ECE 495 — Electromagnetic Warfare and Survivability

Block 2: RF Electronic Warfare
Lesson 15: Electromagnetic Protect

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

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Block 2 · Lesson 15 · Where We Left Off

Where We Left Off

L11–L14 were ES — listening. Hear the emitter, sort it, find its bearing, cross it into a fix.

Now turn the problem around. The threat is doing all of that to us.

Today

Electromagnetic Protect — how we radiate and survive while the enemy intercepts and jams.

Block 2 · Lesson 15 · Objectives

Lesson Objectives

Define EP and place it against ES and EA
Explain how LPI hides a radar that must still radiate
Describe frequency and polarization agility as anti-jam tools
Explain why most jamming enters through the side lobes

Our radars have to keep working while the enemy tries to stop them.

Block 2 · Lesson 15 · Part One

Radiate and Survive

The defensive pillar: what EP is, and the dilemma every transmitting radar lives with.

Block 2 · Lesson 15 · EP Defined

Electromagnetic Protect: Defensive EW

EP protects our own use of the spectrum — against enemy EA and friendly interference.

Make radars and links resistant to jamming and EMI
Harden against large electromagnetic disturbances
LPI systems — be hard to intercept in the first place
Signature reduction — the low-observable half, deferred to B3

ES listens, EA denies — EP keeps us in the fight while both happen.

Block 2 · Lesson 15 · The Dilemma

The EP Dilemma

A radar has to transmit to work. From L11–L12 we know the cost: the one-way listener ($1/R^2$) hears the radar long before its two-way echo ($1/R^4$) closes the loop.

Every watt radiated is a watt the threat RWR can intercept
Every transmission is a chance to be located and jammed
Turning the radar off is safe — and useless

So EP is not hiding. It is staying useful while giving the threat as little to work with as possible.

Block 2 · Lesson 15 · Part Two

Low Probability of Intercept

Two families: radiate less and later, then hide the energy you do radiate in plain sight.

Block 2 · Lesson 15 · LPI

LPI: Emit Less, Emit Later

The cheapest signal to intercept is the one never sent. Before any clever waveform, radiate less — and later.

Discipline, not hardware

EMCON — lean on passive sensors: RWR, IR/EO, off-board data link
Delay radiation — go active at the last moment, not a second before
Power management — emit only enough to close this shot

Why it works

The threat's intercept range scales with our transmit power. Cut power and the RWR's reach falls with it — the listener has to come to you.

Block 2 · Lesson 15 · LPI

LPI: Hide the Energy in Plain Sight

When you must radiate, spread the energy so no single slice of the spectrum looks like much.

Spread, then compress

A long coded pulse — chirp or phase code — smears energy over a wide band $B$
To an intercept receiver it is weak and noise-like: poor wideband SNR
Our matched filter re-concentrates it into a sharp peak

Processing gain

$$G_p = B\,\tau$$

Spread to hide; compress to see. The eavesdropper has neither key.

Block 2 · Lesson 15 · Part Three

Agility and the Side Lobes

Do not sit still in the spectrum — and police everything around the main beam.

Block 2 · Lesson 15 · Agility

Frequency and Polarization Agility

A predictable emitter is an easy target. So do not sit still.

Frequency agility

Hop the carrier pulse-to-pulse — a spot jammer cannot follow
An RWR struggles to sort an emitter whose frequency keeps moving
Bonus: hopping decorrelates clutter and target glint

Polarization agility

Flip the transmit polarization to beat a cross-pol jammer that was matched to the old one. An anti-cross-pol design refuses energy on the wrong polarization.

Agility forces the jammer to spread its fixed power thin.

Block 2 · Lesson 15 · Side Lobes

It's Mostly the Side Lobes

main lobe

side lobethe jammer's way in

jammer

A jammer rarely sits in your main beam. It pours energy in through the side lobes.

Ultra-low side lobes — starve every off-axis path at once
Side-lobe blanker — a guard channel rejects wideband side-lobe pulses
Side-lobe canceler — an auxiliary antenna adaptively nulls a narrowband jammer

Block 2 · Lesson 15 · Side Lobes

Starve Them: Ultra-Low Side Lobes

main lobeunchanged

taperedsame jammer, no door

jammer

Taper the illumination and the off-axis gain falls everywhere at once — the passive baseline under the blanker and the canceler.

A uniform aperture's first side lobe sits at $-13.2$ dB — the textbook constant from L6
Taper the illumination to push it lower, and pay for it in main-beam width — no free lunch

A jammer entering a $-18$ dB side lobe is attenuated by 18 dB — and still gets in if it is loud enough. Ultra-low side lobes raise the price; they do not close the door.

Block 2 · Lesson 15 · Move and Countermove

EP Is the Counter to EA

Each EP technique answers a specific attack — a preview of L17–L18.

EP technique	EA it counters
Ultra-low side lobes	All side-lobe jamming and intercept
Side-lobe canceler	Narrowband side-lobe jamming
Side-lobe blanker	Wideband side-lobe jamming
Anti-cross-pol	Cross-polarization jamming
Pulse compression	Deceptive jamming without the code
Frequency agility	Spot jamming
PRF jitter	Cover pulses

No single trick wins — EP is layered, and every layer costs complexity.

Today's Interactive Demo: Frequency Agility

Companion script: L15_FrequencyAgility.m
The jammer's power is fixed — agility makes it choose where to lose

Live demo

Frequency Agility

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

Demo hand-off; drive it from here. It opens Fixed, with the radar parked on a clear channel and the jammer covering four of twenty, so nothing is denied. Click a channel inside the red block and denial jumps to one hundred percent — a fixed radar lives or dies on one frequency. Switch to Agile and the radar hops across all twenty; the denied fraction settles at W over N, four in twenty. Press Next pulse a few times, or Auto-hop, and let the running tally converge on twenty percent. Then widen the jammer with the Jammer width slider and watch agile denial climb while the per-channel J slash S tile counts down — twenty-two decibels at W of four, nineteen at eight. Now set up the cliff. Leave Burn-through J slash S at its default eighteen decibels. At W equals ten the tile reads exactly eighteen point zero, still green, still denied, and agile denial peaks at fifty percent — the best this jammer ever does. Click one more channel. At W equals eleven the tile falls to seventeen point six, turns grey, reads burned through; the jammed block fades to a dashed outline and P of denied drops to zero in one step. Ask them where the ten came from before you answer: the jammer starts at twenty-eight decibels in one channel, the radar burns through below eighteen, so it has ten decibels of headroom — and ten decibels is a factor of ten, which buys exactly ten channels. A jammer's spare J slash S in decibels is its channel budget. Drag the burn-through slider and the budget moves with it. Finally read the barrage-dilution tile: spreading across all N costs ten log N per channel, thirteen decibels at twenty channels, which the jammer simply gives away. Agility converts a power contest into a coverage contest, and coverage is expensive for the jammer. This is the type-along's exercise, live — companion script runs the same numbers unattended.

Block 2 · Lesson 15 · Quick Exercise

Quick Exercise / Type-along: The Jammer's Budget

Type this with me — the agile radar from the demo, $N = 20$ channels.

N       = 20;                    % channels in the hop set
JSR0_dB = 28;                    % J/S with all power in one channel
JSRmax  = 18;                    % most J/S the radar burns through
W       = 1:N;                   % channels the jammer covers
jsr     = JSR0_dB - 10*log10(W); % per-channel J/S after spreading
den     = (jsr>=JSRmax) .* (W/N);% denied fraction of an agile dwell
fprintf('   W   J/S(dB)  denied\n');
fprintf('%4d %8.1f %7.0f%%\n', [W; jsr; 100*den]);
[best, k] = max(den);
fprintf('\nBest play: W = %d, %.0f%% denied; W = %d denies 0.\n', ...
        W(k), 100*best, W(k)+1);

The denied column falls off a cliff at $W = 11$. Where does the 10 come from?

Then: the radar doubles its hop set to $N = 40$. What changes for the jammer?

Block 2 · Lesson 15 · Wrap-Up

Wrap-Up

Key ideas

EP keeps our spectrum working against jamming and interference
LPI hides a radar that must radiate — emit less, spread, then compress
Agility makes a predictable emitter unpredictable; spot jamming fails
Most jamming enters the side lobes; EP is layered and never free

Next lesson

L16: EP for communications — spread spectrum (DSSS/FHSS) and processing gain
Work the L16 pre-flight before class — you could be the one up front