7/29/2019 Lesson 03 - Radar Principles II (1)

1/17

Radar Principles andSystems

Part II

7/29/2019 Lesson 03 - Radar Principles II (1)

2/17

Learning Objectives

Comprehend the factors that effect radar

performance

Comprehend frequency modulated CW as

a means of range determination

Comprehend the basic principles of

operation of pulse-doppler radar and MTI

systems

7/29/2019 Lesson 03 - Radar Principles II (1)

3/17

Factors That Affect Radar

PerformanceSignal Reception

Receiver Bandwidth

Pulse Shape

Power Relation

Beam Width

Pulse RepetitionFrequency

Antenna Gain

Radar Cross Section ofTarget

Signal-to-noise ratio

Receiver Sensitivity

Pulse Compression

Scan Rate Mechanical

Electronic

Carrier Frequency

Antenna aperture

7/29/2019 Lesson 03 - Radar Principles II (1)

4/17

Radar Receiver Performance

FactorsSignal Reception

Signal-to-Noise Ratio

Receiver Bandwidth

Receiver Sensitivity

7/29/2019 Lesson 03 - Radar Principles II (1)

5/17

Signal Reception

Only a minute portion of theRF is reflected off the target.

Only a fraction of that returnsto the antenna.

The weaker the signal thatthe receiver can process, the

greater the effective range .

7/29/2019 Lesson 03 - Radar Principles II (1)

6/17

Signal-to-Noise Ratio

Measured in dB!!!!!

Ability to recognize target in random noise

Noise is always present. At some range, noise is greater that targets return

Noise sets lower limit of units sensitivity

Threshold level used to remove excess noise

7/29/2019 Lesson 03 - Radar Principles II (1)

7/17

Receiver Bandwidth

Frequency range receiver can process

Receiver must process many frequencies

Pulses generated by summing sine waves of various

frequencies Frequency shifts occur from Doppler Effects

Reducing the bandwidth

Increases signal-to-noise ratio (good)

Distorts transmitted pulse (bad)

7/29/2019 Lesson 03 - Radar Principles II (1)

8/17

Receiver Sensitivity

Smallest return signal that is discernible

against the noise background

Milliwatts range

Important factor in determining units

maximum range

7/29/2019 Lesson 03 - Radar Principles II (1)

9/17

Pulse Effects on Radar

PerformancePulse ShapePulse Width

Pulse CompressionPulse Power

7/29/2019 Lesson 03 - Radar Principles II (1)

10/17

Pulse Shape

Determines

Range accuracy

Minimum and maximum rangeIdeally want pulse with vertical

Leading edge

Trailing edge Clear signal

Easily discernible when listening for echo

7/29/2019 Lesson 03 - Radar Principles II (1)

11/17

Pulse Width

Determines radar range resolution

Minimum detection range

Maximum detection range

The narrower the pulse, the better the

range resolution

7/29/2019 Lesson 03 - Radar Principles II (1)

12/17

Pulse Compression

Increases frequency of the wave within the

pulse.

Allows for good range resolution whilepacking enough power to provide a large

maximum range.

7/29/2019 Lesson 03 - Radar Principles II (1)

13/17

Pulse Power

Efficiency to get signal out a long way

High peak power desirable to achieve

maximum ranges

Lower power radar units mean

Smaller and more compact

Less power required to operate

7/29/2019 Lesson 03 - Radar Principles II (1)

14/17

Other Factors Affecting

PerformanceScan Rate and Beam Width

Narrow beam require slower antenna rotation rate

Pulse Repetition Frequency

Determines radars maximum range(tactical factor)

Carrier Frequency

Determines antenna size, beam directivity and target size

Radar Cross Section (What radar can see(reflect))

- target size, shape, material, angle and carrier frequency

7/29/2019 Lesson 03 - Radar Principles II (1)

15/17

Combined Radar Systems

Frequency Modulated CW

Pulse Doppler

MTI systems

7/29/2019 Lesson 03 - Radar Principles II (1)

16/17

Summary of Factors and Compromises

Summary of Factors and Compromises

Pulse Shape Sharp a rise as possible Better range accuracy Require infinite bandwidth, more complexTall as possible More power /longer range Requires larger equipment/more power

Pulse Width Short as possible Closer minimum range Reduces maximum rangeMore accurate range

Pulse Repetition Freq. Short Better range accuracy Reduces maximum rangeBetter angular resolutionBetter detection probability

Pulse Compression Uses technique Greater range More complex circuitryShorter minimum range

Power More Greater maximum range Requires larger equipment & powerBeam Width Narrow Greater angular accuracy Slow antenna rate, Detection timeCarrier Frequency High Greater target resolution Reduces maximum range

Detects smaller targetsSmaller equipment

Receiver Sensitivity High Maximizes detection range More complex equipmentReceiver Bandwidth Narrow Better signal-to-noise ratio Distorts pulse shape

Factor Desired Why Trade-off Required

7/29/2019 Lesson 03 - Radar Principles II (1)

17/17

Questions?