Vortrag Shalaby Mohammed

8/8/2019 Vortrag Shalaby Mohammed

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Circular

antennaarray

beamformingfor UWB

MohammedShalaby

Contents

IntroductionandMotivation

NarrowbandBeamforming

UWB

Beamforming

SimulationProcess

Future Work

Circular antenna array beamforming for ultra

wideband short pulse applications

Mohammed Shalaby

Fachgebiet Hochfrequenztechnik

Bachelor Thesis Presentation03.05.2007


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Circular

antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Why UWB?

Powerspec

tra

ld

ens

ity Narrow band

Ultra Wide Band

-10 dB

f(Hz)fl fh(fl+fh)2

Enormous bandwidth and therefore according to the

shannons formula

C = B log2 (1 + SN R)

offers very high data rates.


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antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Why UWB?

Powersp

ec

tra

ld

ens

ity Narrow band

Ultra Wide Band

-10 dB

f(Hz)fl fh(fl+fh)2

No need for expensive licensing fees as it can co-exist withexisting radio services due to its low power level


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MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Why UWB?

Power

spec

tra

ld

ens

ity Narrow band

Ultra Wide Band

-10 dB

f(Hz)fl fh(fl+fh)2

Immune against detection and interception (as it appearslike background noise),has all-weather capabilities andhigher angular resolution (very attractive to the military)


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antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Why UWB?

Powersp

ec

tra

ld

ens

ity Narrow band

Ultra Wide Band

-10 dB

f(Hz)fl fh(fl+fh)2

Baseband technique as the pulse can propagate wellwithout any need for additional modulation stages.


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antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Typical Problems and solution

Problems

Like any other wireless technology UWB suffers from multipathpropagation and different kind of interferences leading todecreased date rate level.

Solution

Array Beamforming


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Circular

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beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Why Array Beamforming?

Receiver/Transmitterpossesing (antenna array)Signal of Interest

Signal of NO Interest

Based on exploiting the physical phenomena of the interferenceof Electromagnetic waves. Constructive interference towards Signal of Interest.

Destructive interference towards Signal of NO Interest. implemented using antenna arrays. The extent depends on the phase shift kl. The direction of the mainbeam and the nulls can be changed

electronically


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antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Why Circular Arrays?

Unique Features: Circular Symmetry and lack of edge elements

Consequences: It can scan a beam azimuthally through 360o

with little change in beamwidth and sidelobe levels in contrastto linear arrays as we see in the next diagram


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MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Comparison bet. Linear and Circular Array Radiation

Patterns

0.5

1

30

210

60

240

90

270

120

300

150

330

180 0

Linear Array

0.5

1

30

210

60

240

90

270

120

300

150

330

180 0

Circular Array

o=90 ;N= 8 in both arrays


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antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work


Patterns

0.5

1

30

210

60

240

90

270

120

300

150

330

180 0

Linear Array

0.5

1

30

210

60

240

90

270

120

300

150

330

180 0

Circular Array

o=35

C b L d C l A R d


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antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work


Patterns

0.5

1

30

210

60

240

90

270

120

300

150

330

180 0

Linear Array

0.5

1

30

210

60

240

90

270

120

300

150

330

180 0

Circular Array

o=10


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antennaarray

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MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Linear Narrowband Arrays

Array Normal

d

d

d sin

1 2N3

AF = 1 + exp {jkd sin }+ . . . =N

n=1

exp {j(n 1)kd sin }


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MohammedShalaby

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UWB

Beamforming

SimulationProcess

Future Work

Circular Narrowband Arrays

n

nth element

Incident rays

r

r cos( n)

AFc =

N

n=1

exp {jkr cos( n)}

n =2(n1)

N

Assumption:the elevation angle = 90


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antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work

Difference to Narrowband Beamforming

150 100 50 0 50 100 150

20

10

0

(degrees)

amplitude(dB)

UWB signal has a very wide bandwidth

Each frequency in that band generates its own radiationpattern as seen in the diagram which is undesired

Additional Degree of freedom is needed to ensurefrequency independency

Digital solution is not yet possible as current samplers do

not offer the need sampling rates


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antennaarray

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MohammedShalaby

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UWB

Beamforming

SimulationProcess

Future Work

FIR based Beamforming

Advantages of FIR based Arrays

They are easy to realize as a typical FIR branch consists ofdelay elements which can be implemented using microstriplines and multipliers which can be implemented using FETTechnology, thus eliminating the need for the complex

phase-shifting circuits used in the narrowband case.


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antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work


Advantages of FIR based Arrays

The array physical size is compact as the inter-elementspacing d is determined by

d c

2fh


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antennaarray

beamformingfor UWB

MohammedShalaby

Contents



UWB

Beamforming

SimulationProcess

Future Work


Advantages of FIR based ArraysSince it has wideband properties, it eliminates the need fordifferent antenna spacing for applications involving variouscarrier frequencies.


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UWB

Beamforming

SimulationProcess

Future Work


Advantages of FIR based ArraysThey can compensate for the frequency responses of thetransmitting antenna, receiving antenna and channel(Equalization),so the pulse shape is faithfully reproduced.


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MohammedShalaby

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UWB

Beamforming

SimulationProcess

Future Work

Linear UWB Arrays

Procedure to determine the coefficients of the FIR filter1 we first equate the desired radiation pattern Hd(f, ) to

the array radiation pattern Harr(f, )

Harr(f, ) =

N

n=1

M

m=1 a

nm exp {j2f[(n 1)o + (m 1)]

2 careful examination of equation 4.2.6 reveals that it lookslike a DFT.Thus,by choosing preliminary N and M andapplying the IDFT, we get the sought-after coefficientsanms

3 we autocorrelate the desired radiation pattern Hd and theradiation pattern constructed using the coefficients fromstep 2 and see whether they are similar enough(a criteria

should be defined for that),if not step 2 should be repeated


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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

Circular UWB Arrays

FIR

FIR

FIR

FIR

FIR

FIR

FIR

FIR

yc(t, ) output signal

Time-Domain output signal

yc(t, ) = p(t)N

n=1

M

m=1

anm(t(m1))(t((r/c)cos(n)))

where n =

2(n1)

N


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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work

Analytical problem

Frequency-Domain output signal

Yc(f, ) =N

n=1

M

m=1

anm exp {j2f[(m 1) + (r/c)cos( n

where n =2(n1)

N

Power of the exponential function not a linear function of n

IDFT can not be applied to calculate the coefficients

attempts to linearize the cosine function proves to be very complicated thats why a numerical solution is preferred


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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work

Simulation Process

The influence of the following parameters will be investigated:

The number of the antenna elements N

The order of the FIR filters M


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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

Simulation Process



The order of the FIR filters M

The bandwidth of input pulse

The radius of the circular array r

Si l i P


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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work

Simulation Process


The number of the antenna elements NThe order of the FIR filters M

The bandwidth of input pulse


Si l i P


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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work

Simulation Process



The order of the FIR filters MThe bandwidth of input pulse


Finally a Time-Domain example is given to give an impressionof the whole Procedure involving typical Parameters.

V i ti f th b f th t l t N


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UWBBeamforming

SimulationProcess

Future Work

Variation of the number of the antenna elements N

simulation conditions

3 circular arrays are compared with same:

radius r

filter order M = 8target angle o =80

o

signal bandwidth fh = 2fl where fl =3.1 GHz

but with different number of antenna elements N=

4

8

16

V i ti f th b f th t l t N


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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work




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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work


Conclusions

As the number of antenna elements N increases:

The mainlobe narrows

The number of sidelobes increases

Their peak level decreases

At some value of N saturation is reached

Note:N can not be arbitrarily increased for a fixed radiusbecause of the limitations imposed by the antenna size and themutual coupling

Variation of the order of the FIR filters M


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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work




radius r

number of antenna elements N = 16target angle o =30

o

signal bandwidth fh = 3fl where fl =3.1 GHz

but with different filter order M=

8

12

16



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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work




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arraybeamforming

for UWB

MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work


Conclusions

As the Filter Order M increases:The deviation from the desired radiation pattern decreases

Frequency independency increases

At some value of M saturation is reached

Variation of the bandwidth of input pulse


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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work




radius r

number of antenna elements N = 8

target angle o =30o

filter order M = 8

but with different relative badnwidth=

fh = 2fl

fh = 3fl



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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work




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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work


Conclusions

As the bandwidth of the input pulse increases:Frequency independency decreases especially at the edgesof the band

Higher Filter order is needed

Variation of the radius of the circular array r


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arraybeamforming

for UWB

MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work




number of antenna elements N = 8

target angle o =30

o

filter order M = 8

relative bandwidth fh = 2fl

but with different radius r=

rmax where rmax is c2fh sin(2N )

0.75 rmax

0.5 rmax



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arraybeamforming

for UWB

MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work




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Circularantenna

arraybeamforming

for UWB

MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

a at o o t e ad us o t e c cu a a ay r

Conclusions

As the radius of the antenna elements r decreases:

The number of sidelobes decrease

The the mainbeam widens

Radius and Grating lobes


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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

g

Circular arrays have the inherent characteristics of thepresence of undesired higher sidelobe levels compared tolinear arrays

That can be minimized by exerting a limit on the maximuminterelement spacing and hence a maximum radius as well

According to [Balanis 2004] the maximum interelementspacing is the arc 2r

N.

not convincing

I suggested that rmax isc

2fh sin(2

N)

according to the

following diagram.

Radius and Grating lobes


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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

g

r

r

Position of a far observer

2

N

r sin(2N

)

Not totallyphysically correct due to the double weighting

and interference of opposite elements but mathematicallycorrect as long as it is less and not less than or equal

with a radii in the order 1-2 cm the maneuvering space isvery limited due to the antenna physical size

Smart engineering sense is needed for estimation

Typical Time-Domain Example


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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work

yp p

GOAL to realize a Radiation Pattern for a short pulseapplication using a FIR Circular array. This BroadbandRadiation Pattern should resemble (as far as possible) a desiredRadiation Pattern of a Narrowband Circular Array with numberof antenna elements N=16.

150 100 50 0 50 100 150

30

20

10

0

in degree

|

yo

(t,

)|

in

dB

Desired Radiation Pattern



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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

y

Procedure

1 The number of antenna Elements N is given.

2 fl and fh are determined by the -10 dB marks of theFourier transformed pulse



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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

Procedure



3 The radius of the array is determined using fh to avoidGrating lobes



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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

Procedure




4 An initial Filter order M is tried and see whether thedesired and the synthesized agree ( a criteria should be

defined)5 Step 4 is repeated with different values of M until a

satisfactory result is reached



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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

Procedure




4 An initial Filter order M is tried and see whether thedesired and the synthesized agree ( a criteria should be

defined)5 Step 4 is repeated with different values of M until a

satisfactory result is reached


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arraybeamforming

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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work

150 100 50 0 50 100 150

30

20

10

0

in degree

|

yo(

t,

)|

in

dB

desiredsynthesized

N = 16; o=30o

fh=3 fl where fl= 3.1 GHz

M=14; r=0.016 m

Future Work


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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

Investigate the influence of the real antenna in terms ofphysical size,frequency characteristic and mutual coupling

Try to find an analytical solution for circular arrays

Future Work


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arraybeamforming

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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work


Try to find an analytical solution for circular arraysExamine other geometries, for instance: elliptical arrays

Future Work


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arraybeamforming

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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work



Choose a phase reference other than the array center

Future Work


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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work




Investigate the effect of the tolerances of electronic

components

Future Work


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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work




Investigate the effect of the tolerances of electronic

components

Acknowledgments


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arraybeamforming

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MohammedShalaby

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UWBBeamforming

SimulationProcess

Future Work

I would like to thank Prof.Solbach for letting me do my thesis inhis institute under his supervision.I would like as well to express my endless gratitude toMr.Neinhues for his invaluable support and sincere advices.Last but not least I would like to thank the audience for theirattention

Questions?


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arraybeamforming

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MohammedShalaby

Contents



UWBBeamforming

SimulationProcess

Future Work

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Vortrag Shalaby Mohammed