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INNOVATIVE APPROACH FOR SATELLITE ANTENNA INTEGRATION AND
TEST/VERIFICATION
L.J. Foged, L. Scialacqua, F. Saccardi
SATIMO, Pomezia, Italy
M. Bandinelli, M. Bercigli, G. Guida
IDS, Pisa, Italy
G. Giordanengo, F. Vipiana
Antenna and EMC Lab, ISMB, Torino, Italy
M. Sabbadini
ESA/ESTEC,
P.O. Box 299, AG 2200 Noordwijk ZH, The Netherlands
G. Vecchi
Antenna and EMC Lab, Politecnico di Torino, Torino, Italy
ABSTRACTThe increasing complexity and stringent performances
in RF instruments and payloads often demands that
the final RF functional verification is performed on
the integrated satellite. In order to minimize the
overall time and cost of future Antenna Integration
Verification and Test campaigns (AIV/AIT) it is
necessary to investigate and develop advanced test
methodologies to minimize the test duration.
This paper reports the preliminary results of a
functional testing solutions for RF end-to-end antenna
testing. The proposed approach is based on the
intelligent and innovative use of existing measurementcapabilities and advanced numerical modeling tools.
The scope of the activity is to demonstrate through the
implementation of a demonstrator and measurement
on suitable hardware the possibility to achieve
accurate and fast measurement results using a radical
measurement under-sampling with respect to the
conventional Nyquist criteria.
Keywords: Electromagnetic Testing, Near- Field,
Measurements, Sampling, Verification.
1. Introduction
Modern telecommunication payloads are excellentexamples of the increased satellite testing complexity and
have been subject to the development of dedicated testing
techniques and hardware in the past [1-14]. Today,
complex telecommunication payloads feature tens or
hundreds of beams, each operating with frequency reuse
and variable connectivity, which need to be characterized
accurately to ensure proper in-orbit system performance.
In related the area of space science, future missions
foresee the use of antennas with hundreds of beams
operating over an extremely large frequency band, high
beam efficiency and very low noise figures. Finally, Earth
observation instruments, like imaging radiometers,
synthetic aperture radars and synthetic aperture
radiometers have reached a level of complexity that makes
strategies for test time reduction very appealing if not
already necessary.
Considering future planned satellite missions, the sizes of
the antennas can reach up to 12 meters in diameter at L-S
band and the very large satellites of the next generations
becomes prohibitive for the existing quiet zones ofconventional Compact Antenna Test Ranges (CATR) or
would require major investments into new larger facilities
[6-10]. Very large, dedicated near field systems based on
planar, cylindrical or spherical scanning geometries are
expected to be a viable intermediate solution to achieve a
better compromise between accommodation of the device
under test and the cost of the measurement facility [11-
14]. However, due to the sampling criteria the
measurement time associated with these tests becomes a
serious obstacle.
A new and promising testing strategy for time demanding
satellite tests scenarios has been presented recently in
[14]. The preliminary results, based on theoretical data,
demonstrated the possibility to perform accurate and fast
antenna measurement with a radical under-sampling of the
Near Field (NF) with respect to the conventional Nyquist
criteria. This paper reports on the further developments of
the techniques and present preliminary results from the
testing of a representative multi beam satellite mission in
Ku-band.
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2. Proposed solution
The proposed approach is discussed in some detail in
[14]. The proposed solution is based on a robotic arm
sniffer system, sampling the radiated near field of the
Antenna Under Test (AUT) mounted on the spacecraft.
The use of the robot and non-canonical NF scanning allow
for the antenna not be positioned optimally for traditional
testing. Since the robotic arm NF sampling is slower thana traditional canonical scanning a radical under sampling
is needed to make the proposed approach appealing.
The radical under sampling is obtained by an interpolation
of the measured NF values by a special algorithm taking
advantage of the physical information provided by
numerical modeling of the antenna. The modeling is
performed prior to the measurement. Included in the
modeling are several physical permutations of the realistic
antenna model of the AUT. This is to generate a self-
consistent representative basis for the expansion of the
AUT. If the basis is constructed correctly [14], the
measured antenna can be fully represented by a linear
combination of the permutated numerical modeling. The
actual AUT measurement, then consist in determining the
correct coefficients of the linear combination of the
expansion basis. The coefficients of the expansion basis is
much less than the actual antenna sampling criteria
leading to a drastic reduction in the number of
measurement samples.
2.1 Advanced robotic arm sniffer system
The use of the robotic arm sniffer system approach give
access to different scanning and sampling strategies
including canonical scanning. The system is based on a
Kuka high precision robot [5] and a SATIMO Dualpolarized Open-Ended Waveguide DOEW6000 probe
with interchangeable apertures covering the frequency
band [6-20] GHz as shown in Figure 1. This probe is
designed with a radiation pattern nearly identical to
traditional circular open ended waveguides on a much
wider bandwidth.
Figure 1 - Kuka robot (left) and SATIMO DOEW6000
probe covering the 6-20GHz band (right).
Different examples of scanning surfaces that can be
performed with the sniffer system are shown in Figure 2
and Figure 3. The assembly of the DOEW6000 precision
probe on the robotic arm, is shown in Figure 4.
Figure 2 - Example of planar scanning performed with
the proposed sniffer system.
Figure 3Different sampling strategies: planar,
cylindrical and spherical scan surfaces.
Figure 4Example of assembly for the advanced
measurement sniffer system.
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2.2 Antenna Under Test (AUT)
The AUT for validation and demonstration of the
proposed test technique is a Multibeam antenna system in
the frequency range [14-16] GHz.
The Multibeam antenna is composed by the SATIMO
SR40-A reflector and a feed array of 7 linearly polarized
Ku band horns. The feed array configuration is shown in
Figure 5. Dimensions of the SATIMO high precision
offset parabolic reflector antenna SR40-A are 20
@15GHz. The Multibeam antenna is shown in Figure 6.
The Multibeam antenna is equipped with a high precision
mechanical flange. The alignment is determined by a
precision pin in mechanical interface plate.
The horns can be fed and mounted independently on its
basement, which is connected to the arm of the reflector.
Changing the basement allows to get different array
configurations.
Figure 5Feed array configuration of the AUT.
Figure 6Multibeam antenna.
2.3 Modelling and simulations of the AUT
The AUT, consisting in the Multibeam antenna has been
simulated using ADF-EMS tool [17]. The complete
simulation, electrical current distribution, of the model of
the antenna is shown in Figure 7. Copolar coverage
patterns of all beams are shown in Figure 8.
Figure 7Simulated electrical current distribution on
the Multibeam antenna, beam #5 is fed.
Figure 8Simulated beam coverage patterns
@15GHz.
To obtain the induced electrical currents a full-wave
approach (Method of Moment) was used. The MoM
solution was accelerated by means of Multi-level Fast
Multi-pole Algorithm. The Multibeam antenna was
discretized into a total of 409,090 triangles and 21 wires,
i.e. 613,531 unknowns (613,510 RWG, 14 PWL and 7
attachments). With the purpose of generating a high-
fidelity model, all the initial CAD external surface was
taken into account (i.e. discretized).
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2.4 Reference measurement of the AUT
Preliminary analysis of the test technique has been done
starting from a reference measurement of the antenna,
before using the measured samples by the advanced
robotic arm sniffer system. This reference measurement
has been done in the SATIMO SG-64 Spherical near field
test facility in Paris (SNF), see Figure 9. The measured
results have been preliminary compared with the resultssimulated by ADF-EMS tool. Comparison between
simulation and measurement for the beam #2, see Figure
10, shows that the agreement is good.
Figure 9Multibeam antenna in the SATIMO SG-64
spherical near field test facility in Paris.
Figure 10 Comparison between simulation and
measurements (PNF and SNF) of the AUT. Solid lines
show co-polar components, dashed lines show cx-polar
components.
2.5 Specialized interpolation algorithm
As discussed previously, the interpolation algorithm uses
a reduced expansion base for the near field to far field
transformation formed from permutations of the numerical
modeling of the antenna prior to the measurement.
There are two relevant constituent of the pre and post
processing tools in the proposed approach. The first is the
Equivalent Current (EC) expansion that allows forward
and backward mapping between NF and FF on arbitrary
(non canonical) surfaces. A robust and accurate
formulation has been implemented that has already been
tested by the team with real data and employed in tasks of
industrial relevance [2-4]. The second is the Synthetic
Function eXpansion (SFX) as presented in [15]. This
technique was developed for efficient MoM simulations,
but its theoretical foundations provide an important
framework for the integration of simulation and measured
data in the present application.
3. Preliminary results of test technique emulation
using measured data on the AUT
Preliminary evaluation of the achievable performance in
terms of accuracy and down sampling ration with respect
to conventional measurement techniques has been
performed starting from the samples of the reference
measurement in the SG-64 Spherical Near Field (SNF)
test facility. The simulations of the AUT has been
performed by ADF-EMS tool.
The reference measurement has been done on a spherical
surface constant angular grid set of points and it
represents the target measured field. Emulating a
measurement scenario by the sniffer system, various
subsets of the measured NF points can be selected by the
interpolation algorithm for reconstructing the target
measured field using a reduced set of measurement points.
This approach is not fully representative of the real
sniffer system since all NF points must lie on the
measurement sphere and on the regular angular grid used
by the SG-64, SNF measurement system. However, the
constructed test scenario is nevertheless indicative of what
can be achieved in the final system implementation.
The reference measurement in the SG-64, SNF system
was performed using close to 58.000 measurement points.
This is very close to the minimum criteria for such AUT
measurement considering a minimum sphere of diameter0.5m or 25 at 15GHz. The Nyquist minimum sampling
criteria obtained by dividing the minimum sphere surface
in areas of (/2)2 is 31.416 dual polarized field samples.
The far-field reference field and the reconstructed field
based on only 909 dual polarized field samples are
compared in Figure 11. This number of samples
represents a down sampling factor of 34 with respect to
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the Nyquist sampling criteria and a factor of 63 with
respect to a standard SNF measurement using a regular
angular grid over the spherical measurement surface [16].
The difference in AUT peak directivity between the
reconstructed field and the reference field obtained using
our proposed methodology is shown as a function of the
under-sampling factor in Figure 12 (blue curve). The
Nyquist criteria is used as the reference samplingminimum level. The 0.27dB directivity difference
obtained with under-sampling factor ~34, corresponding
to the plots in Figure 11 is highlighted on the plot.
When the number of the measured samples is increased
the blue curve tends to the red one in Figure 12, which
represents the peak directivity difference between the
measurement and the best single numerical simulation.
The red curve shows the best results that can be expected
starting from the actual measurements and simulations
used for preliminary testing the methodology.
Figure 11 Far Field Reconstruction (Beam #2) with
respect to the measured Field (top =90, bottom
=90).
Figure 12Peak directivity difference (Beam #2) with
respect to the measured samples (the sampling factor
is the ratio between the samples of Nyquist and the
selected samples).
4. Conclusion
The scope of the on-going activity is to demonstrate
through the implementation of a demonstrator and
measurement on suitable hardware the possibility to
achieve accurate and fast measurement results using aradical measurement under-sampling with respect to the
conventional Nyquist criteria.
The proposed solution is based on an intelligent and
innovative use of existing measurement capabilities and
advanced numerical modeling tools. The AUT is a multi-
beam antenna system, widely used in space applications
for mobile and broadband communications.
Preliminary results, emulating a sniffer type measurement
scenario, show that under-sampling factors of ~34 with
respect to the conventional Nyquist criteria and a factor of
~63 with respect to a standard regular angular grid SNF
measurement can be achieved with this approach. Thepreliminary testing scenario has shown that it is possible
to reconstruct efficiently the general shape and level of the
main lobe of the radiation pattern despite the radical under
sampling. Theses preliminary results indicate the
feasibility of this technique in RF test scenarios to
minimize the cost and duration of test campaigns.
While reference measurements (see above) can be used
for preliminary investigations on the testing technique, the
use of the advanced robotic arm sniffer system will lead
to a further optimization of the methodology due to the
increased degree of freedom of the system.
Mechanical aspects of the system, such as the stability andpossible vibrations of the robotic arm during movement
need to be carefully controlled during the measurements
in order to increase the accuracy of the results. Realization
of a measurement scenario fully based on the sniffer
system approach and demonstration of the testing
technique are the next steps of this activity.
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http://www.idscompany.it/page.php?f=92&id_div=7
http://www.idscompany.it/page.php?f=92&id_div=7http://www.idscompany.it/page.php?f=92&id_div=7