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A Miniaturized Archimedean Spiral Antenna with Polarization Diversity
Dr Jonathan M. Rigelsford, SMIEEE
Department of Electronic & Electrical Engineering, The University of Sheffield, Mappin Street, Sheffield S1 3JD, United Kingdom.Email: [email protected]:+44(0)114 2225584
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Overview
• Motivation for this work
• Background to the subject
• The design
• Results
• Conclusions & Comments
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Motivation
• How do you make large antennas smaller?
• How can you maintain their efficiency?
• How can you preserve polarization?
• Can we create a scalable design?
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From A to B
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120m
Why make antennas smaller?
• Easier to fit into devices• Smart phones
• Cars
• Reduced visual impact• Tempest
• Planning permission
• Aesthetics
• Easier to handle
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Background
• How do you make large antennas smaller?• Dielectric loading
• Fractals
• Meander lines
• Spirals
• Meta materials - EBG/AMC/HIS
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The forming of an idea…
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… Eureka!
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Justification: Why a spiral?
• Easily scalable
• Easy to print
• Easy to manufacture
• For tempest applications you can use a pipe bender.
• For HF you can use radial supporting cables.
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The design of a 4-arm Archimedean Spiral Antenna
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r=r0+aφ
a=t/2π
r0
t
g
r
-21
-18
-15
-12
-9
-6
-3
0
1.4 1.6 1.8 2 2.2
Reflection coefficient (dB)
Frequency (GHz)
t=13mm
t=14mm
t=15mm
t=16mm
t=17mm
Reflection coefficient Axial Ratio
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0
5
10
15
20
25
1 2 3 4 5 6 7 8
Axial ratio
Frequency (GHz)
Gain Radiation pattern
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-6
-3
0
3
6
9
12
1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3
Realised Gain (dBi)
Frequency (GHz)
-30
-25
-20
-15
-10
-5
0
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
dB
Angle (degrees)
1.6 GHz
1.65 GHz
1.7 GHz
1.75 GHz
1.8 GHz
1.85 GHz
Results
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-60
-50
-40
-30
-20
-10
0
1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95 2
Reflection coefficient (dB)
Frequency (GHz)
S11
S22
S21
Summary of a Quad-arm Archimedean Spiral Antenna
• Frequency: 1.75GHz• Reflection coefficient: -20dB• Isolation: -45dB• Gain: 9dBi• Axial ratio: 38dB• Diameter: 44.5mm• Aperture reduction: 49%• Thickness: λ/4• Dielectric loading: NONE• Meta-material: NONE
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Dielectric loading
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-15
-12
-9
-6
-3
0
0 0.5 1 1.5 2 2.5 3 3.5 4
Reflection coefficient (dB)
Frequency (GHz)
1.5
2
2.5
3
3.5
4
4.5
5
Variation of S11 with different ε
Reflection coefficient of different turns spacing
Reflection coefficient of different width of arm
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-21
-18
-15
-12
-9
-6
-3
0
0 0.5 1 1.5 2 2.5 3 3.5 4
Reflection coefficient (dB)
Frequency (GHz)
t=13mm
t=14mm
t=15mm
t=16mm
t=17mm
-21
-18
-15
-12
-9
-6
-3
0
0 0.5 1 1.5 2 2.5 3 3.5 4
Reflection coefficient (dB)
Frequency (GHz)
0.5
1
2
Reflection coefficient of different r0
Reflection coefficient of different number of turns
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-21
-18
-15
-12
-9
-6
-3
0
0 0.5 1 1.5 2 2.5 3 3.5 4
Reflection coefficient (dB)
Frequency (GHz)
5
4
3
-21
-18
-15
-12
-9
-6
-3
0
0 0.5 1 1.5 2 2.5 3 3.5 4
Reflection coefficient (dB)
Frequency (GHz)
1.24
1.2
1.15
1.1
Summary of a Quad-arm Dielectrically loaded Archimedean Spiral Antenna
• Frequency: 2.75GHz• Reflection coefficient: -14dB• Diameter: 44.5mm• Aperture reduction: 45%• Thickness: λ/9• Dielectric loading: YES• Meta-material: NONE
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‘Polo’ Loaded
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-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1.5 1.7 1.9 2.1 2.3 2.5
Reflection coefficient (dB)
Frequency (GHz)
1mm larger than spiral
same as spiral
1mm smaller than spiral
2mm smaller than spiral
‘Polo’ Loaded
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Summary of a Quad-arm ‘Polo’ loaded Archimedean Spiral Antenna• Frequency: 2.38GHz• Reflection coefficient: -18.1dB• Isolation: -50dB• Gain: 5.9dBi• Spiral Diameter: 32.5mm• Aperture reduction: 49%• Thickness: λ/8• Dielectric loading: YES• Meta-material: NONE
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• Frequency: 1.52GHz• Reflection coefficient: -20dB• Isolation: -65dB• Gain: 3.7dBi• Spiral Diameter: 32.5mm• Aperture reduction: 72.5%• Thickness: λ/10• Dielectric loading: YES• Meta-material: NONE
Conclusions
With a bit of clever thinking you can:
• Design a dual polarized, miniature Archimedean spiral antenna,
• Which is highly scalable, and
• Can be made even smaller using dielectric loading.
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Comments/Challenges
• Still have to try and make the design even smaller using EBG/AMC/HIS.
• Design an EBG/AMC/HIS which works at 6 MHz without dielectric material.
• Be very careful with your simulations!
(suggestions and/or collaborators welcome)
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Thank you!
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