Text Text Books: 1. Antenna Theory Theory,, Balanis C.A, C.A, John Wiley & sons 2nd
edition Reprint 2008 2. Electromanetic and radiatin systems, Jordan E.C,
!"#., 2nd edition, 2008 (arhe)*a $rd Edition, Edition, $. Antennas, John % ra's & R J (arhe)*a 2002. and Wae Wae !ropaation, !ropaation, .%. !rasad, !rasad, -atya +. Antenna and !ra*ashan, $rd edition 200
CONTENTS Antennas
/'ndamental !arameters o) Antennas Antennas
Arrays
Apert're
Antennas and Re)lector Re)lector antenna
Radio Wae propaation
CONTENTS
Antennas
/'ndamental !arameters o) Antennas Antennas
Arrays
Apert're,
"orn and and Re)lector antennas
Radio Wae propaation
ATEA
#ntrod'ction
Types o) Antenna
Radiation (echanism !hysical concept o) Radiation in sinle ire, to ire
and dipole
C'rrent %istri'tion on a Thin Wire Antenna
#TR3%4CT#3 Antenna
or Aerial Aerial 5 6 is a transd'cer that transmits or receies electromanetic aes 6 conerts the oltae and c'rrent into the electromanetic radiation and ice6ersa 6 is a transitional str'ct're eteen eteen )ree6space )ree6space and a 'idin str'ct're
6 The American "eritae %ictionary5 %ictionary 5 A metallic apparat's )or sendin sendin and receiin electromanetic aes. 6 Wester7s %ictionary5 A %ictionary5 A 's'ally metallic metallic deice as a rod or ire9 )or radiatin or receiin radio aes
#TR3%4CT#3 What
is an Antenna: Antenna:
An antenna antenna is a deice )or )or radiatin and and receiin radio radio aes. The antenna is the t he transitional str'ct're eteen )ree6space and a 'idin deice. deice.
#TR3%4CT#3 A transmission6line
system
Theenin e;'ialent e;'ialent o) the antenna antenna
#TR3%4CT#3 A
transmission6line Theenin e;'iale e;'ialent nt o) the antenna antenna system
#TR3%4CT#3 .
.
#TR3%4CT#3
.
Antennas
#ntrod'ction
Types o) Antenna
Radiation (echanism !hysical concept o) Radiation in sinle ire, to ire
C'rrent %istri'tion on a Thin Wire Antenna
T
antennas
Apert're
antennas
(icrostrip Array
antennas
Re)lector =ens
antennas
antennas
antennas
Wireeeryhere6 antennas seen irt'ally on a'tomoile, 'ildin, ships, aircra)t, and so on.
-hapes
o) ire antennas5
straiht ire dipole9, loop circ'lar9, and heli>, =oop antenna may ta*e the shape o) a rectanle , ellipse or any other shape con)i'ration
Aperture@ Apert're antennas deried antenna )rom ae'ide technoloy circ'lar, rectan'lar9 @
Can trans)er hih poer manetrons, *lystrons9 *lystrons 9 4tiliation
o) hiher )re;'encies
Applications: aircraft, and spacecraft
EM wave
Power absorbed: P [watt]
Effective aperture: A[m2]
ote5 The apert're concept is applicale also to ired antennas. /or instance, the ma> e))ectie apert're o) linear λ?2 aelenth dipole antenna is λ2?8
consist
Microstrip o) metallic patch antenna on a ro'nded s'strate
E>amples5 rectan'lar and circ'lar shape Applications5 Applications5 aircra)t, spacecra)t, satellite, missiles, cars etc RECTANGLE
CIRCLE
Radiation
atc! Antennas λ ε
is )rom to slots on le)t and riht edes o) patch here slot is reion eteen patch and ro'nd plane
=enth
λd D
ο? r
1?2
Thic*ness typically 0.01 λο
The i adantae is con)ormal, i.e. )lat, shape and lo eiht %isadantaes5 %isadantaes5 =o ain, arro andidth oercome y )ancy shapes and other heroic e))orts9, Becomes hard to )eed hen comple>, e.. )or ide and operation
atc! Antenna attern
a collection o) simple antennas
Arra" antennas
6 ies desire d radiation characteristics
6 The arranement o) the array may e s'ch that the radiation )rom
the elements adds 'p to ie a radiation ma>im'm in a partic'lar direction or directions, minim'm in others, or otherise as desired 6 Examples: yai6'da array, apert're array, microstrip patch array,
slotted ae'ide array
Arra" o# patc! Antennas
Re$ector millions o) miles antennas A ery common re)lector antenna F paraolic re)lector
6 'sed in order to transmit and receie sinals that had to trael 6
ara%o&ic Re$ectors
A paraolic
re)lector operates m'ch the same ay a re)lectin telescope does
Re)lections
o) rays )rom the )eed point all contri'te in phase to a plane ae leain the antenna alon the antenna ore siht a>is9
Ty Typically pically
'sed at 4"/ and hiher )re;'encies
@ lenses are primarily 'sed to collimate incident dierent enery to
Lens antennas
preent it )rom spreadin in 'ndesired directions @ Trans) Trans)orm orm ario's )orms o) dierent enery into plane aes @ 4sed in most o) applications as are the paraolic re)lectors,
especially at hiher )re;'encies. Their dimensions and eiht ec0me e>ceedinly lare at loer )re;'encies.
=enses play a similar role to that o) re)lectors in re)lector antennas5 they collimate dierent enery 3)ten pre)erred to re)lectors at )re;'encies G 100 H".
Antennas
#ntrod'ction
Types o) Antenna
Radiation (echanism !hysical concept o) Radiation in sinle ire, to ire and dipole
C'rrent %istri'tion on a Thin Wire Antenna
PHYSICAL CONCEPT OF How is Radiation Accomplished? RADIATION Principle of radiation or RADIATION When electric chares 'ndero acceleration or deceleration, MECHANISM electromanetic radiation ill e prod'ced. "ence it is the motion o) chares i.e., c'rrents9 that is the so'rce o) radiation basic equation of radiation IL !"
#here
#time aryin c'rrent Ichare =lenth o) c'rrent element time chane o) elocity Radiation $echanism in a% &in'le wire, b% (wo (wo wire and c% )ipole
Radiation $echanism &in'le
wire: wire:
Cond'ctin ires ires are characteried y the motion o) electric chares and the creation o) c'rrent o o.. Ass'me that an electric ol'me chare density, ;, co'loms?m$9, is distri'ted 'ni)ormly in a circ'lar ire o) cross6sectional area A and ol'me K ;, 6 ol'me chare density A6 cross6sectional area K6Kol'me
Radiation $echanism &in'le
wire: wire:
#nstead
o) e>aminin all three c'rrent densities, e ill primarily concentrate on the ery thin ire.
The
concl'sions apply to all three. #) the c'rrent is time aryin.
Radiation $echanism
Radiation $echanism (hin wire
Radiation $echanism &in'le
wire: wire:
Radiation $echanism (wo*#ires:
@ Applyin a oltae across across the to6cond'ctor transmission transmission line creates an electric Leld eteen the cond'ctors. @ The moement o) the chares creates a c'rrent that in t'rn creates a manetic Leld intensity. @ The creation o) time6aryin electric and manetic Lelds eteen the cond'ctors )orms electromanetic electromanetic aes hich trael alon the transmission line.
Radiation $echanism (wo*#ires:
@ The electromanetic aes enter the antenna and hae associated ith them electric chares and correspondin
c'rrents. @ #) e remoe part o) the antenna str'ct're, )ree6space aes can e )ormed y connectin the open ends o) the electric lines
Radiation $echanism (wo*#ires:
@ #) the initial electric dist'rance y the so'rce is o) a short d'ration, the created electromanetic aes trael inside the transmission line, then into the antenna, and Lnally are radiated as )ree6space aes, een i) the electric so'rce has ceased to e>ist. @ #) the electric dist'rance is o) a contin'o's nat're, electromanetic aes e>ist contin'o'sly and )ollo in their trael ehind the others. @ "oeer, hen the aes are radiated, they )orm closed loops and there are no chares to s'stain their e>istence. @ Electric chares are re;'ired to e>cite the Lelds 't are not needed to s'stain them and may e>ist in their asence.
Radiation $echanism )ipole Antenna:
A radio antenna that can e made o) a simple ire, ire, ith a centre6)ed drien element
Consist o) to metal cond'ctors o) rod or ire, oriented parallel and collinear ith each other in line ith each other9, o ther9, ith a small space eteen them.
Consider the e>ample o) a small dipole antenna here the time o) trael is neliile
Radiation $echanism /ormation and detachment o) electric )ield line )or short %ipole Antenna
)ipo&e
Current )istri%ution on a t!in *ire antenna =et 's consider the eometry o) a lossless to6ire transmission line The
moement o) the chares creates a traelin tr aelin ae c'rrent, o) manit'de # 0 ?2, alon each o) the ires.
When
the c'rrent arries at the end o) each o) the ires, it 'nderoes a complete re)lection e;'al manit'de and 180 phase reersal9
The
re)lected traelin ae, hen comined ith the incident traelin traelin ae, )orms in a each ire a p're standin ae pattern o) sin'soidal )orm.
Current )istri%ution on a t!in *ire antenna
Current )istri%ution on a t!in *ire antenna
/or
the to6ire alanced symmetrical9 transmission line, the c'rrent in a hal)6cycle o) one ire is o) the same manit'de 't 180 o't6o)6phase )rom that in the correspondin hal)6cycle o) the otherire
Current )istri%ution on a t!in *ire #) s is also ery small, the to )ields are canceled antenna
The
net res'lt is an almost ideal, non6radiatin transmission line.
When
the line is )lared, eca'se the to ires o) the )lared section are not necessarily close to each other, the )ields do not cancel each other
There)ore
system
ideally there is a net radiation y the transmission line
