# L27 Pre-flight **Block 3: IR EW and Signature Management — Lesson 27: RAM, Polarization, and EMCON** *Work this before L27. Pre-flights are never collected — in class, anyone may be cold-called to present any question at the board, and that recitation is the participation grade.* --- ## Assumed pre-class reading - L26 wrap-up (contributors and verdicts; edges left "to be treated"; the loudest-first budget) - The Jupyter Book Reading page for L27 — RAM as an attack on reflectivity, quarter-wave cancellation and the broadband problem, polarization behavior of edges and corners, and EMCON with the intercept asymmetry. --- ## Quiz questions (5 items, ~5 minutes) **Q1.** (Multiple choice) In L25's decomposition $\sigma = A_{\text{geo}} \times \Gamma \times D$, radar absorbent material primarily attacks: - [ ] (a) $A_{\text{geo}}$, by reducing the aircraft's projected area - [ ] (b) $\Gamma$, by converting incident wave energy to heat instead of echo - [ ] (c) $D$, by redirecting the echo away from the radar - [ ] (d) The radar's transmit power --- **Q2.** (Multiple choice) A Salisbury screen absorber is built with its resistive sheet a quarter wavelength above the metal skin. Why does this produce absorption at the design frequency — and what is the catch? - [ ] (a) The sheet blocks the wave physically; the catch is weight - [ ] (b) Front and rear reflections return 180° out of phase and cancel; the catch is that the cancellation only holds near one design frequency - [ ] (c) The air gap slows the wave below detection speed; the catch is altitude dependence - [ ] (d) The sheet re-radiates the wave upward; the catch is that it only works at night --- **Q3.** (Multiple choice) Why do practical broadband LO treatments use layered (Jaumann), magnetic (iron-loaded), or structural RAM instead of a single resonant layer? - [ ] (a) A single layer's notch defends one band while the IADS spans VHF to Ku; bandwidth must be bought with thickness, loss mechanisms, and weight - [ ] (b) Single layers are illegal under arms-control treaties - [ ] (c) Resonant layers only work on flat surfaces - [ ] (d) Magnetic RAM is lighter than any resonant layer --- **Q4.** (Short answer) Using the intercept asymmetry — the enemy RWR receives your radar one-way ($\propto 1/R^2$) while your radar needs the two-way echo ($\propto \sigma/R^4$) — explain in one or two sentences why EMCON is a survivability discipline for an LO aircraft. --- **Q5.** (Multiple choice) A polarization-diverse radar can be a counter-LO tool because: - [ ] (a) Circular polarization penetrates RAM coatings - [ ] (b) Long conductors and straight edges scatter preferentially in the polarization parallel to them, and corners flip circular polarization — tells that a cross-pol channel can flag - [ ] (c) Vertical polarization doubles the radar's transmit power - [ ] (d) LO aircraft only reflect horizontal polarization