Investigations into fixed-pattern and adaptive antennas for use with IEEE802.11b and Bluetooth standards

1
Investigations into fixed-pattern and adaptive
antennas for use with IEEE802.11b and Bluetooth
standards

• by
• K.S. Bialkowski, A. Postula M.E. Bialkowski
• School of Information Technology Electrical
  Engineering
• University of Queensland

2
Presentation Outline

• Rationale
• Problems with traditional antennas
• Antenna diversity techniques to overcome
  propagation problems
• Non-adaptive and adaptive antenna solutions
• Examples of investigated antennas
• PC setup for assessing antenna performances in a
  Bluetooth communication system
• Conclusions

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Rationale

• There is a strong demand for reducing the size of
  wireless communication devices to open new
  application areas
• To meet this demand, reduced-size antennas are
  required
• New antenna designs have to mitigate problems
  associated with multi-path propagation
• The viable option are antennas offering diversity

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Problems with Traditional Antennas

• Traditional antennas (such as monopoles) are of
  fixed pattern and polarization.
• The transmitted wave is affected by multi-path
  propagation resulting in large changes in the
  received signal strength
• In mobile environment, receiving antennas are
  often pattern/polarization mismatched to the
  incident wave

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Options for Solving Propagation Problems

• Increase Transmitted Power
• Disadvantage (i) more battery power
  required
• (ii) more radiated power absorbed by an operator
  
• Use Antenna Diversity
• By matching the receiving antenna pattern,
  polarization or field (E or H) the receiving
  system gain can be improved by several dB
• Advantage
• The quality of communication link can be improved
  without the need to compensate by an active gain
• The battery can operate over an extended time
  period
• Health hazards due to radiation are reduced

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Antenna Diversity Options

• Pattern diversity the antenna pattern is matched
  to the direction from which the wave arrives
• Polarization diversity the antenna polarization
  is matched to the polarization of the incident
  wave
• Field diversity antenna elements are selected to
  couple to E or H field, whichever is maximum at a
  given location

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Antenna Diversity Example

• The following figures show signals received by
  horizontally and vertically polarized antennas in
  a typical indoor environment.
• The signals are affected by multi-path
  propagation.
• However, nulls are at different positions.

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Non-Adaptive and Adaptive Antenna Solutions

• Non-Adaptive solution offered by fixed-pattern
  antennas featuring high cross-polar component
• Used in (some of) current designs (Eg PIFA)
• co-polar and cross-polar components observed in
  far-field radiation pattern.
• Adaptive Diversity solution-offered by antennas
  with pattern controlled by a switching system
• Polarization Diversity
• Signal is received on one of two (or more)
  polarizations, eg Horizontal Vertical, LHCRHC
• Pattern Diversity
• Signal is received only from a selected direction

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Investigated Antennas

• Printed IFA
• Single Slot Ring
• Single Slot Ring
• Polarization Diversity
• Switches ON CP is obtained
• Switches OFF LP
• Dual Slot Ring
• Pattern Diversity Antenna
• - By turning ON or OFF P-I-N diodes
• gives 3 radiation patterns
• They were designed at 2.4GHz using ADS Momentum.

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Printed IFA Design

• Non-adaptive antenna with high degree of cross
  polarization

Current Distribution
ADS Momentum Simulation
The Developed Antenna
3D Far-field
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Single Slot Ring (CP Feed) Design

• Circular Polarization (non adaptive) Antenna

Current Distribution
ADS Momentum Simulation
The Developed Antenna
3D Far-field
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Design of Slot Ring with Perturbation Segments

• Achieves Linear or Circular Polarization
  depending on the state of its switches

With Perturbation Segments
ADS Momentum Simulation
Without Perturbation Segments
The Developed Antenna
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Dual Slot Ring Antenna

• Pattern Diversity Antenna - Generates 3
  independent radiation patterns by turning ON or
  OFF P-I-N diodes

ADS Momentum Simulation
The Developed Antenna
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Bluetooth Experimental Setup

• Includes two Bluetooth Modules connected to
• two PCs running Linux 2.4.20 with BlueZ 2.3
• Uses 'Ping' link application over Bluetooth's
  l2cap layer with ACL (connectionless) packets
• Using this system, performances of a Bluetooth
  link (with antennas described previously) can be
  assessed in real time
• The performance can be measured and plotted vs
  location/distance of the receiving module.

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Bluetooth Experimental Setup
Antenna 1
Bluetooth Module 1
Bluetooth Module 1
Antenna 2
Bluetooth Module 2
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Bluetooth Experiment

• Includes
• Measuring mean packet delay and counting
  error-free packets of information received during
  the transmission between the two PCs.
• Measuring the received signal power using the
  Bluetooth RSSI command.
• Measuring BER estimations using CSRs Bluetooth
  Firmware

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Bluetooth Experiment Results Real-time
RSSI
Packet Delay
The position of dots is related to the link
quality
BER/ Quality
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Bluetooth Experiment Results Power/Delay vs
Distance
Delay
Power
Distance 1m ? cm
?
?
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Conclusions

• Fixed and variable pattern planar antennas to
  mitigate multi-path problems have been designed
  and developed using Agilent ADS Momentum.
• The antennas parameters have been selected for
  operation with Bluetooth (2.4GHz).
• Developed antennas have been experimentally
  tested and showed good performance.

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Conclusions (continued)

• A PC-based system has been developed to measure
  in real time the communication link quality
  between Bluetooth modules.
• The system serves as an experimental platform for
  assessing antenna diversity schemes for Bluetooth.