Reading — SEAD, Maneuvers, and Standoff Jamming#
By the end of this lesson you should be able to:
Distinguish SEAD suppression from destruction, and read a suppression timing window.
Explain the beam/notch maneuver through L5’s Doppler notch, \(f_d = 2v_r/\lambda\).
Compute standoff J/S and the burn-through range, for a jammer in the radar’s mainlobe and in its sidelobes.
Place a standoff jammer and a strike route for deconfliction.
The support package#
Every lever in Block 4 so far has been a choice about the bomber alone: which route it flies (L34), how its signature looks from each threat (L32), how well the adversary can track it (L33), how it localizes a threat that pops up (L35). This lesson adds the help it can bring along, the support package, and the tricks it can play on its own.
There are three ways to take a radar out of the fight without flying around it. You can silence it — destroy the site, or suppress it long enough to get through. You can slip its signal processing — maneuver so that the radar’s own clutter filter throws your echo away. Or you can jam it from outside every ring, with a dedicated aircraft that never comes within reach of the missiles. In the language of L31, none of these adds a link to the kill chain. They change how often, and for how long, each site gets to run the chain against you — the exposure \(\ell_i\) that sets each site’s share of the route’s risk, \(r_i = \lambda_i \ell_i\). That is why all three belong to the Final Project’s task T5.
SEAD: destroy the site, or suppress it#
Suppression of enemy air defenses (SEAD) is the name for any activity that neutralizes, destroys, or temporarily degrades surface-based air defenses. The definition already contains the lesson’s first distinction, because “destroys” and “temporarily degrades” are very different promises to a planner.
Destruction removes the site for the rest of the mission. The classic lethal tool is the anti-radiation missile (the HARM family), which homes on the radar’s own emission — the radar’s transmitter becomes the missile’s beacon. A site that has been located (the geolocation of L14, turned from a warning into a target) can also be struck with any other weapon.
Suppression degrades the site only while something keeps it degraded. The non-lethal tool is electromagnetic attack: the noise jamming of L17, and the standoff jamming this lesson develops. Suppression can also be lethal in means but temporary in effect: a HARM in the air gives an operator a strong reason to shut the radar down, and a radar that is silent cannot guide a missile. The site is suppressed, not destroyed — it comes back on the air when the threat passes.
The same weapon can therefore land in either column. What matters to the planner is not the hardware but the effect: permanent, or for a while.
In Ball’s terms (L31), SEAD is threat suppression, one of the six susceptibility-reduction concepts. It is an unusually powerful one, because a site that cannot radiate cannot detect, track, or guide: it breaks every link of the chain at once instead of shrinking one.
Suppression is a window, not a switch#
Because suppression lasts only while it is applied, it has a start and an end. The jammer arrives on station and leaves; the anti-radiation shooters are airborne for a while and then are not. Between those times is the suppression window, and the only protection it gives is to aircraft that use it.
That couples SEAD to the route. A strike package gains from the suppression only for the part of its time inside the site’s lethal zone that falls inside the window. A package that arrives late, or whose path through the zone is long, leaves the zone after the window has closed and flies the last stretch fully exposed. The planner has three knobs, and they are the three ways to fix a late package: leave earlier, shorten the path through the zone, or buy a longer window. None of them can be set without the others — which is exactly why SEAD is planned together with the route rather than bolted on afterwards.
The Final Project models this simply. One site may be nominated for SEAD, and its hazard \(\lambda\) — its risk per kilometer of exposure from L31 — is multiplied by a stated factor. The factor is not zero, and the window is the physical reason: suppression degrades, it does not delete.
Key Concept
Destruction is permanent for the mission; suppression holds only while it is applied, so it defines a window in time. A route benefits from suppression only for the part of its exposure that falls inside that window, so SEAD and the route are planned together. The same weapon can do either: an anti-radiation missile that forces a radar off the air has suppressed it, not destroyed it.
Defensive maneuvers: beam, notch, turn cold#
Beam the radar: hide in the Doppler notch#
L5 gave the radar a way to find a moving target in ground clutter: the Doppler shift \(f_d = 2v_r/\lambda\) separates a mover from the clutter, which sits at \(f_d \approx 0\), and the MTI canceler notches zero Doppler out. The notch is also a place to hide. The radial velocity is the part of the aircraft’s velocity along the line of sight,
where \(\alpha\) is the angle between the velocity and the line of sight to the radar. Fly perpendicular to the line of sight — put the radar on your beam, \(\alpha = 90^\circ\) — and \(v_r \to 0\), so \(f_d \to 0\): your echo lands on the clutter ridge and the canceler throws it away along with the ground. This is the beam (or notch) maneuver.
The notch is narrow, so the geometry is demanding. Take an S-band radar (\(\lambda = 10\) cm) whose notch rejects \(|f_d| < 500\) Hz: it discards anything with \(|v_r| < f_d\lambda/2 = 25\) m/s. An aircraft at 200 m/s is inside that only if \(\cos\alpha < 0.125\), i.e. \(\alpha > 82.8^\circ\) — within about seven degrees of the beam. Hold that heading, or reappear. And the maneuver has a price you already know from Project 3. The B-21’s X-band pattern has its sharpest spike exactly at the beam, \(-3\) dBsm against \(-15\) dBsm nose-on: 12 dB brighter, and with \(R \propto \sigma^{1/4}\) that doubles the range at which any radar mode that does not rely on Doppler can see you. The notch wants exactly beam, and the signature punishes exactly beam.
Turn cold, drag — and the endgame#
The other family of maneuvers attacks the missile rather than the radar. Turning cold — putting your tail on the site — forces the missile into a stern chase, where it must beat your speed for its whole time of flight. L32’s two rings say when that works. Inside the MEZ but outside the LEZ, a turn away defeats the shot kinematically: the missile runs out of time before it closes. Inside the LEZ, \(R_{\text{LEZ}} = (v_m - v_t)\,t_{\max}\), the missile catches even a target running straight away, and turning cold does not save you. Dragging is holding that cold heading long enough to spend the missile’s energy and time of flight, then turning back to resume the route.
Turning cold has its own cost: it shows the site your tail, which is where the B-21’s IR plume is (L22, L24) and where its X-band return is brighter than the nose. And if the missile does arrive, the last seconds belong to expendables: chaff against radar-guided seekers (L18) and flares against infrared ones (L24).
Every maneuver buys survival with something else — time exposed, aspect presented, or distance flown off the planned route — which is why maneuvers belong in the route planner’s cost, not outside it.
From self-protect to standoff#
L17 derived the jamming scorecard for a self-protect jammer (SPJ): the jammer rides on the target, so the jamming and the skin echo share one range \(R\) to the radar, and
L17 also named the other geometry, the stand-off jammer (SOJ): a dedicated platform that jams from a safe range, outside every threat ring, while the strike package goes in without it. Two things change when the jammer and the target separate.
First, there are two ranges. The echo still makes a round trip over the target’s range \(R_t\), so the signal falls as \(1/R_t^4\). The jamming makes a one-way trip over the jammer’s range \(R_j\), so it falls as \(1/R_j^2\). And while the target closes, the SOJ’s range stays roughly fixed — it is orbiting, not attacking. So the jammer gets none of the “range relief” that made the SPJ’s \(J/S\) grow as \(R^2\): the SOJ’s jamming is constant, and only the echo grows as the target presses in.
Second, there are two gains. The radar’s receiver hears the jammer through whatever antenna gain it happens to be pointing toward the jammer, \(G_r'\), while it hears the target through its mainbeam gain \(G_r\) — the radar is, after all, looking at the target. For an SPJ those are the same number; for an SOJ they usually are not. If the SOJ sits on the same azimuth as the target, within half a beamwidth, it is inside the beam the radar is looking through and enters with the full mainlobe gain: \(G_r'/G_r = 1\), or 0 dB. Anywhere else it enters through a sidelobe, and \(G_r'/G_r\) is the antenna’s sidelobe level (SLL) — L6’s “back door”. A uniformly illuminated aperture’s first sidelobe is \(-13.2\) dB; tapered search and fire-control antennas run \(-25\) to \(-35\) dB and lower.
Keep that antenna apart from a second one, because both have “mainlobes” and they do different jobs. \(G_j\) is the jammer’s own transmit gain toward the radar. A standoff jammer buys its effective radiated power with a directional antenna, and a directional beam points one way: a directional SOJ holds its transmit mainlobe — and with it its ERP — on one victim radar at a time. So there are two questions, answered by two antennas. The radar’s receive lobes (\(G_r'/G_r\)) decide where around a jammed radar the jamming bites hardest — the strobe. The jammer’s transmit beam (\(G_j\)) decides which radar is jammed at all. A radar outside the jammer’s beam still hears it faintly through the jammer’s own sidelobes; the Final Project simplifies that, as a stated assumption, to unjammed.
Standoff J/S#
Put both changes into L17’s equation and the standoff jam-to-signal ratio is
Read it term by term. \(P_jG_j\) and \(P_tG_t\) are the jammer’s and the radar’s effective radiated powers, \(\sigma\) the target’s RCS, and \(B_r/B_j\) is L17’s barrage penalty, unchanged: only the jamming inside the radar’s passband counts. The range terms are the two paths — \(R_t^4\) for the echo’s two-way loss (it sits in the numerator because a weaker echo means a larger \(J/S\)), \(R_j^2\) for the jammer’s one-way loss. And \(G_r'/G_r\) is the geometry: 1 in the mainlobe, the SLL everywhere else.
The check that this is the same physics as L17 is one line. Put the jammer back on the target, \(R_j = R_t = R\) and \(G_r' = G_r\): then \(R_t^4/R_j^2 = R^2\), the gain ratio is 1, and the standoff equation is L17’s self-protect equation. With L17’s Quick Problem numbers (1 MW, 40 dBi radar; 500 W, 10 dBi barrage jammer at \(B_r/B_j = 1/100\); \(\sigma = 2\) m²; 30 km), both forms give \(J/S = +14.5\) dB.
Notice what a sidelobe does. At \(-30\) dB, the jammer’s contribution drops by a factor of 1000 — exactly as if it had thrown away 99.9% of its power. The jammer did not choose that penalty. The geometry did.
Burn-through, standoff#
The radar recovers the target where \(J/S\) falls to what its processing can tolerate. This lesson — like L17’s Quick Problem and the Final Project — takes a pulse-Doppler radar that holds track up to \(J/S = 10\) (+10 dB); some Block 2 exercises (L17’s type-along, HW2) burned through at \(J = S\) (0 dB) instead, so always state your threshold. Setting \(J/S = 10\) and solving for the target’s range gives the standoff burn-through range:
It is a fourth root, not L17’s square root, because only the echo is two-way; the jammer’s \(R_j^2\) is a constant here, fixed by where the SOJ orbits. Inside \(R_{bt}\) the echo climbs out of the jamming and the radar sees the target; outside it, the target is buried. Setting \(R_j = R_{bt}\) recovers L17 again: \(R_{bt}^4 = C\,R_{bt}^2\) with \(C = 10P_tG_t\sigma B_j/(4\pi P_jG_jB_r)\), so \(R_{bt} = \sqrt{C}\) — which for L17’s Quick Problem numbers is its 17.8 km.
And here is the consequence the rest of the lesson turns on. The radar has one SOJ to contend with but two burn-through ranges: a short one on the jammer’s azimuth, where the jamming comes in through the mainlobe, and a long one everywhere else, where it comes in through a sidelobe.
Key Concept
A standoff jammer’s \(J/S\) scales as \(R_t^4/R_j^2\) — the echo’s two-way loss over the jammer’s one-way loss — times the gain the radar points at the jammer, \(G_r'/G_r\). On the jammer’s azimuth that ratio is 1 (mainlobe); everywhere else it is the sidelobe level. So one SOJ gives the radar two burn-through ranges, a short mainlobe one and a long sidelobe one, and setting \(R_j = R_t\), \(G_r' = G_r\) recovers L17’s self-protect equation.
Type-along
One radar, one SOJ, and five ways for its jamming to get in — the mainlobe and four sidelobe levels. Type this and run it:
% L36 -- SOJ burn-through: mainlobe versus sidelobes
PtGt = 10^(87/10); % radar ERP: 87 dBW
PjGj = 10^(45/10); % SOJ ERP toward the radar: 45 dBW
sigma = 0.5; % target RCS, m^2
Rj = 120e3; % SOJ range to the radar, m
BrBj = 0.2; % radar BW over jammer BW
SLL = [0 -20 -25 -30 -35]; % G_r'/G_r in dB (0 = mainlobe)
g = 10.^(SLL/10);
Rbt = (10*PtGt*sigma*Rj^2 ./ (4*pi*PjGj*g*BrBj)).^(1/4);
fprintf('G_r''/G_r(dB) R_bt(km)\n');
fprintf('%12.0f %10.1f\n', [SLL; Rbt/1e3]);
fprintf('sidelobe/mainlobe at -30 dB: x%.2f\n', Rbt(4)/Rbt(1));
Then answer these two:
Every 5 dB of sidelobe moves \(R_{bt}\) by the same factor. What factor — and why a fourth root?
The SOJ backs off from 120 to 480 km. What happens to every row?
Solution
G_r'/G_r(dB) R_bt(km)
0 4.6
-20 14.6
-25 19.5
-30 26.0
-35 34.6
sidelobe/mainlobe at -30 dB: x5.62
A factor of \(10^{5/40} = 1.33\) — check it down the table: \(19.5/14.6\), \(26.0/19.5\) and \(34.6/26.0\) are all 1.33. At a fixed jammer range, \(J/S \propto R_t^4 \cdot (G_r'/G_r)\), so holding \(J/S = 10\) makes \(R_{bt} \propto (G_r'/G_r)^{-1/4}\): the fourth root of the echo’s two-way loss turns every 10 dB of sidelobe into a factor of 1.78 in range, and 30 dB into the 5.62 on the last line. A lower sidelobe level — a better antenna — pushes burn-through out, so the radar recovers the target farther away. The 4.6 km mainlobe row is the jammer’s best case.
Every row doubles — 4.6 km becomes 9.2, and 34.6 becomes 69.2. The jammer’s one-way loss grows as \(R_j^2\) and the fourth root halves that exponent, so \(R_{bt} \propto R_j^{1/2}\) and four times the standoff costs only \(\sqrt{4} = 2\) in burn-through. Backing off is cheap, which is why an SOJ can afford to stay well outside every missile zone.
Quick problem — Sidelobe or Strobe
An SOJ covers a strike package against a SAM acquisition radar. The package is off the jammer’s azimuth.
Radar ERP \(P_t G_t = 76\) dBW
SOJ ERP \(P_j G_j = 40\) dBW, spot (\(B_j = B_r\))
Target \(\sigma = 1\) m², at \(R_t = 40\) km
SOJ range \(R_j = 80\) km
The jam enters through a −32 dB sidelobe
Radar holds track up to \(J/S = +10\) dB
(a) \(J/S\) in dB at 40 km.
(b) The sidelobe burn-through range.
(c) The package turns onto the radar–jammer line, into the strobe: the new burn-through range.
Solution
(a) Work the standoff equation as a dB ladder, one rung per factor:
Factor |
dB |
|---|---|
\(4\pi\) |
\(+11.0\) |
\(P_j G_j = 40\) dBW |
\(+40.0\) |
\(R_t^4\), \(R_t = 40\) km |
\(+184.1\) |
\(1/(P_t G_t)\) |
\(-76.0\) |
\(1/\sigma\), \(\sigma = 1\) m² |
\(0\) |
\(1/R_j^2\), \(R_j = 80\) km |
\(-98.1\) |
\(G_r'/G_r\) (sidelobe) |
\(-32.0\) |
\(B_r/B_j\) (spot) |
\(0\) |
\(J/S\) |
\(+29.0\) |
So \(J/S = +29.0\) dB at 40 km — 19 dB past the radar’s tolerance, and the package is hidden.
(b) At a fixed \(R_j\), \(J/S \propto R_t^4\), so the range where \(J/S\) falls to \(+10\) dB is
\(R_{bt} = 13.4\) km. The burn-through formula gives the same number directly.
(c) On the radar–jammer line the jamming enters through the mainlobe, so \(G_r'/G_r\) goes from \(-32\) dB to 0 dB: 32 dB more \(J/S\) at every range. Burn-through moves in by \(10^{32/40} = 6.31\): \(R_{bt} = 13.4/6.31 = 2.1\) km.
So what: flying the jammer’s azimuth lets the package press 11 km closer before the radar recovers it — a factor of 6.3 in burn-through for zero extra watts. That factor comes from geometry alone.
The jammed contour: a strobe, not a sky#
A radar searching in azimuth looks in every direction in turn. When its beam points at azimuth \(\phi\), the jammer at azimuth \(\phi_j\) gets in through the mainlobe if \(|\phi - \phi_j| \le \theta_B/2\) (half the beamwidth) and through a sidelobe otherwise. So the burn-through range is a function of azimuth, \(R_{bt}(\phi)\), and the radar’s detection contour under jamming is
where \(R_{det}\) is the unjammed detection range from the Block 1 range law — beyond it the radar could not see the target anyway, jammed or not.
Draw it and it has a distinctive shape. Around most of the circle the contour shrinks to the sidelobe burn-through range. On the jammer’s azimuth there is a deep, narrow notch, one beamwidth wide, where it shrinks all the way to the mainlobe burn-through range. That notch is the strobe. The name comes from the radar’s display: when the beam sweeps across the jammer, the receiver fills with noise at every range, and the jammer paints a bright radial line pointing straight at itself.
For the in-class demo’s default radar — a 90 dBW radar, a 40 dBW SOJ at 150 km whose noise spreads over ten times the radar’s bandwidth (\(B_r/B_j = -10\) dB), a target of \(-5\) dBsm, \(-30\) dB sidelobes and a 5° beam — the unjammed range is 75 km, the sidelobe burn-through 48.8 km and the mainlobe burn-through 8.7 km. The contour is a 48.8 km circle with a 5° notch that dives to 8.7 km on the jammer’s bearing.
The part of the strobe between the two burn-through ranges is the protected corridor: a striker there is hidden from this radar even though, a few degrees to either side, the same radar would see it. Its width at range \(R\) is the width of the beam,
which for the demo’s 5° beam is just 2.62 km at 30 km. The standoff jammer does protect the strike — but only inside a lane a few kilometers wide, lined up on the jammer. It protects a corridor, not a sky. To use it, fly in its shadow.
Two scalings every SOJ planner uses#
Two exponents in the burn-through formula decide most standoff-jamming plans.
Standoff range: \(R_{bt} \propto R_j^{1/2}\). The jammer’s one-way loss enters as \(R_j^2\) and the fourth root halves it. Four times the standoff only doubles burn-through; twice the standoff costs a factor of \(\sqrt{2} = 1.41\). Pulling a jammer in toward the threat buys surprisingly little, and backing it off to stay clear of the missiles costs surprisingly little.
Sidelobe level: \(R_{bt} \propto (G_r'/G_r)^{-1/4}\). Every 10 dB of sidelobe suppression is a factor of \(10^{10/40} = 1.78\) in burn-through range; 30 dB is a factor of 5.6. That factor is what the strike route earns, for free, by flying the jammer’s azimuth instead of a few degrees off it.
The other exponents follow the same way: \(R_{bt} \propto \sigma^{1/4}\) (a stealthier target pulls burn-through in, as in L17 — low observability and jamming still reinforce each other), \(R_{bt} \propto (P_jG_j)^{-1/4}\) (sixteen times the jammer power to halve burn-through), and \(R_{bt} \propto (P_tG_t)^{1/4}\).
Key Concept
\(R_{bt} \propto R_j^{1/2}\) and \(R_{bt} \propto (G_r'/G_r)^{-1/4}\). Backing a jammer off is cheap — four times the standoff doubles burn-through — while getting into the radar’s mainlobe is worth a factor of 5.6 at a \(-30\) dB sidelobe level. For a standoff jammer, geometry buys more than power.
Electronic protection strikes back#
L15 met the radar’s answers to exactly this attack. A sidelobe canceler uses an auxiliary antenna to place a null on a jammer coming in through the sidelobes and subtract it from the main channel. A sidelobe blanker rejects pulses that arrive through the sidelobes rather than the mainbeam. And ultra-low sidelobes (L6, L15) lower the SLL itself, which by the second scaling pushes the sidelobe burn-through out toward \(R_{det}\) — at a low enough level, sidelobe jamming stops shrinking the contour at all. All three attack the sidelobe path. None of them can remove a jammer that sits in the very beam the radar is looking through. That is why the mainlobe position is prized, and why the strike route rides the strobe.
The strobe cuts both ways. It points at the jammer, so two radars whose strobes cross have a passive fix on the SOJ — L14’s cross-bearing geolocation, and L33’s information geometry, turned on our own jammer. Some missiles can also guide on the jamming itself. A standoff jammer is a loud, continuously radiating, locatable aircraft, and it stays far from the missiles for good reason.
Deconfliction: four rules for one jammer#
Putting the pieces together gives four planning rules.
The SOJ orbits outside every MEZ, plus a margin. It radiates continuously, so it will be found; the margin covers position errors, the missiles’ reach, and the time to react. Thanks to \(R_{bt} \propto R_j^{1/2}\), the standoff costs little.
One jammer beam, one victim. A directional SOJ holds its transmit mainlobe on one radar at a time; the others are, to a first approximation, unjammed and see the route out to their full detection range. The planner chooses the victim — usually the radar whose lethal zone the route cannot avoid.
The route rides the victim’s strobe. The strobe points at the jammer from the victim’s own position, so the corridor exists only along that one line; a route that wanders off it is back in the victim’s sidelobe contour.
The other sites’ zones are crossed inside the SEAD window — or avoided. The jammer handles one radar’s view of the route; suppression or destruction handles a site the jammer’s beam is not on.
Demo: Standoff Jamming#
The in-class demo, Standoff Jamming, draws all of this on a map. A radar sits at the origin with its unjammed contour, its MEZ and the SOJ keep-out ring; you drag the SOJ and a striker. The jammed contour, the strobe wedge and the green corridor redraw as you move them, and the readouts give the mainlobe and sidelobe burn-through ranges, the corridor width at the striker’s range, and the striker’s \(J/S\). Sliders set the jammer’s power, the sidelobe level, the beamwidth and the target’s RCS. Try the Two radars preset last and move the Jammer beam on switch between the radars: whichever radar the beam leaves goes back to its full, unjammed contour and finds the striker — rules 2 and 3, on a map.
The companion script L36_StandoffJamming.m computes the same numbers: burn-through against a list of sidelobe levels, the jammed contour around the full circle, the corridor width at several ranges, and what pulling the SOJ in to its keep-out line would buy.
Final Project: the support package (T5)#
Task T5 gives you one standoff jammer and one SEAD nomination, and asks what they are worth. The handout states the jammer’s parameters, the victim radars’ sidelobe levels and beamwidths, the SOJ’s keep-out margin, and the SEAD factor. The method is this lesson’s, applied to the survival metric of L31 and the planner of L34:
Choose the SOJ’s victim radar. For that radar, replace its detection contour with the jammed contour \(\min(R_{det}, R_{bt}(\phi))\); the handout treats every other radar as unjammed. A site’s lethal zone is where you are inside its detection contour and its MEZ (L31, L32), so a smaller contour means fewer kilometers of exposure \(\ell_i\) and less risk \(\lambda_i\ell_i\).
Multiply the nominated site’s hazard \(\lambda_i\) by the stated SEAD factor.
Re-plan with the L34 planner, report the change in survival \(\Delta P_S\), and test how sensitive that answer is to one parameter of your choice.
Where you put the jammer, which radar its beam holds, and which site you nominate for SEAD are your decisions — and the paper should defend them with the geometry above.
Wrap-Up#
SEAD takes a radar out of the fight either permanently (destruction) or only while it is applied (suppression), so suppression opens a window in time that the route has to use. Maneuvers attack the radar’s processing and the missile’s kinematics: beaming the radar drives \(v_r = v\cos\alpha\) to zero and hides the echo in L5’s Doppler notch, and turning cold outruns a missile outside L32’s LEZ — each paid for in time, aspect, or distance. A standoff jammer keeps its range \(R_j\) fixed while the target’s \(R_t\) closes, so its \(J/S\) scales as \(R_t^4/R_j^2\), times the gain the radar points at it: the mainlobe on the jammer’s azimuth, a sidelobe everywhere else. That gives the jammed contour its strobe — a narrow, deep notch on the jammer’s bearing — and the strike route its corridor. Burn-through scales as \(R_j^{1/2}\) and as the sidelobe level to the \(-1/4\), so backing off is cheap and lining up is priceless. Next, L37 — Modern Trends in EW looks past the classical toolkit: cognitive EW, machine-learning emitter identification, GPS denial, and electronic warfare in space.