spiral full.pptx
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The Design, Development and Validation of
wideband spiral antenna
12.01.13 Presentation
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Scope of the Work
To design and develop left hand circular polarized wideband spiral
antenna from 1GHz to 18GHz
To validate the designed antennas by fabrication and testing the
prototypes for radiation pattern, axial ratio, VSWR and gain.
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Wideband Spiral antenna
Design Goal
Frequency : 1GHz to 18GHz
Return Loss : Better than 7.36 dB
Polarization : LHCP
Gain : -16dBi at 1GHz
-6dBi at 2GHz
-0dBi at 4-18GHz
3dB beam width : 80 degree
Beam squint : 5 degree max across 1-18GHz
Back lobe level : -20dB max
Power handling : 2W
Connector : SMA jack
Type of Radome : Hemispherical
Antenna Chosen to meet the above Design Goals: Archimedean spiral Antenna
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Project solution approachCalculation of design
parameters
Design of spiral antenna
Simulation of spiral
antenna
Calculation of dimensions for
balun
Design of balun
Simulation of designed
balun
Optimization
Integration of balun with spiral
antenna
Simulation of integrated structure
Back cavity and absorbers in integrated
spiral antenna
Simulation of integrated final
structure
Validation of final structure
Optimization
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Proposed topology
Spiral antenna
Absorbers
Back cavity
Co-axial connector
Tapered balun
Side view
Top view
Advantage of Archimedean spiral
Improved axial ratio
Wider operating bandwidth with
a give antenna diameter
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Spiral Antenna - Theory
Spiral antennas are frequency independent antennas
with circular polarization radiation at its broadside.
In Archimedean spiral antenna each arm is fed 180
degree out of phase, dual arm has symmetrical
radiation pattern and better axial ratio compared to
single arm Archimedean spiral antenna.
For a given diameter of an antenna greater
bandwidth is obtained with more tightly wounded
spirals.
Planar Archimedean spiral antenna is widely useddue to its low profile, light weight, high efficiency,
circular polarization, stable impedance
characteristics and broad bandwidth.
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Spiral Antenna - DesignDesign parameters in the spiral antenna:
Inner radius
Outer radius
Spacing between the turnsWidth of the arm
Inner radius:
High frequency is determined through inner radius of the spiral.
Practically value differs due to reflection from end of the spiral
Outer radius:
Low frequency is determined through outer radius of the spiral.
Practically value differs due to feed region effect
An impedance matching section is needed to match two different
characteristic impedance of spiral antenna and co-axial transmission line.
Since it radiates bi-directionally a cavity filled absorbers are used to
have unidirectional radiation pattern.
souterradiulow
R
cf
2
sinnerradiuhigh
R
cf
2
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Layout Model
The layout of the two arm spiral antenna was simulated using a FDTD based
Simulator (CST microwave Studio)
Spiral antenna Spiral antenna with absorbers
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Return loss
Frequency
(GHz)
Return loss in dB
specification Simulatedvalue
1 < -7.36 -6.73
3 < -7.36 -8.78
5 < -7.36 -11.82
10 < -7.36 -14.95
15 < -7.36 -9.92
18 < -7.36 -5.82
Frequency
(GHz)
Return loss in dB
specification Measuredvalue
1 < -7.36 -8.13
3 < -7.36 -10.51
5 < -7.36 -13.43
10 < -7.36 -17.13
15 < -7.36 -6.33
18 < -7.36 -4.145
Simulated Return loss Return loss with absorbers
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3 D Radiation patternSpiral antenna without absorbers
Freq 1GHz Freq 5GHz Freq 10GHz
Freq 15GHz Freq 20GHz
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3 D Radiation pattern
Freq 1GHzSpiral antenna with absorbers
Freq 5GHz Freq 10GHz
Freq 15GHz Freq 18GHz Freq 20GHz
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Tapered balun
Tapered balun front view and back view: Return loss:
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Modified spiral antenna
Spiral antenna modified structure: Return loss:
Radiation pattern:
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