Electronically Steerable Antennas for Vehicular Communications

1
Electronically Steerable Antennas for Vehicular
Communications

• Radiating Systems Term Paper
• 2nd November, 2007
• Department of Electrical Engineering
• IIT Bombay
• Course Instructor
• Prof. Girish Kumar
• Group Members
• Prakhil Bilaye lt03D07006gt
• Ankoor Das lt03D07028gt

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Introduction

• Concept
• Applications
• Radars
• Cellular Systems
• Vehicular Networks
• Advantages
• Reduced Interference
• Enhanced connectivity interval
• Implementation in Vehicular Networks
• Mobile Station Antenna Design (ESPAR)
• Base Station Antenna Design (Phased Array)

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Electronically Steerable Parasitic Array Radiator
Antenna

• Principle behind ESPAR Antenna
• Basic Design
• Active Element
• Parasitic Elements
• Control over Radiation Pattern
• Bias voltages
• Advantages
• Simplified hardware design
• Antenna Gain and more flexibility
• Power Consumption

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Design Considerations

• Requirements
• Frequency
• Sector Patterns
• Parasitic Element Length
• Desirable Reactance Range -21.1, 21.1
• ohms.
• Spatial Distribution
• Ground Plane
• Radius
• Skirting

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• Biasing Circuit
• Diodes
• RC Time Constant
• 24.7 Ohm shift
• Length Compensation
• increase
• Voltage Range
• Digital Voltage Vector
• (-0.5 Volt to 20 Volt)

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Omni-directional pattern forming
Variation in antenna output power with bias
voltage vector V Vo, Vo, Vo, Vo, Vo, Vo
Three omnipatterns corresponding to the three
bias voltage vectors
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Sector Beamforming

• Single Source Power Maximization
• Gradient Based Algorithm3
• Set of Directors and Reflectors
• Interesting Observations

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Sensitivity to Operating Frequency
30o sector patterns with operating frequencies
f2.473, 2.484, and 2.495GHz

• 0o sector patterns with operating
• frequencies f2.473, 2.484, and
• 2.495GHz

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Phased Array Antenna System

• Multi-Beam Scanning Phased Array (MSPA)
• Cylindrical base, antenna arrays around it

Cylindrical arrays of travelling wave patch
antennas
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Circular Array

• Circular Array
• N array elements around circular (cylinder) base
• Radius of cylinder a
• Analogues to linear array optimum separation
  between array elements

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Field Calculations

• Monopole elements
• Space factor
• Normalized Array Factor

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Beam Direction

• Beam directed to desirable angle
• Fixed no.of elements excited
• Appropriate phase shifted RF signals sent to each
  excited element
• DSP unit stored matrix of phased shifted
  signals for each element for various directions

Fig 1
Fig 2
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Power Supply (1)

• Scanning array antenna system
• Single scanning beam possible

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Power Supply (2)

• Multiple feed points
• Simultaneous scanning in different directions
• More complex hardware, more cost

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Scattering angle

• Scattering observed at mobile networks
• Beamwidth gt Scattering angle for reliable
  communication
• Beamwidth adjustments possible by change in
  excited elements and radius of cylinder

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Beamwidth Adjustments
Beamwidth change with change in no. of excited
elements
Beamwidth change with change in cylinder radius
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More advantages

• High Directional gain compared to linear arrays
• Directivity increases as the no. of elements in
  array increases
• Maximum Directivity observed at ?/2

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Implementation in Vehicular Network

• MObisteer Network
• 802.11 based
• Hardware Used
• 8-element Phased Array from Fidelity Comtech
• Operation Modes
• Cached Mode
• Online Mode
• Data Collection
• Passive Scanning
• Active Probing
• Scenarios

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Mobisteer Experimental Setup
Low Scattering Environment
Access Point Detection Scheme
High Scattering Environment
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Results
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Summary

• Two antenna designs discussed
• ESPAR Antenna
• Average Gain 5.5 dBi
• Adjacent Sector Discrimination 1.3 dBi
• Phocus Array Antenna
• Commercial Products2

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References

• J. Cheng, M. Hashiguchi, K. Ligusa and T. Ohira,
  Electronically steerable parasitic array
  radiator antenna for omni- and sector pattern
  forming applications to wireless ad hoc
  networks, IEE Proc. Microw. Antennas
  Propagation, Vol. 150, No. 4, August 2003.
• H. Kawakami and T. Ohira, Electrically Steerable
  Passive Array Radiator (ESPAR) Antennas, IEEE
  Antennas and Propagation Magazine, Vol. 47, No.
  2, April 2005
• Murata Manufacturing Co. Ltd. http//www.murata.co
  m/
• Hudson J.E., Adaptive Array Principles (Peter
  Peregrinus Ltd., 1991)
• J.H. Winters and M. H. Gans, Phased Array
  Antennas in Mobile Radio Systems, IEEE
  Transactions on Vehicular Technology, 48(2)pg
  353-362, 1999.
• V. Navda, A.P. Subramanian and K. Dhansekaran,
  Mobisteer Using Steerable Beam Directional
  Antenna for Vehicular Network Access, MobiSys
  07, Puerto Rico.
• C. Alakija and S.P. Stapleton, A Mobile Base
  Station Phase Array Antenna, ICWC, Vol. 5, No.
  5, Pg 118-121, 1992.

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• Thank You