presentation - antenna isolation for wireless...

Confidential and Proprietary

ethertronicsethertronics

Ansoft, San Diego 10/12/01

Gregory Poilasne [email protected]

Company History:- Created in May 2000- Funded by Sevin Rosen and US trust

Targeted markets and applications:- Embedded antennas for Cell Phones- Laptops and all wireless applications

between 800 MHz and ISM

ethertronics

Located: San Diego Tech Center9605 Scranton Road, suite 850San Diego, CA 92121


Antenna isolation

for wireless communications systems

Gregory Poilasne, S. Rowson, L. Desclos


OVERVIEW

1 - Antenna and Surrounding Interactiona) Antenna placementb) Radiation pattern - Efficiency evaluationc) Bit rate Measurements

3 - Internal antenna isolationa) Experimental and numerical results

2 - Isolation Measurementsa) Interaction with the case and the componentsb) Interaction with the user

CONCLUSION


1 - Antenna and Surrounding Interaction

a) Antenna placement

Home-RF solution



a) Antenna placement

Proposed solution

Antenna position



b) Radiation pattern - Efficiency evaluation

Efficiency = power at the antenna inputradiated power

Takes into account:input mismatchloss into the antennaloss into the surroundings

Measured by comparing:free space dipole

tothe antenna inside the system



b) Radiation pattern - Efficiency evaluation

Antenna XRipples due to the

interactions

Isolated AntennaSmooth radiation pattern

4dB Efficiency difference



c) Bit rate Measurements

Practical efficiency measurement:

Antenna

LaptopCommunication

channel

Bit rate measurementversus

the distance between the two laptops

Antenna




Distance (feet)0 20 40 60 80 100 120 140

Bit r

ate

(bit/

s)

0

100

200

300

400

500

Proxim facing transmitterPhotonic RF facing transmitterProxim looking away from transmitterPhotonic RF looking away from transmitter

Parking Lot Test - Minimum Possible Multipath(Office test is Isotropic)

ET Antenna is vertical

ET antenna

ET antenna

AUT

AUT




Practical efficiency measurement:

Antenna

Attenuator

LaptopCommunication

channel

Bit rate measurementversus

the attenuation




Ref : Ideal dipole away fromany absorber.

ET ant: Isolated antennaAntenna X: antenna sold with

the Home RF card.

0

50

100

150

200

250

300

350

400

450

500

0 1 2 3 4 5 6 7 8 9 10 11 12Attenuation (dB)

Bit

Rat

e (K

B/s

)

DipolePRFC antSymphonyET ant. Ant. X

Approximately 4.5dB ofefficiency difference

Efficiencydifference


The problem of Efficiency: Isolation

Interaction between the antenna and the case: Reduction of efficiency

Need for a tool to measure the interaction: Antenna IsolationMultiple applications in the same enclosure


a) Interaction with the case and the components

2 - Isolation Measurements

Shields tend to shortcircuit antennas




Example of a PIFA

E field

Metallicshield



d

Point A

Decay associated

Point A

p


Antenna

Shield




0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 420246810121416182022242628

30-3525-3020-2515-2010-155-100-5

antenna Shift in MHz

Distance in mmDistance in mm




y = 0.0245Ln(x) + 0.048

y = 0.0109Ln(x) + 0.0195

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0 0.2 0.4 0.6 0.8 1 1.2

Freq (GHz)

measurements

fitting

Distance in cm




0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 420246810121416182022242628

19-2018-1917-1816-1715-1614-1513-1412-1311-1210-119-108-97-86-75-64-53-42-31-20-1

antenna Shift in MHz

BC

Distance in mm



b) Interaction with the user

3D Radiation patternLoss into the user bodyNeed to shield the user

- Performance- Health

Frequency shift/matching Need for isolated antennas

- Performance




Frequency: 1.575GHzBandwidth: 8MHz

Critical

case

Antenna




Frequency shift: 2.5MHz

Blue curve: free space

Antenna




Hand over the side of the antenna

Blue curve: free space

Frequency shift: 1MHzIncrease of the reflection

Antenna


Improving Antenna Isolation

Current distribution:It has to be confined nearby the antenna.

Nearfield distribution:The nearfield has to be shaped awayfrom parasitic elementsConfined the field as much as possible

Nearfield probing: long and no so accurate

Simulation tools: Faster and faster, easy to visualize


3 - Improving the antenna isolation

Experimental and numerical results

PIFA:

Currents are leakingon the sides.




Isolated Antenna:

Low currents outsidethe antenna.




PIFA with shield:

Coupling with theshield.

Frequency shift:9%




Isolated antenna with shield:

Low coupling withthe shield.

Frequency shift:3%


CONCLUSION

Isolation means:

- Low interaction between an antenna and its surroundingsInside the enclosure: components, caseOutside the enclosure: user body, table,...

- Better efficiency in real world applications

- Semi-standard productsdrop-in componentfast turn-around design and optimization

presentation - antenna isolation for wireless...

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