Overlapped Feeds to Increase the Edge of Coverage Gain in Multi Beam - - PowerPoint PPT Presentation

Overlapped Feeds ... for reflector antennas

Overlapped Feeds to Increase the Edge of Coverage Gain in Multi Beam Reflector Antennas

1 TNO Defense, Security and Safety - The Netherlands 3 ESA-ESTEC - The Netherlands 2 Saab Space - Sweden

• G. Gerini(1) , A. Neto(1), N. Llombart(1), M. Bonnedal(2), P. De Maagt(3)

9 April 2008 Overlapped Feeds ... for reflector antennas 2

Multi Spot Beam Satellite Scenario

Reuse scheme (x4)

Xout Y, Yout X

• Maximize Edge of

Coverage Gain

Focal plane array Four colours reuse scheme

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The Imaging Problem

• 3dB
• 3dB=
• 0/D
• d /F

+

d =

• 0 (F/D)

Similar efficiency for different F/D:

Cosq(

• )

F/D q

• (F/D)=1

Spill over efficiency 58%

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Free Space Configuration EoC Gain

Case 2 EoC Gain for different reflector diameters 38.5 39.0 39.5 40.0 40.5 41.0 9.4 9.6 9.8 10 10.2 10.4 10.6 Frequency [GHz] EoC Gain [dBi] 2.1 m F/D=0.95 2.2 m F/D=0.90 2.3 m F/D=0.87 2.4 m F/D=0.85

Only solution to date: 4 reflector antennas (combined Tx and Rx) Gain is moderate….

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Leaky Wave Approach

Oliner, Jackson, Di Nallo, Jecko, Mittra, Albani etc…

More layers equivalent to higher dielectric constant

Enhanced radiation by leaky-wave excitation Equivalent dielectric layers can be realized with metallic FSS

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Leaky Wave Pole Localization

• lw

ebg

k GF s Y 1 Re

• j

k f klw

• sin

) (

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BW and Coupling Limits

Antenna BW very narrow and mutual coupling very high except for low

• r !
• lw

ebg

k GF s Y 1 Re

• )

( ) ( ) ( ) (

1 2 2 1

f k f k f Y f Y

lw lw ebg ebg

• j

k f klw

• sin

) (

BW

BW , coupling 1/

• j

k f klw

• sin

) (

• lw

jk lw ebg ij

e k GF s Y 1 Re

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Higher order leaky modes

0.5

• Three Leaky Poles + Space Wave

e.g. third leaky mode, TM, …………..neglected by everyone Optimizing the parameters of the dielectric stratification:

• distance of the first dielectric layer from the radiating plane
• distance between layers in a multilayer structure

You can end up with configurations where also higher order leaky- wave modes are excited:

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Mode Suppression

1

• Double Iris design

0.6

• M. Qiu, G. Eleftheriades, A reduced surface-wave…, IEEE Microwave

Wireless Components Lett., pp. 459-461, Nov. 2001.

Cancellation by matching with zero of the Ms current

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Prototype Implementation

Polarization discrimination Frequency discrimination

• Resistive

loading

• Reactive

loading 4x reuse scheme

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Enhanced Feed System Performance

25 30 35 40 45

Nominal Adjacent

50

EoC EoC G [dB]

eoc

• 1
• 0.5

0.5 1 1.5 2 2.5 3 3.5 4 15 20 10

(degrees)

• 1
• 0.5

0.5 1 1.5 2 2.5 3 3.5 4 15 20 25 30 35 40 45

Nominal Adjacent

50 10

EoC EoC G [dB]

eoc

(degrees)

Free Space Enhanced Feed (Resistive loading)

Case 3 EoC Gain for different reflector diameters 38.5 39.0 39.5 40.0 40.5 41.0 9.4 9.6 9.8 10 10.2 10.4 10.6 Frequency [GHz] EoC Gain [dBi] 2.1 m F/D=0.95 2.3 m F/D=0.87 2.4 m F/D=0.85

Enhancement of 0.6 dB over 12% BW: moderate due to:

• Stein Losses
• Pattern widening due to mutual coupling

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Reactive Loading

Same configuration

• r=4.5

Period d= 2.4

• Isolated

Array

Equivalent short circuits loads for neighboring waveguides

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Demonstrator 2: Measured Patterns

E-plane H-plane

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Comparison

• With single dielectric slab, EoC Gain increase 0.85 dB over 3% BW

BestCase(F/D=0.87) WorstCase (F/D=0.85) Reference (F/D=0.85)

9.4 9.6 9.8 10 10.2 10.4 10.6 38.5 39 39.5 40 40.5 41 41.5

G [dB]

eoc

f[GHz]

• Adding reactive loadings (filters), EoC Gain increase 1.6 dB over 3% BW

Matched Loads Reactive Loads

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Larger F/D and more directive feeds

Feeds with higher directivity are required. Analyzed three different solutions, which do not require feeds of larger dimensions:

• Single dielectric layer of high permittivity: r=20.25
• Two dielectric layers of low permittivty: r=4.5
• Metallic FSS (to avoid the use of dielectric layers)

F/D=1.71; Period (d) = 4.8 0 0=17o

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Patterns

Secondary Primary Double Dielectric Case FSS

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h1=15 mm h2=3.535 mm d=144 mm

Impedance Matching

Double Dielectric Case h1=14 mm t=0.25 mm d=144 mm FSS Case

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Comparison

• Frequency range of applicabiltiy -

Best case: 2.0 dB, in 4.0 % BW

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New Demonstrator - Filters

19 elements (F/D=1.7; d= 4.8) 4x reuse scheme (2 pol. – 2 freq.) Filter High (10.01 – 10.10 GHz) Filter Low (9.875 – 9.965 GHz)

• VSWR < -20 dB
• Rejection > 28 dB