L13 Pre-flight

L13 Pre-flight#

Block 2: RF Electronic Warfare — Lesson 13: Angle of Arrival Work this before L13. 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#

  • L12 wrap-up

  • The Jupyter Book Reading page for L13 — why AoA matters, amplitude comparison, the interferometer relation, and phase ambiguity.

Quiz questions (5 items, ~5 minutes)#

Q1. (Multiple choice) Why is angle of arrival the hardest field in the PDW to measure well?

  • [ ] (a) It changes faster than the receiver can sample, so the estimate is stale

  • [ ] (b) It is a spatial measurement, not a timing measurement on one antenna

  • [ ] (c) It needs the threat radar to transmit continuously through the measurement

  • [ ] (d) It cannot be read until the threat’s beam sweeps back across you

Q2. (Multiple choice) An amplitude-comparison RWR determines bearing by:

  • [ ] (a) Measuring the phase difference between two antennas a known baseline apart

  • [ ] (b) Timing the pulse’s arrival against the receiver’s own clock

  • [ ] (c) Comparing received power across beams squinted in different directions

  • [ ] (d) Counting pulses per second and matching the PRF to the library

Q3. (Multiple choice) A two-element interferometer measures a phase difference \(\Delta\phi\) across a baseline \(d\). The bearing is recovered from:

  • [ ] (a) \(\theta = \arcsin\left(\dfrac{\lambda\,\Delta\phi}{2\pi d}\right)\)

  • [ ] (b) \(\theta = \dfrac{2\pi d}{\lambda}\,\Delta\phi\)

  • [ ] (c) \(\theta = \arccos\left(\dfrac{\lambda\,\Delta\phi}{2\pi d}\right)\)

  • [ ] (d) \(\theta = \arcsin\left(\dfrac{\Delta\phi}{2\pi}\right)\dfrac{\lambda}{d}\)

Q4. (Multiple choice) Making the interferometer baseline \(d\) much longer than \(\lambda/2\) buys finer accuracy but introduces what problem?

  • [ ] (a) The antennas decouple and lose their common phase reference

  • [ ] (b) Phase ambiguity — several bearings now share one measured phase

  • [ ] (c) The noise floor rises about 10 dB, since the array spans more bandwidth

  • [ ] (d) Bearing accuracy stops improving once \(d\) passes a few wavelengths

Q5. (Short answer) In one or two sentences, explain the accuracy-versus-ambiguity trade that sets interferometer baseline length, and how a multi-baseline system gets both.

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