SPIRAL FULL.pptx

7/29/2019 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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SPIRAL FULL.pptx