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Third Edition By : Merrill I. Skolnik

Third Edition By : Merrill I. Skolnik. INTRODUCTION TO RADAR SYSTEMS. Chapter 2 : The Radar Equation. The Simple form of Radar Equation . is radar cross section. is effective aperture of antenna . is peak power. is gain of antenna. Minimum of detectable signal by receiver .

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Third Edition By : Merrill I. Skolnik

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  1. Third Edition By : Merrill I. Skolnik • INTRODUCTION TO RADAR SYSTEMS • Chapter 2 : • The Radar Equation

  2. The Simple form of Radar Equation is radar cross section is effective aperture of antenna is peak power is gain of antenna Minimum of detectable signal by receiver Target parameter Under control of Radar designer

  3. The failure of Simple Form • Statistical nature of Smin(determined by reciever noise). • Fluctuation of radar cross section. • Losses. • Propagation effects (earth‘s surface, weather and atmosphere) Therefore: The probability of detection : Pd and The probability of false alarm : Pfa must be considered. This mean:

  4. Detection of Signal in Noise Threshold Detection : A-scope presentation (amplitude versus time or range)

  5. Receiver Noise Thermal Noise Power:

  6. Probability Density Functions (PDF)

  7. Probability of False Alarm Envelope Detector: Probability of Noise Voltage in input of IF stage is Gaussian PDF : Mr. Rice has shown that the noise in output of IF is Rayleigh : Probability of False Alarm :

  8. Probability of False Alarm

  9. Probability of False Alarm

  10. Probability of Detection Rice Probability density function Zero-order Modified Bessel Function

  11. Integration of Radar Pulses is Rotate Per Minute (rpm) of Antenna is Pulse Repetition frequency (PRF) of Radar is Half Power Beam Width (HPBW) of Antenna is number of pulse per scan ( hit per scan ) sec x is time on target

  12. Integration of Radar Pulses Types of Integration: Pre-detection integration (Coherent integration ). Post-detection integration (Non-coherent integration ). Pre-detection integration needs to phase of pulses. Post-detection integration don’t need to phase of pulses Integration Efficiency : Integration Improvement Factor : Integration Loss: J. I. Marcum, 1954, Rand Corporation report

  13. Integration of Radar Pulses

  14. The Radar Cross Section Types of Targets: • Simple targets such as: Sphere, Cylinder, Flat plate, Rod, Ogive and cone • Complex targets such as: Aircraft, Ship, Building, …

  15. The Radar Cross Section Sphere :

  16. The Radar Cross Section Aircraft :

  17. The Radar Cross Section

  18. The Radar Cross Section

  19. The Radar Cross Section Ships: f frequency (MHz) D ship displacement (kiloton)

  20. The Radar Cross Section Ships:

  21. The Radar Cross Section Missiles:

  22. The Radar Cross Section

  23. Radar Cross-Section Fluctuations

  24. Radar Cross-Section Fluctuations target

  25. Radar Cross-Section Fluctuations Swerling Target Models: Case 0: • No-Fluctuation in radar cross section occurs. Case 1: • Scan to Scan Fluctuation (Rayleigh scattering ) or slow Fluctuation with PDF: Case 2: • Pulse to Pulse Fluctuation or Fast Fluctuation with same PDF of case 1: • Scan to Scan Fluctuation with PDF: Case 3: • Swerling assume that target is very big and contain many small targets Case 4: • Pulse to Pulse Fluctuation or Fast Fluctuation with same PDF of case 3:

  26. Radar Cross-Section Fluctuations

  27. Radar Cross-Section Fluctuations Fluctuations loss : • Radar Cross-Section Loss in radar equation:

  28. Radar Cross-Section Fluctuations • Decorrelation by frequency Diversity & Agility : • Frequency Diversity: • Multiple TX/RX in different frequency is used. Example is air traffic control radar for reliability of detection. • Frequency Agility: • Pulse to Pulse change in radar frequency by a wide band TX. • It don’t used for MTI radars.

  29. PRF (Pulse Repetition Frequency)

  30. Antenna Parameters • Gain : • or • is vertical beam width • is horizontal beam width • D is directivity of antenna

  31. Antenna Parameters • Beam Shape : • Pencil Beam : • Fan Beam : • Typical values • Typical values

  32. Antenna Parameters • Cosecant Squared Beam: • Height • Antenna Pattern • TX/RX • Range

  33. Antenna Parameters • Cosecant Squared Beam:

  34. Antenna Parameters • Revisit Time : • Scan rime of antenna • Rotate Per Minute (RPM) • Number of pulse for suitable signal to noise. • Target speed. • is depending to : • Practical value for is : • 5-6 rpm for long range air traffic control radars. • 10-15 rpm for long range military radars. • 30-60 rpm for high speed targets.

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