A key component in the development of the Advanced Communications Technology Satellite (ACTS) ultra small aperture terminal (USAT) earth station is the low noise downconverter (NLD). NASA Lewis Research Center (LeRC) has tested a version of an LND designed by Electrodyne Systems Corporation. A number of tests were conducted to characterize the radio frequency performance of the LND over temperature. The test results presented in this paper are frequency response, noise figure, gain, group delay, power transfer characteristics, image rejection, and spurious product suppression. The LND was one of several critical microwave subsystems developed and tested for the ACTS USAT earth stations

Fujikawa, Gene

Svoboda, James S.

English

NASA Technical Reports Server

https://ntrs.nasa.gov/search.jsp?R=19950023590 2020-06-16T06:28:54+00:00Z
TEST RESULTS OF A 20 GHZ, LOW NOISE DOWNCONVERTER 
FOR USAT APPLICATIONS 
Gene Fujikawa 
National Aeronautics and Space Administration 
Lewis Research Center 
Cleveland, Ohio 44135 
James S. Svoboda 
NYMA, Inc. 
Engineering Services Division 
Brook Park, Ohio 44142 
Summary 
A key component in the development of the ACTS ultra 
small aperture terminal (USAT) earth station is the low noise 
downconverter (LND). NASA Lewis Research Center (LeRC) 
has tested a version of an LND designed by Electrodyne 
Systems Corporation. A number of tests were conducted to 
characterize the radio frequency performance of the LND over 
temperature. The test results presented in this paper are 
frequency response, noise figure, gain, group delay, power 
transfer characteristics, image rejection, and spurious prod- 
uct suppression. The LND was one of several critical micro- 
wave subsystems developed and tested for the ACTS USAT 
earth stations. 
Background 
The Advanced Communications Technology Satellite 
(ACTS) Experiments Program was established to demonstrate 
a number of new telecommunications technologies by carrying 
out a diverse set of experiments. Many of these experiments 
are led by commercial industry to support various business 
applications. Southern California Edison is currently experi- 
menting with ACTS using a NASA-developed USAT for 
supervisory control and data acquisition (SCADA) applica- 
tions (ref. 1). Southern California Edison's service territory is 
largely mountainous and desert terrain with frequent wind 
storms and earthquake activity. The remote substations are 
often separated by very long distances. Monitoring and control 
of these remote substations requires a reliable, low cost 
method of satellite service. The use of small, low power 
USAT earth stations, employing the high gain ACTS Ka-band 
spot beams, have the potential to reduce overall system costs 
compared to Ku-band systems. 
A key component in the development of the USAT earth 
stationis the low noise downconverter. NASALewis Research 
Center (LeRC) has tested a version of an LND designed by 
Electrodyne Systems Corporation. A number of tests were 
conducted to characterize the RF performance of the LND over 
temperature. A photograph of the USAT Ka-band transceiver 
is shown in figure 1. The LND can be seen mounted on the 
inside back right of the housing. 
Introduction 
Five low noise downconverters were designed and built by 
Electrodyne Systems Corporation and procured for use in the 
ACTS USAT experiment. A single unit, serial number 005, 
was tested to characterize its RF performance. A block 
diagram of the LND is shown in figure 2. The front-end of the 
LND consists of a 19.7-20.04 GHz input bandpass filter, 
followed by a low noise amplifier. Downconversion is per- 
formed by a single mixer with IF amplification of the output 
signal. The local oscillator port accepts frequencies in the range 
9.825-9.975 GHz. A frequency doubler and driver amplifier 
provides the mixer with the LO signal at the appropriate 
frequency and power level. An external local oscillator source 
was required. A tunable microwave signal generator and two 
dielectric resonator oscillators @ROY s) were each used as LO 
sources in these measurements. A programmable temperature 
chamber was utilized to obtain datameasurements over a wide 
temperature range. Performance specifications of the LND are 
listed in Table I. 
Connections to the LND were WR-42 waveguide at the RF 
input port; SMA-female at the IF output and LO input ports. 
The packaged unit measured 4.25 x 2.25 x 0.4 in. 
Test Results 
The basis for these tests was to evaluate the performance of 
the LND's for eventual use in the USAT earth stations. Time 
constraints placed on the overall USAT experiment schedule 
limited the number of tests accomplished. The following tests 
were deemed to be most critical by the ACTS Project Office: 
frequency response, gain, noise figure, group delay, power 
transfer characteristics, image rejection, and spurious prod- 
uct suppression. The results of these particular tests are pro- 
vided in this report. 
TABLE I-LND SPECIFICATIONS 
Figure 1 .-USAT Ka-band transceiver. 
.975 GHz 
Figure 2.-Low noise downconverter block diagram. 
Noise Figure 
The noise figure of a system or deviceis defined as the signal 
to noise ratio at the input of a device to the signal to noise ratio 
at the output of the device. Anideal device, theoretically, would 
generate no additional noise and therefore produce a zero dB 
noise figure. 
The test setup is shown in figure 3. The noise figure was 
measured via an automated program which controls a noise 
figure meter. The program measures the noise figure by using 
the Y-factor approach. This method used a solid state noise 
source driven at two temperatures to produce two output 
powers. Extrapolating the straight line to a zero temperature 
yields the noise added by the device (ref. 3). System calibration 
involved connecting the noise source to the location where the 
output of the LND was connected during measurement. Two 
different frequency dependent excess noise ratios (ENR) were 
used. For these tests, the calibration ENR was set to a value of 
13.0 dB corresponding to 70 MHz, while the measurement 
ENR was set to the 20 GHz value of 14.8 dB. Figures 4(a), and 
Figure 3.-Noise figure test setup. 
(b) show the noise figure versus the IF output frequency for two 
different LO sources (9.9 GHz, 9.95 GHz), each at three 
different temperatures (-25 "C, +25 "C, +50 "C). The NASA 
specifications for noise figure require the single side band 
(SSB) noise figure not to exceed 4.5 dB at room temperature 
and overall noise figure over the entire operational temperature 
range not to exceed 5.5 dB. 
The +25 "C room temperature plots show that the noise 
figure did not exceed 4.0 dB for either LO source. The plots also 
show the maximum noise figures are reached when tested at 
+50 "C, where the noise figure climbs to a maximum of 
approximately 4.4 dB, which is still less than the allowable 5.5 
dB. The best noise figures are realized under cold conditions as 
indicated in the -25 "C plots, where the noise figure reached a 
Figure 4.-Noise figure versus output frequency over 
temperature. (a) 9.90 GHz DUO. (b) 9.95 GHz DRO. 
IF output frequency, MHz 
Figure 5.-Amplitude variation versus output frequency, 
9.95 GHz DUO at 12.98 dBm. 
maximum of approximately 3.2 dB. The LND passed both 
NASA required noise figure specifications over the entire 
operational temperature range. 
This test setup also allowed for plotting of the amplitude 
variation over the output frequency band. Figure 5 shows the 
relative amplitude variation over 50 to 90 MHz for the 9.95 
GHz LO case, at the three temperatures. 
Power Transfer Characteristics 
Therelationship of the signal level present at the output of the 
device to its input can be represented by plotting the power 
transfer characteristic, or Pout versus Pi,. The setup for power 
transfer characteristic testis showninfigure 6. Calibratedinput 
signal power levels were controlledusing a synthesized sweeper 
and the output power from the device was measured using a 
power meter. The input power levels were varied in 1-dB steps 
starting at -53 dBm and increased until saturation. Single 
output power measurements were taken at each input level 
setting. A low pass filter (f, = 100 MHz) was inserted at the IF 
output of the LND to reduce the amount of broadband noise 
being detected by the power sensors. 
At signal levels within the expected input power range, a 
linear relationship of the input signal to the output exists. 
However, linearity begins to deviate as the LND begins to 
saturate. When the output signal of the LND has deviated 1 dB 
from linear, this level is known as the 1 -dB compression point. 
The conversion gain can be determined from the curves by 
reading the difference between the output and input power 
levels. The room temperature (+25 "C) specification for con- 
version gain was 26.5 dB + 1.5 dB; the 1 -dB compression point 
was to be greater than -7 dBm. 
Data was taken at three different temperatures (-25 "C, 
+25 "C, +50 "C) using two different DRO's as LO sources 
(9.9 GHz, 9.95 GHz). The drive level for the 9.90 GHz DRO 
wasmeasuredat 12.98 dBm; the 9.95 GHzDRO drive level was 
13.04 dBm. Figures 7(a) and (b) illustrate the power transfer 
characteristics of the LND. As shown in figure 7(a), with the 
9.90 GHz DRO, the LND gain at room temperature was 
approximately 26 dB, with 1-dB gain compression occumng at 
an output power of -5 dBm. Using the 9.95 GHzDRO, theLND 
gain at room temperature was approximately 25.8 dB, with 1- 
dB gain compression occurring at an output power of -5 dBm, 
as shown in figure 7(b). The LND passed gain specifications at 
room temperature. However, it was noted during the testing at 
Synthesized 
measurement 
Figure 6.-Power transfer characteristic test setup. 
Input Power at 19.97 GHz (dBm) 
lnput Power at 19.97 GHz (dBm) 
Figure 7.-Power transfer characteristics. (a) 9.90 GHz 
DRO sn141 at 12.98 dBm. (b) 9.95 GHz DUO sn137 at 
13.04 dBm. 
+50 "C, the gain did not fall within the specified gain tolerance 
level of k1.5 dB, forbothLO sources. Also, for asingle test case 
(T = -25 "C, LO = 9.95 GHz), the 1-dB compression point was 
found to be -8.5 dBm, below the specification of -7 dBm. 
Group Delay 
Group delay is the change in phase with respect to a change 
in frequency and represents a measure of the time delay of a 
device. A constant group delay over a specified band would 
indicate a perfectly linear phase versus frequency response. A 
common method to measure device group delay is to use a 
automatic network analyzer. However, since the LND is a 
frequency translating device, the network analyzer could not be 
used in this application for accurate phase measurement. 
Group delay tests were performed by utilizing an automated 
test program which measures the group delay of a device under 
test. Ablockdiagramis showninfigure 8. The automatedgroup 
delay program measures the group delay by amplitude modu- 
lating a continuous wave test signal input to the device under 
test. The phase shift of the output envelope is measured by atwo 
channel vector voltmeter and compared with the input enve- 
lope. A system calibration is performed which includes all 
components except the LND. A waveguide PIN diode switch 
driven by a 2.778 MHz square wave is used to amplitude 
modulate the cw input tone. The crystal detector samples the 70 
MHz IF output of the LND and translates the IF signal into a 
proportional voltage for the vector voltmeter. The other chan- 
nel of the vector voltmeter receives the 2.778 MHz square wave 
which is attenuated to keep both channels at similar input levels 
to achieve better performance. 
A verification test was performed to insure all components 
other than the LND performed as predicted. This test used the 
same configuration for measurement as during calibration, 
which ideally should yield a group delay of 0 nsec. across the 
40 MHz measurement band. The results for the system calibra- 
tion showed a maximum deviation from zero group delay of 
no more than 0.19 nsec, and a typical value of approximately 
0.05 nsec. 
A total of six group delay measurements were done; at each 
of the two LO frequencies for three temperatures. Figure 9 
shows a typical group delay plot, in this case, for the 9.90 GHz 
HP9836C 
Computer 
IEEE-488 
Bus t 
Figure 8.-Group delay measurement test setup. 
2 5 
19.85 1 9.86 19.87 1 9.88 19.89 
Frequency (GHz) 
Figure 9.--Group delay versus frequency, LO = 9.9 GHz. 
LO. The results indicate that a larger in-band deviation occurs TABLE 11.-IMAGE REJECTION 
at high temperatures than at the lower temperatures. This same 
result was also true for the 9.95 GHz LO. 
The results of the group delay tests passed the ACTS speci- 
fication of 8" peak-to-peak in a 1 MHz band, whichcorresponds 
to a group delay of approximately 1.4 x sec. The mid- 
band (f = 19.87 GHz) group delay observed over the full 
temperature range was typically less than 40 nsec. 
Image Rejection and Spurious Products 
Image rejection tests were conductedusing both LO frequen- 
cies at the three temperature settings. The image rejection test 
setup is shown in the diagram of figure 10. The image rejection 
is defined as the ratio of the IF output power of the desired signal 
to that of the downconverted image signal power. The image 
refers to the undesired input signal at 2fL0 - fRF. The image 
signal appears 140 MHz below the fundamental, or desired 
signal. Thus, for an RF of 19.87 GHz and an LO frequency of 
19.8 GHz, the corresponding image occurs at 19.73 GHz. 
Specifications stated that the image rejection shall exceed 18 
dB. Table I1 lists the fundamental and image frequencies, 
operating temperature, input RF power levels and correspond- 
ing output powers, and the power ratio, or delta, between the 
two IF signals. 
Since mixers are nonlinear devices, the mathematical analy- 
sis of the downconversion process will result in a infinite 
number of output signals being produced. The various 
intermodulation (IM) distortion products can be calculated 
using equation (1). In using equation (1) for our purposes, recall 
that fLO is twice the value of the external LO frequency, due 
to the internal frequency doubler. 
One of the products is the desired signal; the rest of the 
signals can be considered as spurious. These spurious outputs 
can be classifiedinto two main categories: (1) outputs produced 
internally by the desiredm signal, theLO and their harmonics, 
Synthesized 
I t- t &~-J---I GND Power 
HP437B 
I Suppb 1 
Power Meter Sensor 
Figure 10.-Image rejection/spurious 
measurement setup. 
and (2) external RF signals mixing with the LO and its harmon- 
ics, causing spurs in the output passband. A limited set (24 tests 
in all) of single tone IM products were calculated which could 
produce an output at 70 MHz; the corresponding spurs gener- 
ated were measured using a spectrum analyzer. Second through 
sixth order harmonics of the RF signal were mixed with various 
integer multiples of the LO frequency. Spurious products 
appearing within the 50 to 90 MHz output band were then 
recorded. No spurs were detected within the 50 to 90 MHz IF 
passband for m = n = 1. The LND specification for spurious 
outputs was less than -27 dBc. Table I11 shows the set of five 
tests where a measurable in-band spur was observed using both 
TABLE IL(.-SPURIOUS PRODUCT SUPPRESSION 
LO sources, LW1 = 9.95 GHz and L W 2  = 9.90 GHz. The 
maximum spur levels over the 50 to 90 MHz output band at the 
three temperature settings are shown in the table. In the other 19 
tests performed, no significant spurs were observed in the IF 
passband, so these results are not shown. The RF power level 
in each case was set at -25 dBm. 
Concluding Remarks 
Tests were conducted to characterize the radio frequency 
performance of the 20 GHz low noise down-converter over 
temperature. The critical noise figure tests showed that the 
LND did not exceed 4.0 dB at room temperature. Over the full 
temperature range, the maximum noise figure measured was 
4.4 dB, which was 1.1 dB betterthan the worst case noise figure 
specification of 5.5 dB. Conversion gain at room temperature 
was approximately 26 dB, with 1-dB gain compression occur- 
ring at an output power of -5 dBm. The group delay of the L m  
at band center was typically less than 40 nsec. Group delay 
results also indicated that alarger in-band deviation occurred at 
the higher temperatures. Image rejection and spurious product 
suppression were found to be within the acceptable range. 
The test results presented here indicate that the low noise 
downconverter designed by Electrodyne Systems Corporation 
met the critical requirements for use in the ACTS ultra 
small aperture terminal earth station. USAT Ka-band 
transceivers with similar versions of this LND are now in 
operation as part of the NASAISouthern California Edison 
SCADA experiments. 
References 
1. Fernandes, R.A., Whyte, M.D.: Southern California Edison ACTS Experi- 
ment Low Cost SCADA USAT Network, Southern California Edison 
Research Center. 
2. Sohn, P.Y.: LND Specifications Document, ACTS Project Office, NASA 
Lewis Research Center, Jan. 1993. 
3. Hewlett Packard Application Note 57-1: Fundamentals of RF and Micro- 
wave Noise Figure Measurements, July 1983. 
4. Tsui, J.B.: Microwave Receivers and Related Components, Air Force 
Avionics Lab, Wright-Patterson AFB, 1983. 
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Test Results of a 20 GHz, Low Noise Downconverter for USAT Applications I I 
6. AUTHOR@) 
Gene Fujikawa and James S. Svoboda 
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Lewis Research Center 
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11. SUPPLEMENTARY NOTES I 
Gene Fujikawa, NASA Lewis Research Center and James S. Svoboda, NYMA, Inc., Engineering Services Division, 
2001 Aerospace Parkway, Brook Park, Ohio 44142 (work funded by NASA Contract NAS3-27186). Responsible person, 
Gene Fujikawa, organization code 5660, (216) 433-3495. 
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This publication is available from the NASA Center for Aerospace Information, (301) 621-0390. 
13. ABSTRACT (Maximum 200 words) 
A key component in the development of the ACTS ultra small aperture terminal (USAT) earth station is the low noise 
downconverter (LND). NASA Lewis Research Center (LeRC) has tested a version of an LND designed by Electrodyne 
Systems Corporation. A number of tests were conducted to characterize the radio frequency performance of the LND over 
temperature. The test results presented in this paper are frequency response, noise figure, gain, group delay, power 
transfer characteristics, image rejection, and spurious product suppression. The LND was one of several critical 
microwave subsystems developed and tested for the ACTS USAT earth stations. 
14. SUBJECT TERMS 115. NUMBER OF PAGES I 
Test and characterization; 20 GHz; Low noise downconverter; USAT 
NSN 7540-01 -280-5500 Standard Form 298 (Rev. 2-89) 
Prescribed by  ANSI Std. 239-18 
298-102 


Test results of a 20 GHz, low noise downconverter for USAT applications

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