05 - Introduction to RWR

5/27/2018 05 - Introduction to RWR

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GTRI_B-1Copyright by Georgia Tech Research Corporation, 2009

Introduction toRadar Warning Receivers

Robins AFB

February 24, 2009

Presenter: Kim Cole


What is a Radar Warning Receiver?

A Radar Warning Receiver (RWR) is a pass iveEWsystem that does the following:

Detects RF signals transmitted by radar systems

Identifies the signal by radar type

Manages detected signals

Generates visual and audio cues to pilot

Manages interfaces to other systems


What the Pilot Sees


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CVR SUBSYSTEM

FSRS Subsystem

AM-42345

AM-423135

AM-423225

AM-423315

AS-3305

(45) J1

(135) J2

(Omni) J5

(315) J4

(225) J3

ANT7

E, G, I

(135)

E, G, I

(45)

E, G, I

(225)

E, G, I

(315)

IP1310

Diamond Audio

CM-479

J3F1

J1

F2J4 J2

HSDB

2X 2Y

C/D, E, G, I Band Static Video (TTL)

C-10373F1 F3

F2 J1

J2J5

J4J3

Antenna Control (0-3)

R-2094

J1 J3

J2

RI/D, Control (0-3), CW Strobe, PRF Window

Rec. Int., Discrimn. Video, Bandpass Video

AM-423135

(FSRS)

AM-423225

(FSRS)

AM-423315

(FSRS)

AM-42345

(FSRS)

J1

J2

J5

J6

J3

J4

AM-6971J6 J3 J1

J5

J4 J2

J7

N1

SA-2263

E, G, I Band Video (45, 135, 225, 315)

C/D Band Video (45, 135, 225, 315)Omni Video

CVR

135

J1

J2

J3

CVR

45

J1

J2

J3

CVR

225J1

J2

J3

CVR

315J1

J2

J3

ALQ-213 CMSP

ALR-69 System Block Diagram


ALR-69 System


What the Pilot Sees


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(Very) Brief History of RWR

RWRs have been around for about 40 years.

First-generation RWRs were used by the US Air Forceduring the Vietnam War in response to Russian radar-guided SAMs deployed in North Vietnam.

The Israelis suffered heavy losses to radar-directedAAA and SAMs during the 1973 Yom Kippur War.


Example USAF RWR Installations

RWR Type Aircraft

ALR-56C F-15

ALR-56M F-16, C-130, B-1

ALR-69 B-52, A-10, C-130, F-16, C-130

ALR-94 F-22

APR-39 C-130, V-22


How Does an RWR Work?

Hardware handles detection

Hardware detects radar pulses and converts pulse parameters todigital format

Major hardware components: antennas, RF cables, receiver,signal processor, user I/O devices

Software handles identification and aircrew interface

Software processes digital data to determine what type of radarsystem is illuminating the aircraft and then provides aircrew cues

Major software components: operational flight program andmission data file


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Why Do You Need an RWR?

The enemy is out there!

The enemy has air defense systems that are verydependent on radar and RF-guided weapons.

They have surface-to-air-missiles (SAMs), anti-aircraftartillery (AAA), and air-to-air missiles that arecued/targeted/guided by RF signals.

When an enemy radar points at a USAF aircraft, wecan detect that signal and warn the aircrew of thepresence of that weapon system.


Typical Air Defense System Encounter

MISSILELAUNCHER

MISSILE

TRACKER

TARGETTRACKER

COMMAND

STATIONCOMPUTER

VAN


SA-2 Surface to Air Missile


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Processor

RWR Operational Concept

0

0

7

78

8


How Do We Measure RWR Performance?

Typical RWR measures of performance (MOPs) are:

Detection range

Response time

Correct ID

DF accuracy

Age out

Performance is usually measured by conducting aflight test on an open-air range.


Simplified RWR Processing Flow

SignalDetection

SignalProcessing

ManageInterfaces

RF

Input

BufferEmitter

Track

File

Hardware SoftwareSoftware


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Origin of RWR Input


RWR Frequency Coverage

A typical RWR detects pulsed radar signals in the0.5-18 GHz frequency range.

Frequencyis measured in Hertz

Hertzis a unit of frequency of one cycle per second.

One second

6 Hertz

3 Hertz



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Types of Radar Signals

Continuous Wave

Pulsed


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Quick Word About Notation for Pulsed Signals

Time

All meant toillustrate

the same

concept.


What Measurements Does an RWR Make?

For each CW s igna lthe RWR will measure:

Frequency, angle of arrival, and power

For each pulse in a pulsed signal the RWR willmeasure:

Frequency or frequency band, time of arrival (TOA),angle of arrival (AOA or DF), pulse width, and power

For CW or pulsed signals outside the RF coverageof the RWR, no m easurement is made.


First Step: Detect Signal with Antenna

C/D Band antenna -

One per aircraft

E/J Band antenna -

Four per aircraft


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First Step: Detect Signal with Antenna

45

225

315

135

Four E/J band antennas are

installed at quadrant locations

around aircraft.


F-16 Forward Antenna Installation


F-16 Aft Antenna Installation


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Converting RF Pulse to Digital Data

Receiver

PulseMeasurement

Data

To software

For

Signal processing

Quadrant antennas


Basic Analog Receivers1 (1/2)

Receiver Advantage Disadvantage

Wideband CrystalVideo

Simple; InexpensiveInstantaneous

High POI in frequency range

No frequency resolutionPoor sensitivity

Poor simultaneous signal

Tuned RF Crystal Video Simple

Frequency measurement

Higher sensitivity than wideband

Slow response time

Poor POI

IFM Relatively simpleFrequency resolution

Instantaneous; High POI

Simultaneous signal problemRelatively poor sensitivity

Narrow Band Scanning

Superhet

High sensitivity

Good frequency resolution

No simultaneous signals

problem

Slow Response

Poor POI

Poor against freq agility

Wideband Superhet Better response timeBetter POI

Spurious signals generatedPoorer sensitivity


Basic Analog Receivers1 (2/2)

Receiver Advantage Disadvantage

Channelized Wide bandwidthNear instantaneous

Moderate frequency resolution

High complexity, cost

Lower reliability

Limited sensitivity

Microscan Near instantaneousGood frequency resolution

Good dynamic range

Good simultaneous signal capability

High complexityLimited bandwidth

No pulse modulation

information

Critical alignment

Acousto-optic Near instantaneousGood frequency resolution

Good simultaneous signal capability

Good POI

High complexityNew technology

1 Electronic Warfare And Radar Systems Engineering Handbook, NAWCWPNS TP 8347, April 1, 1999


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Most Common RWR Receiver Architectures

Filename - 31

Band 1Video

Band 2Video

Band 3Video

Multi-plexer

CompressiveVideo

Amplifier

RFAmplifier

Crystal Video ReceiverTuned Narrowband Superhet

Video

IFAmp

IFFilter

LogVideoAmp

RFFilter

Local

Oscillator

Tuning


Narrow-Band Superheterodyne Receiver

Narrow bandwidth

-90 dBm sensitivity

Low probability of intercept (POI)

Good signal separation

Measures frequency, PW, power, and AOA

Excellent CW Capability Medium cost

Medium volume


Wideband Crystal Video Receiver

Wide instantaneous bandwidth

- 45 dBm sensitivity

High probability of intercept

Poor signal separation

Measures frequency band, PW, power, and AOA

Poor CW Capability

Low cost

Small volume


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Input Scheduling

Another important RWR term is i npu t schedu l ing.

Both superhet and CVR architectures requiresophisticated input schedulers.

The input schedule is usually defined in the missiondata file.

We have said that a typical RWR covers the 0.5-18GHz frequency range, but they typically do notcollect inputs from the entire range at one time.


CVR Input Scheduling

A typical CVR RF signal is fed to anamplifier/detector that splits the covered RF rangeinto multiple f requency bands.

A typical CVR l ooks(collects input) from a single RFband at a time.

Example band breaks are shown below.

Band 0 Band 1 Band 2 Band 3

0.5 GHz 2 GHz 8 GHz 12 GHz 18 GHz


Example CVR Input Schedules

Band Look Time

0 25 ms

1 25 ms

2 25 ms

3 25 ms

Band Look Time

0 10 ms

1 12 ms

2 15 ms

3 15 ms

0 50 ms (conditional)

2 1 ms

3 1 ms

1 20 ms

3 25 ms

Really simple schedule

More realistic schedule


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Simple Probability of Intercept Example

Filename - 37

Scanning threat radar

RWR input scheduler

Band 0 Band 1 Band 2 Band 3 Band 0


A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

2 4 6 8 10 12 14 16RF (GHz)

18

Emitter TransmittedFrequency Range

Threat ID


Superhet Input Scheduler

The input schedule for a superhet receiver is muchmore complex than the input schedule for a CVR.

This is because the superhet is a narrow-bandreceiver, i.e. the total frequency range is broken intomany smaller segments that must be covered.

Superhet input schedulers contain more numerous,shorter looks.

0.5 GHz 2 GHz 8 GHz 12 GHz 18 GHz


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Pulse Measurements

If the RWR detects a pulse, it collects a set of datafor that pulse.

The formats differ among various RWRs, but thispulse data is generally called a pu lse descr ip to rwo rd(PDW).

The PDW contains all data collected for a s ing leRFpulse.


Pulse Descriptor Word

A typical PDW contains time of arrival (TOA), angle,pulse width, power, and frequency (superhet) orfrequency band (CVR).

The ALR-69 PDW format is shown below:

TIME OF ARRIVAL (16 LSBs)

TIME OF ARRIVAL (8 MSBs)PULSE WIDTH

POWER ANGLE

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

IP PP FO1 FO2 PRI DT RB1 RB2 DCB COR CDM B0 B1 B2 B3 B4


Key Pulse Parameters

Time

FrequencyPulsewidth

Power

PRI

PRI is Pulse Repetition Interval.


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Input Buffer

The final output of the Signal Detection componentof the RWR is an Input Buffer.

An Input Buffer is a series of PDWs that werecollected during a single look.

The Input Buffer is processed by the RWR softwareto determine what type radar (or radars) transmittedthe pulses.



SignalDetection

SignalProcessing

ManageInterfaces

RF

Input

BufferEmitter

Track

File



OFP and MDF

Operat ional Fl ight Program (OFP)

Executable code

Input scheduler

PRI deinterleaver

Track file management

Missile guidancealgorithms

Interface management

Mission Data File (MDF)

Data (no executablecode)

Input schedule

Threat identification

Threat information

Ambiguity resolve tables

Missile guidance data

Filename - 45


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Major Signal Processing Components

Filename - 46

PRIDeinterleave

Threat IDAmbiguity

ResolveTrack File

Management

InputBuffer

EmitterTrack

File


PRI Deinterleaving Algorithm

Many years of research have been done regardingPRI deinterleaving algorithms.

The PRI deinterleaving algorithm is the mostcomplex algorithm, and uses the most processortime, of any function in an RWR OFP.

PRIDeinterleave

InputBuffer

Pulse train statistics:Frequency/band

PRIPower

AnglePulse width

PRI agility info

Quality statistics


PRI AgilityStable

For a stable PRI emitter the interpulse period isthe same for every pulse.

175 175175 175 175 175 175 175 175 175 175 175 175 175 175 175 175 175 175 175 175 175


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PRI AgilityStagger

For a staggered PRI emitter, a set of interpulseperiods are repeated continuously.

2-level stagger

3-level stagger

4-level stagger

150 175175 150 175 150 175 150 175 150 175 150 175 150 175 150 175 150 175 150 175 150

150 150175 225 150 175 225 150 175 225 150 175 225 150 175 225 150 175 225 150 175 225

150 175175 125 200 150 175 125 200 150 175 125 200 150 175 125 200 150 175 125 200 150


PRI AgilityCycler

For a cyclic PRI emitter a stable PRI is generatedfor N pulses followed by another stable PRI for Npulses, etc.

For example, this cycler generates a PRI of 175 forseven pulses and then a PRI of 150 for four pulses.

175 150175 175 175 175 175 175 150 150 150 150 175 175 175 175 175 175 175 150 150 150


PRI AgilityJitter

For a jitter PRI emitter, the interpulse periodvaries between every pulse usually within a knownpercentage range.

For example, the pulse train below is a 200 +/- 10%jitter pulse train, i.e. the interpulse periods varyrandomly between 180 and 220.

200 181183 182 201 199 185 217 216 209 188 181 199 207 207 187 183 184 218 203 204 200


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PRI Deinterleaving

Filename - 52

Radar Signal A

Radar Signal B

Radar Signal C

Interleaved Signal


PRI Deinterleaving - Sorting

Hardware Measurement Useful f or Sorting?

Frequency or Frequency Band Yes

Time of Arrival Yes

Angle of Arrival Yes

Power No

Pulse Width Not so much



Filename - 54

PRIDeinterleave

Threat IDAmbiguityResolve

Track FileManagement

InputBuffer

EmitterTrack

File


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Threat Identification

Initial threat identification is usually a very simpleprocess.

The MDF assigns an initial threat ID based onfrequency/band and PRI.

So, threat ID is simply finding the correspondingentry in a table in the Mission Data File.

Most initial threat IDs are amb iguousand requireamb igu i ty reso lu t ion.


A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

0 500 1000 1500 2000 2500 3000 3500PRI (microseconds)

4000

Emitter PRI Range

Threat ID



Filename - 57

PRIDeinterleave



InputBuffer

EmitterTrack

File


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Ambiguity Resolution

Initial threat ID is done based on frequency/band andPRI.

This usually results in an ID that says this could be either ThreatA, Threat C, Threat D, or Threat H.

Additional measurements are used/required to resolveambiguities and determine which a unique ID.

PRI agility (jitter, stagger, cycler)

Multiband

Scan type/rate

Missile guidance



Filename - 59

PRIDeinterleave



InputBuffer

EmitterTrack

File


Track File Management

All RWRs have some concept of a Track File. It maybe called different names in different RWRs, but theconcept is the same.

The Track File is where the OFP stores all threatinformation that is has measured/computed.


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Track File Management (cont.)

The Track File management software is almost ascomplex as the PRI Deinterleaving software.

The OFP updates the track file as new informationbecomes available.

There are many sources of new information:correlation, missile guidance, angle, power, PRIagility, etc.


Track File Management (cont.)

The Emit ter Track Fi le is the m ost im por tant data

mainta ined by th e RWR OFP.

The ETF content affects operation of almost allother OFP functions

Pilot cues (audio and display)

Initiates additional measurements for ambiguityresolution

Alters input scheduling

The ETF is output to other systems in an integratedEW suite and may drive their operation as well.



SignalDetection

SignalProcessing

ManageInterfaces

RF

Input

BufferEmitter

Track

File



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User Interface

Buttons/Lamps CRT Display

Audio

Missile launch

New guy

Diamond


Interface Management

Besides the user interface the OFP also managesother intrasystem and intersystem input/output.

Intrasystem: Setting up pulse collection hardware,messaging on intrasystem hardware interfaces,messaging between OFPs within the RWR, etc.

Intersystem: MIL-STD-1553B data bus (EW Bus andAvionics Bus), blanking interface, etc.


RWR Challenges

There are many challenges to accurately andeffectively operating an RWR in a real-worldenvironment:

High pulse densities

Interference from other onboard systems

Aircraft maneuvers

Urban noise

Antenna patterns


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CVR SUBSYSTEM

FSRS Subsystem

AM-42345

AM-423135

AM-423225

AM-423315

AS-3305

(45) J1

(135) J2

(Omni) J5

(315) J4

(225) J3

ANT7

E, G, I

(135)

E, G, I

(45)

E, G, I

(225)

E, G, I

(315)

IP1310

Diamond Audio

CM-479

J3F1

J1

F2J4 J2

HSDB

2X 2Y

C/D, E, G, I Band Static Video (TTL)

C-10373F1 F3

F2 J1

J2J5

J4J3

Antenna Control (0-3)

R-2094

J1 J3

J2

RI/D, Control (0-3), CW Strobe, PRF Window

Rec. Int., Discrimn. Video, Bandpass Video

AM-423135

(FSRS)

AM-423225

(FSRS)

AM-423315

(FSRS)

AM-42345

(FSRS)

J1

J2

J5

J6

J3

J4

AM-6971J6 J3 J1

J5

J4 J2

J7

N1

SA-2263

E, G, I Band Video (45, 135, 225, 315)

C/D Band Video (45, 135, 225, 315)Omni Video

CVR

135

J1

J2

J3

CVR

45

J1

J2

J3

CVR

225J1

J2

J3

CVR

315J1

J2

J3

ALQ-213 CMSP

ALR-69 System Block Diagram


The Travels of Joe Pulse

RF RF

Antenna

Pre-amp

AM-6639

J1

J2

Video

pulse

Video

Processor

(A5 CCA)

DMA

Pre-Process

(PRE_PROC)

PRI

Deinterleave

(PRIDE)

Emitter

ID

(EIDR)

ETF Mgt

(ETE)

A6 OFP

Display

Update

A4 OFP

Display

Update

Display

Refresh

IP-1310

Pulse

packet

Input

Buffer

Input

Buffer

Process

BufferPRIDE

Outputs

Threat

ID

ETF

Record

ETF

Record

Display

File

Refresh

Buffer

Air RF cableQuadrant

video signalsFIFO A6 RAM

A6 RAM A6 RAM A6OFP

variables

A6OFP

variables

ETF

ETF A4 RAM A4 RAM I/O

CRTDrive

H/W

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