L6 Pre-flight

L6 Pre-flight#

Block 1: Radar Fundamentals — Lesson 6: Antenna Patterns and Beamforming Work this before L6. 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#

  • L5 wrap-up

  • The L6 Reading page in the Jupyter Book — Antenna Patterns and Beamforming (pattern anatomy, HPBW and SLL, the gain / aperture / beamwidth rules, beam steering, grating lobes, and ESA / AESA).

Quiz questions (5 items, ~5 minutes)#

Each question worth 2 points; total 10. Be ready to defend any answer out loud.

Q1. (Multiple choice) On a polar antenna pattern, the HPBW is measured between the two angles where gain drops to:

  • [ ] (a) 1 dB below peak

  • [ ] (b) 3 dB below peak

  • [ ] (c) 10 dB below peak

  • [ ] (d) The first null

Q2. (Multiple choice) For an aperture of size \(D\) at wavelength \(\lambda\), the half-power beamwidth is approximately:

  • [ ] (a) \(\theta_{\text{HPBW}} \approx \lambda \cdot D\)

  • [ ] (b) \(\theta_{\text{HPBW}} \approx 70 \, \lambda / D\) degrees

  • [ ] (c) \(\theta_{\text{HPBW}} \approx 30{,}000 / D\)

  • [ ] (d) Independent of \(\lambda\)

Q3. (Multiple choice) A uniformly illuminated antenna has its first side lobe at approximately what level relative to the main lobe?

  • [ ] (a) \(-3\) dB

  • [ ] (b) \(-13\) dB

  • [ ] (c) \(-30\) dB

  • [ ] (d) \(-60\) dB

Q4. (Short answer) In one sentence, why are side lobes considered “the back door” for EW?

Q5. (Multiple choice) Which of the following is not typically an advantage of an AESA over a mechanically scanned dish?

  • [ ] (a) Microsecond beam steering

  • [ ] (b) Multiple simultaneous beams

  • [ ] (c) Graceful degradation when modules fail

  • [ ] (d) Wider main-beam HPBW

Contents