Done by لة ج ع ل ل ا ي ل خ ماد ع لة ج ع ل ل ا ي ل خ لاء عInstructor ودة ع مد ح م د.Electromagnetic interference 1
Jan 28, 2016
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