Lesson 36 Flashcards

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1. What is SEAD, and what two kinds of effect can it have?

Suppression of enemy air defenses: activity that neutralizes, destroys, or temporarily degrades surface-based air defenses. Destruction removes a site for the rest of the mission; suppression degrades it only while the suppression is applied.

2. Lethal versus non-lethal SEAD — and can an anti-radiation missile suppress rather than destroy?

Lethal: anti-radiation missiles (HARM) homing on the radar's emission, or weapons on a located site. Non-lethal: electromagnetic attack — noise jamming, including a standoff jammer. Yes: a HARM in the air gives operators reason to shut the radar down, and a silent radar is suppressed, not destroyed — it comes back when the threat passes.

3. What is the suppression window, and why does it couple SEAD to the route?

Suppression lasts only while the suppressor is on station, so it opens and closes in time. A package gains only for the part of its time inside the site's lethal zone that falls inside the window; a late package, or a long path through the zone, flies the rest exposed. Fixes: leave earlier, shorten the path through the zone, or lengthen the window.

4. How does the beam/notch maneuver hide an aircraft?

The radial velocity is \(v_r = v\cos\alpha\). Fly perpendicular to the line of sight (\(\alpha = 90^\circ\)) and \(v_r \to 0\), so \(f_d = 2v_r/\lambda \to 0\): the echo lands in L5's MTI notch with the ground clutter and is canceled with it. The notch is narrow, so the heading must be held within a few degrees of the beam.

5. What does beaming a radar cost the B-21 on its X-band pattern?

The pattern's sharpest spike sits exactly at the beam: about −3 dBsm against −15 dBsm nose-on, 12 dB brighter. With \(R \propto \sigma^{1/4}\) that doubles the range at which a radar mode that does not rely on Doppler can see you. The notch wants exactly beam, and the signature punishes exactly beam.

6. When does turning cold defeat a missile?

Inside the MEZ but outside the LEZ (L32): with your tail on the site, the missile flies a stern chase and runs out of time of flight. Inside the LEZ, \(R_{\text{LEZ}} = (v_m - v_t)t_{\max}\), it catches even a target running straight away. Dragging holds the cold heading to spend the missile's energy; the endgame belongs to chaff (L18) and flares (L24).

7. What two things change when a jammer moves off the target to a standoff orbit?

Two ranges: the echo still travels the target's range \(R_t\) both ways, but the jamming travels the jammer's range \(R_j\) one way, and \(R_j\) stays fixed while \(R_t\) closes. Two gains: the radar hears the target through its mainbeam \(G_r\) but the jammer through the gain it points toward the jammer, \(G_r'\).

8. Write the standoff jam-to-signal ratio.

\(\dfrac{J}{S} = \dfrac{4\pi P_jG_jR_t^4}{P_tG_t\sigma R_j^2}\cdot\dfrac{G_r'}{G_r}\cdot\dfrac{B_r}{B_j}\) — the echo's two-way loss \(R_t^4\) over the jammer's one-way loss \(R_j^2\), times the gain ratio and L17's bandwidth factor.

9. How does the standoff equation reduce to L17's self-protect equation?

Put the jammer on the target: \(R_j = R_t = R\) and \(G_r' = G_r\). Then \(R_t^4/R_j^2 = R^2\) and the gain ratio is 1, leaving \(J/S = 4\pi P_jG_jR^2 B_r/(P_tG_t\sigma B_j)\). With L17's Quick Problem numbers both forms give +14.5 dB at 30 km and a 17.8 km burn-through.

10. Write the standoff burn-through range. Why a fourth root?

\(R_{bt} = \left[\dfrac{10\,P_tG_t\sigma R_j^2 B_j}{4\pi P_jG_j(G_r'/G_r)B_r}\right]^{1/4}\), the target range where \(J/S\) falls to 10 (+10 dB). A fourth root because only the echo is two-way; the jammer's \(R_j^2\) is a constant, fixed by the orbit.

11. When is a standoff jammer in the radar's mainlobe?

When it sits on the target's azimuth, within half a beamwidth — on the jammer's side of the radar. Then \(G_r'/G_r = 1\) (0 dB). Anywhere else the jamming enters through a sidelobe and \(G_r'/G_r\) is the sidelobe level, typically −25 to −35 dB. A target on the far side of the radar from the SOJ is on the same line but not in the mainlobe.

12. What is the jammed detection contour, and what is the strobe?

\(R(\phi) = \min(R_{det}, R_{bt}(\phi))\): the sidelobe burn-through range around most of the circle, and a deep, narrow notch one beamwidth wide on the jammer's azimuth, where it falls to the mainlobe burn-through range. That notch is the strobe — on the radar's display, a bright radial line of jamming pointing at the jammer.

13. What is the protected corridor, and how wide is it?

The part of the strobe between the mainlobe and sidelobe burn-through ranges: a striker there is hidden, while a few degrees to either side the same radar sees it. Its width at range \(R\) is about \(R\,\theta_B\) — for a 5° beam, about 2.6 km at 30 km. A corridor, not a sky.

14. How does burn-through scale with the jammer's standoff range?

\(R_{bt} \propto R_j^{1/2}\): the one-way \(R_j^2\) inside a fourth root. Four times the standoff only doubles burn-through, so backing a jammer off to clear the missile zones is cheap — and pulling it in buys little.

15. How does burn-through scale with the radar's sidelobe level?

\(R_{bt} \propto (G_r'/G_r)^{-1/4}\): every 10 dB of sidelobe is a factor of \(10^{10/40} = 1.78\) in burn-through range, and 30 dB is 5.6. Lower sidelobes push the radar's burn-through out; flying the jammer's azimuth wins that whole factor back for free.

16. What EP defeats sidelobe jamming, and why is the mainlobe position prized?

L15's sidelobe cancelers (an auxiliary antenna nulls the jammer), sidelobe blankers, and ultra-low sidelobes all attack the sidelobe path. None of them can remove a jammer sitting in the beam the radar is looking through — so the mainlobe is the one door EP cannot close, and the route rides the strobe.

17. What are the four deconfliction rules for one standoff jammer?

(1) Orbit outside every MEZ plus a margin — the SOJ radiates, so it will be found. (2) One jammer beam, one victim: a directional SOJ holds its transmit mainlobe on one radar, and the others are (to first order) unjammed. (3) The route rides the victim's strobe. (4) The other sites' zones are crossed inside the SEAD window, or avoided.

18. Standoff jamming has two different "mainlobes." Which is which?

The radar's receive lobes, \(G_r'/G_r\), decide where around a jammed radar the jamming bites hardest: the mainlobe on the jammer's azimuth (the strobe), a sidelobe elsewhere. The jammer's transmit beam, \(G_j\), decides which radar is jammed at all: a directional SOJ aims its ERP at one victim at a time. A radar outside that beam still hears the jammer faintly through its sidelobes; the Final Project treats it as unjammed, a stated simplification.