Phased Array Radars

1
Phased Array Radars

• Naval Weapons Systems

2
Limitations of Mechanical Scanning Radars

• Positioning Antenna is relatively slow due
  antenna inflexibility and inertia.
• Reduced reaction times.

3
Electronic Scanning

• Increased Data Rates
• Instantaneous Beam Positioning
• Elimination of Mechanical Errors
• Multi-mode Operation Multi-target capability

4
Phase Concept

• The electromagnetic energy received at a point in
  space from two or more closely spaced radiating
  elements is a maximum when the energy from each
  radiating element arrives at a point in phase.

5
Phase Relationships

• Constructive Interference
• Destructive Interference

6
Generating a Directional Main Lobe in a Phased
Array Radar
Wave Fronts of Maximum Energy
Beam Axis
Radiating in Phase
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Beam Positioning
P
Point P where all waves arrive in phase
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Beam Positioning
T
d
d Sin T
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Methods of Beam Steering

• Time Delay Scanning
• Use of time delay to achieve the desired phase
  relationship
• Time delay networks installed in front of each
  radiating element
• Expensive, Complex Heavy

10
Time Delay Scanning
d
11
Methods of Beam Steering

• Frequency Scanning
• Simpler Method, Inexpensive, jam resistant
• The physical length of the wave guide to delay
  the frequency interval
• (length between elements is n ?o )
• Vary the frequency about a base frequency
• SPS- 48 air search radar

12
Frequency Scanning
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Methods of Beam Steering

• Phase Scanning
• Radiating elements fed by phase-shifting networks
  (Phasers)
• Phasers are adjustable over a range of 0 to 2?
  radians
• More expensive than frequency scanning but
  cheaper than time delay
• Most widely used SPY-1 in Ageis

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Phase Scanning
d
7
6
5
4
3
2
1
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Fleet Uses of Electronic Scanning

• Ticonderoga
• Arleigh Burke
• SPS-48 Air Search
• Hapan

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SPY-1 Ageis Weapons System
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Synthetic Aperature Array Radar
Uses the same theory of electronic scanning.
Uses the motion of the vehicle to generate
the antenna aperture (sequentially rather than
simultaneously). Used mostly in aircraft to
gain image data of the earths surface.
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Electronic Scanning Advantage in Target Detection
A single radar can can perform multiple
functions previously regulated to several
separate radar systems.
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Homework 5

• Read Countermeasures
• Chapter 11
• Workbook Ch. 7 1,2
• Describe how a phased array radar works
• Explain the 3 methods of beam steering