Tactical COMMS/ESM System for Submarines

–A Front-end Perspective

Uwe Trautwein

South African AOC Chapter (Aardvark Roost) Conference25th - 26th August 2009 at CSIR Conference Centre, Pretoria

uwe.trautwein@medav.de

Overview

Introduction & Motivation• See also Proceedings Big Crow Conference Nov 2008 : Dirk Baker – The Challenges of

Developing a COMINT DF & Monitoring Antenna for … Submarine Operations

COMMS/ESM – the acronym puzzleThe Submarine as a surveillance platform

System Overview Direction Finding Capabilities

Conclusions

2P709uwtr.xxx

Uwe Trautwein

Introduction

COMMS Radio communications reconnaissance system Communications Intelligence - Strategic system component

/ESM Electronic support measures – Tactical system component Identification and tracking of potential threats EOB picture Integration into the Electronic Warfare System

Overlap : detection and interception of signals

3P709uwtr.xxx

Uwe Trautwein

Motivation

Covert operation Submarine stays submerged – only the antenna is deployed above surface Ideal reconnaissance platform for coastal areas and open sea

4P709uwtr.xxx

Uwe Trautwein

h1 h2

~2 m at periscope depth

Submarine wCOMINT antenna Tx antennad2d1

h1 2,0 mh2 5,0 mLOS Distance 13,0 km

No refraction

COMMS/ESM advantage Extended radio horizon for lower frequency COMMS signals

Enables the submarine to “look” behind the horizon

Obvious Benefits of the Direction Finding for COMMS Signals

Provide a bearing for a detected signal

Only this enables ESM capabilities

Allows to focus detection on a target area

Prerequisite for locating Allows intelligence fusion with

other sensor data

5P709uwtr.xxx

Uwe Trautwein

Some Less Known Benefits of the Direction Finding for COMMS Signals

Allows reliable automated emitter detection in dense scenarios By jointly exploiting spectrum and azimuth information

Provide SNR gain for the detection of weak signals

Separation of stations for certain signal types Frequency hopper networks Duplex communications

Separation of multiple co-channel signals

6P709uwtr.xxx

Uwe Trautwein

The Technical Challenges

Wideband DF antenna on very compact space (300kHz – 3GHz) Outer antenna diameter (radome): 510 mm High phase accuracy requirements for the DF system Antenna pattern quality impairments expected due to mutual coupling Pressure-tight, thick radome - Probably affecting wave propagation Integrated monitoring capability

Existing ESM ELINT antenna on top Electromagnetic coupling, space for cable feed-through

Tight specification parameters set by the customer Uncompromised DF accuracy up to 30 deg elevation DF and monitoring operation up to 70 deg elevation

P709uwtr.xxxUwe Trautwein 7

System Overview

System componentsAntenna COMINT Rack

All liquid cooled

MultifunctionalConsoles

Software defined radio concept Medav CCT receiver with

integrated FFT processor, output via Gigabit LAN interface

General purpose computer platform for all processing tasks

8P709uwtr.xxx

Uwe Trautwein

Seamless Submarine Integration

MFCC for alternative systems COMMS/ESM (Medav)

• Brand name: CRS-8000 Communications ReconnaissanceSystem

Radar ESM (Saab Avitronics) RadarOptronics Etc…

COMMS/ESM with up to three simultaneous operator roles SupervisorWideband operator Tracking operator Post-processing operator

9P709uwtr.xxx Uwe Trautwein

Detail of SIGINT Antenna System

10SAAB AVITRONICS

ELINT unit

Radome

VHF arrays

UHF arrays

HF arrayRF assembly

SIGINT antenna comprises ELINT and COMINT antennas on top of one mastELINT antenna is an existing assembly.

COMINT antenna has several key assemblies:* Radome* UHF array* VHF arrays* HF array* RF assembly* Mast interface and clamp* Wet diploops

Basic Principle of the Correlative Interferometer for Direction Finding

Vector correlation of the complex receive voltages with the array manifold The array manifold is obtained by antenna calibration measurements

11P709uwtr.xxx Uwe Trautwein

( ) H ( )c ϕ ϕ= ⋅m a

( )ˆ arg max{ }m cϕ

ϕ ϕ=

Complex voltages!

1

2

3 4

5

φ

Test signal x

r

Plane wave frontk = 2πfc /c

Measurementvector

[ ]

1

25 1

3

4

5

mmmmm

×

=

m Peak search in the angular power spectrum

“For free”: Quality criterion

Angular power spectrum

phase synchronous receive chains

Wideband coverage

Limited array size small phase differences poor correlation properties + high phase measurement accuracy

Wideband use trade-off must consider also the upper band edge

12P709uwtr.xxx

Uwe Trautwein

-200 -150 -100 -50 0 50 100 150 2000

0.2

0.4

0.6

0.8

1

1.2

1.4

DoA [degree]

Corre

latio

n

30 MHz130 MHz230 MHz330 MHz430 MHz530 MHz630 MHz

Very weak spatial selectivity!

High side lobe Ideal 5 element array

Elevation Coverage - Motivation

Operational aspects The submarine is always a

“Low altitude platform”Airborne emissions

Tolerate roll & pitch of the boat

Discriminate between airborne and shipborne emissions

Elevation coverage vs. Elevation estimationNot exactly the same

Elevation angle

13P709uwtr.xxx

Uwe Trautwein

The Common Case: Degradation vs. Elevation

Degradation is frequency-dependent visible even for modest elevation angles Degradation can turn into complete failure

Full 3D calibration was found to be inevitable Requires optimized calibration grid to limit measurement time Benefit: DF provides elevation information

14

500 1000 1500 2000 2500 30000

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Frequency [MHz]

RM

S e

rror [

deg]

-5.0 deg elev.5.0 deg elev.0.0 deg elev.

-10 0 10 20 30 40 50 60 700

1

2

3

4

5

6

7

8

9

10

Elevation [deg]

RM

S e

rror [

deg]

600.00 - 996.00 MHz

-10 0 10 20 30 40 50 60 700

1

2

3

4

5

6

7

8

9

10

Elevation [deg]

RM

S e

rror [

deg]

1008.00 - 3000.00 MHz

RMS of 2 different frequency subbands

P709uwtr.xxxUwe Trautwein

Antenna Calibration and Direction Finding Test Setup

15P709uwtr.xxx

Uwe Trautwein

National Antenna Test Range at Paardefontein, South Africa Fully automated measurements

Prototype DF System

Thorough Prove of Specification Compliance

Factory Acceptance: Measurements over the full specified volume The DF accuracy (RMS azimuth error) The Monitoring Sensitivity (E-Field

strength to achieve 10 dB SNR)

16P709uwtr.xxx

Uwe Trautwein

System Performance Achievements

All specifications parameters are finally met DF accuracy typically better then 2° RMS Monitoring sensitivity with good margin

Even for full elevation range

Comprehensive verification during FAT 202,150 total samples

over azimuth, elevationand frequency

Very good reproducibilitybetween systems

17P709uwtr.xxx

Uwe Trautwein

-10 0 10 20 30 40 50 60 700

0.5

1

1.5

2

2.5

3

3.5

Elevation [deg] / 660.00 - 3000.00 MHz

Azi

mut

h er

ror [

deg]

2008-07-03_FAT-UHF_ExtEl_001.df

Emitter Detection in the Joint Power-Azimuth Domain

Automated Process of identifying individual transmitters incl. base parameters: fc, B, SNR, phi

Used for alarm conditions, reporting, further analysis

Exploits 3D cluster structure of FFT based DF results Reliable results for many scenarios where pure power spectrum analysis must fail

18P709uwtr.xxx

Uwe Trautwein

390.2 390.4 390.6 390.8 391 391.2 391.4 391.6-130

-120

-110

-100

-90

-80

-70

-60

Frequency [MHz]

Raw

PSD

[dBm

]

390.2 390.4 390.6 390.8 3910

30

60

90120

150

180

210240

270

300

330360

Azi

mut

h [°

]

Frequency [MHz]

Co-sited emissions

Foreword on Polarization

Treatment of polarization in the COMINT DF context is rather sparseHF space wave DF = mixed polarization Either monopoles (good Xpol) or combination of monopoles and loops

Common approach for VHF/UHF: The system is specified for vertical polarization

Important figure: Cross polarization (Xpol) attenuation (dB)Horizontal source Vertical element response (HV)

Small elements in compact configurations have typically a low XpolGood values are 15 dB and more, less is not uncommon

Question: What happens if a Vpol system experiences Hpol?

19P709uwtr.xxx

Uwe Trautwein

Vertically polarized source

DF estimates for a defined DOA

20P709uwtr.xxx

Uwe Trautwein

Vertically polarized source

500 1000 1500 2000 2500 30000

30

60

90

120

150

180

210

240

270

300

330

360

Frequency [MHz]

Azi

mut

h [d

eg]

V-Pol source / V-Pol DF

Horizontally polarized source

DF estimates for the same DOA Completely useless

21P709uwtr.xxx

Uwe Trautwein

Horizontally polarized source

500 1000 1500 2000 2500 30000

30

60

90

120

150

180

210

240

270

300

330

360

Frequency [MHz]

Azi

mut

h [d

eg]

H-Pol source / V-Pol DF

Joint Vertical +Horizontal DF

DF estimates for the same DOA Valid DF estimate is retained Source polarization information is provided

22P709uwtr.xxx

Uwe Trautwein

Horizontally polarized source

500 1000 1500 2000 2500 30000

30

60

90

120

150

180

210

240

270

300

330

360

Frequency [MHz]

Azi

mut

h [d

eg]

H-Pol source / V-Pol DFH-Pol source / Joint V-H-Pol DF

Dual-polarization DF

Demonstration of joint V-H-Pol DF in a broadcast band with both vertical and horizontal sources

0

50

100

Ele

vatio

n [°

] 0

100

200

300

Azi

mut

h [°

]

2008-07-03_Env-VHF_AzCut_002

230 235 240 245 250

-120

-100

-80

Frequency [MHz]

Raw

PS

D [d

Bm

]

H-Pol

V-Pol incl. elevation

23P709uwtr.xxx

Uwe Trautwein

Superresolution and the multiple sources problem

Superresolution ≠ high accuracy of the estimated angles Resolution of multiple signals on the same carrier frequency

(Co-channel signals)

Conventional DF system resultBeam former := Peak search in the power azimuth spectrum In general undefined, depends on power ratio of the sources, the azimuth

spacing, the antenna properties, etc. Superresolution DF relies on the suppression of the co-channel signals by a

weighted sum of the N antenna signalsTheoretical limit for the number of resolvable signals is thus N-1 Important distinction: Uncorrelated/Correlated sources

24P709uwtr.xxx

Uwe Trautwein

Superresolution DF Test Setup

P709uwtr.xxxUwe Trautwein

Superresolution DF

The MEDAV submarine based system can resolve up to four co-channels signals by using superresolution DF

0 30 60 90 120 150 180 210 240 270 300 330 3600

5

10

15

20

25

30

35

40

Azimuth [deg]

Mus

ic p

ower

azi

mut

h sp

ectru

m [d

B]

MUSIC pseudo azimuth spectrum with 3 co-channel

sources

26P709uwtr.xxx

Uwe Trautwein

Conclusions

27P709uwtr.xxx

Uwe Trautwein

An ultra compact SIGINT antenna and a completely water-cooled, ruggedized COMMS/ESM system with outstanding DF capabilities was successfully developed, qualified and produced.

It forms an integral part of the submarine‘s combat management system.

It can be used for tactical reconnaissance and radio communications intelligence gathering.

Significant contribution to upgrade the capabilities of submarines for new tasks.

Sea Trials in Progress

28P709uwtr.xxx

Uwe Trautwein