Lesson 34 Flashcards

Lesson 34 Flashcards#

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1. What is RADAR and what does it stand for?

RADAR stands for Radio Detection And Ranging.

It uses electromagnetic waves to:

  • Detect objects (presence)

  • Determine their distance (range)

2. How does a RADAR determine the range to a target?

By measuring the round-trip time of a transmitted signal:

\[ R = \frac{c \Delta t}{2} \]

  • \(c\) = speed of light

  • \(\Delta t\) = round-trip time

3. Why is there a factor of 2 in the RADAR range equation?

Because the signal travels to the target and back.

  • Total measured time is round-trip

  • Distance must be divided by 2 to get one-way range

4. What is line-of-sight (LOS) range for RADAR?

The maximum distance before Earth curvature blocks the signal:

\[ r_{\max,LOS} = \sqrt{2h_{\text{radar}}} + \sqrt{2h_{\text{target}}} \]
5. What is RADAR cross section (RCS)?

A measure of how much energy a target reflects.

  • Denoted \(\sigma\)

  • Units: \(\text{m}^2\) or dBsm

  • Larger RCS → easier detection

6. What is the power density at a target from a RADAR?
\[ S = \frac{P_T G_T}{4 \pi R^2} \]
7. What is the RADAR equation?
\[ P_R = P_T G^2 \sigma \frac{\lambda^2}{(4\pi)^3 R^4} \]
8. How does received power scale with distance in RADAR?
\[ P_R \propto \frac{1}{R^4} \]

  • Doubling distance → power decreases by 16

  • Much steeper than Friis (\(1/R^2\))

9. What improves RADAR detection capability?

  • Higher transmit power \(P_T\)

  • Higher antenna gain \(G\)

  • Larger wavelength \(\lambda\)

  • Larger RCS \(\sigma\)

  • More sensitive receiver (lower \(P_{R,\min}\))

10. What is a RADAR Warning Receiver (RWR)?

A receiver that detects incoming RADAR signals.

  • Acts like a communications receiver

  • Uses Friis equation

  • Alerts target before RADAR detection (ideally)