ECE 495 — Electromagnetic Warfare and Survivability

Block 2: RF Electronic Warfare
Lesson 17: Electromagnetic Attack

Juan Jurado, Col, USAF, Ph.D.
Permanent Professor and Head
Electrical and Computer Engineering
Fall 2026

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Block 2 · Lesson 17 · Where We Left Off

Where We Left Off

L15–L16 were EP: protect our use of the spectrum — hide, hop, spread, survive.

Now switch sides. EA is the offense: deny the enemy their radars and links. Everything the threat did to us in ES and EP, we now turn around.

Today

The jamming toolkit, the J/S scorecard, and the range where it all unravels.

Block 2 · Lesson 17 · Objectives

Lesson Objectives

By the end of this lesson, you will be able to:

Define EA and place it against ES and EP
Classify noise jamming: spot, barrage, and swept-spot
Explain the barrage dilution penalty — coverage costs density
Compute the J/S ratio for a self-protect jammer
Explain and find the burn-through range
Distinguish self-protect from stand-off geometry — only one gets range relief

Block 2 · Lesson 17 · Part One

The Jamming Toolkit

A jammer carries a finite amount of power and one real decision: where to put it in frequency, and where to stand when it goes out. Both choices land in the same equation.

Block 2 · Lesson 17 · Electromagnetic Attack

Electromagnetic Attack: Offensive EW

EA uses EM energy to deny, degrade, or disrupt the enemy's use of the spectrum.

Jamming — raise the noise floor so real returns vanish
Deception — inject false returns so the radar believes a lie (L18)
Directed energy — burn the receiver itself (beyond our scope)

ES listens, EP shields — EA reaches out and breaks the threat's picture.

Block 2 · Lesson 17 · Cover vs Deception

Two Ways to Lie to a Radar

	Cover (noise)	Deception
Goal	Hide the real return	Create false returns
Method	Raise the noise floor	Mimic / replay the signal
Effect	Radar sees nothing clearly	Radar sees the wrong thing
Today	Yes	Preview — full treatment in L18

Noise denies information; deception corrupts it
Today is the noise half — and the math that governs it

Block 2 · Lesson 17 · Noise Jamming

Noise Jamming: Spot, Barrage, Swept

One power budget, three ways to spend it across frequency. The red area is the same in all three.

Spot

All power on one band: high density, but agility escapes it (L15)

Barrage

Whole band at once: jam-proof to hopping, but power per Hz drops

Swept-spot

Sweep a spot across the band: trades dwell time for coverage

Block 2 · Lesson 17 · Jamming Geometry

Where the Jammer Sits

Self-protect (SPJ) — jammer rides the target it defends
Stand-off (SOJ) — a dedicated platform jams from safe range
Escort / stand-in — jam from alongside or from deep inside the threat ring

Geometry sets the range $R$ in the J/S equation — and who is at risk.

Block 2 · Lesson 17 · Part Two

The Scorecard and Its Limit

One ratio says whether the jamming is working. Its range exponent says the advantage cannot last — and hands the radar a number to fly toward.

Block 2 · Lesson 17 · J/S Ratio

J/S: The Jamming Scorecard

J/S is the effective jamming power in the receiver passband over the signal power. For a self-protect jammer:

Self-protect jam-to-signal ratio

\[ \frac{J}{S} = \frac{4\pi\,P_j G_j\,R^{2}}{P_t G_t\,\sigma}\cdot\frac{B_r}{B_j} \]

Skin echo $S \sim 1/R^4$; jammer (one-way) $J \sim 1/R^2$ — so $J/S \sim R^2$
Above $\sim\!10$ dB jamming dominates — but can trip the radar's anti-jam modes
$B_r/B_j = 1$ for a spot matched to the passband, $< 1$ for barrage — the dilution penalty

Block 2 · Lesson 17 · Why $R^2$

Where the Exponent Comes From

The skin echo makes a round trip — out to the target and back:

\[ S \sim \frac{1}{R^{4}} \]

The jammer rides the target and transmits one way:

\[ J \sim \frac{1}{R^{2}} \]

Take the ratio — four powers of range recovered against two:

\[ \frac{J}{S} \sim \frac{1/R^{2}}{1/R^{4}} = R^{2} \]

Same one-way/two-way asymmetry that gives the listener its advantage in ES (L11) — here it sets the limit of jamming instead.

Block 2 · Lesson 17 · Burn-Through

Burn-Through Range

Because $J/S \sim R^2$, the jammer wins far out and loses as the target closes.

The curve is the real thing: $J/S(\text{dB}) = K + 20\log_{10} R$
Every doubling of range is worth $+6$ dB to the jammer

Somewhere on the way in the echo overtakes the jam. Where?

Block 2 · Lesson 17 · Burn-Through

Burn-Through Range

R_bt = 9.97 km

Inside $R_{bt}$ the radar burns through and re-detects
Falling J/S also strips advanced ECM (range-gate pull-off, deception)
Modern pulse-Doppler tolerates J/S up to $\sim\!+10$ dB

Burn-through range 9.97 km

Set the threshold where the radar actually gives up and the marker slides with it.

Block 2 · Lesson 17 · Burn-Through

Now Halve the RCS

R_bt = 7.05 km

$\sigma$ sits in the denominator. Halve it and the whole curve lifts $3$ dB — J/S improves at every range.

The burn-through bubble shrinks: $9.97$ km becomes $7.05$ km
Lower RCS pulls $R_{bt}$ inward — LO and jamming reinforce each other

Burn-through range 7.05 km

Today's Interactive Demo: Jammer J/S Explorer

Companion script: L17_JtoSBurnThrough.m
In L18 we stop shouting and start lying — DRFM deception

Live demo

Jammer J/S Explorer

usafa-ece.github.io/ece-495-ew

Demo hand-off; drive it from here. Read the curve first: J/S in dB rises with range, the dashed red line is the radar's tolerable threshold, and the vertical marker where they meet is the burn-through range. Slide the range cursor across that marker and watch the verdict flip from jammer effective to radar burns through. Then cut the RCS slider: the whole curve lifts and the marker walks inward. Raise the jammer power for the same effect from the other side of the equation. The threshold slider is the interesting one — set it to plus ten and ask what just happened to the burn-through range. Log range axis straightens the curve into the line its equation says it is. Companion script runs on their own.

Block 2 · Lesson 17 · Quick Exercise

Quick Exercise / Type-along: Find Burn-Through

Type this with me — the radar and jammer from today's demo.

Pt = 1e6; Gt = 1e4;        % threat radar: 1 MW, 40 dBi
Pj = 40;   Gj = 1;         % self-protect jammer: 40 W, 0 dBi
sigma = 5;                 % target RCS, m^2
R   = [5 10 20 40]*1e3;    % range to the radar, m
JS  = 4*pi*Pj*Gj*R.^2 ./ (Pt*Gt*sigma);  % spot: Br/Bj = 1
Rbt = sqrt(Pt*Gt*sigma/(4*pi*Pj*Gj));
fprintf('   R(km)   J/S(dB)\n');
fprintf('%8.0f %9.2f\n', [R/1e3; 10*log10(JS)]);
fprintf('\nR_bt = %.2f km  (J/S = 0 dB)\n', Rbt/1e3);
fprintf('half the RCS -> R_bt = %.2f km\n', ...
        sqrt(Pt*Gt*(sigma/2)/(4*pi*Pj*Gj))/1e3);

Each doubling of range adds the same number of dB. What number, and where does it come from?

Then: halving the RCS moved R_bt inward. Why is that good news for the jammer?

Block 2 · Lesson 17 · Quick Problem

Quick Problem: Barrage Jammer Scorecard

The threat radar from today's type-along, now facing a barrage self-protect jammer on a smaller target.

Radar: $P_t = 1$ MW, $G_t = 10^4$ (40 dBi)
Receiver bandwidth $B_r = 5$ MHz
Jammer: $P_j = 500$ W, $G_j = 10$ (10 dBi)
Barrage bandwidth $B_j = 500$ MHz
Target RCS $\sigma = 2$ m², range $R = 30$ km
Radar holds track up to $J/S = +10$ dB

(a) $J/S$ in dB at 30 km.
(b) The burn-through range at $J/S = +10$ dB.
(c) The jammer narrows to spot ($B_j = B_r$): the new $J/S$ at 30 km.

(a) $J/S = +14.5$ dB · (b) $R_{bt} = 17.8$ km · (c) $J/S = +34.5$ dB

Two to three minutes, calculators or a MATLAB console; then click. Worked path for (a), as a dB ladder on the reading's equation: 4 pi is +11.0, the jammer's 5000 W of ERP is +37.0, R squared at 30 km is +89.5, the radar's 10 to the tenth comes off as -100.0, the 2 square metre RCS as -3.0, and the barrage factor of one-hundredth as -20.0. That sums to +14.5 dB, a linear 28.3 — 4.5 dB past the radar's tolerance, so the track is lost. For (b), set J/S to 10 and solve for R; faster, since J/S goes as R squared, 30 km times the root of 10 over 28.3 is 17.8 km. For (c), spot recovers the whole 20 dB barrage penalty, so +34.5 dB — which is exactly why the jammer barrages only when it must: it does not know which frequency the radar is on. Close on the threshold: at 0 dB these same numbers give 5.6 km, so the +10 dB tolerance moves burn-through out by root ten, from 5.6 to 17.8 km.

Block 2 · Lesson 17 · Wrap-Up

Wrap-Up

Key ideas

EA denies, degrades, or disrupts the enemy's spectrum
Noise jamming comes as spot, barrage, or swept-spot
Self-protect J/S grows as $R^2$ — the jammer's edge fades as you close
Burn-through is where the radar wins back the target

Next lesson

L18: Active deception — DRFM, false-target injection, towed decoys
Work the L18 pre-flight before class — you could be the one up front