electromagnetic interference

Done by العجلة خليل عمادالعجلة خليل عالء

Instructorعودة. محمد د

Electromagnetic interference

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Outline Source and victimEmissionsImmunityCauses of internal radar interferenceExternal radar interference EMC design

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Interference coupling mechanisms

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Interference coupling mechanisms

coupling path

Direct coupling

Radiated coupling

Near field coupling

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source

victim

coupling path

1. Direct coupling

Coupling via power or

signal lines

Common impedance

coupling

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1. Direct coupling Coupling via

power or signal lines

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1. Direct coupling Common

impedance coupling

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coupling path

2. Near field coupling

Magnetic or inductive coupling

Electric or capacitive coupling

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2. Near field coupling

Magnetic or inductive coupling

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2. Near field coupling

Electric or capacitive coupling

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2. Near field couplingSpacing

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coupling path

3. Radiated coupling

Wave impedance

Field generation

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coupling path

4. Coupling modes

Antenna mode

Common mode

Differential mode

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Coupling modes

Differential mode

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Coupling modesCommon

mode

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Coupling modesAntenna

mode

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Interference coupling mechanisms

Emissions

Radiated emission

Conducted emission

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Emissions

Radiation from the PCB

Radiated emission

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Emissions

Radiation from cables

Radiated emission

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Interference coupling mechanisms

Immunity

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Causes of internal radar interference

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Standards used : MIL-HDBK-237

What is jamming [2]

jamming is a form of Electronic Warfare where jammers radiate interfering signals toward an enemy's radar, blocking the receiver with highly concentrated energy signals

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jammers can be categorized into two general types: 1- barrage jammers2- deceptive jammers (repeaters).

Barrage jammers attempt to increase the noise level across the entire radar operating bandwidth.

Barrage jammers are often called maskersBarrage jammers can be deployed in the main

beam or in the side lobes of the radar antenna

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Repeater jammers carry receiving devices on board in order to analyze the radar’s transmission, and then send back false target-like signals in order to confuse the radar

There are two common types of repeater jammers: 1- spot noise repeaters2- deceptive repeaters

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Spot and Barrage Jamming

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Self-Screening Jammers (SSJ) [2]

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Self-Screening Jammers (SSJ) The single pulse power received by the radar from a

target of RCS , at range , is

The power received by the radar from an SSJ jammer at the same range is

BJ > Br jammer bandwidth is usually larger than the operating bandwidth of the radar.

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S/J ratio for a SSJ

The jamming power is generally greater than the target signal power.

The ratio s/j is less than unity.

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As the target becomes closer to the radar, there will be a certain range such that the ratio s/j is equal to unity.

This range is known as the cross-over range. The range window where the ratio S ⁄j is sufficiently

larger than unity is denoted as the detection range.

In order to compute the crossover range

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For a radar with a detection range of 100 km for an RCS of 5m2, [3]

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This program calculates the cross-over range and generates plots of relative S and J versus range normalized to the cross-over range

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Wave length in dB

Conversion to db

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By matlab

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Stand-Off Jammers (SOJ)

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Stand-Off Jammers (SOJ)ECM signals from long ranges.The power received by the radar from an SOJ

jammer at range RJ is

The gain term G’ represents the radar antenna gain in the direction of the jammer

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The inputs to the program ‘soj_req.m’ are the same as in the SSJ case , with jammer peak power Pj = 5000w , jammer antenna gain Gj =30 dB, radar antenna gain on the jammer G’ =10dB, and radar to jammer range R= 22.2 Km

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EMC design

There are many design considerations that need to be takenCable wiringConnectorsGroundingShielding

The reference for good consideration is standard

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What is FEKO program?

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Cable coupling analyses

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Cable coupling analyses The result

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EMC analysis of a wire inside a metallic box

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Cont.

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Reference [1] H.-D. Brüns, H. Singer, “Computation of Interference in

Cables Close to Metal Surfaces,” IEEE Int. Symposium on EMC, Denver, 1998, pp 981-986

[2] CRC Press - MATLAB Simulations for Radar Systems Design

[3] Air and Space borne Radar Systems - An Introduction [4] Intro duction to airborne radar second edition George

W. stimson [5] Tim Williams, EMC for Product Designers, Fourth edition [6] CLAYTON R. PAUL, Introduction to Electromagnetic

Compatibility, Second Edition [7] Frank H. Sanders Effects of RF Interference on Radar

Receivers [8] EMI from Cavity Modes of Shielding Enclosures – FDTD

Modelling and Measurements,” M. Li, J. Nuebel et al, IEEE Trans on EMC, Vol. 42, No. 1, February 2000, pp. 29-38.46