ceramic antennas for small form factors

8/17/2019 Ceramic Antennas for Small Form Factors

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© 2007, Ethertronics

Advances in High-Performance Ceramic Antennas

for Small-Form-Factor, Multi-Technology Devices



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© 2007, Ethertronics 2

Presentation outline

• Market Requirements Driving Multiple

Antenna Integration & Thinner Packages

• Antenna Design Requirements

• Advantages of Ethertronics IMD Technology

• GPS Antenna Comparison Testing

• Dual frequency products


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Trend: Multiple Antennas per Phone

Main Cellular

Bluetooth

GPS

WiFi

-

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

2005 2006 2007 2008 2009 2010

U n i t V o

l u m

e

WiFi

GPS

Bluetooth

Main Cellular

Source – Gartner

• Common to have 2-4antennas per phone

• Most popular

features withhighest attach rates

– Bluetooth - 50%

– GPS - 25%


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Trend: Smaller Handsets – Less Volume

• Thin phone trend is accelerating

– Volumes decreasing ~10% per year– Ultra Thin handsets are challenging

• Utilize ~50% of the average volume

55 cubic cm75 cubic cm71 cubic cm 56 cubic cm

Avg PhoneVolume

2004 131 cu.cm

2005 122 cu.cm

2006 106 cu.cm

Ultra Thin 55 cu.cm

Source: Current Analysis

Industry Trendline

Cell Phone Volumes


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Design Challenges

• Overall device size shrinking

– More antennas in less space

– Maximum component heightunder 2.5mm for Ultra models

• More parasitic elements

– Speakers, cameras, flex…

• Less quality real estate

– More I/O connectors on side of the board

• Antenna collocation

– Diversity or different applications

– Example: Bluetooth and WiFi integration

Cell antenna

WLAN antenna

BT antenna

WCDMA antenna


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Antenna Requirements


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Benchmark Dual Band Performance

• Typical antenna

specifications:Better than 10 dB

Return Loss

Better than 20 dB

Isolation

• Benchmark phone

required 25 dB of

isolation to meetOEM performance

specificationsGPS Bluetooth

Return

Loss

Isolation


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Antenna Volume Theory

• Wheeler & Mc Lean provided the basic insights for

identifying the real effective volume of embedded antennas

• Wheeler’s Formula

• Given constraints on design space, how should one compare

two antennas when their “antenna mode volume” will

become altered as part of the mechanical design?– How close is the nearest metal object?

– Should coupling effects and consequences be considered?

( )3wavelengthradiovolumemodeantenna

K f

Δf ×=


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Antenna Requirements

• Smaller antennas in close proximity

– With high efficiency – above 40% threshold

– Well-controlled radiation – resist performance changes

(good for customer as well as designer)– Immunity to other frequencies or diversity antennas

• GPS separation from UMTS-1700, sharing of 2.4 GHz

• How to achieve ideal performance:– Decrease interaction between antennas

– Decrease interaction between phone elements

– Minimize antenna ground dependence

Isolation

SelectivityKey Factors


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Isolation Drives Overall Performance

Isolation describes how an antenna

interacts with its surrounding.

How can isolation be improved ?

By shaping the antenna’s near field away

from the perturbations and the absorbers.

Superior isolation allows:

- better efficiency- easier integration

- semi-standardized products

ET antenna isolation: 2mmfor 0.3% frequency shift


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IMD Provides Superior Isolation

• ET IMD antennas are more tolerant of interfering objects– Hand placement and head significantly impact performance

• GPS signal strength improved by staying on frequency

Isola t i on Test Result s

- GPS Internal antenna example-very sensitive to freq. shift

- IMD antennas stay on frequency

even with interference from

other objects – e.g., hand

Return-Loss ChartBefore / After Hand Placement

Any current flow on the board becomes

a part of the antenna radiating mechanism.

When touched, the characteristics of the antenna change.


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GPS Antenna Comparisons(following vendors recommendations)

• Highest efficiency does not tell entire story– Important to also study the frequency component of antenna’s efficiency

• Selectivity – ability to reject the frequencies outside its range

Antenna Selectivi ty

0

10

20

30

40

50

60

70

80

90

100

1500 1525 1550 1575 1600 1625 1650 1675 1700

frequency, MHz

e f f i c i e n c y ,

%

Ethertronics

Sample 1

Sample 2

Sample 3

Problem Area

Overlap with UMTS,

AWS Band


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Ceramic

GPS AntennaTest Bed


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Several Variables to Consider

• The antenna may require ground plane removal

• It will excite some of the board, but how much?

– the board itself could become the antenna

• What about board placement, and distance to nearest

interferers, eg a shield can, or a battery

• We developed a test bed, focusing on the isolation,

selectivity, efficiency and position of the antenna


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Shield Can Separation Test

• Several Tests utilizingmetal can as interferer

– Measure changes in:• Efficiency

• Center frequency

– At 3 distances• 3, 6 and 9mm apart

• Calculate Volume/Area

– Device size• Footprint & placement

– Real antenna volume• Interaction with can

• Keep-out zone is 3D

shield can

separation

3mm

6mm

9mm


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Efficiency Lowered by Shield Can

• Sample 1, significantly impacted

• Broadband antenna has best performance

• All samples above 40% efficiency threshold in free space

Efficiency

0

10

20

30

40

50

60

70

80

90

100

0 3 6 9 12 15

shield can distance, mm


%

Ethertronics

Sample 1Sample 2

Sample 3


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Frequency Shifted by Shield Can

• Sample 1 significantly impacted• High-efficiency, broadband sample 2 survives shift’s impact

• IMD antenna stays rock solid on frequency

Frequency Shift

0

25

50

75

100

125

150

0 3 6 9 12 15

shield can distance, m m

f r e q u e n c y s h i f t , M H z Ethertronics

Sample 1

Sample 2

Sample 3

Efficiency

15%

70%

40%60%


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Board Position Test Set up

• How often is the best

antenna location where

one has space to place it?

• Determine how muchnormal performance can

vary from the specified

best case…

Position 4

Position 3

P o s i t i o n

1

P o s

i t i o n

2

Board Area

40mm x 80mm


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Typical GPS Antenna Performance

• Average from 3 best positions out of 4 tested

• Samples 1 & 2 show a 5~10% drop from peak efficiency

• IMD stayed consistent across all three locations

Average Per for mance - 3 locat ions

0

10

20

30

40

50

60

70

80

90

100

1525 1550 1575 1600 1625

frequency, MHz


%

Ethert ronics - Avg Bes t 3

Sam ple 1 - Avg Bes t 3

Sam ple 2 - Avg Bes t 3

Sam ple 3 - Location 3 only


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“Worst Case” Performance

• Two antennas still above 40% threshold– Broadband antenna Sample 2 vs IMD Dual Band, Dual Feed

• IMD antenna decreased efficiency by 25% vs >50%+ by all others

Wor st Perform ance - Single Location

0

10

20

30

40

50

60

70

80

90

100

1525 1550 1575 1600 1625

fre quenc y, MHz


%

Ether tro nics - Pos it ion 1

Sam ple 1 - Pos it ion 3




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Summary of Test Results

• Simple Volume test provided valuable

insights on efficiency and freq shifts

• Two antennas excelled throughout

– Ethertronics and Broadband Sample #2

• Design Tradeoffs include:

– Keep Out and Ground restrictions

– Cost & Space needed for Filters

Samples 1 & 2

ET & Sample 3

Keep-out

AreaW1

L1

H

L2

W2

Circuit Board

Antenna

L1 W1 H G r o u

n d C l e

a r a n

c e ( G C )

T o t a l P

C B A r e a

S h i e l d

C a n

O f f s

e t

R e a l

P C B

A r e a

A n t e

n n a ' s

V o l u m

e

M e a

s u r e d E f

f i c i e

n c y

Observations

Samp le 1 10 3 4 3 96 9 336 1,344 65% Limited Isolation from its environment; significant perf changes

Samp le 2 20 3 4 0 60 3 156 624 77% High Gain, but poor GPS band selectivity; need BPFSamp le 3 8 2 1.5 2 48 3 70 105 46% Low Efficiency, stable performance, single location usage

ET BT & GPS 14 4 1.3 1 80 3 140 182 68% Steady performance under all conditions; thinnest package

ET GPS onl y 10 4 1.3 1 60 3 112 146 68% Best efficiency to volume ratio

all measurements in mm , sq mm, or cu mm

Area = (L1 + 2x GC) x (W1 + GC) Use L2 and W2


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New Antenna Up To Market Challenges

• Phone real estate as pricey as Paris

– So combining functions is mandatory

– Yet antennas prefer separation for isolation

• Perform a Best of Performance Criteria Review

– Compact Size, Great Isolation & Freq Stability

– Flexible implementation without sacrificing gain

• ET’s IMD dual band, dual feed antenna products

– GPS and Bluetooth sampling now

– PCS Diversity, WiFi, WiMAX and others in testing

4.5mm gap

Quad Band Antenna


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Next Generation of Ceramic Antennas

• Leverages underlying

IMD technology

• Dual Band, Dual Feed

– Ideal implementation

• Peak Efficiency

– GPS over 68%

– Bluetooth over 50%


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One Antenna Outperforms Two…

• Ceramic version

improves key resultsby approx 4 dB

– GPS isolation


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Conclusion

• Smaller and more complex phone designs make

antenna design more challenging.

• IMD technology allows smaller designs and better

performance in densely populated volumes.

• IMD’s isolation and selectivity allow integration of

multiple antennas in a single ceramic block.

• Ceramic IMD antennas demonstrate ideal

characteristics for next-generation products.

ceramic antennas for small form factors

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