L27 Pre-flight

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 shrinking the projected area the radar illuminates

  • [ ] (b) \(\Gamma\), by converting incident wave energy to heat instead of echo

  • [ ] (c) \(D\), by steering the specular flash away from the threat receiver

  • [ ] (d) None of the three — RAM attacks the radar’s transmit power, not the target’s \(\sigma\)

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 resistive sheet physically blocks the wave from reaching the skin; the catch is its weight

  • [ ] (b) Front and rear reflections cancel 180° out of phase; the catch is that this holds near one design frequency

  • [ ] (c) The air spacer slows the wave enough to delay the echo past the range gate; the catch is altitude dependence

  • [ ] (d) The sheet re-radiates the wave along the skin instead of back; the catch is that it works at one aspect

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 a real IADS spans VHF to \(K_u\)

  • [ ] (b) Single-layer absorbers are export-controlled, so only stacked designs are fielded

  • [ ] (c) A resonant layer works only on flat panels, not on edges or lips

  • [ ] (d) Magnetic RAM weighs less than any resonant screen of the same depth

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 that absorb only linear polarization

  • [ ] (b) Edges and long conductors favor one polarization, and corners flip the circular sense

  • [ ] (c) Vertical polarization puts twice the power on the target that a horizontal channel does

  • [ ] (d) An LO airframe returns only horizontal polarization, so a vertical channel sees nothing

Contents