Radar Principles

Question 1

Describe a pulsed radar system.

Answer 1

Transmission and reception are separated in time.
Only 1 antenna required.
Range ambiguity, poor differentiation between targets & clutter, blind at short range
Surveillance & weather

Question 2

Describe a coherent pulse radar.

Answer 2

Pulses are identical which allows the instantaneous measure of relative radial velocity
Improved detection of targets against clutter.
Complex system and suffers Doppler ambiguity.

If wavelength increases the source is moving away.
If wavelength decreases the source is moving closer.

Question 3

Describe FMCW radar.

Answer 3

Frequency Modulated Continuous Wave radar
Transmits and receives simultaneously.
Simple, cheap, low power, range & Doppler info possible
2 antenna, range * Doppler ambiguity
Airfield surveillance & altimeters.

Question 4

Radar uses in aerospace?

Answer 4

Radar altimeter

Weather radar: h(ft) = 100 * r (n.m) * theta (delay)

Question 5

What is TCAS?

Answer 5

Traffic Collision Avoidance System.
System works independently of air traffic control and effectively ‘watches’ for other transponder equipped aircraft and warns if a mid-air collision is likely.

Question 6

Derive the radar equation & perform calculations based upon it.
Also describe major factors that influence radar detection.

Answer 6

We know that Ep = Gt Et / 4 pi R^2
Over a time period, T, Et = Pt T, so… Ep = Gt Pt T / 4 pi R^2
If the target has radar cross section J, Ea = Ep J / 4 pi R^2
So Ea = Gt Pt T J / (4 pi R^2)^2
For a receiving antenna with area Ar, E = Ea Ar
So E = Gt Pt T J Ar / (4 pi)^2 R^4