Omid Sotoudeh

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Innovative solutions for Multibeam antenna feeds

• Omid Sotoudeh
• omid.sotoudeh_at_chalmers.se
• Antenna group

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• Overview
• Examiner Prof. Per-Simon Kildal, Chalmers, Head
  of Antenna Group
• Industrial supervisor Dr. Per Ingvarson, Chief
  Engineer Antennas, Saab Ericsson Space
• ESA/ESTEC project Innovative solutions for
  muti-beam antenna feeds
• August 2002 September 2003
• Principal investigator Omid Sotoudeh
• Supervisors Per-Simon Kildal (Chalmers)
• Per Ingvarson (SES)
• Contacts from ESTEC
• Antoine Roederer, Head of Electromagnetics
  Division
• Cyril Magenot, Head of Antenna and
  Sub-Millimeter Wave Section
• Arturo Martin-Polegre, Antenna and
  Sub-Millimeter Wave Section
• Teknisk Licentiat
• O. Sotoudeh, Hard horns for cluster-fed
  multi-beam antennas, National Graduate School of
  Space Engineering Chalmers University of
  Technology, Sweden, February 2004.
• Final work in analysis, optimization and design
  of single and multi-mode hard horns for cluster
  fed multi-beam antennas.

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Ka band multimedia satellites

• New generation of satellite networks
• operating in the Ka-band (20/30 GHz)
• Two way high-speed communications
• A broad range of voice, data and video
  communications
• Large coverage area (ex Europe, Asia)
• Low Cost

Source  EuroSkyWay program http//www.euroskywa
y.it
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• Cluster-fed multi-beam antennas for Ka-band
• 4 reflector system
• 17.7 20.2 GHz downlink
• 27.5 30.0 GHz Uplink

One of four antennas
Hard horns proposed as feed
20 GHz
Footprint
30 GHz
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Coverage 4 reflector system
Beam isolation 4 cell reuse scheme
?? 1?
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?d4 2?

• Directivity and directive gain at the weakest
  point of the footprint (EOC)
• Minimum directive gain level

• Max relative co- and x-pol. between the
  neighboring beams
• Max x-pol. in own beam

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System requirementsgiven by ESTEC
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Tools used for the analysis and design of horns

• Theoretical formulas based on modes
• Rotational symmetric problems
• Very fast solution
• Rather accurate for design of single mode horns

• Mode-Matching technique
• 2D solver rotational symmetric problems
• Very accurate and fast
• Used for design of horns traditionally

• Commercial 3D SWs (FDTD)
• Slow and demanding
• Accurate
• Used for verification

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Hard horns as feeds in CF-MBA
Horn types and their radiation patterns at center
frequency
d 5? at 30 GHz
Hard horns Dielectric in the corrugations, er
2.44 Wall thickness 0.21?
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Potter/dual mode horns
Smooth walled horns

• TE11 TM11 modes
• Equal E - and H planes Low X - pol
• Low efficiency
• Narrow bandwidth

• TE11 mode
• Difference in E- and H-plane
• High X-pol
• Medium efficiency
• Wide bandwidth

R.H. Turrin, 1966


Potter
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High efficiency horns

• Multimode
• Complex step geometry
• High efficiency (ex. 90 )
• Low X - pol
• Narrow bandwidth

Bhattacharyya et al 2002
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Hard and Soft surfaces
Soft surface Stops field propagation
Hard surface Enhances field propagation


More on these surfaces I recommend P-S, Kildal,
Artificially soft and hard surfaces in
Electromagnetics, IEEE transactions on Antennas
and Propagations, Vol. 38, No. 10, Oct. 1990.
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The hard horn using longitudinal corrugations

• High efficiency
• Low X pol
• Wide bandwidth
• Complex geometry

Conductor (blue region)
Corrugations filled with dielectric
direction of propagation
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Single and multimode hard horns

• Single mode horn with corrugations of constant
  depth
• Single mode horn with linearly increasing
  thickness
• Multimode horn with hard wall in an outer section
  
• Multimode horn combined with a step-shaped mode
  exciter to improve the performance at high
  frequencies

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Simple single mode hard hornsAnalysed using
asymptotic models
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Study of hard horns Analysis tools
Classical-type model Dominant TEz mode field
distribution
Example d 5? at 30 GHz er 2.5 fTEM
30 GHz
The corrugation period p ltlt ?
1 0
0.6 0
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Multimode hard horns Initial studies Based on
simple manufacturing very simple geometry
Smaller D/t gives shorter L1 Possible for small
radii lt 4-5? Larger apertures need a long PEC
section

• Direct transition from PEC to hard surface

Cylindrical or slightly conical hard surface
Only part of the horn is corrugated
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Dual band multimode hornDesigned using
parametric studiesand Genetic algorithm
optimizationEM solver Mode-matchingTested
with FDTD QW-V2D and QW3D
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Calculated at 19 GHz Tx band
Calculated at 29 GHz Rx band
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Horn performance 2D simulations
Aperture efficiency ()
Return-loss (dB)
Max cross-polar level (dB)
Frequency (GHz)
Frequency (GHz)
Frequency (GHz)
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Total antenna performance in BOR reflector
Directive gain
Co polar BI
Max rel. cross pol in own beam
Cross polar BI
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Hard horn measurements at SES
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Horn performance measurements and MM ? High
sidelobes in E-plane
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Horn performance measurements and MM and 3D
FDTD(40 corrugations)?The 3D simulations agree
with the measurements
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Horn performance measurements and MM and 3D
FDTDN 40 and 80 corrugations?The 3D
simulations of N 40 agree with the
measurements? N 80 and tooth thickness 0.4 mm
agrees with asymptotic design
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Comparison of designs
Best single mode design Ltot 47 cm, corrugated
Lcorr 47 cm
Best multi-mode design Ltot 30 cm, corrugated
Lcorr 22 cm
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Conclusions

• Studies of hard walled horn antennas
• The hard walls may be used in horn antennas in
  order to enhance their performance.
• They can be designed as single mode hard horns or
  multimode hard horns.
• A dual band multi-mode hard horn has been built
  and measured for 20/30 GHz Ka-band operation.
• Horn designed using fast Mode-Matching.
• Present design is smaller than previous single
  mode horns and much more simple to manufacture.
• Discrepancies with measurements have been
  explained.
• For present design we need more than 40
  corrugations and lt 0.5 mm corrugation tooth
  thickness.
• We can use the fast mode-matching codes in the
  future for design of these horns.
• Future work More on the effect of corrugations
  on the hard horn performance and their optimal
  dimensions for our hard horn design is being
  studied at the moment.

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Horn parameters
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BOR reflector model

• Rotationally symmetric reflector, and neglected
  feed blockage (offset reflectors)
• Horns in the focal point of reflector
• Aperture integration method

• Short computational time
• Very fast for parametric studies
• Quite accurate and relevant results

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Theory of BOR, Body of revolution
Aperture fields vertical polarization
Total
BOR1 component
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Theory of BOR, Body of revolution
Far-fields vertical polarization
Total
BOR1 component
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Theory of BOR, Body of revolution
BOR1 relations for RHCP Far-field functions
Aperture field functions
(see e.g. Kildals textbook, Foundations of
Antennas)
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Hard horn analysis Performance as a function of
frequency
Ex d 5?TEM, LH 15 ?TEM, fTEM 31.8 GHz

TE11
TE11
er 5, t 1.2 mm
er 5, t 1.2 mm
er 2.5, t 1.9 mm
er 2.5, t 1.9 mm
eap ()
er 1.5, t 3.2 mm
er 1.5, t 3.2 mm
Max xp level (dB)
er 1.25, t 4.5 mm
er 1.25, t 4.5 mm
Frequency (GHz)
Frequency (GHz)
Frequency (GHz)
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Hard horn analysis Performance as a function of
length
Ex d 5?TEM, f fTEM 31.8 GHz

TE11
er 5, t 1.2 mm
er 1.5, t 3.2 mm
er 1.25, t 4.5 mm
er 2.5, t 1.9 mm
TE11
er 1.5, t 3.2 mm
eap ()
er 1.25, t 4.5 mm
er 2.5, t 1.9 mm
Max xp level (dB)
er 5, t 1.2 mm
Length (mm)
Length (mm)
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Comparison mode-matching classical-type er
1.25, d 5? at 17.7 GHz, fTEM 30.5 GHz LH
25? at 17.7 GHz 424 mm LE 376 mm
Ideal design
Realizable design
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Optimum D 1.25 m, F 1.86 m, subtended semi
angle 19
Horn patterns
Reflector patterns