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The document discusses thin linear wire antennas, including their current distributions, types such as dipole and helical antennas, and their radiation mechanisms. It also outlines the classification of wire antennas based on shape and length, and provides applications for various types of antennas in communication systems. Additionally, it describes steps for calculating characteristics such as radiation resistance and directivity.
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0% found this document useful (0 votes)
14 views46 pagesAWP Unit 2
The document discusses thin linear wire antennas, including their current distributions, types such as dipole and helical antennas, and their radiation mechanisms. It also outlines the classification of wire antennas based on shape and length, and provides applications for various types of antennas in communication systems. Additionally, it describes steps for calculating characteristics such as radiation resistance and directivity.
Uploaded by
kadaboinagirishrajCopyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF or read online on Scribd
/ 46
UNIT-2
Thin Linear Wire Antennas
1) Current distributions
2) Radiation from InfinitesimalDipole (Lertizian dipole)
3) Half wave and Quarter wave Dipole
4) Loop Antennas Slot antennas
5) Helical Antenna sht or
: which is in the shape of straig]
Definition: Wire antennas are thin. conducting wire which &
curved segments
‘They are easy to construct. : sacl
Ske agen avn ihe form of linear that is ealled linear wire antennas
Antennas whieh are in the
Ey: Dipole antennas.
Classification of Wire antenna
Wire antennas are classified based on the shape of the wire and the length.
ire antennas are cla
1) Based on shape of Wire
i) Linear/Straight wire antennas ii) Curved Wire Antennas.
Ex: Dipole, Monopole
Ex: Loop. Helical
2) According to length of wire
Infinitesimal dipole
Small Dipole
(Hertzian dipole)
Quarter wave |
Half Wave
N50 S1 Current distribution is sinusoidal.
> The antennas are symmetrically fed at the center by a balanced two wire
transmission lines.
Applications of Wire Antennas:
Lis Aca aaa NEN
1) Monopole Antennas:
-5 Incar, Radio, Walkie-Talkie ete
2) Dipole Antennas:
> Used as a building blocks of more complex antenna array system,
Ex: Yagi-Uda Antenna—In TV home reception and short distance communications
Log periodic Antennas- HF communication, TV reception
B) Loop Antenna:
> Used in Radio receivers, UHF transmitters ete.
Ay) Helical Antenna
© Used in satellite communication, Radio astronomy, transmitting telemetry data from
moon to earth.
Steps to determine the charact
Steps to determine ee en
STEP 1: Calculate Ele:
STEP 2: Calculate Average Power density.
1CExXt
Foxe LC x)
STEP 3: Calculate Radiated power. __ ea
Prog = “A Rando* AS
Ss
STEP 4: Calculate Radiation Resistance.
sof Antenna:
i¢ & Magnetic field.
STEP 5: Calculate Radiation Intensity, Directivity and Aperture area of antenna.
Vl) = IC Poe
D= 4NVULAG) ‘ Be =(2= yo
Pred an along the 7-axis.
pypothetical)
blocks of comple
hat loaded antenne
where |
a= diameter of antenna
Coordinate system and oriented
fe not very practical (1
Jgedl in array’ antennas Le, buil
or-plate (oF) 0p
Used to represent capacit
Jength of antenna
> Dimensions: 1 << or
© Itisalso called as Hertzian dipole.
Analyze the characteristics of an Antenna:
ee
current dearrilution dipete
Stepi:
ebe veto podenbeal A)
stepr: Pind Magn
Steps: Caberlate oma E
B= UxK = A= 4wxA)
From Moxweulls &a7 , will BE from #
é veo TxB= TetIp
step y: a
PH CohoUatE Pog , Pend) » UCSB, pve -
Flechic. iad orientation,
need to analyze in far field region. ey
Rodiated fielas by an infentlesions Aipole
INNES
~ Ln taPenttevirnal dépete , The end plates oe
wed ko provide Ceypacthve Loncding, do mainlawn
the coment on the dSpete Ontformty.,
— Sire the end plotes Of odaumed to be Aenott
trois, ~adtakions wre nedligtble -
The Speties Vrariatton ef the coment a assumed
Genera) exprovcien ot Bs
IRR
A buy 2) = S| Bo (ty'jat) © PR w —e@
an
Gres
Lshere Re digtence fromm any. ark
petat on hw A0urce to thu
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"Te = Ted
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ALadd
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Then eqn
Me jer
pea a eb ae
- | a
“ae x
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an Up
SPR. & 7
Sane Lo 2 Jelly
~Ae PE, Ge fL-CLI]
A. = Moot ara ——2)
oe
Ke yo UD porerttet
oe a
Conver Rredarguior “inks Spherical cootinalee
Ling, trontfermatton -
Me SInO CY — SinO Sng Coro Aree
Be | =] cmecerg core sing — ting Ayzjo
Ag ee Cores © Aa
Fe LnPenitestenas Aipete Ax sAy 20 (4pete kept
A= a) MEot SPR 25 5 Cord Bou D-
i. Ar
=~AzSno=-f Tot PR ie & Sn®
ceria 4 oD
Ages -O B= VxA
MB= UXA
Oe B 2 7 a
pLV** J UXB= cual in Spherie
VxB= —! By Kae hsmoeag
7S} = 2 2
SING ae 6 Ss
At Hho King Ag y= °
(oat {tea 2,G4e)} foe — {0-2 i nae + {Ber 2
Hsinde |
Wm = Zope \ ot o+ Kafe tp [ZAe)- aed]
rok:
Sub wm 6)
a ay — 2 Ab — ©)
. We oe 2 Ore) se |
Sub (4) % &)
MPA g eR
S3PR Fine )
Tipe a™| Fi ; net & sano) ~ Fe TAR
C:
= Lag - pits sino &PR (jp) — RPA aT See)
rte war nk
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~ hte Saar
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ie jpeselsing [it 3B we ose ap (Ce Rak? P
fe
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ant
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Hyco, tpee . He=0 ) Electric field Pabersoby(E) a" -
From thy Mommsetty 2g i
VxH = TetTy =cE + 2b
= 0+€aE Ce Fer Sreespa.
ue ozo i
YxG= 1 2a) Sade | ae
a 2 2 2
sme] 2 2 B
HAC? HE? Sno
= 2
samo fae Ce HA) ~ 2B 2, (asmopy |
Sub this to eqn®
| — sh Kae a (xsho"
: jue eee eH) sCS7H0 ae i)
Pat ! 2 [sine Hy [Ov— 2 (sr9ti)
a JWEX Gnd Al te | Fuoetend®
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ane Ly Valve fern eqn in above to gek Ey Te valust
ete Ep= 1 2 hsine Hg
ee ‘cing BO L |
a see Tay
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ae
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os
sie (Pzot_ 2P* ip [+ s+ Gael
area
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tet he
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magnebe Prietds nr
w77l) the ele trie
qn
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unte
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ad 1 Rag EX Apt
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fs net So eine Ae dF
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as 4 Biot 1 [oF] [5] Jsitese ‘ose
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= (BY Bred
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ar a B07 TL. oe Hens -
Rea = S07) oh
Redsetten nferwity (VE)
UlCOib) = K* Pong
[vers [eal )|
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D = 4x Ue)
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Be nes(Qeis oy [Lena] Hatfrmome Dipete (Ala
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ends ore ot equa poteasoad welalave ‘to
ward pein ;
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He tad of mvekal Xod Co”) thin Woe
=> DPE hos A prune lengths of holy woe length
in Pree Space et the frequency. of operatten
Uses *
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of Co NOR Com plese
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Used as an cheer
diveckian onroug- soystomn -
Ex: Yagiuda Orreu Ley pertodic mayor
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steps: Poleatote Eat tee enor
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teakea | =
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dixbUowted -
L= Dn Singth-29 for 270 t __o
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Vectes polenial of a distance poive ‘p! dure to
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ince the peint’p) a ara Lager disleance @
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ante
ete (aco th
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i dea ae = cn8 |
= Rim oe a
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er
= Hime iJ [eseeactenery +ca(pecrened =|
ant
a [ reno SOP
. Ronee" \ Sin(p2(.xcese)) = sin (Bzct-corey)] >
Cat (core) P TKO p °
een@IPM( striphi4ee'8)) sin(BhCi-coe)
Grn L BUF OAS) eae (4 c080) Sh,
in fo (et cono YCI-Cos0)
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he Aly ae
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cirvio
* Co(7yp,Co10) — COO noe coo)" +1 CONE Coho)
+ | cos oosn(Ae ovo)
“Si
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comvant B yechanguar inte spheric
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bo | = | Cs@corg carocing —cihe | | Ayt° \ ¢
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/ NBs ux = Beg lven] — ©
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sino | gr $5 8 By
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* ie] Baoy}a — fo- 2 } :
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~ eine ar RS
wsine 1 ae
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vr = 9 Lage] |
eub in ©
a 4, %(2.c-#0? J
ae B= Pi ak ipic ee
ap! 2 [ULon & cosas ) Fo
= ie fa. arp ( sive
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aa ay Him eH(E) geo 3,8")
i ane sre
~ — am ey cos (7,000) oer (-32)
ang Spe
| te §j 2 SPX cos [Zor] ay
| ene Sine
era enrol
eels = ee
Elecite field dnlontipE )
lEol_ N = 1207
[H pe
[Eo = [Yel 1207
= 1S y Len ——
or
| |Eo| = Goto
sme
contort 7]
Se
Prevage | poster dent Gong
Fag = 2 Leen]
= 2 o
> led [
= 1 GOD See |
“a Te LO Sire
a
Bred aay 7 PEO”
: We ew
SinrO
| Bog . Stes fp Cox “cos” Phcoe) Gail
“Th are **)
Trtal Rodiched Bower Cred)
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Jfrse (s Bes" Lotte? Tr Ksine dedg a
in re
15 Der 9 \ ays y coh ise) gC de
aa Tye cre
= Sak Cogty (Frege ae
we le
Sine
AG
a Beg = IF Tes” (29 (1-214)
[ere
Radialien Rertatance (Rood?
Pred = Dei Rood
= (ENVY Rood
(LaF ke
aceiyy= DB ord
2
Rag = 36:54(29
= TSN
Radictien Prbenwky, Ww (or)
UiMg) = 7 Powg., :
OG) = 3 IS DH eh ee TPO)
Shee
Divestvity. CD)
| ae L(E1e)
= ae eee eS (rts cov?)
Sa
BEST DA
eee |
The Momtrun wedicatsen oeus ak O>N
“De pee) Dee
GDM Quattor wowe Monepete- Ce >,
— auarter wave monepote dae :
antenna conmli of one hop of coe
a halpwwe aspete- |
a ee Foye
es te et
ree garksea) potentgedion F We Le
ole, adwentage of TOA TG
antenna e
length an oe pte (2 EN
: cane, Monel
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w you. toowre oF pote onolyed
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he Sve
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oe Sie
wie S o
ce Nr 14 cr(P Beer) d9
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ee © LSInNO
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[Passer] 0 ee
eee) > op’ *
= > "i
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Pred = os Ramd
Is. 32h = (E81 Bred
Yo
y
Rrad = 18-3(29
[Beas 20-0 wh
ve
Rectiekton Dnterwlip (O00
ving) = 9% eh
kee ia Lae > (Eee) JI
sie
Derecravity CP?
pe 4n yom
fees ieee
. are
oe
is es
sare
Ben theaAD yeciodion ocours ak C= Mh
p+3-:2e
poanctersnen sfreutve Apounne O*)
a eS
—
Ao-(Xe D
- Gey
- [Rew one a]
P 1) ) An electric field strength of 10 V/m is to be measured at an observation point
8 = 11/2, 500 km from a A/4 monopole antenna operating in air at 50 MHz.
(a) What is the length of the dipole?
(b) Calculate the current that must be fed to the antenna.
(c) Find the average power radiated by the antenna.
(d) If a transmission line with Z, = 75 © is connected to the antenna, determine
the standing wave ratio.
SOLUTION: ek
a) The wavelength A= c/f=(3 x 16%) / (60x 10%) =6 m.
Length Of The Dipole (|) = /4 = 6/4 = 1.5 2m.
cos )
b)
lEg.1l = Nolo cos( F
[Egs1 27rsind
° ne cos ie cos )
_ 10x 10° ( 2n (500 x 10°)) x sin n/2
120r cos (0)
= 83.33 mA
c) Rraa = 73 Q (For N2 (Half Wave) Dipole Antenna)
Rraa = 36.56 9 (For N'4 Monopole Antenna)
1
Pred = zr lo? Resa
u
5 (83.33 x 10°)? x (36.56)
= 126.8mW d) Standing Wave ratio (5)
s=
Z+Zo
Z, = 73 + j42.5 (For Half wave dipole Antenna)
Z, = 36.5 + j21.25 (For N4 Monopole Antenna)
: 36.5 + j21.25-75
* 36.5 +j21.25+75
= 0,3874 140.3°
_ 1+ 0.3874
1 - 0.3874
= 2.265
/2) Calculate the directivity of
a) The Hertzian monopole
b) The quarter-wave monopole
a) For the hertzian monopole
BARU max
Prag
U (8, ) =sin’?o
0<0 11/2 as shown:
we
17) In free space, an antenna has a far zone field given by
5sin20 _-
E,=———e 1 ag V/m
where B = w | (Hofo)
Determine the radiated power?
lel? _ 25sin?20 ,.
2n 2nr* .
120n
2nr*
= Ss S [J (2sinecose)* sinedode
za 2 Sasinecose d(-cose)
= sS Stcose - cos*@) d(-cos®)
= 25. (cos*@— cose
120. 75 3
Pra = 55.35 mW 18) At the far field, the electric field produced by antenna is
10 6
E,= e
Sketch the vertical pattern of the antent
points as possible.
* cosO cosh a,
na. Your plot should include as many
£(@) = | cos® cose |
For the vertical pattern, » = 0 which means,
{(8) = | cos® | which is sketched below
19) At the far field, an antenna produces
Pave = Benet. a. wim', 0 lo Rios
On substituting we get,
G,= 1.5 sin’e
b) Directivity, D = Gp, max = 1-5
©) Effective Area, Ae = (N"/ 417) Gy = (1.5 2 sin’6) / 417
d) Radiation Resistance Rrat
2
Rreg= 80m” [Mas
A
7 aon’ i
16
= 3.084 f Loop Antenna
Contents:
+ Basics of Loop Antenna
+ Types of Loop Antenna
f + Radiation of Loop Antenna
+ Structure of Loop Antenna
+ Properties of Loop Antenna
+ Applications of Loop Antenna
Basics of Loop Antenna:
E + AnRF current carrying coil is given a single turn into a loop, can be used as an
antenna called as loop antenna, The currents through this loop antenna will be in
phase. The magnetic field will be perpendicular to the whole loop carrying the
current,
+ The frequency range of operation of loop antenna is around 300M Hz to 3GHz. This
t antenna works in UHF range (television broadcasting, cell phones, satellite
communication including GPS, personal radio scrvices including Wi-Fi and
Bluctooth, walkic-talkies, cordless phones, satellite phones, and etc).
+ A loop antenna is a coil carrying radio frequency current. It may be in any shape such
as circular, rectangular, triangular, square or hexagonal according to the designer's
convenience.
WY
Loop Antennas of Different Shapes
etores Dt
Feeding in Loop Antenna:
| SITEIE es of Loo]
1) Small loop antennas
2) Large loop antennas
ically Small Loop Antenna: ; ieee
eS * Sal 0p antennas are also called as magnetic loop os is
> These are less resonant. These 7 ee Sone See
> These antennas are of the size of one-te ng :
pat ses here Lis the length of the antenna and 2 is the wavelengtl
> For N no of tums N(2xr) < 1/10
Properties of Small Loop Antenna:
> Null at perpendicular to plane of loop
> Less radiation resistance;
> Less radiation efficiency
FEATURES OF SMALL LOOP ANTENNAS:
* A:small loop antenna has low radiation resistance. If multi-turn ferrite core
constructions are used, then high radiation resistance can be achieved.
+ Ithas low radiation efficiency duc to high losses.
* Its construction is simple with small size and weight.
* Duc to its high reactance, its impedance is difficult to match with the transmitter. If
Joop antennas have to act as transmitting antenna, then this impedance mismatch
would definitely be a problem. Hence, these loop antennas are better operated
as receiver antennas,
2) Electrically Large Loop Antenna:
> Electrically Large loop antennas are also called as resonant antennas,
> They have high radiation efficiency.
> These antennas have length nearly equal to the intended wavelength i.e. L=i
Where, L is the length of the antenna and 2. is the wavelength
> The radiation resistance is comparatively large
Properties of Large loop antenna:
> Radiates perpendicular to plane of Loop.
» Relatively high radiation resistance and radiation efficiency.
Frequently Used Loops:
> Small loop antennas are mainly of two types ~ Circular loop antennas and Square
loop antennas,
® These two types of loop antennas are mostly widely used.
> Other types (rectangular, delta, elliptical etc.) are also made according to the designer
specifications. The above images show circular and square loop antennas. These types of antennas are
mostly used as AM receivers because of high Signal-to-noise ratio. They are also easily
tunable at the Q-tank circuit in radio receivers.
Radiation Pattern of Loop Antenna:
The radiation pattern of these antennas will be same as that of short horizontal dipole
antenna (i.e Radiation pattern of loop antenna is a doughnut pattern)
+ Electrically Small Loop Antenna: The nulls are perpendicular to the axis of antenna or
the major lobes are in the direction of antenna
+ Electrically Small Loop Antenna: The nulls are in the direction of the axis of antenna
or the major lobes are perpendicular to the axis of antenna.
Advantages and Disadvantages of Loop Antennas:
Advantages:
+ Compact in size
+ High directivity
Disadvantages:
+ Impedance matching may not be always good
+ Has very high resonance quality factor
Applications of Loop Antenna:
+ Used in RFID devices.
+ Used in MF, HF and Short wave receivers.
+ Used in Aircraft receivers for direction finding,
+ Used in UHF transmitters.
HF (3-30 MHz)
VHF (30-300 MHz)
UHF (300-3000 MHz)
Microwave frequency (1 GH -100 GHz) Baye ta Gee)
= Age pore 1.4 BS Seay
+ Dipole 23
ere 0.
fg
é Path difference =A sino
a
Phare angle =p = 2m (yalh diblecne>
ye eis —O
a ee ors
sigpiterrens orn fe
Feta ee Ed = Ee +p
Syle
eG tee 3°38 ° |
~ E025 sinV}zJ (eae il
tng Sin f mae®
f a aja sin [ems] i
ep = = —j 260 Sip PASAET | +7 ©
We Know Tok Ed =o > Uo- B =
Be "o
Je Mognitade of endiucanal Component
| Epo SOOM LL Sings
ja @ wo Din ©
Ep - ideal Seomt sings) oy, ead sine
e dua (==)
cae Sim (PAIN) a, Basin? ( pe
oe a
ale ete Bd smo
est ZI
= eTTi an dsm
SY A
loom DLd sme
pence
= l2on™ ee? C
A>
ae Soe erene B= Free 4 Aine
= ax
Lxd= dxd=d”)
yoom TA Sind ae
Mico emaastnesoe |
ale
gon? A > Sik
Gir as
wat
step3 Radiaked Power = = Prod = gaa
PB cont errno Ksnpacds
con fA Sin? a eo
Prag = SON LA” [an] [4]
4
Feri) Small loop
steps: fine) V (aay
OCS) = VF.
= Gon? LA Sine
3 At
p= GUL)
ee
. oe eg yee
_ OP
d= 3 ste)
ae = Beemrone D*
bea yo oad”
Wah no
@”
Chorostar Lae
Hebe Te chrewmriference C> 7
pier . 220
a Brod = 2207 a
Ae any ne
(BEY
4) fer Longe Losp ovwmenna
hea = cH=a Helical Antenna
+ Outlines
Basics of helical antenna
Structure of helical antenna
Modes of Operations of helical antenna
+ Radiation by helical antenna
+ Applications of helical antenna
Basics of helical antenna:
+ Helical antenna is an antenna consisting of one or more conducting wires wound in
the form of helix
+ Itisa broadband VHF and UHF antenna and used to provide circular polarization
Structure of helical antenna:
Surface of imaginary
helix cylinder
D = diameter of helix (center to center)
C= Circumference of helix = xD
$= Spacing between turns (center to center)
itch angle =
ength of 1 turn
lumber of turns
Axial length = nS
d= Diameter of helix conductor
Ss
Relation between circumferences, spacing, turn length and pitch angle of a helix
ill. VS? + C? and
As per pythaogorus theorem, L=
a=tan!(S/C)= tan! (S /mD)
Pitch angle is the angle between a line tangent to
the helix and plane normal to the helix.
If a = 0, S becomes infinite, helical antenna will
be loop antenna
If a = 90, S becomes zero, helical antenna will
be linear (monopole) antenna
If a is between 0 to 90, this will be helical
antenna
Modes of Operation of Helical Antenna:
1) Normal mode of operation (Broadside)
2) Axial mode of operation
1) Normal mode of operation (Broadside)
* Here, the direction of maximum radiation is perpendicular to axis of helix.
> In this mode, the radiation field is maximum in the direction perpendicular to
the helix axis,
> Here, the radiation is bidirectional and circularly polarized.
> The dimensions (L, D) of helix are small compared to 2.
{tis hardly used due to its lesser bandwidth and ra
-
ion efficiency. 2) Axial mode of operation:
In this mode, the radiation field is maximum along the helix axis.
This mode produces a broad and directional beam in the axial direction
The dimensions (C, $, D) are of the order of one wavelength
The pitch angle a varies from 12° to 18°,
vvv
vv
To achieve circular polarization, 12°