1

Practical RF Immunity System

Design Considerations

CONDUCTED RF EQUIPMENT POWER AMPLIFIERS

Designing a System

• Key considerations are the amplifier and antenna

combination

• Determining what Power Amplifier to select depends on

– The test level required by the standard

– The type of modulation required

– The antenna efficiency (Gain)

– The test environment

– Cable and other component losses

2

Usable Amplifier Power • Saturated Power (Psat) Vs Linear Power (P1dB)

• Definitions

– Psat – Highest power that the amplifier can generate

– P1dB – Highest power where Pin Vs Pout curve is considered to

be straight

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4

Modulation

CONDUCTED RF EQUIPMENT POWER AMPLIFIERS

80% AM

CW AM (80%)

1 kHz

80% higher peak

Effect of Saturation on Modulation

CW Input

Level

required for

10V/m

Modulation

CW Input

Level

required for

10V/m

Modulation

O/P Modulation

Matches the Input

O/P Modulation

does not Match

the Input

Requirement of IEC 61000-4-3

CW Input

Level

required for

18V/m

5.1dB Reduction

>3.1dB

Reduction

Requirement of IEC 61000-4-6

CW Input

Level

required for

10Vemf

5.1dB Increase

3.1 to 7.1dB

Increase

Potential Change to IEC 61000-4-3

CW Input

Level

required for

10Vemf

5.1dB Increase

3.1 to 7.1dB

Increase

CW Input

Level

required

for 18V/m

5.1dB Reduction

>3.1dB

Reduction

Pulse Modulation

CW (unmodulated signal) Pulse Modulation

Pulse

Duration

Period

Effect of Saturation on Modulation

CW Input

Level

required for

200V/m

Modulation

O/P Modulation

Matches the Input

Pulse

Harmonics

Unwanted signals produced at multiples of the required fundamental frequency

Broadband, power and field measuring devices cannot distinguish between the

fundamental and harmonics

Under testing possible

False failures can be caused

It may appear that an DUT has a problem at a frequency but it could be that

the problem is at the harmonic frequency

User may waste time and money on an incorrect fix

Most antenna have better gain at higher frequencies

This can magnify the level of the harmonic compared to the fundamental

What Happens to the Harmonics at and

above P1dB

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 2 3 4 5 6 7 8 9 10 11 12 13

Rela

tiv

e L

ev

el

Harmonic Number

Harmonics of a Square Wave

Harmonic Distortion

f1 3 x f1

Antenna Gain

Frequency

IEC 61000-4-3 requires that the level of the harmonics measured at

the uniform plane is at least 6dB less than the fundamental signal

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Conducted RF Immunity

CONDUCTED RF EQUIPMENT POWER AMPLIFIERS

Coupling devices

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CDN M CDN A CDN S CDN T

Current injection probe

EM clamp Attenuation clamp

(decoupling only)

Calibration adapters

Coupling Devices

• CDN

– Good Decoupling performance

• Majority of the injected signal goes towards the DUT

• Very little signal goes back to the mains or AE

– Most efficient Device

• Least power required from the amplifier

– Needs to be inserted in the cable

• May not always be convenient

• Can affect normal operation of the DUT

Testing with Coupling Devices other than a CDN

• EM Clamp

– Like a CDN have good Decoupling performance

• Majority of the injected signal goes towards the DUT

• Very little signal goes back to the mains or AE

– Not as efficient as a CDN

• Requires more power from the amplifier

– Physically larger than a CDN

• May not always be convenient

– Clamp on device

• Does not require cable under test to be broken

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Testing with Coupling Devices other than a CDN

• BCI Clamp

– No Decoupling performance

• Injected signal goes in both directions

• Same signal goes to the mains or AE

– Not as efficient as a CDN or EM Clamp

• Requires more power from the amplifier

– Clamp on device

• Does not require cable under test to be broken

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Example

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Example

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Bulk Current Injection (BCI)

Power required depends on the test level and the selected BCI Probe

Power = I2 * 50 plus the Insertion loss of the probe

Testing with Coupling Devices other than a CDN

• Both devices have a low source impedance

• Not 150 Ω

• Although the calibration procedure is the same

• Attempt to achieve target level at output of the calibration jig

• When connected to a DUT with low common mode impedance much higher currents

can be induced compared to a CDN

• User is required to monitor the RF current on the cable under test and limit it to the

maximum level possible from a CDN

• Imax = U0/150

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150 Ω

Vemf

I = Vemf /150

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Radiated RF Immunity

CONDUCTED RF EQUIPMENT POWER AMPLIFIERS

Radiated Immunity Power required depends on the test level and the selected antenna

Trade of between efficiency and size

Larger antenna are more efficient, if they will fit in the chamber

Basic Radiated Field/Power Calculation

Power required to generate a field of E V/m

at a distance d metres from the antenna

Power (watts) = (E2 * d2) /( 30 * g)

g = 10 (G/10) {g = ratio gain, G = gain (dBi) }

Additional Factors to be included

Chamber variation

No chamber is perfectly uniform

The ‘so called’ uniform area can have variation up to 6dB

Potentially you could require 6dB more power = 4 times more

Additional Factors to be included

Modulation

80% Sinusoidal Amplitude Modulation (AM)

Requires 1.82 (= 3.24) times the power or +5.1dB

Pulse Modulation (Pulse) and Frequency Modulation (FM)

Requires no additional power

0

5

10

15

20

25

30

0 1000 2000 3000 4000 5000 6000T

est F

ield

V/m

Frequency MHz

Radiated System (80MHz to 6GHz)

Chamber1

C

1

2

3

4

Switch1

-

ITS6006

Coupler1

Coupler2

Coupler3

C

1

2

Switch2

-

ITS6006 or External Switch

SigGen1

(none) -

ITS6006

Amp1

(none) -

80RF1000-500 or -10000

Amp2

(none) -

AS 0825-300 or -500

Amp3

(none) -

AS1860-50

Antenna1

STLP 9128E

Antenna2

STLP 9149

PowerMeter1

(none) -

PM6006

PowerMeter2

(none) -

PM6006

PowerMeter3

(none) -

PM6006

StressSensor1

0

5

10

15

20

25

30

0 1000 2000 3000 4000 5000 6000

Test

Fie

ld V

/m

Frequency MHz

Radiated System (80MHz to 6GHz)

Chamber1

C

1

2

3

4

Switch1

-

ITS6006

Coupler1

Coupler2

Coupler3

C

1

2

Switch2

-

ITS6006 or External Switch

C

1

2

3

Switch3

SigGen1

(none) -

ITS6006

Amp1

(none) -

80RF1000-500 or -10000

Amp2

(none) -

AS 0825-300 or -500

Amp3

(none) -

AS1860-50

Antenna1

STLP 9128E

Antenna2

3161-1

PowerMeter1

(none) -

PM6006

PowerMeter2

(none) -

PM6006

PowerMeter3

(none) -

PM6006

StressSensor1

Antenna3

3161-2

Antenna4

3161-3

Radiated System (80MHz to 6GHz)

Loss in Cables and components

Test Rack to Antenna

1.5m rack to penetration (Loss 0.25 dB @ 1GHz)

5m penetration to floor panel (underfloor cable) (Loss 0.8 dB @ 1GHz)

3m floor panel to antenna (Loss 0.5 dB @ 1GHz)

Internal to rack

0.4m RF switch output – rack bulkhead (Loss 0.1 dB @ 1GHz)

0.4m Directional Coupler output – RF switch input (Loss 0.1 dB @ 1GHz)

Werlatone C5982 Directional Coupler (Loss 0.1 dB @1GHz)

RF Switch – 2 Way N type (Loss 0.1 dB @ 1 GHz)

TOTAL LOSS 1.95 dB @ 1 GHz

Would be lower at 80MHz but much higher at 3GHz

Typical example

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Frequency Loss Chamber AM Power

MHz dB dB Watts

80 2 3 494.5

85 2 3 492.2

90 2 3 489.9

95 2 3 482.2

100 2 3 468.9

110 2 3 430.6

120 2 3 368.1

130 2 3 422.9

140 2 3 391.1

150 2 3 333.4

160 2 3 298.8

170 2 3 313.4

180 2 3 310.4

190 2 3 303.6

200 2 3 310.4

220 2 3 309.1

240 2 3 344.5

260 2 3 374.3

280 2 3 340.6

300 2 3 336

350 2 3 320.2

400 2 3 348.3

500 2 3 307.2

600 2 3 339

700 2 3 335.1

800 2 3 316.3

900 2 3 350.9

1000 2 3 339

5dB

Frequency Loss Chamber AM Power

MHz dB dB Watts

80 2 4 622.5

85 2 4 619.5

90 2 4 616.6

95 2 4 606.9

100 2 4 590.4

110 2 4 542.1

120 2 4 463.7

130 2 4 532.1

140 2 4 492.2

150 2 4 420

160 2 4 375.9

170 2 4 394.7

180 2 4 391.1

190 2 4 382

200 2 4 391.1

220 2 4 389.2

240 2 4 433.6

260 2 4 471.1

280 2 4 428.7

300 2 4 422.9

350 2 4 402.8

400 2 4 438.7

500 2 4 386.6

600 2 4 426.8

700 2 4 421.9

800 2 4 398.2

900 2 4 441.7

1000 2 4 426.8

Frequency Loss Chamber AM Power

MHz dB dB Watts

80 2 5 783.5

85 2 5 779.9

90 2 5 776.4

95 2 5 764

100 2 5 743

110 2 5 682.4

120 2 5 583.6

130 2 5 670.1

140 2 5 619.5

150 2 5 528.5

160 2 5 473.4

170 2 5 496.7

180 2 5 492.2

190 2 5 480.9

200 2 5 492.2

220 2 5 489.9

240 2 5 546

260 2 5 593

280 2 5 539.5

300 2 5 532.1

350 2 5 507.1

400 2 5 552.1

500 2 5 486.4

600 2 5 537.2

700 2 5 531.1

800 2 5 501.3

900 2 5 556

1000 2 5 537.2

7dB 6dB

Summary

• In order to accurately design a system the following

information is required:

– Required Frequency range and Field level

– Modulation type

– Chamber dimensions

– Chamber performance

– Cable routing, lengths

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Thank You for your Attention

CONDUCTED RF EQUIPMENT POWER AMPLIFIERS