Surveillance RADAR and Stealth Engineering

Surveillance RADAR

• Scan sky to locate targets

• Antenna with narrow beam gives good angular resolution but means more scan positions

• Hemisphere of sky contains 2π steradians

  • In practice do not need to scan the full hemisphere

• Gain of antenna = 2 * Number of beam positions = 2 * (2π/∆θ∆φ)

Airport Surveillance RADAR

• Primary Surveillance RADAR

  • Works like traditional RADAR

  • Non-cooperative targets

  • Mechanical rotation

  • Antenna has a ‘fan-beam’ pattern

• Secondary Surveillance RADAR

  • Works with cooperative targets

  • Transponder on aircraft sends details on location, speed, heading

  • Mechanical rotation

Tracking RADAR

• Lock on to a target and provide continuous information

• Tracking RADARs use an error signal to control the pointing angle of the antenna main beam

• Can use phased array RADAR or older (less expensive) techniques

Sequential Lobing

Antenna has 2 displaced main beams: Lobe A at time 1 and lobe B at time 2

When the two returns are equal, target on tracking axis.

Need 4 beams for azimuth and elevation tracking

Conical Scan

Conical scanning is similar to sequential lobbing but rotate and a main beam that is off-set from tracking axis.

If target is off the rotation axis, then the output signal will vary in amplitude.

Monopulse RADAR

Uses two (azimuth tracking) or four (azimuth and elevation) simultaneous beams.

Received signal processed too give a sum output and a difference output

Stealth Technology

• Also known as Low Observable technology (LO technology)

• Techniques to make an object less detectable by sensors

  • Object - Aircraft, Ships, Submarines, People, Land vehicles, Missiles, Windfarms

  • Sensors - RADAR RF, Thermal, Visual, Acoustic

RADAR Stealth

• Involves reducing the target RADAR Cross Section (RCS)

• Geometrical shaping and careful design – about 99%

• Coatings – paints , composite structures

• “Meta-surfaces” and “Active” surfaces.

• Aerodynamics and Stealth engineering have different requirements – most stealth aircraft are unstable

RADAR Cross Section (RCS)

RCS of geometric shapes

RCS vs angle variation of geometric shapes

RADAR Absorbing Materials (RAM)