12-13 February 2002 8th Australian Symposium on Antennas 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

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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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RationaleThere 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 gainThe battery can operate over an extended time periodHealth 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

All the above schemes do not require large real estate and can be realized using a single or few antenna elements.

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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.

– By alternating between the two polarizations good quality signal reception can be maintained.

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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, LHC+RHC• Pattern Diversity

– Signal is received only from a selected direction

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Investigated Antennas

Ericsson PIFASmart Clothing IFAF Shaped MonopoleCPW Feed Patch AntennaSingle Circular Slot Antenna (LP and CP

Polarized)Dual Slot Ring Antenna

All of them have been designed for operation at 2.4GHz using Agilent ADS Momentum.

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Fully Developed Antennas

Printed IFA

Single Slot Ring

Single Slot Ring

Polarization Diversity

Dual Slot Ring

Pattern Diversity Antenna

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Printed IFA Design with the Use of Momentum

3D Radiation Plot and Current Distributions

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Fully Developed Printed IFA

Non-adaptive antenna with high degree of cross polarization

The developed antenna

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Single Slot Ring (CP Feed) Design with the Use of

Momentum

3D Radiation and Current Plot shown

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Fully Developed Single Slot Ring (CP Feed) Antenna

Circular Polarization (non adaptive) Antenna

The developed antenna

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Operation of Single Slot Ring with Perturbation Segments

Antenna

Perturbation segments– Are ON: circular polarization is obtained– Are OFF: linear polarization is achieved

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Design of Single Slot Ring with Perturbation SegmentsCurrent Plots

– With and without perturbation segments

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Fully Developed Single Slot Ring with Perturbation Segments

Able to achieve Linear or Circular Polarization depending on the state of its switches

• Photographs of the developed antenna

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Dual Slot Ring Antenna

OFFOFF

ONOFF

Generates 3 independent radiation patterns by turning ON or OFF P-I-N diodes

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Fully Developed Dual Slot Ring Antenna

Pattern Diversity Antenna

The developed antenna

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Experimental Results for Antennas

The inverted IFA, Single Slot Ring, Single Slot Ring with Perturbation Segments and Dual Slot Ring antennas have been tested in terms of their Return Loss using HP8510 Vector Network Analyser

In general, good agreement with the Momentum simulated results has been obtained

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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 [Photo]

T module R module

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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 CSR’s Bluetooth Firmware

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Bluetooth Experiment Results [Real-time]

RSSI

BER/Quality

Packet Delay The position of dots is related

to the link quality

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Bluetooth Experiment Results [Power/Delay vs Distance]

Delay

Power

50 1002.5m + Distance (cm)

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Conclusions

●Fixed and variable pattern planar antennas to mitigate multipath problems have been designed and developed using Agilent ADS Momentum.

● The antennas parameters have been selected for operation with Bluetooth (2.4GHz).

●Developed antennas were 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.