chapter 1 introduction to radar - ee.fju.edu.tw
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1 - 1Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Applications of Radars
Civil Applications
•Weather Avoidance
•Navigation
•Maritime Uses
•High Resolution AreaMapping
•Sounding
•Space Flight
Military Applications
•Navigation
•Early Warning and SeeSurveillance
•Fighter/Interceptor Mission
•Air-to-Ground Operations
•Air-to-Surface NavalApplications
•Proximity Fuses
•Countermeasures
1 - 2Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
SAR MAP
1 - 3Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Airbone Radar
1 - 4Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Fighter/Interceptor
1 - 5Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
F-15 Multimode APG-63 Radar
1 - 6Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
F-20 Multimode APG-67 Radar
1 - 7Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Phase Array Radar
愛國者飛彈射控雷達 神盾雷達系統
1 - 8Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Surface-to-Air Radar
1 - 9Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Missile (AMRAAM)
1 - 10Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Missile Guidance
1 - 11Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Missile Guidance
1 - 12Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Basic Element of Radar
Transmitter
• RF amplifier• TWT
Antenna
• Parabolic Reflector• Phase-array
Receiver
• Crystal detector• RF amplifier• homodyne• Superheterodyne
Indicator
• PPI (position)• Speaker or earphone
(Doppler)
RADAR (Radio Detection and Ranging)
1 - 13Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Basic Radar Operation•Radar derives target information by correlating the received signal with the transmitted signal.
Target information Table 1-1.
Size -> strengthRange -> time delayAngular -> Antenna beamVelocity -> Doppler
1 - 14Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Radar Equation
• Transmit Power• Range• Radar Cross Section (RCS)• Frequency• Antenna Gain
- Effective ReceivingAperture (area)
- Wave length
• Other aspects for equation- Prop. Medium & Path
- Atmospheric noise
- System losses (Nonidealcomponents)
- Thermal noise
- Signal process losses(nonideal)
- Other Losses withparticular configurationsand applications
• Powerdensity atRange R
1 - 15Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Radar Cross section (RCS)
1 - 16Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Noise Factor and Noise Figure•Noise Factor: account for noise effects of the receiver
While antenna is matched to the receiver circuit, the thermal noise input tothe receiver is , ,often
. : Bandwidth
•Noise Figure: NF = 10 Log(Fn) in dB
FnSNR iSNR o
--------------------Si NiSo No----------------
No NiSo Si----------------= = = No A Fn Ni =
Ni kTB= k 1.38 10 23–=
T To 290k= = kTo 4 10 21–= B
A
FNi
Si
No A Fn Ni =
Equivalent input noise
So ASi=
Ni
Si Loss = LSo Si L=
No Ni=
kTB is the minimum level forThermal noise
1 - 17Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Maximum Detection Range
Rmax dBm
14--- Pt
dBW2 GdB 2 dBcm dBm 2 BdBMHz Fn
dBLdB
SoNo-------
min dB––– 71dB+–+ + +=
1 - 18Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Other Factors for Radar Equation
Hidden in the radar equation is the fact that the signal receivedis not fixed rather the signal is usually considered be random.
The target return is corrupted by
•Atmospheric &Thermal noise
•EMI, ECM
•Undesired returns from other targets (clutter)
•Propagation medium anomalies (irregularity)
The target RCS often changes in an unknown way due to a changeof position
1 - 19Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Radar Detection
Statistical Process
• Atmospheric, thermal noise,electromagnetic interference,background clutter, propagationmedium anomalies, electroniccountermeasures.
• Target’s RCS
Detection
• Single Pulse Probability of False Alarm• Probability of Detection• Output SNR
1 - 20Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
pdf of Detection Output (No Target)
False Alarm
• SNR = 0, no Target is present• Rayleigh Distribution Approach• Threshold
• Due to Random Signals
1 - 21Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
pdf of Detection Output (Target)
Probability of Detection
• SNR= 1, 2, 3... with target• Rican Distribution -> Direct ray + Rayleigh• Threshold
Maximum Detection Range
• Single Pulse Probability of FalseAlarm (Pfa)
• Probability of Detection (Pd)• Output SNR
1 - 22Chapter 1: Introduction to Radar Dr. Sheng-CHou Lin
Radar System Design
Other Factors of Pd
•Effects of unmatched receiver
— Receiver frequency response relative to a matched filter
•Effects of target signal (Steady or Fluctuating)
— Target reflexivity characteristics
•Effects of antenna pattern (scan modulation, multipath)
• Interference other than noise (clutter, electromagneticinterference, electronic countermeasures)
— Propagation medium and path
•Number of samples included in decision
— Coherent or Noncoherent
— Independent or dependent