very-near-field solutions for far-field problems

Very-Near-Field Solutions

for

Far-Field Problems

Local representation by Electronic Instrument Associates

Frank Krozel – (630) 924-1600

[email protected]

http://www.electronicinstrument.com

Agenda

Corporate Information

Introduction to Near-Field

Very-Near-Field Solution

Very-Near-Field Implementation

RFxpert Validation

RFxpert Test Applications

RFxpert Demonstration

Conclusion

Corporate Information

An Established Company

Private Canadian corporation since 1989

– Coverage in 49 countries

Unique and patented products for RF and EMI

– Very-near-field magnetic measurements

Recognized innovative products

A Leader

World Leading Developer of Visual Real-Time

EM and RF Diagnostic Solutions

Antenna and PCB Designers

Product Integration and Verification Engineers

Pre-Compliance Not Compliance

Exciting Value Proposition

Substantially Reduce Project Development Costs

Dramatically Increase Designer Productivity

Significantly Accelerate Time-to-Market

1 Hour in a Chamber or 1 Second with EMSCAN?

Chamber on your Desktop

EMxpert– EMC/EMI diagnostic tool enabling

designers to rapidly diagnose and

solve EM problems in a single design

cycle in their own lab environment

RFxpert– APM tool enabling engineers to

quickly evaluate and optimize their

designs with real-time antenna

performance characterization at their

desk

Fundamentals

High-density planar antenna array

High-speed electronic switching

Very near-field measurements

Far-field predictions

Real-time real-fast

No chamber

Introduction to Near-Field

Near-Field Scanning

Near-field scanning for antenna measurement

Near-field scanning for EMC applications

What is Near-Field?

Anything not in

the far-field

Far-field is where

the pattern is not

changing with the

distance

Common definitions

Usually stay out of the

reactive region

Where is Near-Field?

Emissions approximate

a plane wave when the

maximum phase difference

between any point

on the source is 22.5°

The equates to �� ⁄

Fields from Infinitesimal Dipole

C.A.Balanis – Antenna Theory : Analysis and Design 3rd Ed.

��

��1 �

�

��

�� 0

Distances should be

measured form the

edge of the reactive

region

For low frequencies the

dimensions most devices

are not≫ �

More Realistic Approximation

For a case of D = 1m

No radiating

near-field

for low frequencies

Situation for many EMC

problems

Reactive region can extend

beyond the measurement

distance of EMC test

J.C.Bolomey - Engineering Applications of the Modulated Scatterer Technique

RF Test Solution

Typically looking for far-field parameters

– Gain, efficiency, pattern are basic measures

– More complex applications such as Envelope

Correlation, Axial Ratio and Beam Forming

Debugging via near-field

Far-Field Measurements

Far-field site far and demanding a large area

Open-air-test-site (OATS) avoids reflections

Almost impossible in an urban environment

Far-Field Measurements cont.

Controlled environment

Collimation or compact

Near-Field Alternative

Various competing parameters

– Not always clear cut answer

Near-field is much smaller

– Less area

Theoretically no loss of information

Near-Field Measurements

Near-field measurement

Near to Far projections

Far to Near projections

Near to other Near projections

Near-Field Transformations

Plane Wave/Modal Expansion

Magnetic currents

Genetic algorithms

Far-field holography

Time domain near field approach

Near-Field Modal Expansion

Mainly three different

implementations– Planar

– Cylindrical

– Spherical

Each has its strength and

weaknesses

Planar Cylindrical Spherical

High Gain Excellent Good Good

Low freq. Poor Poor Good

Cost Low Moderate Moderate

Speed Good Moderate Low

Planar Near-Field Theory

The radiation of the antenna

can be described in terms of

angular spectrum of waves

Based on Huygen’s principle

Fourier transform from near-

field space to propagation

vectors in far-field

Image: www.schoolphysics.co.uk


An antenna can propagate in

all directions

The phases and amplitudes in

each directions will vary

In the near field all elements

are interdependent


Sample near field elements

along a planar surface

Measure amplitude and phase

in each point

Combination of phase fronts


Use sampled points to

reconstruct new phase fronts

No difference between this

and the original phase front

that was sampled


Separate the various phase

fronts or plane waves based

on their weightings

This set of plane waves in all

directions is the plane wave

spectrum

The term k may be called the wave number vector and the terms

in the integration represent a uniform plane wave propagating in the k direction

yx

j

yx dkdkekkzyxrk

AE•−∞+

∞−

∞+

∞− ∫∫= ),(2

1),,(

π

yx

j

yx dkdkekkzyxrk

AkH•−∞+

∞−

∞+

∞− ∫∫ ×= ),(2

1),,(

π

0),(),(),( =++ yxzzyxyyyxxx kkAkkkAkkkAk

Based on Maxwell’s equations and a source-less

boundary condition we can construct the following equations

zzyyxx akakak)))

++=k

where,

rk

A•− j

yx ekk ),(

zyxzyyxyxyxxyx akkAakkAakkAkk)))),(),(),(),( ++=A

and,


yx

ykxkjzkj

yxxtx dkdkeekkAzyxE yxtz)(

),(2

1),,(

+−−∞+

∞−

∞+

∞− ∫∫=π

yx

ykxkjzkj

yxyty dkdkeekkAzyxE yxtz)(

),(2

1),,(

+−−∞+

∞−

∞+

∞− ∫∫=π

The two tangential components are sufficient to fully construct the third

component

With a Fourier transformation we can obtain the PWS terms

∫∫∞+

∞−

+∞+

∞−= dydxezyxEekkA

ykxkj

tx

zkj

yxxyxtz)(

),,(2

1),(

π

∫∫∞+

∞−

+∞+

∞−= dydxezyxEekkA

ykxkj

ty

zkj

yxyyxtz)(

),,(2

1),(

π

),(),(),( yxy

z

y

yxx

z

xyxz kkA

k

kkkA

k

kkkA +=


In the far-field zone of the antenna ( kz >> 1), based on the method of

steepest descent, the E field can be represented by the asymptotic expansion

as long as the following relationships are maintained

),(),,( yxz

rjk

kkkr

jezyx AE

−

=

,rkr

k = ,rk=• rkr

zkk

r

ykk

r

xkk zyx === ,,

which means that k and r are in the same direction and that E(r) in the far

field can be determined by the plane wave travelling in the direction k,

rk

A•− j

yx ekk ),(



Traditional approach ignores coupling so the measurement plane

must be at a larger distance.

As scan area is reduced, truncation of the near-field will create far-

field pattern variations

Maintaining a sampling internal of λ/2 and sufficient scan area will

need many measurements


Simple Fourier transform

Easy to calculate quickly

No probe coupling

Knowledge of the probe response

Formulas: NIST Course

Traditional near-field scanning can be done at any distance but non

coupling assumptions means actually far away

Implications for planar are bad

Still requires shielded room

Passive OK but active hard

Near-Field Scanning Problems

Very-Near-Field Solution

Very-Near-Field Challenges

Coupling unavoidable so make it predictable

Static array has constant effect for each sample

Results with Ideal Data

Still have limitations of

finite planar scans

Hemispherical results

Limited angular coverage

E-theta always reduces

to zero at horizon

-40

-30

-20

-10

0

0

30

60

90

120

150

180

210

240

270

300

330

-40

-30

-20

-10

0

Erh HFSS

Elh HFSS

Erh RFX

Elh RFX

Erh Chamber

Elh Chamber

Ideal Probe Response Real Probe Response

Proper Probe Compensation

Advantages

Maximum Angular Coverage

Using 16 cm x 24 cm scan area at 2.5 cm distance

General rule of thumb: L = D + 2s tanθ


Array of probes

Addressable array of probes

makes very-near-field

sampling very fast and

repeatable

Small loops not sensitive but

very broadband, with good

isolation and polarization

specifications

Reference channel for phase

measurement of active

devices

Very-Near-Field Benefits

Visualizing interference in the near-field

– Resonance and mutual coupling


Antenna position

Loading and field perturbation


Effects of Surrounding Material

Aggregated Very-Near-Field

Multiple planar measurements combined together to provide larger

effective scan area

Multiple planar scans do not need to be co-planar

– Can used to created 3D scan surfaces or even enclosed surfaces

Aggregated Very-Near-Field

RFxpert

Real-time measurement

(<1 sec)

Compact tabletop instrument

Cost effective solution

RFX and RFX2

Hardware

Spacer

Scanner

Signal Processing

Power/USB to PC

Functionality

300 MHz to 6.0 GHz– +/- 1.5 dB accuracy in FF > 700 MHz

– TBD < 700 MHz

Far-field patterns – EIRP / TRP

– Circular and linear polarization

Near-field insights– Amplitude and phase

– Polarization

Calculates gain and efficiency

Multiple modulation formats– Cellular / Wi-Fi / WiMAX / LTE

– Bluetooth

– RFID

– GPS

Technical Specifications

Configuration

USB USB

RFxpert

EMSCAN Application

VNA or BSE

Power Meter

USB

RF

GPIB USB

Fixed Frequency Scan

Gain, efficiency, EIRP and PRAD measurements of a device under test

at a discrete frequency

Swept Frequency Scan

Gain, efficiency, EIRP and PRAD measurements across a range of

frequencies through remote control of a Network Analyzer

Circular Polarization

LHCP / RHCP / AR over a range of ±30° from the center line

Aggregate Node

Combined frequency

scanning results for full

spherical far-field view

User defined elevation for

asymmetrical devices

S11 Scan Display

S11 amplitude and phase measurements at a single frequency or

range of frequencies through the remote control of a Network

Analyzer

Very-Near-Field

Insights into design issues

User-Defined Separation

Accommodation of packaging

High gain and/or narrow band antenna

Simulation

RFxpert Validation

Simulation

Agilent EDA simulation

Toyo corporation (EMSCAN Representative)

Tokyo, Japan

June 19, 2012

3D Farfield

3GHz 4GHz 5GHz 6GHz

Farfield 2D pattern (Gain Total)

phi=0 phi=90

3GHz 4GHz

5GHz 6GHz

3GHz 4GHz

5GHz 6GHz

3cm上方磁界強度遠方界位相重みづけ

4 ブランチアンテナ

Mode3:

左右で逆相

Mode2:

上下で逆相

Mode4:

斜め同士が同相

Mode1:

4つとも同位相

mag(Hx) mag(Hy)Farfield(dBi)

EMPro RFexpertEMPro RFexpert EMPro RFexpert

Comparison with Chamber Results

RFxpert Validation

Note: Low band offset

applied by customer

Mobile Phone Efficiency

Very-Near-FieldTRP (dBm)

Figure 7: Comparison of Chamber Results (in blue) with Very-Near-Field Results obtained from

an implemented very-near-field scanning system.

Chamber vs. Very-Near-Field Scanning System (Wi-Fi 2.4GHz)

Mobile Phones TRP

Figure 8: Comparison of Chamber Results (in blue) with Very-Near-Field Results obtained from an

implemented very-near-field scanning system.

Chamber vs. Very-Near-Field Scanning System (WCDMA Band 5 &6)

Mobile Phones TRP

TRP of Various Mobile PhonesChamber

Result

(dBm)

EMSCAN

Result

(dBm)

Frequency

(MHz)

Difference

(dB)

Measurement Notes

Nokia E71x 27.52

28.44

28.75

27.56

28.40

28.81

824.7

836.5

848.3

-0.04

0.04

-0.06

CATL at ETS in Austin, TX

Nokia E71x 25.25

25.61

25.88

24.58

25.21

25.59

1930.2

1960.0

1989.8

0.67

0.40

0.29


LG-VX9200 18.58

17.06

17.79

16.35

16.91

16.73

824.7

836.5

848.3

2.23

0.15

1.06


LG-VX9200 16.91

17.50

18.21

16.03

16.81

17.61

1851.2

1880.0

1908.7

0.88

0.69

0.60


Nokia E71x 30.0

30.7

30.9

28.86

29.71

29.95

824.7

836.5

848.3

1.14

0.99

0.95

CATL in Seoul, Korea

Nokia E71x 26.67

26.75

26.05

27.02

1851.2

1880.0

0.62

-0.27

CATL in Seoul, Korea

CTIA

RFxpert

Patterns of Various Mobile Phones

Peak Gain

Test Applications

Cellular Phone

Power and pattern measurements at a single channel or a series of

channels through the remote control of a Base Station Emulator

Cellular Phone

Performance measurements with phantom head and hand

Cellular Base Station

Wi-Fi

Any customized pulse up to 60-second timeout

Smart Meters

Embedded antenna

Effects of packaging,

positioning etc.

RFID

High frequency RFID 840–960 MHz

Picture from www.instrumentel.com/

Phased Array Antenna

Phase balancing

Picture from www.mathworks.com/

GPS Antenna

Circular Polarization

MIMO

Near-field for antenna

diversity and mutual coupling

Far-field for real-time tuning

Automated Testing

DLL programming

Easy and fast pass/fail decision

– Integrated R&D test system

– Production test stations

Demonstration

Conclusion


Ability to see surface

currents

Very fast scanning

Repeatable

No chamber

Low maintenance

Easy to use

RFxpert Advantages

Interaction effects in real-time

Near-field measurements

Fast and repeatable

Low CAPEX

Zero OPEX

RFxpert Value

Improved TTM and R&D productivity

– Test time reduction > 100 x

– Rapid design iteration, prototyping &

optimization

Reduced chamber CAPEX and OPEX

– Or a tool for each designer for better

productivity

Cost effective preparation to compliance

www.emscan.com

Thank You

very-near-field solutions for far-field problems

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