE, deg
Fig. 1. DSS 14 64-m S-band (2295-MHz) area efficiency with
atmospheric attenuation included
0.55
0.54
0.53
0.52
0.51
0.50
0.49
0.48
0.47 u{
0.46 _-%0.45
0.44
0.43
0.42
0.41 u
0.40
0
o a__.,
o "*
2O 4O 6O
ELEVATION ANGLE, deg
8O
Fig. 3. DSS 14 64-m X-band (8420-MHz) area efficiency with
atmospheric attenuation included
0.65
0.64
0.63
0.62
0.61
0.60
0.59
0.58
0.57
0.56
0.55
0
..... u_ H_
1
!
I
20 40 60 80
ELEVATION ANGLE, deg
Fig. 2. DSS 14 64-m S-band (2295-MHz) area efficiency
without atmospheric attenuation
0.55
0.54
0.531
0.52
0.51
0.50
o
0.49 [33
0.48
0.47 D
o46/L
0.45
0.44
[]
0.43
0.42
0.41
0.40
0
n
_, _,,_,____,_ _,._L._,_
_=-'-.-t,
_ o_
rrl
20 40 60 80
E LEVATtON ANGLE, deg
;,,,,%
rb .,_
Fig. 4. DSS 14 64-m X-band (8420-MHz) area efficiency
without atmospheric attenuation
144
m<
uJ
O
z
LU
_q
50
45
40
35
30
25
20
1
1,
0
-%
_ F BLK V MASER
20 40 60 80
ELEVATION ANGLE, deg
Fig. 5. DSS 14 64-m S-band (2295-MHz) system noise
temperature, including atmospheric contribution
60
55
v
5o
I.-
<
a: 45
uJ
N 4o
_ 35
_- ao
25
\
_ _,4L,,,,-
2O
0 80
TWM-2 -
I
2O
WM-1
40 60
ELEVATION ANGLE, deg
Fig. 7. DSS 14 64-m X-band (8420-MHz) system noise
temperature, including atmospheric contribution
<
O
Z
50
45
40
35
30
2O
15
10
0
_=
SPD MASER _-.-_ 4.u c:_:_ u _
I I I
20 40 60 80
ELEVATION ANGLE, deg
Fig. 6. DSS 14 64-m S-band (2295-MHz) system noise
temperature without atmospheric contribution
60
55
v
50
I.-
<
45
4o
o 35
_ ao
25
20
0
TWM-1
TWM 2_ _
20 40 60 80
ELEVATION ANGLE, deg
Fig. 8. DSS 14 64-m X-band (8420-MHz) system noise
temperature without atmospheric contribution
145
0.60
0.58
0,56
0.54
0.52
0.50
0.48
0.46 _
v _
0.44
0.42
0 AO
0.38 /0.36
0.34
0
jfv
f
GTD +
1.6 mm,-._
f j-
f-
OSS 14
ACTUAL _
20 40 60
GTID +
_""" ,_,,_ m m
GTD +
DSS 43
_UAL
8O
ELEVATION ANGLE, deg
Fig. 9. Comparison of DSS 14, 43, and 63 64-m X-band
measured efficiency and GTD-calculated efficiency for
various Ruze surface tolerance values, without atmosphere
146


DSS 14 64-meter antenna S- and X-band efficiency and system noise temperature calibrations, September 1987

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