A 32-GHz six-element linear transmitter array utilizing monolithic microwave integrated circuit (MMIC) phase shifters and power amplifiers was designed and tested as part of the development of a spacecraft array feed for NASA deep-space communications applications. Measurements of the performance of individual phase shifters, power amplifiers, and microstrip radiators were carried out, and electronic beam steering of the linear array was demonstrated. The switched-line phase shifters were accurate to within 7 percent on average and the power amplifier 1-dB compressed output power varied over 0.3 dB. The array had a beamwidth of 7.5 deg and demonstrated acceptable beam steering over + or - 8 deg. From the results, it can be concluded that this MMIC phased array has adequate beam-scanning capability for use in the two-dimensional array. The areas that need to be improved are the efficiency of the MMIC power amplifier and the insertion loss of the MMIC phase shifter

Duffy, L.

Huang, J.

Lubecke, V.

Rascoe, D. L.

Riley, A. L.

English

NASA Technical Reports Server

TDA Progress Report 42-98
N90-12so3
August i5, 1989
/?
/I0-
Ka-Band MMIC Beam Steered Transmitter Array
D. L. Rascoe, A. L. Riley, J. Huang, V. Lubecke, and L. Duffy
Spacecraft Telecommunications Equipment Section
A 32-GHz six-element linear transmitter array utilizing Monolithic Microwave
Integrated Circuit (MMIC) phase shifters and power amplifiers has been designed
and tested as part of the development of a spacecraft array feed for NASA deep-space
communications applications. Measurements of the performance of individual phase
shifters, power amplifiers, and microstrip radiators were carried out, and electronic
beam steering of the linear array was demonstrated.
I. Introduction
Downlink communication systems for NASA deep-
space missions presently operate at X-band (8.5 GHz).
However, in the mid-1990s, advanced deep-space missions
may utilize Ka-band systems (32 GHz downlink, 34 Giiz
uplink) to achieve communications enhancement on the or-
der of 8 dB. A receiver Monolithic Microwave Integrated
Circuit (MMIC) array at Ka band has been reported [1],
but a transmitter array, a critical element in these systems,
has not.
At JPL, a 32-GtIz solid-state transmitter is under de-
velopment utilizing state-of-the-art GaAs MMIC devices.
The initial goal of this work is to produce a Ka-band pla-
nar phased array with 5-W output power to feed a 4-m
reflector system. The electronic beam-scanning capability
of the phased array will allow the narrow beam (._ 0.2
deg) of the large reflector to perform fine beam pointing
toward the Earth (=t:l deg). As a first step in this effort,
a linear array composed of six subarrays of microstrip ra-
diators, six MMIC switched-line phase shifters, and six
MMIC power amplifiers was designed and tested. The
MMIC devices were developed under programs funded by
the NASA Lewis Research Center. This article reports
the performance results and mathematical modeling of the
JPL linear transmitter array incorporating these devices.
II. MMIC Devices
The MMIC phase shifters were designed and fabri-
cated on GaAs by the Honeywell Sensors and Signal Pro-
cessing Laboratory [2, 3]. A photograph of a phase shifter
is shown in Fig. 1. A single phase shifter contains 12
MESFETs in a three-bit switched-line configuration and
2 MESFETs in an analog loaded-line configuration. The
switched-line circuit provides nominal phase changes of 45,
90, and 180 deg. The loaded-line design provides a nomi-
ned continuous phase variation from 0 to 45 deg. These de-
vices were originally designed for operation at 30 GI-Iz for
NASA's ACTS program rather than at the slightly higher
Deep Space Network frequency of 32 GHz.
The MMIC power amplifiers were designed and fabri-
cated by the Texas Instruments Central Research Labora-
tory [4]. A photograph of an amplifier is shown in Fig. 2.
207
https://ntrs.nasa.gov/search.jsp?R=19900003487 2020-03-19T23:46:48+00:00Z
The devices used in the array were two-stage amplifiers
utilizing GaAs MESFETs with a 0.25-_um gate length and
gate widths of 0.1 mm and 0.3 mm for the first and second
stages, respectively. The design goal of this device was to
produce 20 dBm of output power.
III. Array Design
The linear phased array, shown in Fig. 3, is com-
posed of four major "building blocks:" (1) a six-way mi-
crostrip power divider, (2) a carrier strip of six MMIC
phase shifters, (3) a carrier strip of six MMIC power am-
plifiers, and (4) an antenna array of 6 pairs of microstrip
patch radiators. All blocks were separately fabricated and
tested to allow evaluation of the performance of each de-
vice and for building a detailed model of the linear array.
This "building-block" design approach of the array also
allows for ease of replacement of any of the major compo-
nents. Thus as improved MMIC devices become available
or evaluation of different antenna elements is desired, the
devices or elements may be readily integrated into this
test-bed.
The RF input to the array is through a WR-28
waveguide-to-microstrip transition of the Van Heuven [5]
antipodal finline type. The double-sided transition pat-
tern is etched on 0.25-mm-thick Rogers 5880 Duroid and
attached to the gold-plated aluminum housing using In-
dalloy 121 solder.
The six-way microstrip power divider consists of a set
of 90-deg branch-line couplers with compensating lengths
of microstrip interconnecting transmission lines to produce
equal amplitude and phase at all six outputs. A close-up
of the divider is shown in Fig. 4. The divider pattern was
etched on 0.12-mm-thick Rogers 5880 Duroid laminated
on an aluminum carrier. Each coupler was terminated by
a 50-_ TaN thin-film chip resistor connected to an approx-
imately quarter-wave-length radial line open-circuit stub.
The power divider was designed using the EEsof Touch-
stone simulation and MiCAD layout systems. A table of
simulated versus measured data for all six ports at 32 GHz
is shown in Table 1.
The MMIC carrier strips were designed to permit
measurement of each MMIC device and to interface with
the array. Individual devices were measured by attach-
ing waveguide-to-microstrip transitions to the carrier as
shown in Fig. 5. The carrier strips consisted of laser cut,
0.25-mm-thick alumina substrates with etched TiW/gold
circuit metalization that were soldered to gold-plated ko-
var carrier strips. The dc and control lines were brought
through the carrier and substrate via miniature coaxial
feedthroughs mating on the underside with dual in-line
pair (DIP) socket connectors. The MMICs were attached
to the carriers with silver epoxy and wire bonded to the
alumina substrates with 25-pm-diameter gold wire.
The antenna array, consisting of six pairs of microstrip
radiators that radiate in a direction normal to the plane
of the dielectric, was designed using the multimode cavity
theory [6]. This theory assumes that the electric field in
the cavity underneath the patch can be precisely modeled
by a series of cosine modal functions. Since the funda-
mental mode, as well as the higher-order modes, can all
be included in the analysis, accurate prediction of the res-
onant frequency, copolarization and cross-polarization ra-
diations, input impedance, and bandwidth effect can be
achieved.
The antenna array was etched on a 0.25-mm Rogers
5880 Duroid substrate. Each etched radiator pair consists
of two rectangular microstrip patches combined by a two-
way reactive power combiner. A typical input return loss
for a two-patch array, shown in Fig. 6, at 32 GHz was
nominally -20 dB with 2.5 percent bandwidth. The sep-
aration between radiator pairs was 1.08 free-space wave-
lengths. This spacing was chosen to allow ease of assembly
so that DIP sockets could be used at each MMIC position.
Since only -4-10 deg of beam scan is needed for the array
to achieve the required reflector fine beam pointing of less
than 1 deg, the relatively wide subarray spacing did not
generate any serious grating lobe problems. Figure 7 is a
calculated far-field pattern [7] of the 12-patch linear array
with a 10-deg beam scan and 1.08-wavelength subarray
spacing.
IV. Test Results
To ensure that the microstrip array gives adequate
performance, the six pairs of patches were connected di-
rectly to the six-way power divider without the amplifiers
and phase shifters. The far-field pattern was measured
and compared with the calculation as shown in Fig. 8. It
demonstrated excellent pattern performance. The mea-
sured array gain, excluding the power divider loss, was
15.9 dBi, which indicates an efficiency of 83 percent. In-
dividual measurements of single and double patches pre-
ceded the 12-patch array measurement, and Table 2 shows
a comparison of the radiator efficiencies in these three
ca.._.
The MMIC devices were measured on an extended
HP8510 at 32 GHz in the carriers. Phase-shift measure-
ments were referred to the nominal zero phase state of
208
each device and attenuation was referred to back-to-back
waveguide-to-microstrip transitions. Figure 9 is a plot
of nominal phase versus measured phase for six phase
shifters. The devices used in the array were from two
wafers, each made with slightly different mask sets. The
mean and standard deviation of the phase shift was 7.0 +
1.6 percent over the range 0 to 300 deg. Attenuation as
a function of nominal phase angle is shown in Fig. 10.
The mean attenuation at zero phase shift is 10.4 dB for
the first group and 8.0 dB for the second. The attenuation
changed at a rate of approximately 0.8 dB/100 deg and 2.8
dB/100 deg for the two groups. For phase settings larger
than 250 deg, two units fail to track the other four, and
their attenuations become larger. This large variation in
attenuation performance is partially explained by the fact
that these devices were originally designed for a lower fre-
quency, 30 GHz, and for another application. Despite this
variation in attenuation, however, reasonable array beam
steering was obtained.
The gain versus input power of the MMIC power am-
plifiers is shown in Fig. 11. The six amplifiers were fabri-
cated from the same wafer and have a low power-gain mean
and standard deviation of 13.7-4- 1.7 dB. The mean and
standard deviation of output power at 1-dB gain compres-
sion is 13.6 =t=0.3 dBm. Several amplifiers were externally
tuned and were found to be capable of producing as much
as 21.5 dBm with an efficiency of 14.5 percent at 1-dB gain
compression.
The complete integrated linear phased array was
tested by measuring its beam steering pattern. This pat-
tern, shown in Fig. 12, was measured with a different tech-
nique from the conventional method. Both the receive
antenna, which was a 10-cm reflector, and the test trans-
mit array were placed in fixed positions facing each other.
Then the array's phase shifters were adjusted to scan the
beam at 1-deg intervals from -25 deg to 25 deg. Both the
measurement system and the phase-shifter bias switching
system were controlled by a PC. A program was written to
set the phases based on keyboard entries of beam-steering
angles. The pattern was then recorded with the received
power versus the scan angles. Although the pattern was
measured from -25 deg to 25 deg, our primary interest
is in the =l=10-deg region. Nevertheless, excellent compar-
ison between the calculated and measured results can be
observed in Fig. 12. The relatively high sidelobes were
caused by improper operation of one of the middle am-
plifier modules. The calculation included the effect of the
failed module as well as randomized errors in both phase
and amplitude. If all the six subarrays were functioning
properly, the calculation predicted that the sidelobes are
-12 dB below the beam peak. The array had a beamwidth
of 7.5 deg and demonstrated acceptable beam steering over
:t:8 deg.
V. Conclusions
A 32-GHz six-element linear transmitter array utiliz-
ing MMIC phase shifters and power amplifiers has been
developed and tested as a precursor to the design of a
two-dimensional array for use in a NASA spacecraft array
feed. The switched-line phase shifters were accurate to
within 7 percent on average and the power amplifier 1-dB
compressed output power varied over 0.3 dB. The array
had a beamwidth of 7.5 deg and demonstrated acceptable
beam steering over =t:8 deg.
From the above results, it can be concluded that this
MMIC phased array has adequate beam-scanning capa-
bility for use in the two-dimensional array. The areas
that need to be improved are the efficiency of the MMIC
power amplifier and the insertion loss of the MMIC phase
shifter.
Acknowledgment
The authors wish to acknowledge the contributions of C. Cruzan for his efforts
in assembling the array.
209
References
[1] Honeywell Physical Sciences Center, Electronically Steerable Patch Panel Array
Antenna, Final Report (Oct. 1, 1985-Sept. 30, 1986) AFATL-TR-87-19, USAF
Armament Laboratory, Eglin AFB.
[2] V. Sokolov et al., "A GaAs Monolithic Phase Shifter for 30 GHz Application,"
1983 IEEE Microwave and Millimeter-wave Monolithic Circuits Symposium
Digest, pp. 40-44, 1983.
[3] P. Bauhahn, C. Butter, V. Sokolov, and A. Contolatis, "30 GHz Multi-Bit
Monolithic Phase Shifters," 1985 1EEE Microwave and Millimeter-wave Mono-
lithic Circuits Symposium Digest, pp. 4-7, 1985.
[4] P. Sanier, H. Q. Tserng, N. Camilleri, K. Bradshaw, and H. D. Shih, "A High
Efficiency Ka-Band Monolithic GaAs FET Amplifier," GaAs IC Symposium
Technical Digest 1988, pp. 37-39, 1988.
[5] J. H. C. Van Heuven, "A New Integrated Waveguide-Microstrip Transition,"
IEEE Trans. Microwave Theory and Techniques, vol. MTT-24, pp. 144-147,
March 1976.
[6] W. F. Richards et al., "An Improved Theory for Microstrip Antennas and Ap-
plications," 1EEE Trans. Antennas and Propag., vol. AP-29, pp. 38-46, January
1981.
[7] J. Huang, "The Finite Ground Plane Effect on the Microstrip Antenna Radi-
ation Patterns," IEEE Trans. Antennas and Propag., pp. 649-653, July 1983.
210
Table 1. Simulated versus measured data for six-way power divider
Simulated
Out Port 1 2 3 4 5 6 Avg. a
MAGS21 -10.6 -10.7 -10.6 -10.5 -10.6 -10.6 -10.6 0.1
ANGS21 -11.0 -9.0 -9.0 -10.0 -8.0 -8.0
adjANG 0.0 1.0 1.0 1.0 2.0 2.0 1.0 1.0
Measured
Out Port 1 2 3 4 5 6 Avg. a
MAGS21 -11.1 -10.9 -11.3 -11.9 -11.5 -11.8 -11.4 0.4
ANGS21 71.0 52.0 77.0 77.0 54.0 75.0
aAjANG 0.0 --19.0 6.0 6.0 --17.0 3.0 --4.0 11.0
IMeasured-Simulatedl
Out Port 1 2 3 4 5 6 Avg. o"
MAGS21 -0.5 -0.2 -0.6 -1.4 -0.9 -1.2 -0.8 0.4
ANGS21 0.0 -20.0 4.0 5.0 -20.0 1.0 -5.0 11.0
Table 2. Ka-band microstrip antenna gain and efficiency
Parameter
Single Two-Patch 12-Patch
Patch Array Array
Calculated directivity, dBi 7.3 10.7 16.7
Measured gain, dBi 6.9 10.2 15.9
Efficiency, percent 91 89 83
211
212 
Fig. 1. Honeywell MMlC phase shifter. 
Fig. 2. Texas Instruments MMlC power amplifier. 
ORIGINAL PAGE 
BLACK AND WHITE PHOTOGRAPH 
Fig. 3. Six-element linear transmitter array. 
Fig. 4. Six-way microstrip power divider. 
ORIGINAL PAGE 
BLACK AND WHITE PHOTOGRAPH 
213 
Fig. 5. M MIC phase-shifter carrier strip between two waveguide-to-microstrip 
transitions. 
0 I I I I I I I I I 1 
1 
-25 
30 32 34 
FREQUENCY. GHz 
Fig. 6. Measured input return loss for a two-patch array. 
0 I I I 
SCAN ANGLE, deg 
Fig. 7. Calcufated far-field pattern of the 12-patch 
array with a 10-deg beam scan. 
214 
XIG"A.L PAGE 
BLACK AND WHITE PHOTOGRAPH 
O! I I f_ I I
£ I
| •
-90 -60 -30 0 30 60 90
ANGLE, deg
Fig. 8. Comparison of calculated and measured far-field pattern for the linear
array without MMIC carrier strips.
215
300
250
-o
LU"
O3
<
r_ 200
03
150
100
50
I I I I I I
I I I I I I
0 50 100 150 200 250 300
NOMINAL PHASE, deg
Fig. g. Phase deviations measured against the nominal phase shift
(dashed line) for six phase shlfters.
350
-7
-8
-14
I I I I I I
-16 _
-17 I I I I I I
0 50 100 150 200 250 300
NOMINAL PHASE, deg
Fig. 10. The spread in measured attenuation for six phase shifters.
350
216


Ka-band MMIC beam steered transmitter array

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