Consideration of Electromagnetic Effects in Aircraft Design Thomas Jerse Department of Electrical and Computer Engineering Sigma Xi Brownbag Presentation.

Consideration of Electromagnetic Effects in Aircraft Design

Thomas JerseDepartment of Electrical and Computer Engineering

Sigma Xi Brownbag Presentation10/17/08

Electromagnetic Environmental Effects

• Safety of flight

• Radiation Hazards

• Cosite interference

E3

Who Makes the Rules?

• FAA– DO-160

• JAA

• Department of Defense– MIL-STD-461E– MIL-STD-464A

Safety of Flight

• Power Systems– Fly-by-wire controls

• 3x or 4x redundancy

• Air Traffic Control (ATC) radios

• Navigation Systems

Response to External Field

AIRBORNE

HIRF Testing

HIRF Limits

Fre

quen

cy B

and

Pea

k F

ield

(V

/m)

Avg

Fie

ld (

V/m

)

10 kHz-100 MHz 50 50100 kHz-500 kHz 60 60

500 kHz-2 MHz 70 702-30 MHz 200 200

30-100 MHz 30 30100-200 MHz 90 30200-400 MHz 70 70400-700 MHz 730 80

700-1000 MHz 1400 2401-2 GHz 3300 1602-4 GHz 4500 4904-6 GHz 7200 3006-8 GHz 1100 170

8-12 GHz 2600 33012-18 GHz 2000 33018-40 GHz 1000 420

FIXEDWINGAIRCRAFT

Response to External Field

ON THE TARMAC

Radiation Hazards

• Personnel (RADHAZ)

• Fuel (HERF)

• Ordinance (HERO)

Hazard to Personnel

• 10 W/m2 maximum averaged over a 6 minute period

• Corresponds to 61.4 Vrms/m

Flight Deck Hazard

E-Field Map

USS Forrestal

USS Forrestal

USS Forrestal

162 SAILORS PERISHED

Electromagnetic Environmental Effects

• Safety of flight

• Radiation Hazards

• Cosite interference

E3

US AWACS

Co-Site Interference Analysis

Tx

Rx

H

H

Output PowerHarmonicsSpurious OutputsSignal Spectrum

Sensitivity

Image

Subharmonics

OBRTRR

Intermods

CouplingPath LossReflectionDiffraction

GainPattern

FiltersMulticouplers

Isolators

Broadband Noise

Tuning Range

Tuning Range

IF Feedthrough

Passband Shape

Cable Loss

Polarization SIR

A Gigantic Spreadsheet Problem

• NTx = number of transmitters

• NRx = number of receivers

• Nb = number transceivers

RxTxb

bRxTxnscombinatio NNN

NNNN

22

SINGLE-TONE ANALYSIS

A Gigantic Spreadsheet Problem

• NTx = number of transmitters (8)

• NRx = number of receivers (16)

• Nb = number transceivers (12)

RxTxb

bRxTxnscombinatio NNN

NNNN

22 (548)

SINGLE-TONE ANALYSIS

Linear Analysis

MSIRSP RxRx

RxCRxCTxTxTxRx HLCLHPP

PTx Tx POWER HTx Tx FILTER RESPONSE LCTx Tx CABLE LOSS C COUPLING LCRx Rx CABLE LOSS HRx Rx FILTER RESPONSE SRx Rx SENSITIVITY (MDS) SIR SIGNAL TO INTERFERENCE RATIO M MARGIN

Friis Equation

FAR-FIELD

C = COUPLING IN dB

R = SEPARATION DISTANCE = WAVELENGTH

G = ANTENNA GAIN

POLRxTxt

r LGGRP

PC

4log20 10

L = CROSS-POLARIZATION LOSSPOL

Antennas

• Antenna gain is directional

1010 2020

EXAMPLE ANTENNA PATTERN

Field from Isotropic Source

Reflections

SOURCE

SE

Diffraction and Reflection

SOURCE

SE

Modified Friis Equation

FAR-FIELD

C = COUPLING IN dB

R = SEPARATION DISTANCE = WAVELENGTH

G = ANTENNA GAIN

L = CROSS-POLARIZATION LOSSPOL

SE = SHIELDING EFFECTIVENESS

SELGGRP

PC POLRxTx

t

r

4log20 10

Nonlinear Effects

• Harmonic distortion

• Intermodulation distortion

• Gain Compression

Harmonic Distortion

• All transmitters generate harmonics.

• Harmonics can also be generated from a single tone applied to the receiver input circuitry.

f0 2f0 3f0 4f0

Intermodulation Distortion (IMD)

• Two transmitters, one receiver

f = f1-f2

FREQUENCY

f 1 f 2

2f -

f1

2

2f -

f2

1

3f -

2f1

2

4f -

3f1

2

3f -

2f2

1

4f -

3f2

1

Weierstrass Approximation Theorem

Third-Order IMD Example

Rx

Tx 1

Tx 2

f = 280 MHz

f = 284 MHz

f = 288 MHz

f = 276 MHzOR

Two-Tone Combinations

• NTx = number of transmitters

• NRx = number of receivers

• Nb = number transceivers

bTxbb

TxbRx

Txbnscombinatio NNNN

NNN

NNN 1

233

2

Two-Tone Combinations

• NTx = number of transmitters (8)

• NRx = number of receivers (16)

• Nb = number transceivers (12)

bTxbb

TxbRx

Txbnscombinatio NNNN

NNN

NNN 1

233

2

(5092)

Re-Radiated IMD

Tx1

Tx2

Rx1

Rx2

Cross Modulation

• Modulation from one signal is transferred onto another

Rx

Tx 1

Tx 2

MOST SEVERE ON AM SIGNALS

Cosite Interference Mitigation Options

• Coupling reduction• Filtering• Tuning rules• Blanking• Statistical Characterization• Active cancellation

Coupling Reduction

• Separation increase• Absorber• Cross polarization

Filtering

TxPOSTSELECTOR

RxPRESELECTOR

Active Cancellation

Tx

Rx

COUPLER

AMPLITUDE &PHASE ADJUST

+

Accuracy Required

150 160 170 180 190 200 210-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

PHASE IN DEGREES

AM

PLI

TU

DE

IN

dB

-10

-15 -10 -15 -20

-25

-30

-40

CONTOURS OFCANCELLATION

IN dB

Summary

• E3 analysis is a significant portion of modern aircraft development.

• Interference from both internal and external sources must be considered for safety of flight.

• A thorough cosite interference analysis requires the evaluation of a large number of combinations.