Lecture_6 - x ChineseExport Modulatingthe RadarsWave 4...

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Combined Radar Systems
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Japanese Kong ō  Class DDG
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Chinese Export
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Modulating the            Radar’s Wave Amplitude Modulation Vary the amplitude of the carrier sine wave Frequency Modulation Vary the frequency of the carrier sine wave Pulse-Amplitude Modulation Vary the amplitude of the pulses Pulse-Frequency Modulation Vary the Frequency at which the pulses occur
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Types of Combined             Radar Systems Frequency Modulated CW Radar  Use for radar altimeters and missile guidance. Pulse Doppler Carrier wave frequency within pulse is compared with a reference  signal to detect moving targets. Can use Bandpass Filter to remove signals that do not have a  specific Doppler shift Moving Target Indicator (MTI) System Signals compared with previous return to enhance moving targets   Search radars
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Continuous Wave Radar Radiates uninterrupted energy at a fixed frequency Continuous transmission Relies on “Doppler shift” Can’t determine range because there is no interval between pulses Second most popular type of radar
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Doppler Frequency Shifts Motion Away Motion Towards Echo Frequency Decreases Echo Frequency Increases
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Continuous Wave Radar Doppler frequency shift describes the effect that motion has on a reflected frequency If the wall is moving away, a basketball will have to travel farther than the previous basketball, so the reflected basketballs are further apart If the wall is moving toward you, the opposite occurs— reflected basketballs are closer together
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Doppler Frequency Shifts Motion Away Motion Towards Echo Frequency Decreases Echo Frequency Increases
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Continuous Wave Radar Assume that each ball represents the top of a wave… So, the distance between each ball represents a wave cycle Then you find: The frequency of the echo is lower if the target is moving away The frequency of the echo is higher if the target is coming towards This is why the sound of a passing train or airplane goes from higher pitch to lower pitch
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Continuous Wave Radar  Components Oscillator
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Continuous Wave Radar Transmit/Receive Antennas Since must operate simultaneously, must be located separately so receiving antenna doesn’t pick up transmitted signal Oscillator or Power Amplifier
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  • Spring '14
  • Sonar

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