Development on Ku-Band Feed Chains for Satellite Antennas

Development on Ku-Band Feed Chains for Satellite
Antennas
Christian Hartwanger1, Ralf Gehring1, UnPyo Hong1, Helmut Wolf 1
1
EADS Astrium GmbH, D-81663 Munich (Germany), Email: [email protected]
Short Abstract—The payload of next generation multimedia
telecommunication satellites demands on an increased number of
communication channels and improved EIRP and G/T
performance. Especially in Ku-band, the request for combined
BSS/FSS Transmit / Receive antennas grows. The feed system is
considered to be the key component of an antenna. EADS
Astrium responds to the needs of the market regarding feed
systems with two major developments under ESA contract.
Keywords: Ku-band; Feed Chain; OMT; Horn; High Power;
Wide Band;
I.
INTRODUCTION
The
payload
of
next
generation
multimedia
telecommunication satellites demands on an increased number
of communication channels and improved EIRP and G/T
performance. Especially in Ku-band the request for a combined
BSS (Broadcast Satellite Services) / FSS (Fixed Satellite
Services) Tx (Transmit) / Rx (Receive) feed chain grows.
Therewith, the Tx and Rx functions for the FSS and BSS
services could be combined in a single dual polarized antenna.
Thus the mass and space required for the individual top floor
Rx antenna can be saved and allows for the accommodation of
additional antennas and services.
Consequently the overall frequency band, the numbers of
channels and the RF power per channel to be operated by the
antennas will considerably increase. Therefore the
requirements on the linearity have to be further improved,
compared to state of the art systems, in order to avoid the
generation of Passive Intermodulation Products (PIMP). For an
effective re-use of the frequency bands it is obvious to use both
polarizations for the individual channels with an excellent
polarization decoupling. These major requirements are mainly
influenced by the feed systems of the antennas. A thorough and
mature design of the feed systems is a key factor for a
successful antenna design. EADS Astrium responds to the
needs of the market regarding feed systems with two major
developments under ESA contract.
and the RF performance of the Wide Ku-band Feed Chain
Bread Board Model (BBM).
The main foci for the development of the High Power Feed
Chain were:
•
Significantly higher multipacting threshold,
•
Combined Tx/Rx operation with reduced PIM risk,
•
Improved thermal performance,
•
Remain excellent RF performance,
compared to state of the art feed chains.
While the High Power Ku-band Feed Chain covers the
frequency band from 10.7GHz to 14.5GHz (FSS Tx/Rx and
BSS Tx), the main focus of the wide band feed chain
development is the extension to the frequencies 17.2GHz –
18.4GHz (BSS Rx). The success of this enormous
enhancement could not be presumed, hence, the development
was split into two phases. During the current finalized first
phase the feasibility of a wide Ku-band feed chain has been
demonstrated based on BBM measurements. For phase two a
detailed design update will be performed and an EQM will be
manufactured and fully RF qualified.
Both feed chains consist of:
•
A conical horn;
•
A circular to square wave guide transition;
•
An Orthomode Transducer (OMT).
Benefiting from past feed product developments and
extensive heritage, an innovative High Power Ku-band Feed
Chain (HPFC) [1] was developed and qualified for space
applications. Based on those results, an enhancement regarding
the band width of the feed chain is currently under
development (concluded 2006).
This article summarizes the performance of the High Power
Ku-band Feed Chain Engineering Qualification Model (EQM)
Figure 1. EQM High Power Feed Chain assembly.
See for example the yellow chromated EQM of the High
Power Feed Chain in Fig. 1. The feed chain is mounted on an
aluminium honeycomb structure, which radiates the
temperature resulting in cause of power dissipation. Via three
titanium brackets, the plate is mounted on a space craft.
A typical application for both feed chains as source in a
Gregorian satellite antenna is illustrated in Fig. 2. Just as well,
the feed chains can be utilized in a single offset reflector
antenna.
The mechanical requirements are derived from an internal
EADS Astrium document describing the Design, Interface,
Construction and Test Requirements for Antennas on Eurostar
3000 Spacecraft.
Based on the requirements from previous commercial Kuband projects the temperature range for qualification of the Kuband feed chain shall be -150° C to +146° C.
B. EQM Qualification Tests
To qualify the High Power Feed Chain to EQM-status, a
special test philosophy is necessary. The test flow is shown in
Fig. 3.
Visual inspection of the
components
Figure 2. Typical antenna geometry for the feed chain.
RF test (S-parameters) on
component level
Intermediate RF check
Multipacting tests, only if
analysis margin < 6 dB*
Thermal cycling feed
chain
Initial RF test feed chain
(S-parameters, pattern)
Final RF test feed chain
(S-parameters, pattern)
Vibration test feed chain
PIMP test vs.
temperature
* Due to the high number of channels it is permitted to use the "20 gap crossing rule"
II.
HIGH POWER KU-BAND FEED CHAIN
A. General RF- Specifications of the High Power Ku-Band
Feed Chain
The specifications are derived from the requirements of
past and planned Ku-band missions to ensure that the needs for
future applications will be covered. The relevant RF
specifications are summarized in Table I.
TABLE I.
RF-SPECIFICATION OF HIGH POWER KU-BAND FEED CHAIN
Item
Operating
frequency
Polarisation
Power handling
3rd order PIMP
Return loss
Maximum
Cross-polar Peak
Insertion loss
Specification
10.70-13.20 GHz (Transmit)
13.70-14.50 GHz (Receive)
Dual linear
24x110 Watt carriers per polarisation
< -135 dBm with 2x110W carriers
over Temperature (-135° C to +135° C)
< -23 dB
< -43 dB
< 0.12 dB
Figure 3. Test flow for qualification tests.
After an initial visual inspection of the feed chain, the Sparameters are measured on component level. When the
components are integrated to the feed chain, a multipaction
test has to be done, if the analysis margin is lower the 6dB. An
initial RF test is performed to verify the feed design and to
have a data base to which the results can be compared after the
environmental tests. The intermediate RF check is an Sparameter measurement to be sure that the hardware did not
change during vibration test. After the thermal cycling test, a
final RF measurement is made and the results are compared to
the initial test. The EQM qualification ends with a thermal
PIMP test. This proceeding guarentees a proper workmanship.
C.
EQM Qualification Test Results of High Power Ku-Band
Feed Chain
According to the test flow (Fig. 3), all tests have been
performed for the High Power Ku-band Feed Chain.
Fig. 4 shows the measured return loss of the feed chain for
both polarizations. The specification of -23dB is fulfilled with
margin.
The structural analyses of the feed chain assembly were
done using NASTRAN and the pre-/ and post processor
PATRAN. Static and dynamic analyses were performed to
verify the overall strength and integrity. The test predictions
based on a sine response analysis with 1g input up to 2000Hz
were carried out for several accelerometer positions and for the
main interface loads.
Fig. 7 shows an example for the results of stress and
strength analysis for the horn and the OMT.
Figure 4. EQM feed chain – Final measured return loss of the horizonatal
and vertical port.
A picture of the HPFC installed in the feed chamber for
pattern measurement is shown in Fig. 5.
Figure 7. Stress plot with maximum stress at the horn (left) and the
Orthomode Transducer (right)
A picture of the HPFC on the shaker for vibration test is
shown in Fig. 8.
Figure 5. EQM feed chain in feed chamber.
A result of the pattern measurement is illustrated in Fig. 6.
As well as the measured co polar pattern, the measured cross
polar coincides with the predicted values.
0
High Power Ku Band Feed Chain EQM: Final Measurement - TP - Ver
Measured vs. Predicted Performance, Phi = 45.0 Deg., Freq. = 12.70000 GHz
Measured Co-Polar (Feed)
Measured X-Polar (Feed)
Predicted Co-Polar (Horn)
Predicted X-Polar (Horn)
Figure 8. EQM feed chain on shaker for vibration test.
-10
In Table II the analysed worst case multipacting
performance for the yellow chromated horn and the OMT is
summarized. The MP margins are calculated in comparison to
the standard wave guide R 120.
Gain [dBi]
-20
-30
-40
TABLE II.
MP ANALYSIS RESULTS FOR THE HIGH POWER FEED CHAIN
FOR 2 X 24 CARRIERS, 110 W PER CARRIER.
-50
-60
-60
-40
-20
0
Scan Angle [deg]
20
40
Figure 6. Pattern Measurement at 12.7GHz (Vertical port).
60
WG R 120
OMT
Horn
Margin N2P-rule
[dB]
- 0.8
-2.4
3.4
Margin P20
[dB]
13.0
10.8
17.2
Because the margin of the analyzed multipaction threshold
is larger 6dB, a multipaction test was not required.
A thermal PIM test has been performed over a thermal
cycle between +135ºC and -135 ºC. Two 120 Watt carriers at
11.0 GHz and 12.5 GHz respectively were applied to the feed.
A sketch of the set up is shown in Fig. 9. The PIMP was
measured at 14.00GHz. Temperature was controlled by
thermocouples attached to the OMT, transition and horn. A
PIM level of -120 dBm could be demontrated based on a
limited available test setup performance of -123 dBm.
TABLE III.
RF-SPECIFICATION OF WIDE KU-BAND FEED CHAIN
Item
Service frequency
bands (BSS/FSS)
Polarisation
Power handling
3rd order PIMP
Return loss
Maximum
Crosspolar
Insertion loss
Specification
10.70-14.50 GHz
17.20-18.40 GHz
Dual linear
20x110 Watt carriers per polarisation
< -135 dBm with 2x110W carriers
over Temperature (-135° C to +135° C)
< -21 dB
< -40 dB
< 0.18 dB
B. Rf-Performance of BBm Wide Ku-Band Feed Chain
Due to the wide frequency band (10.7GHz - 18.4GHz), two
RF interfaces (R 120 and R 140) were used for the scattering
parameter measurements in order to achieve minimum
measurement errors.
Fig 10. shows the result of the return loss measurement of
the BBM Wide Band Feed Chain for the vertical polarization.
The result for horizontal port also fulfills the requirement.
Figure 9. PIM test configuration
0
All tests were performed successfully which leads to an
EQM qualification of the High Power Ku-Band feed chain.
Interface R 120 (10-14GHz)
Interface R 140 (14-19GHz)
-5
-10
-15
Return Loss [dB]
The losses of the OMT including transition were measured
to be less than 0.07dB. Together with a conservative
assessment of the horn losses of 0.04dB, the requirement for
the feed chain is fulfilled.
BBM Wide Ku-Band Feed Chain: Return Loss Measurment
Vertical Polarisation (Through Port)
-20
-25
-30
-35
-40
III.
WIDE KU-BAND FEED CHAIN
As a consequent enhancement of the High Power Ku-band
Feed Chain, a Wide Ku-band Feed Chain is currently under
development in EADS Astrium. In order to verify the design
and to demonstrate the feasibility of such a component, a Bread
Board Model was manufactured.
A. General RF-Specifications of the Wide Ku-Band Feed
Chain
The specifications for the Wide Ku-band Feed Chain are
given in TABLE III. As well as the specifications for the
HPFC, they are based on customer requests.
The thermal and mechanical requirements and the principle
thermal and structural design of the Wide Band Feed Chain are
similar to the High Power Feed Chain. Therefore, an RF
qualification of the Wide Ku-band Feed Chain is sufficient.
-45
-50
10
11
12
13
14
15
16
Frequency [GHz]
17
18
19
Figure 10. Wide Band BBM Feed Chain – Return loss: vertical polarization.
In Fig. 11, the measured isolation is recorded, which
satisfies the requirement of 50dB with margin. A typical co and
cross polar pattern cut is shown in Fig. 12. The pattern
coincides with the prediction.
The multipaction analysis shows a worst case result of 8dB
margin with respect to the 20 gap crossing rule. Hence, no
multipaction test had to be performed. Compared to the High
Power feed chain, only a slightly degradation of 2 dB can be
observed.
The measured data demonstrate the feasibility of a dual
polarized high performance feed chain covering the entire
FSS/BSS frequency band from 10.7GHz to 18.4GHz.
IV.
BBM Wide Ku-Band Feed Chain: Isolation Measurment
Horizontal Port (Dual Side Port)
0
Two feed chains for Ku-Band have been presented.
Interface R 120 (10-14GHz)
Interface R 140 (14-19GHz)
-10
Port-Port Isolation [dB]
-20
-30
-40
-50
-60
-70
-80
10
11
12
13
14
15
16
Frequency [GHz]
17
18
19
Figure 11. Wide Band BBM Feed Chain – Isolation measurement.
Wide ku Band Horn (BBM_Horn_CC_10_CR_140)
Measured vs. Predicted Performance, Phi = 45.0 Deg., Freq. = 17.30000 GHz
0
Measured Co-Polar (Horn)
Measured X-Polar (Horn)
Predicted Co-Polar (Horn)
Predicted X-Polar (Horn)
CONCLUSION
A High Power Feed Chain for applications in Ku-band
Satellite Communication Systems was developed and qualified
to EQM-status at EADS Astrium GmbH. The RF design of this
feed chain was optimized for high RF power applications, i.e.
high multipaction threshold (closed to standard waveguide),
low losses (less than 0.12 dB) and high linearity (3rd order
PIM < -120 dBm, based on an available PIM setup validation
of about -123 dBm), while maintaining excellent radiation
characteristics. All scattering parameter requirements (return
loss > 24 dB, port to port isolation > 58 dB) are fulfilled. The
mechanical and thermal design of the feed chain allow for
applications in single or dual offset reflector systems,
accommodated either at the Earth faced panel or the side panels
of a GEO positioned satellite.
Based on the design and results of the High Power Feed
Chain, a design for a Wide Ku-Band Feed Chain was
optimized and a BBM was built. The BBM was RF tested in
order to demonstrate the feasibility of a wide band feed chain.
The results are promising and therefore, following an update of
the initial design, an EQM will be manufactured and RF
qualified during 2006.
-10
V.
Gain [dBi]
-20
ACKNOWLEDGMENT
The above described hardware has been developed under
ESTEC Contracts. EADS Astrium is grateful to ESA / ESTEC,
especially to Arturo Martín Polegre and Luca Salghetti Drioli
for the support of the development and qualification activities.
-30
-40
-50
-60
-80
-60
-40
-20
0
20
Scan Angle [deg]
40
60
80
Figure 12. Wide Band BBM Feed Chain – Pattern measurement at 17.3GHz.
[1]
R. Gehring, C. Hartwanger, U. Hong, M. Schneider, H. Wolf, "Ku-Band
High Power Feed Chain", Proc. 28th ESA Antenna Workshop on Space
Antenna Systems and Technologies, ESTEC, Noordwijk, The
Netherlands, 2005