bakshi unit 4 special antenna

7/25/2019 Bakshi Unit 4 Special Antenna

1/8

Propagation

log

period

10.

MoDERN

ANTENNAs

lg:LllEcoNFrGuRABle

aHreniie

t

A

reconJigurable

antenna

is

en

antenna

capabre

of

modifying

,tyrr*rroffi

/i"equency

and

radiation

properties

in

a

controlled

and

reversible

manner..

'

Reconfigt*able

antenncr.s,

with

the

ability

to

radiate

more

than

dffirent

frequencies

and

porarizations,

are

necessary

t

e

I

e

c

ommuni

c

ation

sy

s t e

m.s.

'

These

anlinnas

can

address

complex

system

requirements

by

modifying

their

eeometry

and

electrical

behavior.

thereby

adapting

to

changes

in

environmental

conditions

or

system

requirements

(i.e.,

enhanced

band-width.

changes

in

operating

frequency,

polarization,

and

radiation

pattem).

Neutralizing

line

Fig.

I

0J.

ReconJiguroble

antenno

one pqttern

al

in

modern

I

t_

I

I

RF

switches


2/8

r0,

Antenna

and

Vl/ave

Propagation

In

order

to

provide

a

dynamical

response,

reconfigurable

antennas

integrate

an

inner

mechanism

(such

as

RF

switches.

varactors,

mechanical

actuators

or

tunable

materials)

that

enable

the

intentional

redistribution

of

the

RF

currents

over

the

antenna

surface

and

produce reversible

modifications

over its properties.

Reconfigurable

antennas

differ

from

smart

antennas

because

the reconfiguration

mechanism

lies

inside

the

antenna

rather

than

in

an

external

beamforming

network.

The

reconfiguration

capability

of

reconfigurable

antennas

is

used

to

maximize

the

antenna

performance

in

a

changing

scenario

or to

satisfy

the

changing

operating

requirements.

10.1.1.

TYPES

OF

ANTENNA

RECONFTGURATION

o

Reconfigurable

antennas

can

be

classified according

to

the

antenna

parameter

that

is

dynamically

adjusted,

typically

the

frequency

of

operation,

radiation

pattem

or

polarizatibn.

(i)

Freq

uency

Reconfig

uration

o

Frequency

reconfigurable

antennas

can

adjust

dynamically

their

frequency

oi

operation.

They

ate particularly

useful

in

situations

where

several

communications

systems

converge

because

the

multiple

antennas

required

can

be

replaced

by a

single

reconfigurable

antenna.

.

Frequency

reconfiguration

is

generally

achieved

by modifying

physically

electrically

the

antenna

dimensions

using

RF-switches,

impedance

loading

tunable

materials.

(ii)

Radiation

Pattern

Reconfig

uration

Radiation

pattern

reconfigurability

is

based

on the

intentional

modification

of

the

spherical

distribution

of

radiation

pattern.

Beam

steering

is

the most

extendec

application

and

consists

in

steering

the

direction

of

maximum

radiation

tc

maximize

the

antenna

gain

in

a

link with

mobile

devices.

Pattern

reconfigurable

antennas

are

usually

designed

using

movable/rotatabl;

structures

or

including

the switchable

and

reactively-loaded

parasitic

elements.

rdl*

frn

1[L'

oi

o:

'm"

;

X{


3/8


4/8

@

Antenna

ancl

l|/crve

propagation

1g{.

AcilvEANTENNA

.

An

active

antenna

is

an

antenna

that

contains

active

electronic

components.

dipole

antenna.

;;;;;ffi;.';

in^lo

^h+^.^-^

A

simple

definition

of

active

sntennas

are

ony

antennas

with

integrated

signar

amplifier'r

built

right

into

rhe

unit.

Passive

antennas

are

antennas

that

have

no

mplificution

stdges'

An

active

antenna

is

a

passive

ontenna

that

simpry

includes

an

onboard

amplifier.

Most

active

antennas

have

onry

one

erectricar

connection.

that

is,

RF

signar

and

he

power

for

the

amprifier

are

suppried

on

the

,";;;;;;,;.,"..

o

f

I

I

t_

PdSsMEANTENNA

mrm

flril'i

miinru

gnim

rilm

lhFp"

&rc

U[t

L,r

6t

ffIr;'

mmrir.ii

ACTIVEANTENNA

)lt

rutr1lilill

$*qwut*r/rmryd.t'ir.

Fig.l0.2.

Simple

active

antenna

An

active

design

allou's

the

construction

of

antennas

of

limited

size

and

/

or

wide

frequency

range'

and

are

primarily

used

in

situations

where

a

simpler

and

more

receptive

large

antenna

is

either

impractical

(inside

a

portable

radio)

or

impossible

(suburban

residentiar

area

trrat

disarows

use

of

rarge

outdoor

low_frequency

antennas).

Most

active

antenxas

use

antenna

parts

of

minimar

conducting

area,

e.g.,

a

smail

whip'

connected

to

the

active

component

(usually

a

FET).

The

signal

attenuation

caused

by

the

anten

circuit.

ura-srze-to-wa'erength

mismatch

is

compensated

by

an

active


5/8

as

a

signal

hove

no

include,s

and

I

or

wide

more

a

small

active

\ odern

Antenn(ts

.

The

active

circuit

consists

of rmpedancc

translating

stage

and

an optional

amplification

stage.

This

arrangement

is

especially

useful

for

constructins

compact

low

frequency

antennas

due

to

budgetary,

spatial,

or

practical

requirements

(e.g.,

installation

in vehicles),

must be downsized.

Low frequencl,

signal

wavelengths

range

from

one

to ten kilometers.

.

Power

for

the

active

components

may

be

supplied by

batteries,

a filtered

power

supply,

or

through

the

signal

feeder

itself

(phantom

power).

Antennas

containing

active

impedance

translating

and

optionally

amplifuing stages

are usually

used

only

for receiving,

since

operation

of

such

stages

is

unidirectional.

.

Without

amplifiers,

the

loss

of

the coaxial

cable will have

a severe

impact

on

performance.

With

an

active

uirt.nnu,

it

is

possible

to

use

long

cables

and

still

maintain

pgrformance.

,

0.2.1.

INTEGRATED

ACTIVE

ANTENNAS

.

Integrated

active

antennas

are

a

single

column

antenna consists

of

multiple

elements.

If

all

the elements

are

fed

in

phase.

a narrow horizontal

beam

is

formed.

.

By

adjusting

the

phase

of

the

signal

to

each

element

causes the

beam

to tilt..This

is

known as

"electrical

downtilt"

and

it

is

in

common usage

throughout

the

digital

mobile

radio

industry.

:

JB

I

Fig. I 0.3.

Integrilecl

sctive ontenno

.

If

the

antenna

column

has

a

single

transceiver,

all carriers

will

be

approxirnate;ty

ifre same

amount

in

both

transmit

and receive directions.

rilted by

D

E

F

u

H


6/8

To

achieve

this,

antenna

element

transceivers.

The

requirements

size,

weight,

cost,

receiver

electronic

it

a

is'required

to

have

a

.separate

transceiver

controller

would

be necessary

to

control

Antenna

and

Ll/ave

propagat

fbr

(ideally)

/synchronise

for

success

are

that

each

transceiver

is

and

performance.

Each

transceiver

has

devices.

acceptable

in

terms

the

transmitter

and

10.2.2.

ADVANTAGES

The

advantages

of

active

antennas

are

as follows:

(i)

Increased

coverage

and

capacity.

(ii)

Independent

optimisation

per

carrier

and

per

technology.

(iii)

Reduced

item

count

at

ground

level

and

on

the

mast

(iv)

Pcoducing

duplexing

filters

that

deliver

high performance.

ll-0f

:|p1F}EgISl_c.BFggNAroRANrENNA(DiA,

o

The

DRA

is

an

antenna

that

makes

use

of

a

radiating

mode

of

a

dielec

resonator

(DR)

and resonance

frequency

determined

by

the

its

dimensions

dielectric

constant

s

Fig.

1

0.4.

Dielectric

resonator

antenna


7/8

Modern

Antennas

each

the

of

and

o

A

Dielectric

Resonator

Antenna

(DRA)

is

a radio

anteniia

mostl\,

used

at

the

microwave

frequencies

and

higher,

that

consists

of

a

block

of

ceramic

material

of

various

shapes,

the

dielectric

resonator,

mounted

on

a metal

surface

and

a

sround

plane.

'

Radio

waves

are

introduced

into

the

inside

of

the

resonator

material

from

the

transmitter

circuit

and

bounce

back

and

forth

between

the

resonator

rvalls.

forming

standing

waves.

The

walls

of

the

resonator

are

partially

transparent

to

radio

waves,

allowing

the

radio

power

to

radiate

into

space.

'

An

advantage

of

dielectric

resonhtor

antennas

is

they

lack

metal

parts,

which

become

lossy

at

high

frequencies,

dissipating

energy.

so

these

antennas

can

have

lower

losses

and

be

more

efficient

than

metal

antennas

at

high

microwave

and

millimeter

wave

frequencies.

'

The

dielectrii

waveguide

antennas

aro

used

in

some

compact

portable

wireless

devices,

and

military

millimeter_wave

radar

equipment.

'

The

dimension

of

a DRA

is

of

the

order

of

+

where

]..

is

the

free-space

It,

wavelength

and

e

,

is

the

dielectric

constant

of

the

resonator

material.

Thus,

by

choosing

a

high

value

of

e,

(=

r

0

-

r

00),

the

size

of

the

DRA

can

be'iignificantly

reduced.

10.3.1.

FEATURES

Dielectric

resonator

antennas

offer

the

following

attractive

features:

(i)

There

is

no

inherent

conductor

loss

in

dielectric

resonators.

This

leads

to

high

radiation

efficiencS'

of the

antenna.

This

feature

is

especially

attractive

for

millimeter

(mm)-wave

antennas,

where

the

loss

in

metal

fabricated

antennas

can

be

high.

(ii)

DRAs

offer

sirnple

coupling

schemes

to

nearly

all transmission

lines

used

at

microwave

and

mm-wave

frequencies.

This

makes

them

suitable

fbr

integration

into

different

planar

techno

I

o

gi

es.


8/8

Antenna

and

Wave

Propagation

(iiD

The

operating

bandwidth

of

a DRA

can

be varied

over

a wide

range

by

suitably

choosing

resonator

parameters.

(iv)

Use

of

multiple

modes

radiating

identically

has

also

been

succegsfully

addressed.

(v)

Each

mode

of a DRA

has

a

unique

intemal

and

associated

exterpal

field

distribution.

Therefore,

different

radiation

characteristics

can

be obtained

by

exciting

different

modes

of

a DRA.

10.4.

.TIIUO:MARKS

QUESTIONS

AND

ANSWERS

't:

n,

,&

lt.

U

l:Tl

[ ilf,r:c

;

:"-

a

-'.

1.

What

is

reconJigurable

antenna?

A

reconfigurable

antenna

is

an

antenna capable

of

modifying

dynamically

its

frequency

and

radiation

properties

in

a controlled

and

reversible

manner.

Reconfigurabli'antennas,

with

the

ability

to

radiate

more

than

one

pattern

at

different

frequencies

and

polarizations,

are

necessary

in modem

telecommunication

systems.

List

the

types

of

reconfiguration.

Reconfigurable

antennas

can

be

classified

according

to the

antenna parameter

that

is

dynamically

adjusted,

typically

the

frequency

of

operation,

radiation

pattern

or

polarization.

(i)

Frequency

Reconfiguration

(ii)

RadiationPatternReconfiguration

(iii)

Polarization

Reconfiguration

(iv)

CompoundReconfiguration

Deft

ne

freq

uency

reconfigurab

I

e

ante

nnas.

Frequency

reconfigurable

antennas

can adjust

dynamically

their

frequency

of

operation.

They

are

particularly

useful

in

situations

where

several

communications

systems

converge

because

the

multiple

antennas

required

can

be replaced

by

a single

reconfigurable

antenna.

2.

3.

bakshi unit 4 special antenna

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