Introduction to Radar Warning Receiver

2/23/2009

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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 passive EW system 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

J3F1J1

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

CVR135

J1

J2

J3

CVR45

J1

J2

J3

CVR

225

J1

J2

J3

CVR

315

J1

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 Force during the Vietnam War in response to Russian radar-guided SAMs deployed in North Vietnam.

• The Israelis suffered heavy losses to radar-directed AAA 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 to digital 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 radar system is illuminating the aircraft and then provides aircrew cues

• Major software components: operational flight program and mission 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 very dependent on radar and RF-guided weapons.

• They have surface-to-air-missiles (SAMs), anti-aircraft artillery (AAA), and air-to-air missiles that are cued/targeted/guided by RF signals.

• When an enemy radar points at a USAF aircraft, we can detect that signal and warn the aircrew of the presence of that weapon system.


Typical Air Defense System Encounter

MISSILELAUNCHER

MISSILETRACKER

TARGETTRACKER

COMMANDSTATION

COMPUTERVAN


SA-2 Surface to Air Missile

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Processor

RWR Operational Concept

0

0

7

7

8

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 a flight test on an open-air range.


Simplified RWR Processing Flow

Signal

Detection

Signal

Processing

Manage

Interfaces

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 the 0.5-18 GHz frequency range.

• Frequency is measured in “Hertz”

• Hertz is 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 to

illustrate

the same

concept.


What Measurements Does an RWR Make?

• For each CW signal the RWR will measure:

• Frequency, angle of arrival, and power

• For each pulse in a pulsed signal the RWR will measure:

• 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 coverage of the RWR, no measurement 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

Pulse

Measurement

Data

To software

For

Signal processing

Quadrant antennas


Basic Analog Receivers1 (1/2)

Receiver Advantage Disadvantage

Wideband Crystal

Video

Simple; Inexpensive

Instantaneous

High POI in frequency range

No frequency resolution

Poor sensitivity

Poor simultaneous signal

Tuned RF Crystal Video Simple

Frequency measurement

Higher sensitivity than wideband

Slow response time

Poor POI

IFM Relatively simple

Frequency resolution

Instantaneous; High POI

Simultaneous signal problem

Relatively 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 time

Better POI

Spurious signals generated

Poorer sensitivity


Basic Analog Receivers1 (2/2)

Receiver Advantage Disadvantage

Channelized Wide bandwidth

Near instantaneous

Moderate frequency resolution

High complexity, cost

Lower reliability

Limited sensitivity

Microscan Near instantaneous


Good dynamic range

Good simultaneous signal capability

High complexity

Limited bandwidth

No pulse modulation

information

Critical alignment

Acousto-optic Near instantaneous


Good simultaneous signal capability

Good POI

High complexity

New 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 1

Video

Band 2

Video

Band 3

Video

Multi-

plexer

Compressive

Video

Amplifier

RF

Amplifier

Crystal Video ReceiverTuned Narrowband Superhet

Video

IF

Amp

IF

Filter

Log

Video

Amp

RF

Filter

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 input scheduling.

• Both superhet and CVR architectures require sophisticated input schedulers.

• The input schedule is usually defined in the mission data file.

• We have said that a typical RWR covers the 0.5-18 GHz frequency range, but they typically do not collect inputs from the entire range at one time.


CVR Input Scheduling

• A typical CVR RF signal is fed to an amplifier/detector that splits the covered RF range into multiple frequency bands.

• A typical CVR looks (collects input) from a single RF band 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 much more complex than the input schedule for a CVR.

• This is because the superhet is a narrow-band receiver, i.e. the total frequency range is broken into many 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 data for that pulse.

• The formats differ among various RWRs, but this pulse data is generally called a pulse descriptor word (PDW).

• The PDW contains all data collected for a single RF pulse.


Pulse Descriptor Word

• A typical PDW contains time of arrival (TOA), angle, pulse width, power, and frequency (superhet) or frequency 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 component of the RWR is an Input Buffer.

• An Input Buffer is a series of PDWs that were collected during a single look.

• The Input Buffer is processed by the RWR software to determine what type radar (or radars) transmitted the pulses.



Signal

Detection

Signal

Processing

Manage

Interfaces

RF

Input

BufferEmitter

Track

File



OFP and MDF

Operational Flight Program (OFP)

• Executable code

• Input scheduler

• PRI deinterleaver

• Track file management

• Missile guidance algorithms

• Interface management

Mission Data File (MDF)

• Data (no executable code)

• Input schedule

• Threat identification

• Threat information

• Ambiguity resolve tables

• Missile guidance data

Filename - 45

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Major Signal Processing Components

Filename - 46

PRI

DeinterleaveThreat ID

Ambiguity

ResolveTrack File

Management

Input

Buffer

Emitter

Track

File


PRI Deinterleaving Algorithm

• Many years of research have been done regarding PRI deinterleaving algorithms.

• The PRI deinterleaving algorithm is the most complex algorithm, and uses the most processor time, of any function in an RWR OFP.

PRI

Deinterleave

Input

Buffer

Pulse train statistics:

Frequency/band

PRI

Power

Angle

Pulse width

PRI agility info

Quality statistics


PRI AgilityStable

• For a “stable PRI” emitter the interpulse period is the 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 interpulse periods 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 generated for N pulses followed by another stable PRI for N pulses, etc.

• For example, this cycler generates a PRI of 175 for seven 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 period varies between every pulse usually within a known percentage range.

• For example, the pulse train below is a 200 +/- 10% jitter pulse train, i.e. the interpulse periods vary randomly 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 for Sorting?

Frequency or Frequency Band Yes

Time of Arrival Yes

Angle of Arrival Yes

Power No

Pulse Width Not so much



Filename - 54

PRI


Ambiguity

ResolveTrack File

Management

Input

Buffer

Emitter

Track

File

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Threat Identification

• Initial threat identification is usually a very simple process.

• The MDF assigns an initial threat ID based on frequency/band and PRI.

• So, “threat ID” is simply finding the corresponding entry in a table in the Mission Data File.

• Most initial threat IDs are ambiguous and require ambiguity resolution.


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

PRI


Ambiguity

ResolveTrack File

Management

Input

Buffer

Emitter

Track

File

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Ambiguity Resolution

• Initial threat ID is done based on frequency/band and PRI.

• This usually results in an ID that says “this could be either Threat A, Threat C, Threat D, or Threat H”.

• Additional measurements are used/required to resolve ambiguities and determine which a unique ID.

• PRI agility (jitter, stagger, cycler)

• Multiband

• Scan type/rate

• Missile guidance



Filename - 59

PRI


Ambiguity

ResolveTrack File

Management

Input

Buffer

Emitter

Track

File


Track File Management

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

• The Track File is where the OFP stores all threat information that is has measured/computed.

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Track File Management (cont.)

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

• The OFP updates the track file as new information becomes available.

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


Track File Management (cont.)

• The Emitter Track File is the most important data maintained by the RWR OFP.

• The ETF content affects operation of almost all other OFP functions

• Pilot cues (audio and display)

• Initiates additional measurements for ambiguity resolution

• Alters input scheduling

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



Signal

Detection

Signal

Processing

Manage

Interfaces

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 manages other 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 and Avionics Bus), blanking interface, etc.


RWR “Challenges”

• There are many challenges to accurately and effectively operating an RWR in a real-world environment:

• 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

J3F1J1

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

CVR135

J1

J2

J3

CVR45

J1

J2

J3

CVR

225

J1

J2

J3

CVR

315

J1

J2

J3

ALQ-213 CMSP

ALR-69 System Block Diagram


The Travels of “Joe Pulse”

RF RF

Antenna

Pre

-am

p

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

CRT

Drive

H/W

Introduction to Radar Warning Receiver

Documents

j1 j5 j6

basic analog receivers1

prf window rec

2x 2y j1f2

emitter track file

track file management

etf record etf

diamond audioj2 j3