1 Antenna design and optimisation Test-bed of mechanical tilt CSEM

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Antenna design and optimisationTest-bed of mechanical tilt

CSEM

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Document Properties

Document Title Antenna design and optimisation Test-bed of mechanical tilt

Document Number CAP-0322

Author (s) Q. Xu

Date 07.07.2005

Participant (s) (short names) P. Spanoudakis, E. Onillon

Workpackage(s) WP3.2

Total number of slides (including title and this slide)

21

Security level (PUB, RES, CON)

Internal confidential

Description / Abstract

- Array design and optimisation: grating lobe issue and gain

enhancement - Meander-line polarizer - Test-bed specification of mechanical tilt

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Reminder: antenna specification

Frequency range and BW:down link 27.5-28.35 GHz, up link 31-31.3 GHz -> 13% BW

Half power beam width (HPBW): 5° (best result 2°)

Gain:30 dBi

Polarisation: circular polarisation (CP)

Size: 25255 cm

Scan angle and speed:180° semi-sphere by mechanical steering system0.4°/s for train running at 500 Km/h

Scan angle precision0.8° for 5° HPBW0.32° for 2° HPBW

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Array factor (1)

Angle referred to far field observation point

Normalized Array Factor (AF) of a 8-element linear array with spacing d = 2

= 90° = -90°

= 0°

x

y

z

array

dxdy

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-50

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-10

0

theta [°]

Nor

mal

ize

d A

F [

dB

]

Array Factor, N= 8 elements and d = 2*lambda

N

n

kdnjeAF

1

)2

cos()1(

Nearest grating lobes at 30°

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Array factor (2)

Non-uniformly spaced array reduces side lobes when d /2

Non-uniform power distribution reduces side lobes but not grating lobes

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-40

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-20

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-10

-5

0

theta [°]

Nor

mal

ize

d A

rra

y F

act

or

[dB

]

N= 8elements and d = 2*lambda

UniformDolph-TschebyscheffBinomial

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-70

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0

theta [°]

Nor

mal

ize

d A

F [

dB

]

N= 24 elements and d = 0.5*lambda

Uniform spacingcase B

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-70

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-50

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0

theta [°]

Nor

mal

ize

d A

F [

dB

]

N= 24 elements and d = 1*lambda

Uniform spacingcase B

dn =

(n/2

+

n)d

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Single element design (1)

Technology giving large bandwidth

SSFIP – Strip Slot Foam Inverted Patch antenna

Substrate

Inverted patchFoam

Slot

Strip

Substrate

BW achieved with one patch was as large as 14% and can be improved to 33% with stacked patches.

Gain for single element is about 8 dBi.

(Reference: J.-F. Zürcher, F. E. Gardiol, “Broadband Patch Antennas”,Artech House,1995)

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Single element design (2)

ADS simulation resultsSSFIP with fundamental mode: patch size /2

Zin = 100

Substrates:

- RT/Duroid 5870 (for strip and slot layers)

r = 2.33, tan = 0.0012, h = 0.254 mm

- Foam Rohacell (spacer)

r = 1.07, tan = 0.001, h = 1 mm

- Kapton (for patch layer)

r = 3.2, tan = 0.005, h = 0.1 mm

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Single element design (3)

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-40

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-10

0

-50

10

THETA

Mag

. [dB

]

Gain Directivity

Key results (not optimised)

f0 = 29 GHz

BW > 27.6%

Gain = 5.2 dBi

HPBW = 66°

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Single element optimisation (1)

SSFIP with high-order mode: patch size 3/2

Zin =

50

Modelling by Ansoft Designer

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Single element optimisation (2)

Key results

f0 = 28.5 GHz

BW = 10.9%

Gain = -5.7 dBi (broadside)

HPBW: -

Conclusion

Not a good solution

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HPBW=0° = 40°HPBW=90° = 90°

f0 = 29.9 GHz

Single element optimisation (3)

SSFIP with gap-coupled patches: patch size /2

Asymmetricalradiation pattern

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Single element optimisation (4)

SSFIP with gap-coupled patches: patch size /2

f1 = 29.75 GHz

BW = 30.7%

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Single element optimisation (5)

Key resultsf1 = 29.75 GHz

BW =30.7%Gain = 9.8 dBiHPBW=0° = 40°, HPBW=90° = 50 °

ConclusionProbably a good solution but need more refinement to improve the gain

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Radiation of the array

+

=

There should be a way to do better…

Element radiation: EM simulation

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0

10

theta [°]

Gai

n [

dB]

Simulated single element radiation pattern

phi=90°phi=0°

AF: theoretical computation

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-50

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0

theta [°]

Fie

ld i

nte

nsit

y [d

B]

Non-uniform spacing, N= 8 elements and d = 2*lambda

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-60

-50

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-20

-10

0

10

theta [°]

Gai

n [

dB]

Array radiation pattern, N= 8 elements and d = 2*lambda

phi=90°

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PrincipleArray of structures which appears to be predominantlyinductive to one polarization and predominantly capacitive tothe orthogonal polarization. (Ref. L. Young, L. A. Robinson and C. A. Hacking, “Meander-line Polarizer”,

IEEE Trans. on Antenna and Propagation, pp. 376-378, May, 1973)

Meander-line polarizer (1)

Kapton & meander line

Rohacell

Layer 1

Layer 2

Layer 3

Layer 4

AdvantagesHigh polarization puritycompact size at Ka bandLow complexitylow cost

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Meander-line polarizer (2)

Layer 1 & 4

Layer 2 & 3

Zoom

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Antenna test-bed description

Fixed transmitterAntennaSignal generator

Mobile platformPan-tilt unitAntenna & supportRF detectorLow frequency amplifierPC with DAQ card running tracking algorithm

Power Lines

RxMotor/

encoder

RyMotor/

encoder

RF detector

BF amplifier

PCLabview

DAQCard-1200Control Alg.

Perturbations generation

RSSI

AxeControl

AxeControl

3D accelero

meter

Transmitter

Receiver

Antenna

Antenna

Mobile platform

PAN-Tilt Unit

37°

Signal Generator

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Antenna test-bed signal acquisition

In order to see a significant power change, a filtered white noise perturbation is injected, amplitude 5° on the pan and tilt angles.

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-5

0

Opening angle

Atte

nu

atio

n [d

B]

Attenuation diagram

Transmitter a

ttenuatio

n

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Tracking algorithm description

To find an RF signal, the pan-tilt mechanism will follows a spiral trajectory

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0

10

20

30

40

50

Pan angle [deg]

Tilt

ang

le [d

eg]

Tracking trajectory

Nominal Pos0, power P0

Move to Pos1, power P1

Move to Pos2, power P2

Move to Pos3, power P3

Move to Pos4, power P4

Pmax = max(P0, P1, P2, P3, P4)

Pos0 = corresponding position

Move to Pos0,

Maximum found using the algorithm

To determine the algorithm performances, a trajectory perturbation is added on the pan and tilt angle commands.

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Pan-Tilt mechanism requirements

Item Specification Comment

Payload

Antenna size 250mm x 250mm x 50 mm

Mass 1 kg

Scan angles

Azimuth ±180°

Elevation 0-90° (15°-90°)

Angular speed 0.4°/sec 4°/sec

20 km high balloon tracking by high-speed train Tilting speed of high-speed train

Pointing angle precision

HPBW 5° ±0.8° 5dB loss of signal

HPBW 2° ±0.32°

Pan-Tilt mechanism specifications

Payload 1.8 kg

Max speed 300°/sec

Resolution 0.05°

Tilt range 111°

Pan range 360°

Market survey performed to identify available mechanisms:

High-speed pan-tilt unit identified

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Pan-Tilt mechanism

Commercial off-the-shell motor units

Algorithm to be developed to provide the tracking error

Mechanical mount for antenna support

Preliminary tests with horn antennaFinal configuration with flat antenna

Material needed for the test-bedRF detector and amplifierPC with acquisition card