1Introduction to Radar

Lorenzo Lo MonteMichael WicksBraham Himed

2Welcome

Thank you for attending In this lecture we will: Introduce Radar Fundamentals The Radar Range Equation Loss Budget Formulation

3Overview

These lectures provide a background on uses, advantages, limitations, and operating principles of prevalent radars You will gain a familiarity with major radar components and their function along with radar target and clutter characteristics These lectures also emphasizes radar analysis, waveforms, and modeling Upon completion of the course, you will have the necessary knowledge and building blocks to analyze modern radar research in the area of target detection, pulse compression, waveforms, and signal design

4Books

5Books

6A Special Thank You

U.S. Air Force Research Laboratory University of Dayton Research Institute IEEE AESS Dayton Chapter IEEE New Hampshire Section Dr. Robert ODonnell Dr. Chris Baker (OSU)

Dr. Hugh Griffiths (UCL) Georgia Tech Research Institute Dreamcatcher Dr. Ian Cummings Dr. Peter Tait Dr. Mark Richards William Melvin Dr. Eli Brookner MITRE Corporation

7Two Inventions ThatChanged the Outcome of WW2

According to George Patton

Radar Proximity Fuze

8Radar =RADIO DETECTION AND RANGING

9Radar Block Diagram

Display

ModulatorSynchronizer

SignalProcessorTrackProcessor

Transmitters

ReceiversReceiverProtectorDuplexer

ServoControl

10

Pre-Radar Detection

Visual

Acoustic

RoyalObserver

Corp.

11

Heinrich Hertz confirmed by experiment that electromagnetic radio waves have the same velocity as light and can be reflected by metallic and dielectric bodies

James Clerk Maxwell predicted the existence of radio waves in his theory of electromagnetism

Christian Doppler noted how frequencies shift when the radiator is in motion with respect to the observer.

Historical Background

12

The First RadarHlsmeyer, 1904

Motivated by the desire of understanding how bats could fly at night without vision

Replicated the experiments of Hertz in large scale

He developed the first bistatic radar to detect approaching boats at night

But the German government didnt show much interest

13

Measurements of the Ionosphere

Sir Edward Victor Appleton constructed the first HF radar to measure the height of the ionosphere. The processing was based on what it is today called FMCWGregory Breit and Merle Tove continued the study of the Ionosphere, but they used short pulses, leading to the development of pulsed-radars

14

Robert Watson Watt

In 1935, Watson Watt had been asked by the UK Air Ministry to investigate the feasibility of electromagnetic death rays to disable aircrafts The idea was proposed by Nikola Tesla, but never verified

He concluded that it would not be feasible, but that detection of aircraft using radio waves should be possible The same year he demonstrated detection of aircraft at a range of up to 8 miles in what has become known as the Daventryexperiment by June 1935 he had demonstrated the pulsed radar technique to measure aircraft range.

15

The Chain Home Radar Project

16

The First Report Mentioning RADARNov 19, 1940

17

Radar and Pearl Harbor Attack

Radar Screen at Opana Point7:02AM on December 7th , 1941SCR-270 at Opana Site(106MHz carrier)

18

Boot, Randall, and the Magnetron

Low frequency forced extremely large antennas. The first radar stations used aerials over 100 m in height to produce a directional beam of radio waves But if aerials were much smaller and could be steered, they would be much more useful However, to make smaller aerials meant using radio waves of shorter wavelengths The cavity magnetron was created to generate such waves Randall and Boot of the Physics Department, Birmingham University, made the first cavity magnetron work in February 1940

19

Worlds First Magnetron

20

Klystron

William Hansen began work on the problem of detecting approaching aircraft. Working Russell and Sigurd Varian, he developed the klystron Based upon amplitude modulation of an electron beam rather than on resonant circuits permits the generation of powerful and stable high-frequency oscillations Advances made the klystron the primary method used in radar

21

The First Klystron

22

Radar Taxonomy

RADAR

GroundBased

ShipBased Airborne

SpaceBased

AirSearch

AirTrack

FireControl

BallisticMissile

Weather

Other- GPR- Traffic

FAA Intrusion OTH/SurfaceWave

23

TPS-59

The TPS-59 is a solid-state L-Band, three-dimensional air defense radar which provides long range surveillance and ground control intercept capability in atactically mobile environment Full 360 coverage 400 nmi (740 km) range to 106 ft (305 km) altitude Increased alert time for military and civilian personnel Accurate launch and impact point determination Target classification and debris/missile discrimination Effective anti-missile battery cueing Increased defended footprint

24

FPS-117

The AN/FPS-117 is a phased array, 3-dimensional air search radar. It is produced by the LMCO. The system is a low power, long range (200-250 nautical miles), L-band pencil beam, solid-state transmitter and beacon interrogator search radar.

25

Ground Penetrating Radar

Applications

Mine detection and marking Detection and marking of buried unexploded ordinance (UXO) Detection and marking of buried hazardous waste, electrical cables, telephone cables and pipelines. Detection and marking of leakage from petrol, gas and water pipes Measurement of thickness of road layers Detection of tunnels and bunkers

Features Low magnetic and acoustic signatures Modular hardware and flexible software High reliability/high MTBF Fully digital and solid state

Characteristics

Vehicle movement velocity: 1 meter/sec Detection Width: 2-3 meters Detection Depth: 0.3 - 15 meters GPR Sensor Weight: 52 kps

26

Enhanced Performance High clutter rejection MTI Automatic plot and track extractor Modular upgrades to existing systems Low Cost

Key Features E/F-band operation for long range performance Unstabilized or stabilized antenna group High data rate, high PRF, short pulse operation for target indication/tactical role Low data rate, low PRF, long pulse operation for maximum early warning Variable antenna polarization to minimize the effects of precipitation Wideband tuneable magnetron for frequency management Receiver system with optional comprehensive ECCM and anti-clutter features

Performance

General surveillance operation: operating at 10 rev/min with low PRF and long pulse, the AWS-4 provides vertical coverage on a 4m2 target beyond 120 km range and 12 km in height.High resolution operation: For optimum target resolution and higher data rate, the radar is operated at 20 rev/min, high PRF and short pulse. For a 4m2 target, vertical coverage extends beyond 90km range and 9km height.

AN/SPS-52C3D Shipboard Air Defense Radar

27

Terrain Avoidance

Forward Looking Terrain Avoidance and AltitudeProvides terrain collision warning and altitude in adverse weather with minimal modification to aircraft

Features Multifunction Altitude and Range Altitude range to 5,000 feet Forward range to 10,000 feet- Az, El and Range to Obstacle 50 x 20 Forward Scanning Antenna Spread spectrum, milliwatts of transmitted power and frequency diversity provides excellent covertness 4.3 and 35 GHz MMICs Operates in fog, dust, smoke and >10mm/hr rain rate

28

APS-145 Airborne Early Warning (AEW)

29

AWACS

30

Multimode Fire Control Radar(IAI)

Main Features Pulse doppler, all aspect, look-down shoot down capabilities TWT coherent transmitter Ultra low sidelobe planar antenna Two axes monopulse, guard channel Programmable signal processor Full software control Most advanced architecture, technology and components Adaptability and growth potential

MIL 1553B interface to avionic system Modular hardware configuration Spare memory space and computation power

Typical Performance Detection range at fighter aircraft

Look-up, 35-55 NM Look-down, 30-45 NM

Physical Characteristics Weight: 78-100 Kg depending on antenna size Power: 2-2.5 KVA Antenna Size: adapted to aircraft nose limitations

31

Global Hawk Sensor Suite

32

The Radar Range Equation

Lorenzo Lo MonteMichael WicksBraham Himed

33

Electromagnetic Spectrum

34

Radar Range Equation;Rationale

The Radar Range Equation is the fundamental tool for engineers to determine some of the radar specifications to guarantee a required performance The typical parameters that engineers can manipulate using the radar range equation are: Transmitted peak power Antenna Gain Frequency of Operation Bandwidth of the Signal

35

Radar Range Equation:Warnings

There is no unique definition of a radar range equation. Depending upon the application, some variable are expressed in different ways The radar range equation wont suffice to design a modern radar The radar range equation derived here (and in most books) assumes an old-fashion mode of operation, which is currently superseded At the end of the lecture, we will tweak the radar equation to account for some of the modern processing techniques

36

Radar Range Equation:System Parameters

For a given Radar, we can define a few parameters Peak transmitted power Antenna Gain and Assumed equal for both Tx and Rx, i.e., = Frequency of operation The wavelength will be more useful

37

Radar Range Equation:Power Density

The radar sends a pulse. As the pulse propagates in the space, its power spreads out in the space At a given point in the space, one can define a power density function

= 42

38

Radar Range Equation:Power Density at the Target

However, due to the antenna pattern of the Radar, this power is not equally distributed in the space Usually, the target will be in the main beam of the antenna This means that, in the direction of the target, the power density can be expressed as:

= 42 2

39

Radar Range Equation:Radar Cross Section

The pulse will eventually hit the target, and some energy will be re-radiated back to the radar The amount of reflected power depends on many factors, such as: Shape of the target Aspect angle of the target A common way to quantify the re-radiated field back to the radar is the radar cross section The theory of radar cross section is complicated, and it will be discussed later At this stage, we can account for the target scattering properties with the variable

40

Radar Range Equation:Received Power Density

The power reflected by the target is: The power density re-radiated to the receiver is:

42 []42 2 2

41

Radar Range Equation:Effective Area

By multiplying the received power density with a surface area we obtain the received power For any antenna, one can define an effective area which relates the power density to the actual power captured by the antenna

The effective area is in general smaller than the true aperture . In general = , where is the aperture efficiency

42

Radar Range EquationExpressed in terms of Received

Power

Therefore, the power reflected by the target and captured by the antenna is equal to: In typical electrically large antennas there exist a good approximation between the effective area and the gain So, the received power can be expressed as

= 42 2 [] = 4 2

= 24 34 []

43

Radar Range Equation

We derived the simplest form of the radar range equation, relating transmitted power with received power However, engineers prefer to design the system in terms of signal to noise ratio We need to recast the equation for this To achieve that, we need to introduce a few other assumptions: The radar is limited by thermal noise: no signal can be detected if resides below the thermal noise floor The radar is simply sending pulses: no pulse compression or integration gain is considered at this stage

44

Radar Range Equation:The Noise Power

The thermal noise power measured at the receiver is: K is the Botlzmann Constant T is the ambient temperature in Kelvin B is the bandwidth of the signal, usually then inverse of the pulse width F is the noise figure of the system, usually 3dB

The derivation and complete understanding of such equation will be discussed in a future lecture

=

45

Radar Range Equation:The SNR Formulation

Let us call the signal Let us call the noise: The signal to noise ratio becomes:

This is the radar range equation in its classical form

= = 24 34 =

= 24 34 4 = 24 3

46

Radar Range Equation:Integrating Pulses

The radar range equation can be extended to incorporate more phenomenology and more advanced signal processing When integrating the return of n coherent pulses, the radar range equation becomes When integrating the return on n incoherent pulses, the overall effect in the range equation is

= 1 = 24 34 = 0.8 1

47

Losses: Fluctuation (Swerling) Loss

The true target scattering is better explained statistically Because some pulse echoes could be randomly occurring below the noise floor, the effective SNR is somewhat reduced This can be taken into account by adding a loss factor due to the statistical nature of the target

The actual value of is complicated and depends upon the number of pulses and type of target We will discuss and quantify this loss factor in a future lecture

48

Losses: System, Atmosphericand Propagation

System losses, , due to cables and imperfect conducting materials. Atmospheric losses, , due to water content Propagation losses, , are due to several factors : Earth curvature variation of atmospheric refractive index with height ground reflections anomalous propagation

less sensitive areas due to

ground reflections

blind - due to Earth curvature

blind due to high gain

requirement

49

Losses: Beamshape Loss

This loss term accounts for the fact that, as the beam scans across the target, the signal amplitudes of the pulses coherently or non-coherently integrated varies. Typical values are: 1.6 dB for a scanning, fan beam radar 3.2 dB for a thinner beam, scanning radar 3.2 dB for a phased array radar Other factors not directly accounted for include the possibility of the target not being centered in the beams path, typical for phased array radars

50

Losses: Signal Processing

Signal processing occurs in the digital domain, and it usually consists of a discrete series of filters or FFTs Filters and FFTs have inherent losses due to the sinc-shape functions This loss may be overcome by using more filter banks or FFTs with more samples, at the expenses of more computational cost In worst cases, this loss may be up to 3dB We call this loss

51

Range Equation including Losses

By adding all the losses contribution, the radar range equation can be written as = 24 34

52

Radar Range Equation when using Pulse Compression

In future lectures we will see that, with opportune signal processing, radar pulses can be compressed to obtain a much higher peak, with respect to the noise floor. This is equivalent to a SNR increase The approximate SNR gain is equal to =

T

53

Radar Range EquationUsing Pulse Compression

By accounting for pulse compression, the SNR becomes However, this simplifies to

In a system using pulse compression, it is the energy to the target (not the peak signal power) that matters!

= 24 34 = 24 34 = =

54

The Range Equation for a Search Radar

( )0 0 0/ /s A Et t t =

( ) ( )0

2 2 4 40

4

4

4 44 effe fff efAvg eff s

nAvg T eff o Avg eff s

nn

P G A t P A tSNRR KTFLR

P A t

R KTFKTF LL

pipi

pi

pi

=

= =

04 /TG pi 24 /R effG Api =

Radar Range EquationFor a Search Radar

The earlier radar range equation applies to a radar that dwells on the target for n pulses. Surveillance radar searches a specified angular region in a given time. Scan Time Time that the Radar beam dwells on the target 0 = Area covered (steradian) Beam area 0

55

Graphical Solution to the Radar Range Equation

56

Summary

A wide range of radar systems are currently deployed world wide. Legacy radars custom designed to application and location Modern radars more flexible Performance prediction and analysis critical as modern uses are varied and subject to change

Introduction to RadarWelcomeOverviewBooksBooksA Special Thank YouTwo Inventions ThatChanged the Outcome of WW2Slide Number 8Radar Block DiagramPre-Radar DetectionHistorical BackgroundThe First Radar Hlsmeyer, 1904Measurements of the IonosphereRobert Watson WattThe Chain Home Radar ProjectThe First Report Mentioning RADARNov 19, 1940Radar and Pearl Harbor AttackBoot, Randall, and the MagnetronWorlds First MagnetronKlystronThe First KlystronRadar TaxonomyTPS-59FPS-117Ground Penetrating RadarAN/SPS-52C 3D Shipboard Air Defense RadarTerrain AvoidanceAPS-145 Airborne Early Warning (AEW)AWACSMultimode Fire Control Radar(IAI)Global Hawk Sensor SuiteThe Radar Range EquationElectromagnetic SpectrumRadar Range Equation;RationaleRadar Range Equation:WarningsRadar Range Equation:System ParametersRadar Range Equation:Power DensityRadar Range Equation:Power Density at the TargetRadar Range Equation:Radar Cross SectionRadar Range Equation:Received Power DensityRadar Range Equation:Effective AreaRadar Range EquationExpressed in terms of Received PowerRadar Range EquationRadar Range Equation:The Noise PowerRadar Range Equation:The SNR FormulationRadar Range Equation:Integrating PulsesLosses: Fluctuation (Swerling) LossLosses: System, Atmosphericand PropagationLosses: Beamshape LossLosses: Signal ProcessingRange Equation including LossesRadar Range Equation when using Pulse CompressionRadar Range EquationUsing Pulse CompressionThe Range Equation for a Search RadarGraphical Solution to the Radar Range EquationSummary