ICTA Draft Amended In-Situ Measurement Protocol

Jerome LOUIS CEng MIET RPEM

Contents

•

What is an In-Situ Measurement Protocol•

History of ICTA In-Situ Measurement Protocol

•

Proposed Changes to the Protocol•

Organisation of Amended Protocol

•

General Process•

Description of Protocol

What is an In-Situ Measurement Protocol?

•

An In-Situ measurement protocol describes methods to effect measurements where the instrumentation is located directly at the point of interest

Why an In-Situ Measurement Protocol?

•

Effecting measurements in accordance with a defined protocol standardizes the measurement and enables the measurement to be repeated by anyone who follows the protocol

History of the ICTA In-situ Measurement Protocol

• The protocol was released on 30 April 2009

• The objective of the protocol is for the determination of RF fields for the frequency band 300 MHz –

6 GHz

in the vicinity of RBS for the purpose of determining general public exposure to these fields

• The protocol covers only frequency selective measurement methods based mainly on:-

– The Electronic Communications Committee (ECC) Recommedation

(02)04 on “Measuring Non-Ionising

Electromagnetic Radiation (9kHz – 300 GHz)”;–

The International Electrotechnical

Commission, IEC

Standard 62232 on “Determination of RF fields and SAR in the vicinity of radio communication base stations for the purpose of evaluating human exposure”

History of the ICTA In-situ Measurement Protocol (Cont’d)

•

Frequency selective methods are relatively complex, time consuming and utilizes equipment that is cumbersome

•

Whereas frequency selective methods have a number of advantages, they are not always necessary and may be substituted by broadband methods which are less complex and use lighter equipment

•

For this reason, an amended version of the In-situ protocol has been prepared

Proposed changes to protocol•

Increasing applicable frequency range from 300 MHz -

6 GHz to 80 MHz –

8 GHz

•

Extending the scope of protocol to include slef- conformity assessment of radio infrastructures by

operators•

Addition of procedures for broadband measurement

•

Addition of frequency selective procedures for Analogue television Broadcasting, DVB-T and FM Radio

Organization of Amended Protocol

Exposure Limits –

Basic Restritions (based on Thermal Effects)

•

The transfer of energy from electric and magnetic fields to charged particles in an absorber is described in terms of the specific absorption rate (SAR)

•

SAR is defined as the time rate at which energy is deposited in any kind of material per unit mass; i.e. the power absorbed by the tissue per unit mass

•

SAR is the parameter employed to quantify the electromagnetic absorption inside biological tissues like the human body and can be seen as the velocity at which the human body absorbs the electromagnetic energy

mass lincrementaan is dm andenergy lincrementa theisdW where)/(dmdW

dtdkgWSAR =

Exposure Limits –

Basic Restritions (cont’d)

•

Restrictions on the effects of exposure are based on established health effects are termed basic restrictions

•

Depending on frequency, the physical quantities used to specify the basic restrictions on exposure to EMF are current density, SAR and power density

•

Protection against adverse health effects requires that these basic restrictions are not exceeded

Exposure Limits –

ICNIRP Basic Restrictions

•

International Commission on Non-Ionizing Radiation Protection

•

Body of independent scientific experts•

Non-profit making organization

•

No income from industry•

ICNIRP 1998 “Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields (up to 300 GHz)”, Health Physics, April 1998, vol. 74 no. 4, pp. 494-522

Exposure Limits –

ICNIRP Basic Restrictions

•

Established biological and health effects in the frequency range from 10MHz to a few GHz are consistent with responses to a body temperature rise of more than 1°C

•

This level of temperature increase results from exposure of individuals under moderate environmental conditions to a whole-body SAR of about 4 W/kg for about 30 min

•

Safety factor of 50 for general public: whole body SAR limit of 0.08 W/kg

•

Higher values for localized SAR:–

Head/trunk: 2W/kg, limb: 4W/kg

–

Averaged over 10g contiguous tissue

4. ICNIRP Basic Limits for General Public

Exposure Limits –

ICNIRP Reference Levels

•

SAR is complicated to measure on the field•

ICNIRP defines also “reference values”

which are

field values outside the body:–

Electric/magnetic field strength

–

Power density•

Reference levels are computed from basic restrictions for maximal coupling of fields into the body–

Compliance with reference levels ensures compliance with basic restrictions

–

Special testing of SAR required when reference levels are exceeded

5. ICNIRP Reference levels for General Public

6. General Process

Site Analysis and Source Determination

•

Ambient fields need not be evaluated in the following cases:-–

When the requirement is to establish only exposure from a particular Radio communication Base Station (RBS) RF fields;

–

When the critical exposure condition from the RBS is localized specific absorption rate (SAR). For example a microcell

with localized exposure. E.g. a person standing in close proximity to the antenna;

–

For situations where the antennas are operating above 6 GHz, (which are typically point to point sources) and the evaluation locations are beyond the main beam.

Measurement Quantity Determination: Near and far fields

•

Far-field:–

Region where the field has a predominantly plane-wave character i.e. locally uniform distribution of electric field strength and magnetic field strength in planes transverse to the direction of propagation

•

Near-field:–

Exists in proximity to an antenna–

The electric and magnetic fields do not have a substantially plane wave character but vary considerably from point-to-point

–

Far-field antenna gain over-estimated

Ω==

===

=

=

377space free of impedence intrinsic theis

Wmdensity flux Power

A/mHStrength Field Magnetic

V/m Strength Field Electric

0

02

0

22-

0

0

HE

HEEHS

EHE

η

ηη

η

η

Measurement Quantity Determination: Near and far fields

Reactive near-field region

Radiating near- field region

Far-field region

Lateral edge of the region, measured from antenna

0 to λ λ

to λ+2D2/λ λ+2D2/λ

to ∞

E ⊥

H No Quite

Yes Yes

Z = E / H ≠

Zo ≈

Zo = Zo

Component to be

measured

E & H E or H E or H

Broadband Measurement System•

Broadband measurements can give the instantaneous sum of the field in the measurement band of the probe and is adequate in monitoring the RF field and may be helpful in determining if a more comprehensive assessment using the Frequency Selective method is required.

Broadband Measurement System•

Correction Factor (CF) –

For each measurement,

the input power to the test facility is adjusted so that the actual field strength is set to a specific value. The field strength indicated by the probe under calibration is then read and the correction factor calculated using the following definition

•

The indicated filed strength must be multiplied by the appropriate correction factor to give the actual field strength

Broadband Measurement System

•

Linearity –

calculated as the variation of the Correction factor as a function of the field strength applied to the probe for a frequency value

•

Frequency response – calculated as the variation of the Correction Factor as a function of the frequency for a fixed field value applied to the probe

Requirements for Broadband Measuring Equipment (EN50492)

FrequencyResponse

MinimumDetectionlimit

Dynamicrange

Linearity Isotropy

Below 900MHz andabove 3GHz

±

3 dB ≤2mW/m²(i.e. 1V/m or

0.003 A/m)

≥40dB ±

1.5 dB <2dBEvaluatedfor completeMeasurementsystem

Between900 MHzand 3 GHz

±

1.5 dB

Measurement System for Frequency Selective Measurement

•

This technique employs spectrum analysis or channel decoding to isolate and identify RBS source and ambient frequencies.

Calibrated log-per antenna

Calibrated coaxial cable

Calibrated Spectrum Analyzer

Measurement System for Frequency Selective Measurement

•

The method is used:–

To discriminate signals from different sources

–

When ambient fields are comparable to, or may exceed, the level of the RBS source;

–

When information is needed to enable extrapolation for the purpose of demonstrating compliance with a limit or exceedance

of a limit;

–

For measurements in low field strength environments (e.g. public areas) where the higher sensitivity of spectrum analysers/receivers compared with broadband probes makes this method especially suitable.

Presentation of Results (Broadband Measurement)

PROBE(type and reference)

VALUE Used correction

factor

RESULT UNIT START TIME

STOP TIME

DATE

V/m hh

: mm

: ss

hh

: mm

: ssdd-mm-

yyyy

A/m

Presentation of Results (Frequency Selective)

•

Where,•

Column 1: System is the type of system such as GSM, UMTS etc…•

Column 2: Freq (MHz) is the frequency measured;•

Column 4: Pmeas

(dBm) is the measured signal level;•

Column 5: Lcable

(dB) is the cable losses available from calibration report;•

Column 6: Kant (dB/m) is the antenna factor available from manufacturer’s information;•

Column 7: E (dBV/m) is the field strength measured, E(dBV/m) = Pmeas(dBm) –

13 + Lcable

(dB) + Kantenna

(dB/m);

•

Column 8: U (dB) is the expanded uncertainty;•

Column 9: Ecorr

(dBV/m) = E (dBV/m) + U (dB)•

Column 10: Ecorr

(V/m) is the field strength in V/m, ;•

Column 11: β

is the extrapolation factor, for example in GSM where is the number of Transmit channels (TRX) and for WCDMA

•

Column 12: Eeff

(V/m) is the effective field strength which is the worst case field strength derived after extrapolation, Eeff

(V/m) = Ecorr

×

β

;•

Column 13: ICNIRP Ref level (V/m) is the ICNIRP reference level for general public exposure at the frequency Freq (MHz)

•

Column 14: % ICNIRP is (Eeff/ICNIRPRef

level) x 100%•

Column 15: S(W/m2) is power density •

Column

16:

Sguid(W/m2)

is

the

ICNIRP

reference

level

power

density

Measurement Uncertainty -

Basics

•

Uncertainty of measurement is the doubt that exists about the result of any measurement

•

For every measurement-even the most careful- there is always a margin of doubt

•

Quantifying the margin of doubt is made through the width of the margin or interval and the confidence level which states that the ‘true value’

is within that margin

•

E.g. 20cm ±1 cm, at a level of confidence of 95%

Measurement Uncertainty (Broadband Measurement)

Measurement Uncertainty (Frequency Selective Measurement)

Sample of Report

•

Measurement Report sample.pdf

THANK YOU FOR YOUR KIND ATTENTION

QUESTION TIME