Moving Target Indicators and the Doppler Effect

Moving Target Indicators and the Doppler Effect

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When this author entered the radar field in 1955, moving target indicator (MTI) systems had been in existence for less than 10 years and were still viewed as new. The non-MTI AN/MPN-1 was still the world's most extensively used air traffic control radar. Of all radar subject material, technicians and engineers in 1955 saw MTI as the greatest mental challenge. With that challenge to his senses of responsibility and competence, the author has devoted the years since 1955 to learning about, writing, and teaching MTI theory. The approach in this chapter is purely his own, and represents years of work and study.

Chapter Contents:

  • Introduction
  • The Frequency and Time Domains
  • Christian Doppler
  • Upward Doppler Shift
  • Downward Doppler Shift
  • Basic Doppler Equation
  • 'Apparent Doppler'
  • Radial Velocity
  • Radar Doppler Shift
  • Radar Doppler Equation with Transmitter Frequency
  • Bidirectional Wave Travel and Speed of Light
  • Speed of Light in Nautical Miles per Hour
  • Incorporating the Radial Velocity Calculation
  • The Tangential Effect
  • The Doppler Effect and Phase Detection
  • First and Second Phase Detectors
  • Phase-Detector Response
  • Phase Response of the Signal Mixer
  • The Phase-Detector Operation
  • Comparing Different Frequencies in a Synchronous Phase Detector
  • Doppler Shift Representation at the Phase-Detector Output
  • The Doppler Effect in Pulsed Systems
  • The Echo-Marking Approach
  • The Identical Doppler Effect in c-w and Pulsed Echoes
  • Synthesis System Block Diagram, Incorporating the MTI Principle
  • Cancellation
  • The Difference between Radar Doppler and T r-to-T r Echo Phase Change
  • The 'Butterfly'
  • Blind and Optimum Velocities
  • Blind Velocity Calculation
  • Blind Velocity and Staggered fp
  • Optimum Velocity Calculation
  • The Blind Phase Effect
  • Quadrature Phase Detectors
  • The Triangular Phase-Detector Response
  • The Velocity Response Shape
  • Improvement to the Velocity Response Shape
  • Cascaded Cancelers and Feedback
  • Bipolar and Unipolar Velocity Response Shapes
  • Sweeping the Canceler with Audio
  • Mathematical Relationships from the Velocity Response Shape
  • Finding Δφ from fD and fp
  • Finding the Δφ from V r, xmtr , and fp
  • Finding the Δφ from Aircraft Course, Radar Bearing, fp, and fxmtr
  • T r-T r Radial Target Movement
  • The MTI Reflector
  • The Magnetron MTI System
  • Achieving Coherence
  • Summary of Magnetron Coherence
  • Magnetron System Maintenance Techniques
  • The Locked Test Pulse Generator
  • i-f Test Pulse Generators in Synthesis Systems
  • The Composite Video Test Target Generator
  • Live Video
  • Output Limiting
  • Complex Doppler Echoes and Subclutter Visibility
  • Simultaneous Multiple Dopplers
  • i-f Limiting for a Consistent Phase-Detector Response
  • Echo Phase 'Pulling,' Competition, and Resultant
  • Those Phase-Detector Outputs Variable with Signal Power
  • Optimum i-f Amplifier Adjustment
  • Payoff Adjustment Procedure
  • Maximum i-f Gain
  • Clutter Strength Photographs
  • Subclutter-Visibility Measurement
  • Echo Box SCV Procedure
  • The Passive High-Beam Receiver System
  • Isolating Performance Derogation
  • Poor Cancellation
  • Echo-Box Cancellation Ratio
  • Video Cancellation Ratio
  • Echo-Box Ratio Poor, Video Cancellation Ratio is Satisfactory
  • i-f Cancellation Ratio
  • Causes of Cancellation Failures
  • Further Implications of the Velocity Response
  • Doppler Ambiguity
  • Increasing the fp Decreases Antenna Scanning Residue
  • Range Ambiguities, Magnetron versus Synthesis
  • Different fps Provide Different Blind Velocities
  • Staggered fps and Canceler Velocity Response
  • MTI and Weather
  • The SSR/DMTI Modification for Early ARSR and FPS Series Radars
  • Current ('Soft') Limiting in the MTI i-f Amplifier
  • Multiple Staggered fp
  • Four-Pulse Canceler
  • Review Questions
  • Answers to Review Questions

Inspec keywords: Doppler effect; airborne radar; air traffic control

Other keywords: nonMTI AN-MPN-1; radar field; MTI theory teaching; MTI systems; Doppler effect; air traffic control radar; moving target indicator theory

Subjects: Air traffic control; Radar equipment, systems and applications

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