Nationaal Lucht- en Ruimtevaartlaboratorium – National Aerospace Laboratory NLR

About NLR and Smart Antennas

Harmen Schippers, Pieter Jorna, Guus Vos, Adriaan Hulzinga, Jaco Verpoorte

Avionics Systems department

2

Introduction

The Netherlands

Where is NLR?

N L R - A m s t e r d a m N L R - F l e v o l a n d

3

Introduction

NLR: The Netherlands national knowledge centre for aeronautics and space technology

� NLR Mission

�To develop high-tech aerospace products and processes

�To provide market-driven, socially relevant products and services on a not-for profit basis

�To support the Netherlands government and businesses in staying innovative and effective

4

What & how

NL Userscivil & military

NL Industry

EnvironmentEconomy Safety

Education

Mission subsidy

Europe

World

NL Government

NLR

NLR's position in the Netherlands and the world

5

Civil aviation:

• Airports• Air Traffic Control Authorities• Aviation Regulatory Authorities• Airlines• Air Transport Industry

Aeronautics industry (civil/defence):

• Lead Aeronautics industries• Systems & Component providers• MRO and Logistics companies• Training and ICT providers

Defence - Government:

• Defence Materiel Command andOperational Commands

• International Armed Forces

Space:

• Space industry• European Space Agency (ESA)

NLR Stakeholders

Introduction

Government

6

Board of

Directors

Strategy and Policy

Other Staff &Supporting Services

Personnel & Organisation

Gas Turbines & Structural IntegrityFlight Physics & LoadsHelicopters & AeroacousticsCollaborative Engineering SystemsStructures TechnologyEngineering & Technical ServicesStructures Testing & Evaluation

Avionics Development & QualificationFlight Test Systems & ApplicationsAvionics SystemsMilitary Operations ResearchSpace

NLR Air Transport Safety InstituteAir Traffic Management & AirportsAir Transport Systems TechnologyTraining, Human Factors & Cockpit OperationsEnvironment & Policy Support

Aerospace Vehicles

Aerospace Systems& Applications

Air Transport

Work Force and Organisational Structure

Work force: about 700 employees,

51% university-trained and 24% with a higher professional qualification

Introduction

7

Research facilities

What & how

8

Smart Antennas: Overview

� Introduction

� Some examples

� Antenna arrays

� Signal processing

� Beam forming and beam steering

� Ku-band receive antenna array for SATCOM

� Antenna array on vibrating plate

9

Introduction

� Smart antennas are antenna arrays with:� signal processing algorithms used to identify spatial signal signature such as the direction of arrival (DOA) of the signal,

� and use it to calculate beam forming vectors, to track and to steer antenna beams in a certain direction (on a moving target).

� Antenna array consists of a group of radiating or receiving antenna elements, coupled to common electronic hardware to produce a directive radiation pattern.

10

Introduction

Directive radiation pattern

Concept of array antenna:

• Multiple antenna elements

• Beam forming hardware

11

Introduction

� Consider an array antenna consisting of two isotropic radiators at distance along the x-axis

� Then the total radiated field reads

/ 2d λ=

1 1 2 2TE w E w E= +

0.5

1

1.5

2

30

210

60

240

90

270

120

300

150

330

180 0

radiation pattern

angle (degrees)

dire

ctiv

ity (

lin)

0.5

1

1.5

2

30

210

60

240

90

270

120

300

150

330

180 0

radiation pattern

angle (degrees)

dire

ctiv

ity (

lin)

1 2 1w w= = 1 21 , jw w e π= =

12

Introduction

� Same array antenna consisting of two isotropic radiators at distance along the x-axis

� Letsin

1 21 , jw w e π θ−= =

/ 2d λ=

0.5

1

1.5

2

30

210

60

240

90

270

120

300

150

330

180 0

radiation pattern

angle (degrees)

dire

ctiv

ity (

lin)

θ π= −0θ =

0.5

1

1.5

2

30

210

60

240

90

270

120

300

150

330

180 0

radiation pattern

angle (degrees)

dire

ctiv

ity (

lin)

0.5

1

1.5

2

30

210

60

240

90

270

120

300

150

330

180 0

radiation pattern

angle (degrees)

dire

ctiv

ity (

lin)

10

20

30

30

210

60

240

90

270

120

300

150

330

180 0

radiation pattern (gain:3.01dB)

angle (degrees)

rela

tive

dire

ctiv

ity (

dB)

/ 6θ π= / 6θ π= −

13

Introduction

� By choosing appropriate weights for the elements of the antenna array we can form and steer the antenna radiation pattern

� Maximize antenna gain in a certain direction, for instance to establish links with communication satellites

� Minimize antenna gain in a certain direction, for instance to avoid signal from jammers

14

Some examples

• Very Large Array for astronomical radio observatories.

• Array consists of 27 radio antennas in a Y-shaped configuration.

• Data from the antennas is combined electronically.

15

Some examples

Early warning radar system for detection of ballistic missiles

Active phased array radar onboard of ship for multiple target detection and tracking

16

Some examples

Connexion by BoeingAdvanced Electronically Steerable Antenna array for communication with geostationary satellites

� Overall Bandwidth: 11.45 GHz to 12.75 GHz

� Active Aperture: 43 x 66 cm

� Antenna Thickness: 4.3 cm

� Antenna Beamwidth: 2° x 3°

17

Some examples

� Three inverted F-antennas in a PDA housing

� Antenna suitable for MIMO and diversity systems at WLAN frequency bands

� MIMO technology increases data throughput and link range withoutadditional bandwidth or transmit power.

18

Summary of examples

� A smart antenna array may refer to:

� an interferometric array of Radio telescopes used in radio astronomy.

� an electronically steerable directional phased array antenna typically used in RADAR and

� phased array antenna for wireless communication systems, in view to achieve beamforming, multiple-input and multiple-output(MIMO) communication

19

Antenna arrays

� Consider a uniform linear array

� An incoming plane wave has a delay at element k

� A small time delay can bemodelled as a phase shift:

kτ

sin2 2sink

k k k k

dcd

c

φπ πψ ω τ φλ λ

= = =

20

Antenna arrays

� The received signals at the antenna elements due to D wave fronts Fand noise W are

� The steering vector has the form

� The angle can be estimated; note that

1 1 1

2 2 21 2( ) ( ) ( )D

M D M

X F W

X F Wa a a

X F W

φ φ φ = +

⋯

⋮ ⋮ ⋮

1 2 1( ) 1 MTi i ia e e eψ ψ ψφ −− − − = …

φ2

sink kdπψ φλ

=

21

Signal processing

� Let be the measured set of signals at time step .

� Hence,

� A matrix of snapshots can be defined by a set of subsequent measurements in time. Let this matrix of T snapshots be given by

� The covariance matrix R of X is computed as

nX�

nt

[ ]1 2( ), ( ), , ( )T

n n n M nX X t X t X t=�

⋯

1 1n n n TX X X X+ + − =

� � �…

*( )R XX= Ε

22

Signal processing

� The eigen decomposition of covariance matrix R reads

� where the d-dimensional subspace of signal eigenvectors

with eigenvalues larger than and the (M-d)-dimensional

subspace of noise eigenvectors

� MUSIC algorithm computes spectrum as

* 2 *s s s n nR V V V Vσ= Λ +

sV

2σ nV

* *

1( )

( ) ( )MU

n n

Pa V V a

φφ φ

=

23

Signal processing

� Consider a linear array of 8 equally distributed patch antennas on a steady horizontal plate

� The centers of the patch antenna are at

� The direction of arrival is estimated to be

� This information can be used to steer and to form the beam

( 1) 0.6jx j λ= −

38φ =

24

Beam forming and beam steering

Conformal Phased ArrayPattern Samples onFar Field Sphere

25

Beam forming and beam steering

Desired pattern Phased array pattern

( ) ( )∑=

⋅=N

nn

urjkn ugeauE n

1

0�� ��( ) ( )ϕθ ,DuD =�

Least squares minimization

( ) ( )kk uEuD�� − To be determined:

[ ]TNaaA ,,1 ⋅⋅⋅=

26

Beam forming and beam steering

� Least Squares Method

HUVX ++ Σ=

D XA−

LSA X D+= with

=Σ+

0.01

0000

0.00.000

0.0001

00

0.0000.0

0.000001

1

N

i

σ

σ

σ

Minimize:

27

Beam forming and beam steering

� Planar array (=> Desired Pattern, f=11.7GHz):

� Ku-band phased array (10.7-12.75 GHz)

� Circularly shaped boundary (radius 10λmax)

� Square lattice (d=0.55 λmid)

� 1237 elements

� One-parameter circular aperture distribution (SLL=30dB)

� Circularly polarized patch antennas

28

Beam forming and beam steering

� Conformal array:

� Planar array curved around a cylinder of radius 1.65m(≈ radius fuselage Fokker 100 )

29

Beam forming and beam steering

−100 −80 −60 −40 −20 0 20 40 60 80 100−90

−80

−70

−60

−50

−40

−30

−20

−10

0Planar array(Desired pattern) LSM

Desired pattern and synthesis by LSM

30

Beam forming and beam steering

� Taper efficiency of curvedarray via LSM:

εT=0.027 (-15.7 dB)

( )

( ) ∑

∑

=

⋅

==N

nn

urjkn

N

nn

T

ag

euga

N

n

1

22max

2ˆ

scanco,1

scan0ˆ1

�

ε

� Taper efficiency of initial(planar) array:

� εT=0.76 (-1.19 dB)

Taper efficiency:

31

Beam forming and beam steering

DXAAXDAXDED +=⇒−≈−=− ~~~LS

HUVX ++ Σ= ~~

=Σ+

0.000000

0.000000

0.0001

00

0.0000.0

0.000001

~

min

1

σ

σ

Approximate Least Squares Solution via

truncated singular value decomposition of X

32

Beam forming and beam steering

−100 −80 −60 −40 −20 0 20 40 60 80 100−90

−80

−70

−60

−50

−40

−30

−20

−10

0Planar arrayTruncated SVDFull SVD / LSM

Desired pattern, and synthesis by LSM and truncated SVD

33

Beam forming and beam steering

� Taper efficiency of initial(planar) array:

εT=0.76 (-1.19 dB)

� Taper efficiency of curvedarray via LSM:

εT=0.027 (-15.7 dB)

� Taper efficiency of curvedarray via TSVD depends onsmallest singular value:

σmin=0.01σmax: εT=0.74(-1.31 dB)

σmin=0.1σmax: εT=0.75(-1.22 dB)

34

Beam forming and beam steering

� Least-Squares Synthesis Method may yield:– unrealistic amplitude distributions– amplitude distributions with unnecessary low taper efficiency

� Approximate least-squares solution obtained withpseudo-inverse based on truncated SVD is a simpleadjustment

� Approximate least-squares solution yields efficient weights for the beam formingof conformal phased arrays.

na

35

Design of Ku-band receive antenna array for SATCOM

SATCOM onboard aircraft

Cockpit requires voice services and data link Services (AFIS, AoC, CNS/ATM), can be provided by Inmarsat L-band systems

Passengers want� Voice services (e.g. VoIP)� High-speed internet (web, multi-media)� Television (Digital Video Broadcast via Satellite)

This requires additional Ku-band network services to be provided by GEO Ku-band satellites (Astra, Connexion by Boeing, ARINC Skylink), based on DVB-S2, DVB-RCS

� Some services operate in L-band, others are in Ku-band

36

Design of Ku-band receive antenna array for SATCOM

Inmarsat

(L-band)

DVB-S/Internet

(Ku-band)

Ground Earth Station

37

Design of Ku-band receive antenna array for SATCOM

Inmarsat

(L-band)

DVB-S/Internet

(Ku-band)

Ground Earth Station

Asynchronous data link (internet)

38

Design of Ku-band receive antenna array for SATCOM

� Lack of surface area for installation of antennas

� EU project ANASTASIA: L-band and Ku-satcom in ONE antenna

� Novel concept for satcom based ATM and Internet:� Ku-band antenna for receive only� L-band antenna for Tx and Rx

39

Design of Ku-band receive antenna array for SATCOM

� Ku-band receive-only antenna system with broadband optical beam-forming network and broadband phased array antenna

}AES receive band 1: 10.70 – 11.70 GHzSatellite TV: 11.70 – 12.50 GHzAES receive band 2: 12.50 – 12.75 GHz

2 GHz bandwidth

2o beamwidth κ1 κ2 κ7

φ1 φ2

in

T T

κ3

φ3

out 2T

κ4

φ4

T

κ6

out 1

out 4

out 3κ5

True Time Delays

40

Key technologies

� Development of broadband L/Ku-band antenna element

� Development of broadband optical beam forming network on CMOS chip

+

41

� Gain decreases:

� Beamwidth increases:

( )0cos θ≈

( )0

1

cos θ≈

� Polarization loss and errorsincrease:� Cross Polarization increases� Polarization Mismatch increases

Grating lobes / Side lobes:

0,max1 sind

λθ

<+

Design of Ku-band receive antenna array for SATCOM

42

Routes covered by CBB

Design of Ku-band receive antenna array for SATCOM

43

Phased Array Antenna Position(s) on the aircraft

Design of Ku-band receive antenna array for SATCOM

SATCOM HIGH GAIN(BOTH SIDES)

44

Antenna array on vibrating plate

� Vibration of surveillance array antenna on wings

� Compensation of vibrations via adaptivecorrection of phases of antenna signals

Demonstrator:

• Antenna array on vibrating plate

• Electronics for mutualtuning of antenna elements

• DSP based real-time control system

45

Antenna array on vibrating plate

� Vibrating plate with:

� stationary position.

� position caused by shaker vibration.

� position due to 1st

vibration mode.

)()()()(),( 110 xZtqtxZtxz ++= α

)(0 xZ

)(tα

)()( 11 xZtq

46

Antenna array on vibrating plate

� Electric field received at antenna j :

� with:

� Total electric field:

�

( sin cos ( , )cos )ˆ( ) j jik x z x tij oE t E e e

θ ϕ θ− + +=�

0 1 1( , ) ( ) ( ) ( ) ( )z x t Z x t q t Z xα= + +

tot j jjE A E=∑� �

47

Antenna array on vibrating plate

� Vibrating plate without compensation

48

Antenna array on vibrating plate

� Phase difference between antenna patch j and reference antenna patch 0 :

� Phase difference is approximated by:

� Adaptive phase compensation:

� Total electric field:

�

0ˆ{ ) i

j jk r r kϑ∆ = − − •� �

tot j jjE A E=∑� �

0{( ( , ) ( , ))cos }j jk z x t z x tϑ θ∆ =− −

: jij jA A e

ϑ− ∆=

49

Antenna array on vibrating plate

� Compensation of vibrations by synthetic beam steering (Computer simulations)

50

Compensation techniques for vibrating arrays

� Real-time amplitude & phase measurement of array elements� Phase Detector AD8302

� Radiation pattern computation (distorted)

� Real-time computation of counter phase.� DSPACE digital control system (with A/D and D/A converters)� PC Interface: instantaneous adaptation of weights

� Radiation pattern computation (compensated).

Antenna array on vibrating plate

51

Antenna array on vibrating plate

A/φ A/φ A/φA/φ A/φ A/φ A/φ

ϕ ϕ ϕ ϕ ϕϕ ϕ

ref

Phasecontrol

DSP/computer

52

Antenna array on vibrating plate

� vibrating array Transmit antenna at ceiling

53

Antenna array on vibrating plate

�Adaptive Digital Beam-forming aspects

� The measurement system yields time-varying amplitudes and phases:

� The summed result without compensation becomes:

� Adaptive digital compensation

� Instantaneous calibration� Determine in the computer the weight � Multiply each antenna signal with

� Then the compensated summed signal becomes

and , for 1, ,7.k kA kφ = ⋯

kik

k

S A e φ=∑

( )k kikw e φ ε− −=

kw

kik

k

S A e ε=∑

54

Antenna array on vibrating plate

� Received Signal Computation

� Vibrating antenna

� (Distorted +compensated)

55

Antenna array on vibrating plate

� Effects of vibrations and deformations on performance of large array antennas might be significant

� Vibrating radiation pattern – direction of main beam changes� Increase of Side Lobe Levels

• Compensation concept investigated:� Digital adaptive (real time) correction of phase deviations� Measuring phase differences

� Demonstrator appears to be efficient

56