workshop national graduate school for space technology, 2005-09-13omid sotoudeh omid sotoudeh...

Workshop national graduate school for space technology, 2005-09-13 Omid Sotoudeh

Omid Sotoudeh

[email protected]

Antenna group

Innovative solutions for Multibeam antenna feeds


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 SectionArturo 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.


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.euroskyway.it

Ka – band multimedia satellites


Footprint30 GHz20 GHz

One of four antennas

1 1

1 1 1

1 1

2 2

2 2

4

4 4

4

3 3

3 3

Hard horns proposed as feed

Cluster-fed multi-beam antennas for Ka-band

4 reflector system

17.7 – 20.2 GHz downlink

27.5 – 30.0 GHz Uplink


Max relative co- and x-pol. between the neighboring beams

Max x-pol. in own beam

f1 f1

f1 f1 f1

f1 f1

f2 f2

f2 f2

f4

f4 f4

f4

f3 f3

f3 f3

Beam isolation: 4 cell reuse scheme

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

Minimum directive gain level

Coverage: 4 reflector system

1 1

1 1 1

1 1

2 2

2 2

4

4 4

4

3 3

3 3

Δ = 1

d4 = 2


System requirementsgiven by ESTEC

Downlink Tx: 17.7 – 20.2 GHz

Uplink Rx: 27.5-30 GHz

End of Coverage directivity 39.5 dBi

XPD within own beam < -27 dB

Co-polar beam isolation relative to weakest useful point

>25 dB

Cross-polar beam isolation relative to weakest useful point

>27 dB

Reflection coefficient at feed port < -27 dB

Polarization between frequency bands Dual polarization system, individual beams remain single polarized.

Polarization within each band Dual, linear or circular

Operating frequency band Tx and Rx


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 SW’s: (FDTD)

• Slow and demanding

• Accurate

• Used for verification


Smooth walled, TE11 mode

Corrugated soft

Ideal soft or dual mode

Corrugated hard

Ideal hard

H-planeE-plane

Aperture distribution

Horn types

Horn types and their radiation patterns at center frequency

Hard horns as feeds in CF-MBA

Hard horns: Dielectric in the corrugations, εr = 2.44 Wall thickness ~ 0.21

d = 5 at 30 GHz


Potter/dual mode horns

TE11 + TM11 modes Equal E - and H – planes: Low X - pol Low efficiency Narrow bandwidth

R.H. Turrin, 1966

TE11 TM11

+ =

Potter

Smooth walled horns

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


High efficiency horns

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

Bhattacharyya et al 2002


Hard and Soft surfaces

direction of propagation

Conductor


Corrugations filled with dielectric

Conductor (blue region)

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.

l̂

n̂

t̂

l̂

n̂

Soft surface: Stops field propagation

Hard surface: Enhances field propagation

t̂

t

ll H

EZ 0

l

tt H

EZ

0t

ll H

EZ

l

tt H

EZ


The hard horn: using longitudinal corrugations

High efficiency Low X – pol Wide bandwidth Complex geometry


Corrugations filled with dielectric

Conductor (blue region)


Single and multimode hard horns

a b

cd

a. Single mode horn with corrugations of constant depth b. Single mode horn with linearly increasing thickness c. Multimode horn with hard wall in an outer section d. Multimode horn combined with a step-shaped mode exciter to improve the

performance at high frequencies


Simple single mode hard horns

Analysed using asymptotic models

LH

LE

Har wall region

dt


Co

Cro

ss

19 GHz 23 GHz 27 GHz TEM 30 GHz 30.5 GHz 31 GHz

The corrugation period p <<

Classical-type model: Dominant TEz mode field distribution

Example: d = 5λ at 30 GHz εr = 2.5 fTEM = 30 GHz

εr

d = 50 mm

t = 2 mm

0.6

0

1

0

Study of hard horns: Analysis tools


Multimode hard horns: Initial studies Based on simple manufacturing – very simple geometry

Direct transition from PEC to hard surface

Cylindrical or slightly conical hard surface

Only part of the horn is corrugated

Smaller D/t gives shorter L1

Possible for small radii < 4-5λ

Larger apertures need a long PEC section


Dual band multimode horn

Designed using parametric studiesand

Genetic algorithm optimizationEM solver: Mode-matching

Tested with FDTD: QW-V2D and QW3D


Calculated at 29 GHzRx band

Calculated at 19 GHzTx band


Horn performance: 2D simulations

Aperture efficiency (%) Return-loss (dB)Max cross-polar level (dB)

Frequency (GHz) Frequency (GHz) Frequency (GHz)


Total antenna performance in BOR reflectorDirective gain Co polar BI

Cross polar BI Max rel. cross pol in own beam


Hard horn measurements at SES


Horn performance: measurements and MM

→ High sidelobes in E-plane


Horn performance: measurements and MM

and 3D FDTD(40 corrugations)

→The 3D simulations agree with the measurements


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


Comparison of designsBest single mode design Ltot = 47 cm, corrugated Lcorr = 47 cm

Best multi-mode design Ltot = 30 cm, corrugated Lcorr = 22 cm


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 < 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.


Horn parameters


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


Theory of BOR, Body of revolution

Aperture fields: vertical polarization

1

1 1

2

0

2

0

1 1

21

0

21

0

ˆ ˆ, sin cos

1, sin

1, cos

ˆ ˆ, sin cos

1, sin

1, cos

n nn n

n

n

BOR BORE plane H plane

BORE plane

BORH plane

a n c n

a E n d

c E n d

E E

E E d

E E d

BOR

E ρ φ

E θ φ

Total:

BOR1 component:


Far-fields: vertical polarization

1

1 1

2

0

2

0

1 1

21

0

21

0

ˆ ˆ, sin cos

1, sin

1, cos

ˆ ˆ, sin cos

1, sin

1, cos

n nn n

n

n

BOR BORE plane H plane

BORE plane

BORH plane

a n c n

a G n d

c G n d

G G

G G d

G G d

BOR

G θ φ

G θ φ


Total:

BOR1 component:


BOR1 relations for RHCP

Far-field functions Aperture field functions

1 1 145 45

1 1 245

1 1 145

1 1 145

, cos 2

, sin 2

1

21

2

BOR BOR BORco RHCP co xp

BOR BOR jxp RHCP xp

BOR BOR BORco E plane H plane

BOR BOR BORxp E plane H plane

G G G

G G e

G G G

G G G

1 1 145 45

1 1 245

1 1 145

1 1 145

, cos 2

, sin 2

1

21

2

BOR BOR BORco RHCP co xp

BOR BOR jxp RHCP xp

BOR BOR BORco E plane H plane

BOR BOR BORxp E plane H plane

E E E

E E e

E E E

E E E


(see e.g. Kildal’s textbook, Foundations of Antennas)


Hard horn analysis: Performance as a function of frequency

Ex: d = 5λTEM, LH = 15 λTEM, fTEM = 31.8 GHz

εr = 1.25, t = 4.5 mm

εr = 5, t = 1.2 mm

εr = 1.5, t = 3.2 mm

εr = 2.5, t = 1.9 mm

TE11

Frequency (GHz)

eap (%)TE11

Frequency (GHz)

Max xp level (dB)

εr = 1.25, t = 4.5 mm

εr = 1.5, t = 3.2 mm

εr = 5, t = 1.2 mm

εr = 2.5, t = 1.9 mm

Frequency (GHz)


Hard horn analysis: Performance as a function of length

Ex: d = 5λTEM, f = fTEM = 31.8 GHz

εr = 1.25, t = 4.5 mm

εr = 5, t = 1.2 mmεr = 1.5, t = 3.2 mm

εr = 2.5, t = 1.9 mm

TE11eap (%)

TE11

Length (mm)

Max xp level (dB)

εr = 1.25, t = 4.5 mm

εr = 1.5, t = 3.2 mm

εr = 5, t = 1.2 mm

εr = 2.5, t = 1.9 mm

Length (mm)


Comparison mode-matching – classical-type εr = 1.25, d = 5λ at 17.7 GHz, fTEM = 30.5 GHz LH = 25λ at 17.7 GHz ≈ 424 mm LE = 376 mm

Frequency (GHz)

Max

XP

(d

B)

e ap (

%)

Frequency (GHz)M

ax X

P (

dB

)e ap

(%

)

Ideal design Realizable design


Horn patterns

Reflector patterns

Optimum D = 1.25 m, F ≈ 1.86 m, subtended semi angle ~19˚

workshop national graduate school for space technology, 2005-09-13omid sotoudeh omid sotoudeh...

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