1

What is RADAR?

(RAdio Detection And Ranging)

Presentation on April 8, 2019, by

Chris StewartPresident/COO

Pocket Radar, Inc.

What is RADAR? (RAdio Detection And Ranging)

RADAR is a method of using electromagnetic waves to determine the position (range and direction), velocity and identifying characteristics of targets.

2

The Basics

Waves Reflect

3

The BasicsDoppler Shift

4

The Basics

“RADAR” = RAdio Direction And Ranging

Some Examples of Applications using RADAR:

DefenseWeatherSecurity SystemsAutomotiveGuidance SystemsLaw EnforcementSportsAutomatic Door OpenersAgricultureNavigationMotion SensingTank Level SensingTraffic SafetyMilitaryHealth CareHandicap Assistance DevicesWater Flow

Collision AvoidanceOceanographyMappingGeologySelf Driving CarsAir Traffic ControlUnderground SearchesBoat SafetyAstronomyImagingRoboticsForensicsSearch and RescueOil Slick TrackingAtmospheric StudiesLandmine DetectionRailway Safety

6

• Faraday - Electromagnetic Induction (~ 1831)

• Doppler – Discovery of the Doppler Effect (~ 1842)

• Maxwell - Theory of Electromagnetic Waves (~ 1865)

• Hertz - Demonstration of Electromagnetic Waves (~ 1887)

• Tesla - Invention of Radio and the Resonant Circuit (~ 1897)

• Hülsmeyer – Telemobiloscope: First working RADAR (~ 1903)

• Armstrong - Superheterodyne Receiver (~ 1918)

• Marconi - Proposal of RADAR concepts (~ 1922)

• Watson-Watt – Working RADAR systems in the UK (~ 1935)

Early History:

7

First Working RADAR:

The Telemobiloscope:

The Telemobiloscope was primarily a spark-gap transmitter connected to an array of dipole antennas, with a coherer based receiver and a parabolic antenna that could rotate 360 degrees. While the transmitted signal had a broad coverage, the receiving antenna was narrowly focused. When a reflected signal reached the receiver, a relay was actuated and, in turn, rang an electric bell.

8

WWII Era RADAR:

The H2S was the first ground-scanning radar to be mounted on an aircraft, and made it possible to find long-range targets at night and in bad weather from 1943 on.

9

Ground Penetrating RADAR:

Through the Wall RADAR:

10

Types of RADAR

PrimaryRADAR

SecondaryRADAR

CWRADAR

UnmodulatedCW RADAR

RADAR

FM CWRADAR

Active Response to RADAR Signal

Passive Response to RADAR Signal

PulseRADAR

MTI PulseRADAR

Pulse DopplerRADAR

Types of RADAR

PrimaryRADAR

SecondaryRADAR

CWRADAR

UnmodulatedCW RADAR

RADAR

FM CWRADAR

Active Response to RADAR Signal

Passive Response to RADAR Signal

PulseRADAR

MTI PulseRADAR

Pulse DopplerRADAR

Pulse RADAR:

The maximum non-ambiguous range is:

Rna = (PRI-PW)·c/2

where: c =1

μ0ξ0= the speed of light

Good for long distance range measurements but not instantaneous velocity, trade-offs with choice of PRI and Pulse Width, Problems with “Clutter”

C=1Μ 0 ϵ 0 − − − − √ C=1Μ0ϵ0

C=1Μ 0 ϵ 0 − − − − √ C=1Μ0ϵ0

Pulse Radar

Basic Radar Uses On/Off Keying of a CW Waveform

t

14

Pulse Radar

Pulse Distortion

Long returns from P1 causes distortion to the returns of P2

15

Pulse Radar

Range Ambiguity

c

16

Pulse Radar

Pulse Range

• Speed of travel for radio waves = Speed of Light = c• c = 3x108 meters/sec = .984x109 feet/sec• So a Radar pulse travels about 1 foot in a nanosecond

17

Types of Pulse RADAR

Moving Target Indicator (MTI) and Pulse-Doppler RADAR

• MTI (Moving Target Indicator) RadarThe MTI radar uses low pulse repetition frequency (PRF) to avoid range ambiguities, but these radars can have Doppler ambiguities. Helps distinguish moving objects from fixed objects to remove Clutter

• Pulse Doppler RadarContrary to MTI radar, pulse Doppler radar uses high PRF to avoid Doppler ambiguities, but it can have numerous range ambiguities

18

Types of RADAR

PrimaryRADAR

SecondaryRADAR

CWRADAR

UnmodulatedCW RADAR

RADAR

FM CWRADAR

Active Response to RADAR Signal

Passive Response to RADAR Signal

PulseRADAR

MTI PulseRADAR

Pulse DopplerRADAR

Continuous Wave (CW) RADAR:

fD = 2·v/λ

fD = Doppler Frequency [Hz]λ = wavelength of transmitted signal [m]v = speed of the moving object [m/s]

Good for velocity measurements but does not determine range.Simple CW RADAR does not distinguish direction.

20

Continuous Wave (CW) RADAR:

fD = 2·v/λ

fD = Doppler Frequency [Hz]λ = wavelength of transmitted signal [m]v = speed of the moving object [m/s]

Good for velocity measurements but does not determine range.Simple CW RADAR does not distinguish direction.

Calculate fD in Hz per MPH = 2/λc = 186,000 Miles per sec * 3600 sec per Hour c = 669,600,000 Miles per Hourλ = c/fc = 669,600,000 MPH/24.125 GHz = .0278fD = 2/.0278 = 72 Hz per MPH

21

Example of Simple CW RADAR

Low-cost CW RADAR module is used for door openers and alarm systems.

Types of CW RADAR

• UnmodulatedAn example of unmodulated CW radar is the speed radar used by the police. The transmitted signal of these equipment is constant in amplitude and frequency. CW radar transmitting unmodulated power can measure the speed by using the Doppler-effect. It cannot measure a range and it cannot differ between two reflecting objects.

• ModulatedRange can be added to CW radars by using the frequency shifting method. In this method, a signal that constantly changes in frequency around a fixed reference is used to detect stationary objects. Frequency is swept repeatedly between f1 and f2. On examining the received reflected frequencies (and with the knowledge of the transmitted frequency), range calculation can be done. If the target is moving, there is additional Doppler frequency shift which can be used to find if target is approaching or receding.Frequency-Modulated Continuous Wave radars (FMCWs) are used in Radar Altimeters.

Sawtooth modulationThis modulation pattern is used in a relatively large range (maximum distance) combined with a negligible influence of Doppler frequency (for example, a maritime navigation radar).

Triangular modulationThis modulation allows easy separation of the difference frequency Δf of the Doppler frequency fD

Square-wave modulation (simple frequency-shift keying, FSK)This modulation is used for a very precise distance measurement at close range by phase comparison of the two echo signal frequencies. It has the disadvantage, that the echo signals from several targets cannot be separated from each other, and that this process enables only a small unambiguous measuring range.

Stepped modulation (staircase voltage)This is used for interferometric measurements and expands the unambiguous measuring range.

Sawtooth

Triangular

Rectangular

Staircase Voltage

FMCW Modulation Patterns:There are several possible modulation patterns which can be used for different measurement purposes:

Modulated CW RADAR: Sawtooth Modulation

The maximum non-ambiguous range is:

Rna = c·T/2

Mod / Demod

Range = Δt·c/2 The time delay is calculated as follows: Δt = T·Δf/(f2-f1) where: f2 = maximum frequency f1 = minimum frequency T = period of sweep from f1 to f2, Δf is the difference between transmitted and received frequencyΔf = ((f2-f1)/ T)·((2·d)/c)where d = distance to target

25

FSK RADARCan determine velocity and range on moving objects

FMCW RADAR with Triangle Wave ModulationCan determine range on fixed objects or moving objects and velocity of moving objects

uW Amplifier

uW Amplifier uW Amplifier

IF Amplifier

Horn Antenna

Horn Antenna

Isolator

Isolator

Mixer

Low Pass Filter

Directional Coupler

FFT Signal Analyzer

fD = (2·v)/λ

Continuous Wave RADAR Demo System: Velocity Measurement

Oscillator

28

Modulated CW RADAR Demo System: Distance Measurement

uW Amplifier

uW Amplifier uW Amplifier

IF Amplifier

Horn Antenna

Horn Antenna

Isolator

Isolator

Mixer

Low Pass Filter

Directional Coupler

Voltage Controlled Oscillator

Trigger In

Sweep Ramp

FFT Signal Analyzer

Theory: Δf = ((f2-f1)/ T)·((2·d)/c)

Sweep (Hz/sec) Delay (sec)

29

Modulated CW RADAR Demo System: Distance Measurement

uW Amplifier

uW Amplifier uW Amplifier

IF Amplifier

Horn Antenna

Horn Antenna

Isolator

Isolator

Mixer

Low Pass Filter

Directional Coupler

Voltage Controlled Oscillator

Trigger In

Sweep Ramp

FFT Signal Analyzer

Actual: Δf = ((f2-f1)/ T)·(((2·d)/c)+τg)

Sweep (Hz/sec) Delay (sec)

Free Space

GroupDelay

30

Basic RADAR Range Equation: (Monostatic = Single Antenna)

σ = RADAR Cross Section (RCS) is a measure of how much radar energy is reflected back to the source. The factors that influence RCS include:The material of which the target is made;The absolute size of the target;The relative size of the target, (in relation to the wavelength of the illuminating radar);The incident angle, (angle at which the radar beam hits a particular portion of target which depends upon shape of target and its orientation to the radar source);The reflected angle (angle at which the reflected beam leaves the part of the target hit, it depends upon incident angle);The polarization of transmitted and the received radiation in respect to the orientation of the target

31

More Complete RADAR Equation: (Monostatic = Single Antenna)

Power Density vs. Range

33

Key Enabling Technology:

Gunnplexer

Klystron

Magnetron

Antennas:

Most communications systems want to have omnidirectional antennas that cover all directions equally. RADAR antennas want to focus the radio waves into a narrow beam so that they only cover a small angle so that the operator can resolve the specific direction of the target.

“Ideally” radiates equally in all directions

Radiates most of the energy in a specific direction

Antennas:

Horn Parabolic Reflector Patch Array

36

Stealth Technology: How to Minimize the Radar Cross Section

𝑍0 =μ0ξ0

~ 377 𝑂ℎ𝑚𝑠Characteristic Impedance of Free Space:

Its All About The Angles: Another stealth tactic is to make sure the surfaces that reflect radio waves do not reflect the signal directly back to the source.

When an electromagnetic wave encounters a matched impedance the energy is absorbed and not reflected. If you can make an object out of materials that have the same characteristic impedance as free space then they will have minimal reflection of radio waves.

37

The Future?

Questions ?

Homework for LAB Class: (For a given fstart, fstop, Tsweep and τg)

Create Spreadsheet to Graph Predicted and Measured Freq vs Distance

uW Amplifier

uW Amplifier uW Amplifier

IF Amplifier

Horn Antenna

Horn Antenna

Isolator

Isolator

Mixer

Low Pass Filter

Directional Coupler

Voltage Controlled Oscillator

Trigger In

Sweep Ramp

FFT Signal Analyzer

Actual: Δf = ((f2-f1)/ T)·(((2·d)/c)+τg)

Sweep (Hz/sec) Delay (sec)

Free Space

GroupDelay

8360

3561

Fmin=7 GHzFmax=13 GHzTs_min=20 msTs_max=100ms

τg_min= 1 ns

τg_max= 5 ns

Where: d = Distance

40

y = 50.8x + 680.6

y = 52.56x + 680.6

-

500

1,000

1,500

2,000

2,500

3,000

0 5 10 15 20 25 30 35 40

Difference Freq versus Range

Calc Freq Meas Linear (Calc Freq) Linear (Meas)

Δf (Hz)

Distance (inches)

Review Questions:

• What does RADAR stand for?

• When was the first working RADAR system deployed?

• What is the Doppler equation?

• How long does it take a radio signal to travel 1000 feet?

• What is “non-ambiguous range”?

• What is “RCS”?

• What type of RADAR can measure speed?

• What type of RADAR can measure distance?

Back-up Slides

Early History:

Acoustic “RADAR” ~ 1920s and 1930s

44

The 40’s

45

The 50’s

46

The 70’s

47

The 90’s

The 2000’s

The 2010’s