Phased Array Radars Naval Weapons Systems Limitations of Mechanical Scanning Radars Positioning Antenna is SLOW Reduced reaction times Blind Sided! Mechanical error Electronic Scanning Increased Data Rates Instantaneous Beam Positioning Elimination of Mechanical Errors Multi-mode Operation Multi-target capability Phased Array / SPY – 1D Phase Concept Think about this: 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. Phase Relationships Constructive Interference Destructive Interference Generating a Directional Main Lobe in a Phased Array Radar Wave Fronts of Maximu m Energy Boresight Boresight Axis Axis Radiating in Phase Altering the Phase to Change the Axis Beam Positioning P Point “P” where all waves arrive in phase Methods of Beam Steering 3 Kinds Time Delay Scanning Frequency Scanning Phase Scanning 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 Time Delay Scanning d Methods of Beam Steering Frequency Scanning The physical length ofthe wave guide to delay the frequency interval frequency about a base Vary the frequency Very simple and relatively inexpensive. Frequency Scanning Wave guide feed horns Case #1 All Waves transmitted are in phase Wave guide Case #2 Waves transmitted are phase shifted Wave guide Methods of Beam Steering Phase Scanning Radiating elements fed by phase- shifting networks (Phasers) Phasers are electronically adjustable More expensive, than frequency scanning but cheaper than time delay Most widely used – SPY! Phase Scanning Phasers!! Fleet Uses of Electronic Scanning Ticonderoga ArleighBurke SPS-48 Air Search AN/SPS – 48 Synthetic Aperture Array Radar * Uses the same theory of electronic scanning. * Motion of the target used as the antenna aperture * Sequential instead of simultaneous * High resolution imaging from aircraft ISAR Electronic Scanning Summary • Electronic scanning is GROOVY! • Yeah Baby, Yeah!!! • Multiple functions • Search • Track (so, TWS) • Beam Steering • Time delay, Frequency, and Phase scanning • VERY BASIC LOOK AT ELECTRONIC SCANNING! QUESTIONS?
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