Helical Antennas with Improved Gain 1 School of Electrical - - PowerPoint PPT Presentation

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Helical Antennas with Improved Gain 1 School of Electrical - - PowerPoint PPT Presentation

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A.R. Djordjevi 1 , D.I. Ol an 1 , J.R. Mosig 2 Helical Antennas with Improved Gain 1 School of Electrical Engineering, University of Belgrade, Serbia 2 Ecole Polytechnique Fdrale de Lausanne, Switzerland COST Action IC0603 Workshop

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SLIDE 1

Helical Antennas with Improved Gain

1School of Electrical Engineering, University of Belgrade, Serbia 2Ecole Polytechnique Fédérale de Lausanne, Switzerland

A.R. Djordjević1, D.I. Olćan1, J.R. Mosig2

COST Action IC0603 Workshop Joint session with COST 297 Cyprus, April 2008

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SLIDE 2

Contents

Classical helical antennas

uniformly wound and above infinite ground plane

  • ptimization and new design data

Influence of the reflector

finite ground, cup, cone

  • ptimization and design data

Nonuniformly wound helical antennas

with infinite ground plane without any reflector interim results

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SLIDE 3

Helical antennas

Uniformly wound Axial mode Discrepancy among design data Influence of the reflector

not widely recognized

Maximize gain

bandwidth elipticity matching

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SLIDE 4

Classical design data

Optimal circumference Independent on wire diameter Optimal pitch angle Minimal size of square ground plane

(counterbalance, reflector)

Gain (Kraus)

3 / 4 / 4 / 3 < λ < C 05 . / 005 . < λ < d ° < α < ° 14 12 75 . /

c =

λ b         λ       λ = L C g

2 dBi] [

15 log 10

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SLIDE 5

Discrepancies

1 2 3 4 5 6 7 10 11 12 13 14 15 16 17 18 19 20 Formula (Kraus) Experiment (King, Wong) Simulation (Emerson) Design curve (Poynting) NB design WB3 design

gmax [dBi] L/λp

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SLIDE 6

Comments

Formula by Kraus overestimates the gain Simulations (Emerson, Poynting, our results) for

infinite ground plane

Experiment for antenna with a cup (King, Wong)

influence of the cup remained unnoticed wrong estimation of the antenna center contradictory data for distance between transmitting

antenna and receiving antenna

Data by Poynting for a wide range of pitch angles Our design: narrowband and broadband

  • ptimized over wide range of parameters
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SLIDE 7

Narrowband and broadband

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1

9 10 11 12 13 14 15 16

WB3 NB

Gain [dBi] f [GHz]

Simulation Measurement

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SLIDE 8

Our design data

Infinite ground plane Narrowband design: smaller pitch angles Wideband design: larger pitch angles

increased bandwidth at lower frequencies caused

by reflections from the ground plane

the ground plane must be sufficiently large (2λ)

Optimal pitch angles strongly depend on wire

radius

Optimal pitch angles

° < α < ° 16 3

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SLIDE 9

Our design curves

1 10 11 12 13 14 15 16 17 18 19 20 21 NB WB1 WB2 WB3

gmax [dBi] L/C

1 10 0.7 0.8 0.9 1.0 1.1

NB WB1 WB2 WB3

C/λc L/C

1 10 2 4 6 8 10 12 14 16

NB

α [

  • ]

L/C 1 10 2 4 6 8 10 12 14 16

WB3

α [

  • ]

L/C

r/C =0.00015 r/C =0.0015 r/C =0.015 P

  • ynting 1

P

  • ynting 2
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SLIDE 10

Influence of reflector

Reflector has significant

influence on radiation pattern and gain

Optimal square Optimal cup Smallest optimal truncated

cone λ = 5 . 1 b λ =1 D λ = 25 . h λ = 75 .

1

D λ = 5 . 2

2

D λ = 5 . h

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SLIDE 11

Influence of reflector

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 10 11 12 13 14 15 16 17

Infinite ground plane Square conductor of side b=0.5λ Optimal square conductor Optimal cylindrical cup Optimal truncated cone

Gain [dBi] Frequency [GHz]

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SLIDE 12

Optimal helix and cone

Simultaneous optimization of helix and cone Nelder-Mead simplex algorithm Very large pitch angles (30°

)

Many local optima Cone collects radiation from the lowest helix

turns and redirects it upwards

Low side lobes For large heights – helicone antenna (Carver)

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SLIDE 13

Optimal helix and cone

1 2 3 4 5 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Helix (Milligan) Hansen-Woodyard NB design WB3 design Cone, h=0.5λ Cone, h=2λ

gmax [dBi] L/λ

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SLIDE 14

Optimization of pitch and diameter

Simultaneous optimization of helix pitch and

diameter (for constant wire radius)

No reflector

simple launcher (with choke) results comparable to classical antenna with

ground plane

Infinite ground plane

helix radiates backwards ground plane acts as a reflector results comparable to optimal cone

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SLIDE 15

Preliminary results

1 2 3 4 5 9 10 11 12 13 14 15 16 17 18 19

Optimal, no ground Optimal, infinite ground NB design WB3 design Cone, h=0.5λ Helix (Milligan)

gmax [dBi] L/λ

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SLIDE 16

Example: 5λ λ λ λ, classical

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SLIDE 17

Example: 5λ λ λ λ, no reflector

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SLIDE 18

Example: 5λ λ λ λ, infinite ground

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SLIDE 19

Future work

Further optimization of helix with truncated

cone for wide range of wire radii

previous results only for one wire radius

Include taller cones to cover transition to

helicone antenna

previous optimization up to h=2λ

Further optimization of helix pitch and

diameter; experimental verification

Compare the influence of the reflector to the

influence of wave launchers

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SLIDE 20

References

  • A.R. Djordjević, A.G. Zajić, M.M. Ilić, G.L. Stueber,

“Optimization of helical antennas “, IEEE Antennas and Propagation Magazine, vol. 48, December 2006, pp. 107-115.

  • D.I. Olćan, A.G. Zajić, M.M. Ilić, A.R. Djordjević, “On the
  • ptimal dimensions of helical antenna with truncated-cone

reflector”, Proc. of EuCAP, ESA SP-626, Nice, November 2006.

  • A.R. Djordjević, A.G. Zajić, M.M. Ilić, “Enhancing the gain of

helical antennas by shaping the ground conductor”, IEEE Antennas and Wireless Propagation Letters, Vol. 5, 2006, pp. 138-140.

  • A.R. Djordjević, D.I. Olćan, A.G. Zajić, M.M. Ilić, "Optimization
  • f helical antennas ", Cost Action IC0603 Workshop, Bonn,

October 2007.