Lesson 34 Flashcards — The Radar Range Equation#
Click a question to reveal the answer.
1. How does a radar link differ from a communications link?
The signal makes the trip twice — out to the target and back — so spreading loss applies twice, giving \(1/R^4\) instead of \(1/R^2\).
2. What is radar cross section?
A measure of how much power a target scatters back, in square meters — but it is not physical size. It varies enormously with aspect (the direction the radar views the target from), shape, and coatings. The slides write it \(\sigma\); the equation sheet writes RCS.
3. Write the radar range equation.
\(P_R = P_T G^2 \sigma \lambda^2/[(4\pi)^3 R^4]\).
4. Why does G appear squared in the radar range equation?
Because the same antenna both transmits and receives. The equation sheet prints it as \(G_T^2\).
5. Give the maximum detection range.
\(R_{\max} = \sqrt[4]{P_T G^2 \sigma \lambda^2/[(4\pi)^3 P_{R,\min}]}\) — every term sits under a fourth root. \(P_{R,\min}\) is the radar's sensitivity, its minimum detectable signal.
6. What must you do to double a radar's detection range by transmit power alone?
Raise \(P_T\) by a factor of 16. That is the fourth root working against the designer.
7. Cutting RCS by a factor of 16 does what to detection range?
Halves it. The target's lever is equally fourth-rooted — but it is one-time engineering rather than a continuing power bill, which is why stealth wins.
8. A 100× RCS reduction cuts range by how much?
\((1/100)^{1/4} = 0.316\), so range drops to about a third. Modest on paper, but the defended area scales as \(R^2\) and so shrinks tenfold.
9. On an RCS polar plot, what do the angle and the radius show?
The angle is the aspect — where the radar is, as seen from the aircraft, with 0° at the nose and 180° at the tail. The radius is \(\sigma\) in square meters.
10. What is the fuzzball on an RCS plot, and when do you use it?
The low RCS level the target shows at every aspect between the narrow spikes. Use the fuzzball value unless the problem names an aspect that falls on a spike.
11. What is the depression angle named on an RCS plot?
How far below the aircraft's horizon the radar sits, looking up at it. A plot is drawn for one frequency band and one depression angle, so pick the plot that matches the problem.
12. How does an RWR detecting a radar differ from a radar detecting an aircraft?
The RWR is a one-way problem (\(1/R^2\)); the radar is two-way (\(1/R^4\)). Which one detects first depends on the two sensitivities and on \(\sigma\) — compute both ranges.
13. How do you find the range at which an RWR detects a radar?
Friis solved for \(R\), with the radar as the transmitter: \(R = \frac{\lambda}{4\pi}\sqrt{P_T G\,G_R/P_{R,\min}}\), using the RWR's own antenna gain \(G_R\) and sensitivity.
14. Why is listening free for the aircraft?
Because the radar has to transmit to do its job. Transmitting is what gives you away — the foundation of electronic support.