arun verma thesis

7/17/2019 Arun Verma Thesis

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Chapter 1

Microstrip Patch Antenna

1.1 INTRODUCTIONIn now a day’s the wireless system has become a part of human life. Most

of the electrical and electronics equipment around are using the wireless system.

An antenna is an electrical device which transmits the electromagnetic waves in

to the space by converting the electrical power given at the input into the radio

waves and converts them bac into the electrical power. !here are so many

systems that uses antenna such as remote controlled television" cellular phones"

satellite communications" spacecraft" radars" wireless phones and wireless

computer networs. #ay by day new wireless devices are introduce ding which

increasing demand of compact antennas. Increase in the satellite communication

and use of antennas in the aircraft and spacecraft has also increased the

demands a low pro$le antenna that can provide a reliable communication.

A microstrip antenna is one who o%ers low pro$le and light weight. It is a

wide beam narrowband antenna can be manufactured easily by the printed

circuit technology such as a metallic layers in a particular shape is bonded on a

dielectric substrate which forms a radiating element and another continuous

metallic layer on the other side of substrate as ground plane. &ot only the basis

of shapes any continuous shape can be used as the radiating patch. Instead of

using dielectric substrate some of the microstrip antennas use dielectric spaces

which results in wider bandwidth but in the cost of less ruggedness. Microstrip

antennas are low pro$le antenna and mechanical rugged and can be easily

mounted on any planar and non planar surfaces. !he si'e of microstrip antenna

is related to the wavelength of operation generally ()*. !he application of microstrip antennas is above the microwave frequency because below these

frequencies the use of microstrip antenna doesn’t mae a sense because of the

si'e of antenna. At frequencies lower than microwave" microstrip patches don+t

mae sense because of the si'es required. &ow a day’s microstrip antenna is

used in commercial sectors due to its ine,pensiveness and easy to manufacture

bene$t by advanced printed circuit technology. #ue to the development and

ongoing research in the area of microstrip antenna it is e,pected that in future

after some time most of the conventional antenna will be replaced by microstripantenna.

1



1.2 Objective of the work

!he common shapes of the microstrip patch are rectangular" square"

circular" triangular" etc. All these have been theoretically studied and there are

well established design formulae for each of them. Antenna design is an

innovative tas where new types of antenna are studied. -o" here a new shape of

microstrip patch antenna is designed which will cover the entire ltra /ide 0and.

ne of the ma2or problem for /0 systems are electromagnetic

interference 34MI5 from e,isting frequency bands" because there are many other

wireless narrowband application that are allocated for di%erent frequencies band

in the /0 band .

!herefore it is necessary for the designer to design the /0 antenna they

can re6ect the interference from the other e,isting bands. !o overcome this

interference problem /0 antennas should have band notches therefore they

can re2ect the e,isting frequency bands within the ultra7wide band. 8ere three

designs with di%erent band notches for /0 applications are proposed.

!he goal of this thesis is to study how the performance of the antenna

depends on various parameters of microstrip patch antenna. !his is a simulation

based study. MA!9A0 simulation software" one commercial :7# full7wave

electromagnetic simulation software tool is used for the design and simulation of

the antenna. !hen" the antenna parameters are varied to study the e%ect of

variation of the antenna parameters on the antenna performance.

1.: utline of the thesis

Chapter 1; of thesis contain the overall introduction to the microstrip

antenna and this chapter also concluded with the details of outline of the present

thesis.

Chapter * ; !his chapter dedicated to the 9iterature survey of the thesis

gives an overview about the microstrip antenna ; the mechanism of radiation

behind the microstrip antenna" advantages and disadvantages as compare to

their counterpart and $nally the ma2or applications in di%erent $elds . All the

*



popular feeding methods used in microstrip antenna with their signi$cance are

also discussed in this chapter.

Chapter :; !he basic parameters on which the selection and performance

of an antenna is characteri'e" are 0andwidth" Antenna Polari'ation" radiation"Pattern" 4<ciency" Antenna =ain are described in brief in this chapter.

Chapter >; In this Chapter two basic and mostly used microstrip patch

?ectangular and Circular patch is discussed this chapter also deals that how the

design parameters are calculated and their e%ect on the antenna performance.

Chapter @; !his chapter deals with the design and simulation of four

microstrip patch antenna of di%erent shapes. arious methods for increasing the

bandwidth are also applied. arious simulation results and graphs characteri'ing

the antenna performance are plotted and the e%ect of various antenna

parameters on the antenna performance is also observed and compared and

shown in the chapter. !his proposed antenna structures are simulated in MA!9A0

-oftware" one commercial :7# full7wave electromagnetic simulation software.

Chapter B; Contains the conclusion of the thesis and future wor.

Chapter7*

undamentals of Antennas

#i%erent types of application requires antenna with di%erent parameter. 9ie

:



for cellular mobile communication a circular polari'ed antenna is requires with

high gain and for satellite communication in downlin a high directive antenna is

required. less environment introduces a variety of challenges to the physical

channel of communication system. the selection and the performance of an

antenna is characteri'e on the basis of some parameters these are 0andwidth"

Polari'ation" radiation" Pattern" 4<ciency" =ain. !hese parameters are described

in brief below.

*.1 ?adiation patterns

Also nown as antenna patterns or ar7ield Pattern. ?adiation pattern of

an antenna is graphical representation of radiated power at as $, distance from

the antenna as a function of a'imuth and elevation angle. -o the antenna

pattern shows that how the power is distributed in the space. or simplicity the

radiation pattern can be drawn in *# plane for di%erent a'imuth and elevation

angle referred as a'imuth plane pattern and elevation plane pattern. It is good to

plot the radiation patterns in Cartesian 3rectangular5 coordinates" especially

when antenna radiation pattern consists of di%erent side lobes and where these

side lobes levels plays an important role. !here are di%erent types of antenna

patterns described below.

*.* mni7directional Antennas

mni7directional antenna can be referred as an antenna has radiation

pattern uniform and equally distributed in one plane generally referred to

hori'ontal planes. -ome applications lie mobile" cell phones" M radios" walie

talies" wireless computer networs" cordless phones" =P-" many portable

handheld devices and in base stations antenna required with the characteristics

that can radiate equally in a plane. mni7directional antenna has radiation

pattern lie doughnut shaped. -lot antenna and dipole antenna" whip antenna"discone antenna" duc antenna are some good e,ample of low gain mni7

directional antenna. mni7directional antenna with high gain can also be design

by narrowing the beam width of the antenna in the vertical plane will result in

concentrating of energy in hori'ontal plane. !herefore a narrow beam width

antenna has a high gain and di%erent type of mni7directional antenna with

various gains can be design. A Dd0d gain antenna radiates more e<ciently in

vertical plane.

*.: #irectional Antennas>



As the name suggest directional antennas concentrate their radiation in a

particular direction. !hey are also nown as 0eam Antenna. !hey are useful in

some point to point application lie satellite communication" in base station

antenna to transmitting energy in a particular sector. Eagi " horn" log7periodic

antenna and panel antenna are some e,ample that have directional radiation

pattern.

*.> Isotropic radiator

An Isotropic antenna has the radiations distributed uniformly in all

direction. An isotropic antenna radiates all the power given. It is an imaginary

antenna does not e,ist practically. It is used as a reference to compared with the

other antennas.

*.@ ield ?adiator

!he radiations from antennas are varies when we go apart from the

antenna. !he $eld regions can be categori'ed in ar $eld region and &ear ield

3resnel5 ?egion. ar $eld region is the region beyond the raunhofer distance

called raunhofer region. It is the region after that the radiation patter does not

change with the distance. !he raunhofer distance is related to antenna’s larger

dimension and can be calculated as.

R=2 D

2

λ

/here

?F distance from antenna

#F larger dimension of antenna

(F wavelength in free space

*.B #irectivity

#irectivity of an antenna shows that how much the antenna is able to

radiate in a particular given direction. It is a ma2or requirement when antenna is

woring as a receiver. If an antenna radiates equally in all direction then the

directivity of antenna is 1 or when measured with respect to isotropic antenna is

@



Dd0. #irectivity in its simple form can be described as the comparison of

ma,imum radiation intensity to average radiation intensity.

Directivity=maximumradiationintensity

avarage radiationintensity

#irectivity of an antenna with given angle shows that the antenna radiations are

more concentrated in that given direction when taling about antenna at

transmitting end. /hile in case of receiving antenna it will receive the power

e<ciently from the particular direction.

*.G =ain

Antenna =ain is also referred as Power gain or simply =ain. !his combines of

antenna e<ciency and directivity. or a transmitting antenna it shows how

e<ciently antenna is able to radiate the given power into space in a particular

direction. /hile in case of receiving antenna it shows how well the antenna is to

convert the received electromagnetic waves into electrical power. /hen it is

calculated with e<ciency Eantenna and directivity D it is referred as Power

=ain.

Power =ain F Eantenna.D

/hen the directivity with a particular direction is given it is nown as #irective

=ain.

#irective =ain 3H "5 F4antenna . D ( H " )

*.J Antenna Polari'ation

Polari'ation of an antenna is polari'ation of the electromagnetic waves

radiated from the antenna. Polari'ation on a wave is the orientation or pathtraces by the electric $eld vector as a function of time. Polari'ation can be

categori'ed in three parts.

a. Linear polarization

b. Circular polarization

c. Elliptical polarization.

If the electric $eld vector of the wave at a given point in space follows a

B



linear path then the polari'ation is linear. 9inear polari'ation is of two types

ertical and 8ori'ontal. In case of circular and elliptical polari'ation electric $eld

vector follows a circular and elliptical path. !hey can be 9eft hand polari'ed" if

the electric $eld vector tracing the path by maing clocwise rotation and ?ight

hand polari'ed" if the vector tracing the path by maing anti clocwise rotation.

*.K Antenna 0andwidth

Antenna bandwidth is another important parameter of antenna can be

described as the range of frequencies over which antenna ful$ll some desired

characteristics. 0andwidth can be described on the basis of gain" a,ial ratio

bandwidth" Impedance or -/? bandwidth. !he impedance bandwidth is the

range of frequencies over which the input impedance of antenna is perfectly

matched to the characteristic impedance of the feeding transmission line.

Impedance bandwidth related to L factor can be described as

0/Fs−1

Qt √ s 3-/?;15

=enerally ractional bandwidth is used for microstrip antenna. =iven by

0/F fh− flfc

/here fh and fl are the upper and lower frequencies where the -/?

matches to -; 1. =enerally -/? is taen *;1 and ideally it is 1;1. !o ma,imi'e

the impedance bandwidth for -/? *;1 proper impedance matching is required.

!hat is we have to feed at the driving point where antenna impedance is NF @D

ohm generally. ne can get a little bit more bandwidth by feeding at the point

where the antenna impedance is B@ohm.

G



igure*.1 0andwidth

-ome of the ma2or advantages of microstrip antenna as discussed by ?andy

0ancroft O: and =arg O1D are given below;

*.1D Advantages And #isadvantages

• Ine,pensive and easy to fabricate.• Can be planted easily on any surface.• Can be easily get recon$gurable characteristics.• Can be easily design antenna with desired polari'ation.• Mechanically robust" resistant against vibration and shoc.• -uitable to microwave integrated circuits 3MICs5.• or high gain and directivity array of antenna can be easily formed.

.

Conversely microstrip antennas also have a number of disadvantages and

limitations when compared to other antennas. -ome of the ma2or disadvantages

of microstrip antennas are written below;

• 8igh quality factor.• Cross polari'ation.• Poor polari'ation e<ciency.• -u%ers from spurious feed radiation.• &arrow impedance bandwidth3@Q to 1DQ without any technique5.• 8igh dielectric and conductor losses.

J



• -ensitive to environment conditions lie temperature and humidity.• -u%ers from surface wave when high dielectric constant material is

used.• 9ow gain and power handling capability

Chapter :

!heory of Microstrip Patch Antenna

:.1 8istory

4arlier in the 1Kth century in microwave circuitry we have started using

coa,ial cable and twin parallel wire line as the transmission lines. In the mid7*Dth

century the invention of printed circuit board technology allow us to mae the

printed circuit versions of these transmission lines which were very ine,pensive

and simple. !he two wire transmission line in printed circuit version is nown as

microstrip line" has a metallic ground plane providing the virtual *nd conductor

and the coa,ial line cable is adapted in printed circuit version as -trip line. !he

K



attention on the fact that these microstrip structures can be used as radiator for

electromagnetics wave got in 1K@Ds. irst in year the 1K@: #eschamps

introduces the concept of microstrip radiatorsO1. In 1K@@ a patent on the name

of =utton and 0aissinot was issued in rance O*" :. After getting the concept of

microstrip radiator about *D year a practical microstrip antenna was fabricated.

4arlier these microstrip radiators were limited in the laboratories no commercial

antennas are available at that time due to high loss and poor radiation. ne of

the reasons was unavailability of good dielectric material with minimum loss

tangent which can use as substrate and can radiate e<ciently. At that time strip

line got more attention due to easy to design" analysis and suitable to microwave

planar structure and it also allows transverse electromagnetic wave 3!4M5 O:. In

1K@@ ?. M. 0arret commented that Radvantages of strip line and microstrip line

are essentially the advantage of coa,ial and twin wire transmission lineSO@. May

be these were some reasons microstrip radiators didn’t get the instant attention

in that period.

!he research on microstrip radiator got attention when some good

dielectric material were found with better thermal and mechanical properties has

a low loss tangent. In 1KBK #enlinger found the microstrip radiators with

rectangular and circular shape could be able to radiate e<ciently OB.

?esearchers had found previously that the half of the input power would escape

in microstrip radiator as a radiation. #enlinger found the mechanism behind the

radiation that if microstrip line is left open ended at the end this discontinuity will

cause the electromagnetic waves to arise from the each open end. It was

reali'ed that the radiations will be more from the discontinuity when these are

separated by half of wavelength distance or a multiple of that long to each other.

It was also reali'ed that the amount of power radiated from the open ends will

increase if the height of the dielectric substrate increases. #enlinger noted that

by increasing the height of substrate microstrip radiators was able to radiate the

GDQ of power available. 8e also carried his research on circular microstrip

radiators and found that it was possible to attain up to G@Q of radiation from a

circular microstrip radiators. Microstrip radiators were now termed as microstrip

antenna. ne of the ma2or bene$t of microstrip antenna is that they are very

comfy to planar and non7planar surfaces can be easily mounted on that. !his was

the main reason that the microstrip antenna acquired the serious attention to the

researchers in early 1KGDs when high performance application such as aircraft"spacecraft" missile" satellite communication put the motivation for researchers to

1D



investigate on usefulness of conformal microstrip antennas. After about * years

8owell introduced a basic rectangular shape microstrip antenna that was fed

using the microstrip transmission line. In that days microstrip antenna was a

ma2or focus for investigators. ?esearchers introduced many various designs. 0ut

it was di<cult to get the better radiation e<ciency that was limited up to KDQ.

&arrow bandwidth was also a severe problem for microstrip antenna. 0y 1KJ1

research and study of microstrip antenna got a drift when I444 made the

microstrip antenna a special issue in the I444 transaction on antenna and

propagation OG

:.* 9iterature -urvey

-umita -hehawat" Pratibha -era" #eepa 0hatnagar, Senior Member,IEEE" irender Tumar -a,ena" and Uaswant -ingh -aini 3*D1D5V. #esign and

analysis of a single7feed arrangement of staced rectangular patches is

proposed" which is capable of providing circular polari'ation along with

broadband performance. An antenna is designed on a glass epo,y ?7> substrate

with overall thicness of the structure less than Jmmor D.11. !his technological

trend has focused much e%ort on the design of a Microstrip patch antenna" by

T.. deyemiW #.. Aande* and 4.. guntiWV 3*D1*5V the pattern of two

designs of a Microstrip patch antenna have been analy'ed and studied .O:G

Md. Maruf AhamedW Tishore 0howmiW Md. -hahidullaWMd. -hihabul Islam"

Md.Abdur ?ahmanW3*D1*5 the result for di%erent dielectric constant values and

the result is performed by thicness of *.JJmm and resonance frequency of

*=8' where *.:* 3#uroid5 are gives the best result.. !his technological trend has

focused much e%ort into the design of a Microstrip patch antenna O:J.

&eha Ahu2a" ?a2esh Thanna" Uaswinder Taur 3*D1*5 A microstrip patch antenna

for /i 7 Ma, and =-M application is proposed. !he antenna has a frequency

bandwidth of 1.*> =8' 3>.BD@: =8' X @.J>J1 =8'5 for /9A& and /i7Ma, and

1.D> =8' 3B.1*> =8' X G.1B =8'5 for -atellite application. !he microstrip antenna

has a planar geometry and consists of a defected ground" a substrate" a patch" a

feed" one slot in patch and a defected ground which consists of a pie slot and

reduced area from all three sides e,cept the feed side.O:K

9afond et al. presents aperture coupled microstrip patch antenna with thic

ground planeO>D.!he thicness has a strong e%ect on impedance matching at

11



high frequencies owing to the ratio between the thicness and the wavelength"

which increases with frequency. !he ground plane thicness is a critical

parameter in aperture coupled patch antennas at millimeter wave frequencies

due to the reduction of the input impedance when the slot thicness becomes

signi$cant with respect to the wavelength. inally" it appears that it is possible to

design a slot fed patch on a thic ground plane which e,hibits good impedance

matching owing to the proper choice of slot length and patch si'e for a given

ground plane thicness.

Patch Antennas on 4,ternally Perforated 8igh #ielectric Constant -ubstrates are

presented by Colburn et al.O>1. !he idea of e,ternal substrate perforation was

introduced in this paper and applied to a patch antenna to help mitigate the

drawbacs of thic high dielectric constant substrates without sacri$cing the

patch element miniaturi'ation or bandwidth. !he introduction of the e,ternal

perforation improved the far7$eld radiation pattern of a patch antenna on a

relatively thic substrate without any reduction in bandwidth or increase in patch

si'e. !he authors found that the perforation must not be located too close to the

patch due to fringing $elds" or the resonant frequency would shift up. It was also

seen that the position where the perforation is started or terminated does have

some a%ect on the far7$eld radiation pattern. ?.9eclaratne et al. presents a novel

microstrip patch.

?.9eclaratne et al. presents a novel microstrip patch antenna suitable for satellite

communications O>*. It is designed by using two semi7discs with single feeding.

!he antenna is circularly polari'ed and suitable for mobile satellite

communications and if fed as individual semi7rings as a dual band orthogonally

polari'ed antenna.

:.: Microstrip antenna

In a most basic form a microstrip antenna comprises of two thin metallic

layers 3tYY (N" where (N is wavelength of free space5 one as radiating patch and

second as ground plane and a dielectric substrate sandwiched between them.

!he conductor patch is placed on the dielectric substrate and used as radiating

element. n the other side of the substrate there is a conductive layer used as

ground plane. Copper and gold is used normally as a metallic layer. ?adiating

patch can be of any shape but simple shapes are used to design a patch becausepatches basic shapes are easy to analysis by the available theoretical models

1*



and it is easy to predict the performance. -quare" rectangular" dipole" triangular"

elliptical" circular are some basic shapes. Circular" rectangular and dipole are the

most often used shapes because of easy of analysis and fabrication. A variety of

dielectric materials are available for the substrate with dielectric constants

*.*Z[\ ] 1*OJ. !he height of substrate plays an important role in antenna

characteristics generally are in the range 0.003 λo≤ h≥ 0.05 λo .

igure :.1 Microstrip Patch Antenna

igure :.* -ide iew Microstrip Patch Antenna

Microstrip antenna su%ers from very &arrow frequency bandwidth.

8owever some application where narrow bandwidth is essential such as

government security systems" microstrip antennas are useful. 0andwidth of

microstrip antenna is directly proportional to height of substrate. !here are two

main techniques two improve the bandwidthW one circuit theory and second

structural.

An antenna characteristics is not only depends on the antenna element

1:



but also be in6uenced by the !^7line and antenna combination. =enerally the

input impedance of microstrip antenna is comple, and the characteristic

impedance of !^7line is real 3usually @D ohm5. !his will results in impedance

mismatching and causes a voltage standing wave pattern on transmission line

results in low impedance bandwidth. ne way to overcome this problem is use of

impedance matching networs between antenna and transmission line. !here

are several impedance matching techniques are available" Circuit theory deals

with the impedance matching techniques.

-tructural technique deals with the modi$cation of substrate properties

such as height and dielectric constant. 0y increasing the height we can increase

the bandwidth. 0ut it will also introduce surface waves which increases loss of

the power and leads to performance and characteristics degradation. arious

types of methods are introduced by the researchers such as stacing" defected

ground plane" parasitic patches and improvement of bandwidth of microstrip

antenna is still an interesting topic for investigation. 0y choosing a particular

shape one can easily design an antenna with desired resonance frequency

radiation pattern" polari'ation. It is easy to design a microstrip antenna with

recon$gurable polari'ation" resonance frequency and radiation patterns 2ust by

adding loads lie PI& diode" aracter diodes.

:.> ?adiation Mechanism

In 1KBK #en linger noted that if the microstrip line left open ended on one

end and fed on the other end then due to the discontinuity created some part of

the power is radiated in the space from both the ends as electromagnetic waves.

#enlinger also reali'ed that the amount of power radiated in space is ma,imum

when both the discontinuities ept a half wavelength or a multiple of half of

wavelength apart from each otherOB. #enlinger concluded that radiations tooplace from the open end due to the fringing $elds arising from the discontinuity.

!o understanding the mechanism behind the radiation from microstrip antenna

considers a rectangular antenna with a half wavelength long radiating patch fed

by microstrip feed line. A rectangular antenna can be considered as a microstrip

line left open ended on one side and energy is fed from the other end. -ince the

patch is half wavelength long and left open ended on other side" the current at

the corners 3at the beginning and end5 of the patch should be 'ero and is

ma,imum at the centre of the patch. Current and voltage will be KD degree out

1>



of phase. !he voltage will be ma,imum positive at the beginning and ma,imum

negative at the end of patch OK.

igure :.: Current And oltage ariation along !he Patch

9ength

ield distribution along the patch is lie shown in $gure below. !he $eld lines are

below the patch towards corner are opposite in direction. !his $eld lines does not

stop abruptly ant the end. At the corners fringing $elds are created and the $eld

lines are in bow shape. More the fringing $eld bow more the radiation. !herefore

these fringing are the reason behind the radiation from the microstrip antenna.

igure :.> ringing ield

Microstrip antenna is a low pro$le antenna that has light weight and is

very easy to installation due to which it is very popular in handheld wireless

devices such as cell phones" pagers and in some high performance

communication systems such as in satellite" missile" spacecraft" aircraft etc.1@



!here are various methods to overcome this limitations" bandwidth of

microstrip antenna can be increase by using some special methods lie defected

ground plane strategy" staced patches" slotted patches" parasitic patch. =ain

and the power handling ability of antenna can be improved by maing an

antenna array. se of 4lectromagnetic 0and =ap 340=5 structure and

Metamaterial also results in the improvement of the antenna characteristicsO*D.

:.@ Applications

After a number of limitations due to the several advantages microstrip

antenna found very useful in di%erent applications. Microstrip antenna widely

used in the defense systems lie missiles" aircraft" satellites and rocets. &ow a

day’s microstrip antenna is used in commercial sectors due to its

ine,pensiveness and easy to manufacture bene$t by advanced printed circuit

technology. #ue to the development and ongoing research in the area of

microstrip antenna it is e,pected that in future after some time most of the

conventional antenna will be replaced by microstrip antenna. -ome of the ma2or

applications of microstrip antennas are;

• Mobile Communication

Antenna used in mobile applications should be light weight" small si'e.

Microstrip antenna possesses this entire requirement. !he most of mobile

applications are handheld gadgets or pocet si'e equipment" cellular phones"

8 pagers and the radar applications in vehicles lie car" planes" and ships.

arious types of designs are made and used for radar applications lie marine

radar" radar for surveillance and for remote sensing.

• -atellite Communication

In satellite communication antenna should have the circular polari'ation. ne

of the ma2or bene$t of microstrip antenna is that one can easily design an

antenna with require polari'ation by using dual feed networs and di%erent

techniques. Parabolic antennas are used in satellite communication to

broadcasting from satellite. A 6at microstrip antenna array can be used in the

place of parabolic re6ector.

• =lobal Positioning -ystem

Initially the satellite based =P- system are used for only in military purposes

but now a day’s =P- found a large application in everyone’s life and now used

1B



commercially. =P- found an essential requirement in vehicles" ships and planes

to trac the e,act location and position. *> satellites are woring in =P-

encircling the earth in every 1* hours at altitude *D"*DD m. =P- satellite using

two frequencies in 97band to transmit the signal which is received by thousands

of receivers on earth. !he receiver antenna should be circularly polari'ed. An

omnidirectional microstrip antenna has wide beam and low gain can be easily

design with dual frequency operation in 97band.

• #irect 0roadcast -atellite -ystem

In many countries direct broadcasting system is used to provide the

television services. A high gain 3_::db5 antenna should be used at the ground

by the user side. A parabolic re6ector antennas are generally used are buly

requires space and a%ected by snow and rain. An array of circularly polari'ed

microstrip antenna can be used for direct broadcasting reception. /hich are easy

to install" has less a%ect from snow and rain and cheaper also.

• Antenna for Pedestrian

In many countries direct broadcasting system is used to provide the

television services. A high gain 3_::db5 antenna should be used at the ground

by the user side. A parabolic re6ector antennas are generally used are buly

requires space and a%ected by snow and rain. An array of circularly polari'ed

microstrip antenna can be used for direct broadcasting reception. /hich are easy

to install" has less a%ect from snow and rain and cheaper also.

• In radar Application

?adar application such as Man pac radar" Marine radar and -econdary

surveillance radar requires antenna with appropriate gain and beam width. An

array of microstrip antenna with desired gain and desired beam width can be

used. or some application such as sensing the ocean wave speed and directionand for determining the ground soil grades -ynthetic Aperture radar method is

used. !wo arrays of patch antennas separated by a proper distance are used in

this system.

• Application in Medical -cience

In medical science for treating the malignant tumors microwave energy is

used to induce hyperthermia. !he microwave energy radiator used for this

should be adaptable to the surface being treated and should be light weight.Microstrip patch antenna is the only one that can ful$ll that requirement. Annular

1G



ring and circular dis microstrip antenna are some e,amples. A half circular

6e,ible patch monopole microstrip applicator used is shown in $gure below.

igure shows the geometry of the applicator that how it is conform on the curved

surfacesO11.

igure :.@ Microstrip Applicator used or 8yperthermia application

:.B ading !echnique

arious types of feeding techniques are available to feed microstrip

antenna. 4ach of them has their own merits or demerits. A number of factors are

used to choose which type of feeding is suitable for the designed antenna. !hemain consideration is e%ectual power transfer from feed line to the antenna

radiating element that is proper matching between the feed and antenna.

arious techniques lie impedance transformer" stubs are used for impedance

matching. eed structure should lie that these matching structure could be

fabricated with radiating element easily. -purious feed radiation and surface

wave losses are also the ma2or factors which depend on the feeding methods

which a%ects the antenna characteristics. -urface waves decreases the

e<ciency of antenna and spurious feed radiation results in undesired radiationwhich will give rise to side lobe level and also increases level of cross

polari'ation. Another main feature is that feed networ should be well7suited to

mae an array" feeding methods can be divide in two categories one is

contacting feeds and other one is non contacting feeds or electromagnetic

coupled feed. In contacting feeds the feed line is directly connected to radiating

element. !he main drawbac of contacting feeds are that it shows inherent

asymmetry which produces the higher order modes that leads to increase in

cross polari'ation level. !o minimi'e these no contacting feeds are used.

1J



Microstrip line feed and coa,ial probe feeding are two mainly used direct contact

feedings and aperture coupled and pro,imity coupling are two non contacting

couplings which are described in brief below;

:.B.15 Microstrip 9ine eedingIn this type of feeding the radiating patch is directly fed by the microstrip

feed line has a narrow width as compare to patch. It is the simple and mostly

used feeding method. 0ecause microstrip line can be treated as e,tended part of

radiating patch and fabricated on the same substrate on the board. !his feeding

simple to fabricate and it’s easy to impedance matching techniques are very

compatible with this type of feed. 0ut this feed also have some drawbacs"

su%ers from spurious feed radiation and surface wave losses also has low

bandwidth.

igure :.B Microstrip patch Antenna

:.B.*5 Coa,ial probe feed

ne of the widely used feeding for microstrip antenna. In this type of

feeding core of coa,ial cable is directly connected to the patch using the

soldering and the outer cable is connected to the ground. Core conductor is

inserted in the substrate via a hole. !he main advantage of this feeding is that

we can directly feed or connect the inner conductor to the feed point where the

input impedance is equal to the characteristic impedance of the feed line.

1K



igure :.G Coa,ial Probe eed

:.B.:5 Pro,imity coupled feed

!wo types of dielectric substrates are used in this type of feeding.

Microstrip line is not directly connected to patch and left open ended and is

sandwiched between the substrates. 4nergy from feed line is coupled

electromagnetic to the radiating patch. !he microstrip line can be e,tended as

stub to increase the bandwidth. -ubstrates dielectric constants play a lead role

and selected to increase the bandwidth and decrease the spurious feed

radiations from the feed line. !hic Material with low dielectric constant is

selected for pper substrates because lower the dielectric constant more the

fringing $eld and more the radiations from patch and thin substrate with high

dielectric constant is selected for lower substrate. !his type of feeding has

largest bandwidth as compared to others. It is easy to model and has low

spurious feed radiation however its fabrication is more di<cult because the e,act

alignment of feed line is required. !he length of the e,tended stub and width to

line ratio of patch can be optimi'ed to control the antenna characteristics.

*D



igure :.J Pro,imity Coupled Antenna

:.B.>5 Aperture Coupled feed

-tructural view of this type of feeding is shown in $gure. As shown this

feeding also uses two type of substrate ground plane is placed between them

and microstrip line is used generally to feed which is placed below the lower

substrate. As name suggests in aperture coupling feeding the energy is

electromagnetically coupled to the patch through an aperture or slot made in the

ground plane. #i%erent types of aperture shapes are used generally rectangularand circular shapes are widely used. Cross shaped and annular ring shape slots

are used for e,citing the circular polari'ation. !he parameters of slots are used to

improve the antenna characteristics. As in pro,imity coupled feeding substrates

dielectric constant is selected to get better radiation and bandwidth. !hic

substrate with low dielectric constant is used for the upper substrate to get the

good radiation and bandwidth. /hile thin and high dielectric constant material is

used for the upper substrate to for e<cient transfer of energy from feed line to

patch. !o get the ma,imum coupling between feed structure and the patch slotshould be located at the place where the magnetic $eld is ma,imum O1B. /e

now that from the current and voltage distribution along the patch length"

electric $eld is ma,imum at the ends and magnetic $eld is ma,imum at the

centre of the patch. !he microstrip feed line is e,tended a length e,tra and is

used as a stub. -tub wors as an open circuited transmission line has admittance

is in parallel to that of the slot. 0y optimi'ing the e,tended length of feed line

3stub5 the reactive components of slot can be cancelled out to that of the stub

that will result in better impedance matching.

*1



igure :.K Aperture Coupling

!he area of slot is ept small to minimi'e the radiation below the ground

plane. !his type of feeding has better polari'ation purity" low spurious feed

radiation and large bandwidth as compared to microstrip and coa,ial probe

feeding. !he equivalent circuit for each of them is shown in $gure below.

igure :.1D 4quivalent Circuit for eeding !echnique

Chapter >

?ectangular and Circular Microstrip Antenna

**



>.1 Microstrip Antenna

In telecommunication" there are several types of microstrip antennas 3also

nown as printed antenna5 the most common of which is the microstrip antenna

or patch antenna.

>.1.1 Patch Antenna

A patch antenna is a narrowband" wide7beam antenna fabricated by

etching the antenna element pattern in a element pattern in metal trace bonded

to an insulating dielectric substrate " such as a printed circuit board "with a

continuous metal layer bonded to the opposite side of the substrate which forms

a ground plane. Common microstrip Antenna shapes are square" rectangular"

circular" elliptical" but any continuous shape is possible. -ome patch antennas donot use a dielectric substrate and instead are made of a metal patch mounted

above a ground plane using dielectric spaces" !he resulting structure is less

rugged but has a wide bandwidth. 0ecause such antennas have a low pro$le" are

mechanically rugged and can be shaped to con$rm to the curving sin of a

vehicle" they are often mounted on the e,terior of aircraft and spacecraft" or are

incorporated in to mobile radio communications device.

>.1.* Advantages

Microstrip antennas are relatively ine,pensive to manufacture and design

because of the simple *7#imensional physical geometry. !hey are easily

employed at 8 and higher frequencies because the si'e of antenna is directly

tied to the wavelength at the resonant frequency. A single patch antenna

provides a ma,imum directive gain of around B7Kd0i. It is relative easy to print

an array of patches on a single substrate using lithographic techniques. Patch

arrays can provide much higher gains then a single patch at little additional

cost" matching and phase ad2ustment can be performed with printed microstrip

feed structures" again in the same operations that forms the radiating patches.

!he ability to create high gain array in a low7pro$le antenna is one reason that

patches array are common on airplanes and in other military applications.

-uch an array of patches antennas is an easy way to mae a phased array

of antennas with dynamic beam forming ability.O:1

An advantage inherent to patch antennas is the ability to have polari'ed

diversity. Patch antennas can easily be designed to have vertical" hori'ontal"right hand circular3?8CP5 or left hand circular398CP5 polari'ation" using multi

*:



pole feed points" or a single feed point with asymmetric patch structure.O:* this

unique property allow patch antennas to be used in many types of

communications lins that may have varied requirements.

>.1.: ?ectangular patch !he most commonly employed microstrip antenna is a rectangular patch

antenna is appro,imately a one7half wavelength long section of rectangular

microstrip transmission lines. /hen air is the antenna substrate" the length of

the rectangular microstrip antenna is appro,imately one7half of wavelength. As

the antenna is loaded with a dielectric as its substrate" the length of the antenna

is decreases as the relative dielectric constant of the substrate increases. !he

resonant length of the antenna is slightly shorter because of the e,tended

electric Rfringing $eldsS which increase the electrical length of antenna slightly.

An early model of the microstrip transmission line with equivalent loads on either

end to represent the radiation loss.

>.1.> -peci$cation

!he dielectric loading of a microstrip antenna a%ects both its radiation

pattern and impedance bandwidth. As the dielectric constant of the substrate

increases" the antenna bandwidth decreases with L factor of the antenna

therefore decreases the impedance bandwidth. !his relationship did not

immediately follow when using the transmission line model of the antenna" but is

apparent when using the cavity model which was introduced in the late 1KGDs by

9 et al.O:: !he radiation from a rectangular microstrip antenna may be

understood as a pair of equivalent slots. !hese slots acts as an array and have

the highest directivity when the antenna has an air dielectric and decreases as

the antenna is loaded by material with increasing relative dielectric constant.

!he half7wave rectangular microstrip antenna has a virtual shorting planealong its center. !his may be replaced with a physical shorting plane along its

center. !his may be replaced with a physical shorting plane to create a quarter7

wavelength microstrip antenna. !his is sometimes called a half patch. !he

antenna only has a single radiation edge 3equivalent slot5 which lowers the

directivity ` gain of antenna. !he impedance bandwidth is slightly lower than a

half7wavelength full patch as the coupling between radiating edges has been

eliminated.O:>O:@

*>



>.*5 ?ectangular Microstrip Antenna

!he rectangular microstrip patch is probably the most common designed

antenna. !he $gure shows a normal rectangular patch antenna. 8ere a designer

has two degree of freedom length and width of patch. !he metallic patch is

separated from the ground plane by a fraction of wavelength distance above by

the dielectric substrate. !he $eld varies over the length are shown. !he fringing

$elds are coming out from the two edges are referred as radiating edges and

other two edges as non radiating edges.

igure >.1 ?ectangular Patch Antenna

Patch shown in $gure has length b and width a. !he patch antenna is fed by

using coa,ial line feed and the feed point is on the middle line on the patch y’

distance apart along the length b.

>.*.15 Method of Analysis;7

A number of methods are available for analy'ing the microstrip antenna. !wo mostly used models are named below. !ransmission line model is easiest one

and provides a simple physical implementation of the antenna but is less

accurate" /hile the Cavity model is di<cult but more accurate.

• !ransmission 9ine Model.• Cavity model.

>.*.1 a5 !ransmission 9ine Model

!he transmission line model treated rectangular microstrip as a part oftransmission line. As the rectangular microstrip antenna consists two radiating

*@



slots" transmission line model represents each radiating slots by an equivalent

admittance which are separated by a distance equal to the length. !he resistive

part of them represents the radiation loss from the each slot. At the resonance

the reactive part of the input impedance cancelled out and the input impedance

become pure resistive. !ransmission line model consider the e%ects of various

parameters described below.

a. ringing $eld;

!he fringing $eld in rectangular microstrip antenna arises from the radiating

edges shown in the $gure below. ringing $eld are mainly depends on the

dielectric constant and length 9 to height h ratio. -ince in most of the cases the

9`h ratio is 1 therefore the fringing $elds are less.

igure >.* ringing ield 4%ect

8igher dielectric constant substrate leads to bounded electric $elds more

enclosed in the substrate as used in the microstrip lines. /hile the lower

dielectric constants substrates results in loosely bounded electric $elds means

they will go more further from the patch. 9esser the dielectric constant material

used in substrate more bowed the fringing $elds. /e now that the fringing $elds

are responsible for the radiations from microstrip antenna. !herefore lower

dielectric constant more the fringing $elds and more the radiations leads to

better e<ciency and better antenna performance. rom $gure it can be seen that

fringing $elds lines are not only enclosed in substrate but also go further out in

the air. As the $eld lines travels in substrate and air also we have to calculate an

4%ective #ielectric constant by taing the air also in account.

*B



igure >.: 4%ective #ielectric Constant

!he e%ective dielectric constant is a dielectric constant of the material for

which the antenna characteristics are same as for the real one. !he range of

e%ective dielectric constant varies from 1 ε eff ᵣ ˂ε ᵣ . In most cases the ε eff ᵣ

value is close to [\. If the air is used as a substrate then the effective dielectric

constant is equal to dielectric constant ε eff ᵣ =ε ᵣ F . !he ε eff ᵣ is also depends

on frequency. As the operating frequency increases the value of e%ective

dielectric constant reaches to the real value of dielectric material used. =raph

below showing the variation of e%ective dielectric constant with the frequency

below. or the lower frequency the e%ective dielectric constant does not varies

but as the frequency increases the e%ective dielectric constant approaches

towards the actual dielectric constant of substrate material.

igure >.> dielectric constant v`s frequency curve

!he [\eff for /`h 1 can be gives as

ε eff ᵣ =ε ᵣ+12 +

ε ᵣ−1

2 (1+12 h

w )−1/2

*G



b. 4%ect of fringing $elds on length;

#ue to the fringing $eld coming out from the radiating slots the actual

length of rectangular patch is more than the physical length. !hen we have to

introduce a length e,tension factor. !his is in the case when modes are

generated along the length or linear polari'ation is made. 9ength e,tension

should also be considered when $elds are generated by radiating edges along

width. !he best appro,imated value of this length e,tension normali'ed to

dielectric material height can be given by formula.

igure >.@ 9ength 4,tension

Δl

h =0 .412

(ε eff ᵣ +0 .3)(W

h +0 .264)

(ε eff ᵣ −0 .258 )(w

h +0 .8)

!his 9 value mainly depends on the effective dielectric constant and the width

to height ratio. #ue to this length e,tension length of patch is about D.>J( rather

than D.@(. !herefore to get the actual physical length of the patch equal to (`*

we have consider the e,tension on both the ends and that is"

9 F eff 7 *9

As we now for dominant mode!"

010 the length pf patch is equal to (`*

therefore the eff is given by

eff =c / f ᵣ

Fc ˳

2 f ᵣ√ ε ff ᵣ ᵨ

/here CN is the velocity of light in free space and f\ is the resonance

*J



frequency for which antenna is to be design.

C. Patch width;7

or the dominant mode!"

010 there is no fringing $eld along the width

therefore there is no need to consider the e%ective dielectric constant /idth of

the patch can be calculator by the formula

/Fc ˳

2 f ᵣ (ε ᵣ+12 )

−1 /2

d. ?esonance frequency;

or the dominant mode!"

010 the antenna resonates 3without taing

fringing into account5 at the frequency given by

f\F

+2 Δ√ ε eff ᵣ

2¿# ˳¿

e. Input Impedance;7

It is important for perfect impedance matching to $nd the point along with

the patch dimension where the input impedance is equal to that of that of the

feed line referred as eed point or #riving point. !he input impedance at feed

point or driving point is nown as #riving Point Impedance. !he current and

voltage distribution over the patch length is shown in $gure. oltage is ma,imum

at the corners and current is ma,imum at the centre. As we now that the

resistance is the ratio of voltage and current. !herefore the resistance will be

ma,imum at the corners and minimum at the centre. Input impedance of the

rectangular patch antenna along the centre line at any point can be determined

by the transmission line model. !he transmission line model for rectangular

patch antenna is shown in $gure. 4ach radiating edge is shown by parallel

equivalent admittance y and are separated by a distance equal to length 9F(`*.

!he edge admittance consist equivalent conductance = and susceptance 0.

!he feed point is located 91 distance away from edge. Input admittance y¿ at

the end of a 9 length long transmission line with characteristic admittance y0

can be given by equation;

*K



2

$¿¿¿¿

$¿

¿e+ %y ˳ tan ¿

y¿

¿= y ˳¿ y¿

/here is the phase constant. sing the above equation the input impedance at

the driving point can be e,pressed by;

1

$¿¿¿¿1

$¿¿¿¿2

$¿¿¿

¿2$¿

¿¿❑

e+ %y ˳ tan ¿e+ %ye tan ¿e+ %y ˳ tan ¿

y¿

¿'o¿

driving (oint =¿ y¿

5

!he total input admittance at the corner of patch is;

y¿=2 y e

/here"

e=¿$e+) e

y¿

:D



Appro,imated values of $e and

)e can be given by;

)e=0 .0836W

λ ˳

$e=0 .01668 Δ

h

W

λ ˳εreff

At the resonance the imaginary parts of the edge admittance are equal

and out of phase and they will cancel out each other. -o the total input

admittance at the edge at resonance become real and is equal to

¿=¿2)e

y¿

-o at the resonance the total input impedance become pure real.

R¿= 1

2)e

/hen we consider the mutual conductance into account then the input

resistance will become

¿=¿ 12()e * )12)

R¿

)12=

1

120 + 2∫

0

+ [ sin (, ˳ W

2 cos-)

cos- ]2

% ˳ ( , ˳ sin- )sin2-d-

sing the model e,pansion analysis the input resistance at a point yo away

from the edge of patch along the centre line can be calculated by the formula;

+

yo

R¿( y= yo)= 1

2() e *)12)cos

2 ¿

F R¿( y=0)cos2 +

y

0

A graph below shows that the input impedance of the rectangular patch antenna:1



varies according to square of cosine" which shows that the input resistance is

ma,imum at the corner of patch and it is 'ero at the centre of patch.

igure >.B &ormali'ed Input ?esistance

>.*.1b5 Cavity Modal

!he cavity model $rst described by 9o et al. in late 1KGDs. As the name

says Cavity model treated the rectangular patch antenna as a cavity with electric

walls above and below at metallic patch and ground plane" and magnetic walls

along the edges of patch O1>"1@. !he $eld under the patch is the summation of

the resonance modes created by these radiating walls. !he cavity model based

on the assumption that only '7a,is component of electric $eld and , and y a,is

components of magnetic $eld e,ist. A simple rectangular antenna used for the

calculation in cavity model is shown in $gure.

:*



igure >.G ?ectangular Patch for Cavity Model

!he electric $eld below the patch at a point , "y can be given by e,pression

below;

E =∑m=0

/

∑n=0

/

0mn 1mn ( x 2 y )

¿1mn 2 1mn>¿( 1

, c2−, mn

2 )¿ %

1mn>¿

¿ 0mn= %34¿

1mn ( x 2 y )=cos (mnx

aeff ) cos (n+y

5eff )

#ue to the fringing $elds the cavity walls are somewhat larger than the actual

length. !herefore by considering the fringing e%ects from edges the length and

width becomes;

aeff =a+2

6

5eff =5+26

, c2=ε ᵣ(1− % 7 eff ), 0

2

, mn2 =cos(mn

aeff )+( n+

5eff )

!he driving or feed point impedance at a point ," y can be given by

8 drv=∑m=0

/

∑n=0

/ %3 9 mn

3mn

2 −(− %7 eff )32

3mn=co , mn

, mn

::



9 mn= h7 m 7 n

aeff 5eff εr ε0

cos2(

m+x

aeff

)cos2(m+x

5eff

)cos2(m+ w (

2aeff

)

/here w ( is width of feedline cable

7 i={1if i=1

2if i=2

!he e%ective loss tangent related to dielectric loss" conduction loss" radiation

loss and surface wave loss

7 eff = 1

Q!

= 1

Qd

+ 1

Q c

+ 1

Q r

+ 1

Qsw

Qd= 1

tan7

Qc=1

2:0 4

r (, 0

h

Rs )

Rs=

√

3 40

2;

Qr=2w W es

<r

8ere W es refers to energy stored

W es=ϵ ˳ ε a5 ᵣ v0

2

8h

!he radiated powerrad=¿

= o0

2+

4

23040 [ (1−$ )(1− 0

15+

02

420)+$2

5 (2−

0

7 +

02

42189)]

<¿

0=(+a

λ0 )

2

:>



$=( +5

λ0 )

2

!heQsw in form of radiation quality factor

Qr

Qsw=Qr

er

hrd

1−e r

hrd

/here er

hrd=

(rhrd

(r

hrd− (r

hrd

1

80+ 2 4r

2c¿

¿(,

0h )2¿

(r

hrd=¿

c1=1−

1

n1

2 +

2

5n1

4

n1=√ ε 4 ᵣ ᵣ

1+ε ᵣ

2 x1

¿ x

0

2−1¿

ε ᵣ (1+ x1 )+h, ˳ √ ¿

(sw

hed=n0, 0

2

8

ε ᵣ ( x0

2−1)3

/2¿

, ˳ h√ ε ᵣ−1

9 0=√ ε ᵣ−1tan ¿

, ˳ h√ ε ᵣ−1+ , ˳ h√ ε ᵣ−1

cos2, ˳ h√ ε ᵣ−1

¿tan ¿¿

>1=−¿

!he cavity model is more accurate as compared to transmission line model but it:@



is based on many assumptions and appro,imations that is e%ective only for

electrically thin substrate.

>.:5 circular Microstrip Antenna

Circular patch is the second most widely used geometry for the microstrip

patch antenna. As in rectangular microstrip antenna we have two degree of

freedom 3length and width5 to control the antenna characteristics" here we have

only radius of circular patch. A circular microstrip antenna is shown in $gure

below.

igure >.J Circular Patch Antennas

As shown in $gure Metallic Circular patch with radius a is placed a height h

above the ground plane. #ielectric substrate separates the patch and ground

plane and the patch is fed at a point r distance from the centre at a angle L

from the ,7a,is. !he circular patch antenna can be analysis by considering the

patch as a cavity with two perfect conductor electric wall above and below

3patch and ground plane5 and magnetic walls along the edges. !he electric $eld

below the circular patch can be given by;

E = E0

? n (, ᵣ) cos (n∅)

And the magnetic $eld components can be given by;

@ r=− %3εn

, 2r

E ˳? n (,r ) sin (n∅ )

@ ∅=− %3ε

, E

0 % nʹ (,r ) sin (n∅ )

:B



entire frequency band of a given system. 8owever" a single type of antenna may

not possess all the desirable features. ne type of antenna that possesses most

of the desirable features is a microstrip patch antenna. Microstrip patch antennas

are light in weight" cheap and conformable maing them attractive for

applications such as high performance aircraft" spacecraft" satellite and missile

applications.

8owever" they have low radiation e<ciency" low power" high L" poor polari'ation

purity" poor scan performance" spurious feed radiation and very narrow

frequency bandwidth.

Microstrip patch antennas are named based on the shape of the radiating

patch. !hus" many con$gurations are in e,istence such as square" rectangular"

dipole" circular" elliptical" triangular" disc sector" circular ring" and ring sector

among others. -quare" rectangular" dipole and circular microstrip patch antennas

are easy to design and analy'e and have desirable radiation characteristics 3low

cross7polari'ation radiation5. !hese mae them more common .

Circular microstrip patch antenna is more advantageous compared to rectangular

one. irst" it has one degree of freedom to control 3radius5 as compared to

rectangular one which has two 3length and width5. !herefore" circular microstrip

patch antenna is more convenient to design and its radiation can easily be

controlled. -econdly" the physical si'e of the circular patch is 1BQ less than that

of the rectangular one at the same design frequency.

A microstrip patch antenna consists of a conducting metallic patch

separated from the ground plane by a dielectric substrate. igure >.K below

illustrates the structure of a circular microstrip patch antenna. !he thicness of

the metallic patch" t (D 3where (D is free space wavelength5. !he height ofthe substrate" h (D 3usually D.DD: (D Z h Z D.D@ (D5.

:J



>.K Circular Microstrip Patch Antenna

!here are many substrates that can be used with dielectric constants

ranging from *.* to 1*. !hic substrates with low dielectric constants result in

good antenna performance in terms of better e<ciency" larger bandwidth and

loosely bound $elds that can easily be radiated into space. 8owever" they result

in larger element si'e. n the other hand" thin substrates with high dielectric

constants are suitable for microwave circuitry because their $elds are tightly

bound resulting in minimal undesired radiation and coupling. Moreover" the

element si'es will be smaller. 8owever" the losses will be great maing them less

e<cient. !hey also result in smaller bandwidthsO:B.

A number of methods can be used to feed microstrip patch antennas. !he

common ones are microstrip line" coa,ial probe" aperture coupling and pro,imity

coupling . !he methods can broadly be classi$ed into contacting and non

contacting methods. In contacting method" there is direct feeding of ? power to

the radiating patch by use of a connecting element 3microstrip line5. or the non7

contacting case" power transfer between microstrip line and radiating patch is

achieved through electromagnetic $eld coupling. igure >.1D illustrates the

structure of a microstrip line feed for a circular microstrip patch antenna. It is a

contacting method and consists of a conducting strip of a very small width

compared to that of the patch. It is easy to fabricate" simple to match and simple

to model. 8owever" surface waves and spurious feed radiation increases with

increase in height of the substrate. !his limits the bandwidth to *7@Q .

:K



Patch Microstrip feed -ubstrate

=round Plane

>.1D Microstrip eed 9ine

igure >.11 illustrates the structure of a coa,ial line feed 3probe feed5 for a

circular microstrip patch antenna. It is a contacting method in which the inner

conductor of the coa, is connected to the radiating patch whereas the outer

conductor is connected to the ground plane. It is easy to fabricate and match

and has low spurious radiation. 8owever" it has narrow bandwidth and it is more

difficult to model especially when the substrates are thic 3h D.D* (D5O:B.

>D



>.11 Probe feed

igure >.1* illustrates the structure of an aperture coupled feed for a

circular microstrip patch antenna. It is a non contacting method that consists of

two substrates separated by a ground plane. A microstrip feed line is on the

bottom side of the lower substrate and is used to couple the energy to the patch

through a slot on the ground plane. /ith this method" it is possible to optimi'ethe feed and the radiating element independently. It is easier to model and has

moderate spurious radiation. 8owever" it is most di<cult to fabricate and has

narrow bandwidth.

>.1* Aperture Coupled feed

>1



Chapter7@

-imulation And ?esults

After declaring the ultra7wide band 3/05 from frequency band :.1 to 1D.B =8'

by ederal Communications Commission 3CC5 in *DD* for the use of indoor and

hand7held systems" ltra7wideband 3/05 antennas have gained so much of

interest by the researchersO1G. or an antenna to be considered ultra wideband

3/05 or not there are two criteria available on the basis of fractional bandwidth.

ne de$nition 3by #efense Advanced ?esearch Pro2ects Agency report5 requires

an antenna to have fractional bandwidth greater than D.*@. An alternate and

more recent de$nition by ederal Communications Commission 3CC5 places the

limit at D.*.

0/F*

f h−h1

f h+h1

≥(0.25 D0R<00 .2 C## )

>:



!he ma2or disadvantage of microstrip antenna is narrow bandwidth. or the

enhancement of impedance bandwidth" several types of techniques such as uses

of high value dielectric constantOJ" parasitic coupled patchesO1K" defected

patch structure" use of Metamaterial O*D" staced structure O1Jand using a

matching networ for proper impedance matchingO*1 have been reported. 8ere

in the proposed designs for broadening the impedance bandwidth of the

antennas defected ground plane strategy is used. In some designs circular shape

partial ground plane with an elliptical notch is used. -ome designs have partial

ground plane with curvy edges and a narrow rectangular slit is also used.

@.15 Modi$ed Circular Patch Antenna for /ide 0and Application

@.1.15Antenna design and parameters

>>



@.1.1 ront and 0ac iew of abricated Antenna

@.1 #imensions f !he Proposed irst #esign

Parameters #escription alue

r ?adius of half circular

patch

J.@

a verlapping 9ength >Lf 9ength of eed line K.J

>@



W f /idth of eed line :.D>J

stu5 9ength of -tub D.G

W stu5 /idth of -tub J

¿ 9ength of -ubstrate *K.B

W ¿ /idth of -ubstrate 1*.>

Proposed microstrip antenna is fed by standard @Dohm microstrip feed

line. #i%erent parameters with their ptimi'ed value of the proposed antenna

are listed below in table;

A circular shape partial ground plane is used in the design. !o increase the

bandwidth of antenna defected ground plane strategy is used. An elliptical notch

is created in the ground plane" ma2or a,is and minor a,is radius of which is

,F1.B and yF:.1 respectively. !he s11 vs frequency curve for the optimi'ed

parameters is shown below.

@.1.*5 -imulation ?esult

>B



!o increase the bandwidth of antenna defected ground plane strategy is

used. An elliptical notch is created in the ground plane" ma2or a,is and minor a,is

of which is ,F1.> and yF:.D respectively. !he s1 vs. frequency curve for theoptimi'ed parameters’ is shown below;

It is observed that when we increase the radius the s11 vs. frequency

curve shifts toward lower frequency while decreasing it shifts toward right.

!herefore we can conclude that the two resonance frequency we are getting are

inversely proportional to the radius of circular patch. It is also observed that

optimum value of radius rFJ.@ the s11 is more deep.

Frequency vs s11 curve for different values of radius

>G



Frequency vs. s11 curve for different values of a .

!he overlapping of circular patches also a%ects the antenna

characteristics and the value of overlapping length a is manually optimi'ed.

igure shows s11 results for di%erent value of a.

igure below showing the =ain vs. frequency curve. Antenna have

ma,imum gain at 1* =8' >.* d0 and minimum [email protected] d0 and 71.1 d0 at * =8' and1D =8' respectively

igure below showing the =ain vs. frequency curve. Antenna have

ma,imum gain at 1* =8' >.* d0 and minimum [email protected] d0 and 71.1 d0 at * =8' and

1D =8' respectively

>J



?eali'ed =ain vs requency plot

@.*.5 Modi$ed ?ectangular Candy shape Patch Antenna for /ide

0and Applications

!he rectangular patch antenna is appro,imately a one7half wavelength long

section of rectangular Microstrip transmission line O*G. /hen air is the antenna

substrate" the length of the rectangular Microstrip antenna is appro,imately one7

half of a free7space wavelength O*G" *J. As the antenna is loaded with a

dielectric as its substrate" the length of the antenna decreases as the relative

dielectric as its substrate" the length of the antenna decreases as the relative

dielectric constant of the substrate increases O*K. !he antenna has become a

necessity for many applications in recent wireless communication such as radar"

microwave and space communication. !he speci$cations for the design purpose

of the structure are as follows

!ype of antenna; ?ectangular Microstrip Patch antenna

?esonance frequency; *=8'

Input impedance; @D

eeding method; Microstrip 9ine eed

@.*.15 #esign -peci$cation

!he three essential parameters for the design of a rectangular microstrip Patch

Antenna are;

• requency f peration 3 f

0 5

!he resonant frequency of the antenna must be selected appropriately.

!he resonant frequency selected for design is *.> =8'.

• #ielectric Constant f !he -ubstrate 3 εr 5

!he dielectric material selected for design is glass epo,y which has a

dielectric constant of >.>.•

8eight f #ielectric -ubstrate 3h5 or the microstrip patch antenna to be used in cellular phones" it is

>K



essential that the antenna is not buly. 8ence" the height of the dielectric

substrate is selected as 1.B mm.

@.*.*5Antenna #esign And Parameters

@.*.* -tructural #iagram of Proposed Antenna

@.*.: #imensions f !he Proposed #esign

@D



#i%erent Parameters used" with their values are written in the table below. All the

dimensions are in millimeter.

@.*.: #imensions f -econd Proposed #esign

Parameter #escription alue

? Radius of the circles J.@A Distance between circles

center

>

^ 9ower radius of ellipse > E 9arge radius of ellipse B.@9f 9ength of feed line 1DW f /idth of feed line :.D@@

¿ 9ength of substrate :@.@

W ¿ /idth of substrate *@.1

0 9ength of notch *.DA /idth of notch >

@.*.> -imulation result

!he return loss curve of designed antenna is shown.

igure @.*.: ?eturn loss vs frequency curve of proposed antenna.

4%ect of the length a on the return loss curve is observed. !he plot shown

below shows the return loss curves for di%erent values of a. It is seen that thee%ect of length a is lesser as compared to lower and higher frequency.

@1



igure @.*.: ?eturn loss vs. frequency curve for di%erent values of a.

!he e%ect of the position of rectangular slit with respect to centre line is

also observed. Plot below shows the return loss curves for di%erent value of the

position d of slit. It is seen that the e%ect of d on return loss curve is less at the

lower frequency and more at the higher frequencies.

igure @.*.: ?eturn loss vs frequency curve for di%erent values of d

ar $eld ?adiation pattern with principal 47plane and 87plane for the di%erent

frequencies are shown in $gure below. /e can observe that the 87Plane patterns

are mni directional and the 47Plane patterns have dumble shape pattern.

@*



igure @.*.: ?adiation Pattern for frequency :.*J>" K.DB and 11.>:> respectively.

!he reali'ed gain plot are shown below. It can be observe that the antenna

has ma,imum gain >d0 at 1* =8' and 7*.J d0 minimum at K =8'.

igure @.*.: ?eali'ed =ain vs requency plot

@:



@.:5 0and &otch ltra /ide 0and Antenna

A number of applications are there which e,ist between the /0

frequency bands. ne of the ma2or problem for /0 systems are

electromagnetic interference 34MI5 from e,isting frequency bands" because thereare many other wireless narrowband application that are allocated for di%erent

frequencies band in the /0 band" such as

(Wi MAX operatin! in "."#".$ %&z,

(WLA' for EEE )*+.a -.-#-.)+- %&z,

Downlin X#band satellite co//unication s0ste/s in $.+- # $.$- %&z.

1.-#1.) %&z '2A3 4 2uper#E5tended C#6and (ndian 'ational 2atellite s0ste/s.

3herefore it is necessar0 for the desi!ner to desi!n the 7W6 antenna the0 can reflect the

interference fro/ the other e5istin! bands. 3o o8erco/e this interference proble/ 7W6

antennas should ha8e band notches therefore the0 can re9ect the e5istin! fre:uenc0 bands

within the ultra#wide band. Recentl0 different t0pes of 7W6 antennas ha8in! the wide

bandwidth and band notch characteristics ha8e been de8eloped for 7W6 applications ;#<=.

3he easiest and /ost co//on /ethod to achie8e a band notch is /ain! a narrow slot of

different shapes into the radiatin! patch of the antenna, will affect the current flow in the

patch, as de/onstrated in ;+1=>;+-=. Different t0pe of shapes is used to /ae the slots (i.e.,

s:uare rin! and folded trapezoid, 7#shape, C#shape are used to !et the band#notched in the

desired fre:uenc0 band. n this chapter four co/pact 7W6 antenna desi!ns are proposed.

?ne of the antennas has a wide bandwidth fro/ +.)%&z to *.@%&z with triple band notches

for re9ectin! the WLA', downlin X#band satellite co//unication and '2A342uper

E5tended C#band application respecti8el0. A 7#shape slot in the radiatin! patch, an open end

split rin! slot in patch and two C#shaped slits are used to !et the proper band re9ection.

@>



Chapter7B

Conclusion and uture /or

!his thesis describes two di%erent microstrip patch antenna designs with

di%erent shapes. !hese are designed for use in /0 application without any

band notches. !he easiest and most common method to achieve a band notch is

maing a narrow slot of di%erent shapes into the radiating patch of the antenna"

will a%ect the current 6ow in the patch" di%erent type of shapes is used to mae

the slots are used to get the band7notched in the desired frequency band. !heseproposed antenna structure’s simulation is carried out using the MA!9A0

-imulation -oftware" one commercial :7# full7wave electromagnetic simulation

software. !he -imulated results are presented" shows the usefulness of the

proposed antenna structure for /0 applications. !he simulation results of band

notch antenna indicate that the proposed antenna ful$ls the e,cellent triple band

notch characteristics for various frequency bands and showing the good return

loss and radiation patters in the interested /0.

ro/ the E:uation of the Rectan!ular /anual calculation of all para/eter is co/ple5. 60 the

use of the %7 this can be eas0 to calculate it. 3he Effect of the Chan!es in input para/eter

on radiation pattern can be easil0 anal0zed b0 the use of %7. As /entioned in results b0

chan!es in the /aterial of the patch ph0sical para/eter of the Microstrip Batch is chan!es,

this will be help desi!ner to deter/ine the antenna perfor/ance and /ae necessar0

ad9ust/ent before fabrication. n thesis different dielectric constants are used for a sin!le

fre:uenc0 operation. 60 eepin! the fre:uenc0 constant calculation of !ain, directi8it0,

&B6W, char. /pedance, is done. A further stud0 can be loo into the desi!n of a /icrostrip

patch antenna arra0 operatin! at 7& fre:uenc0. 3his will further i/pro8ed the antenna with

8er0 directi8e characteristics or 8er0 hi!h !ains to /eet the de/ands for lon! distance

co//unication as well as pro8idin! a fi5ed bea/ of specified shape (shape bea/ or a bea/

that scans in response to s0ste/ sti/ulus. ?ne of the applications is to use a 7& /icrostrip

antenna arra0 for 20nthetic Aperture radar on board an aerial platfor/.

sing Mat lab for antenna design simulation is very challenging as it will

tae very comple, programming to achieve the desire results and it is very time

consuming. 8owever" this can be easily solved by using ? simulation software@@



lie ealand I4:#. If future wor is to be carried out" it is recommended to use

this advance software for the initial design and simulation and should there be

facilities available" is microwave anechoic chamber" hardware implementation

and testing should be carried out.O*B

&ew techniques should be e,plored to reduce the si'e of the /0

antennas to suit more practical applications. Metamaterial is a promising

candidate since it can reduce the si'e greatly. -ome optimi'ation techniques

should be used to optimi'e the optimum results lie P-" =enetic algorithm.

?4?4&C4-

O1 #eschamps" =.A." RMicrostrip Microwave AntennasS" !hird symposium on the

-A Antenna ?esearch and development program" niversity of IIinois "

Moticello" IIIinois" ctober 1J7**" 1K@:.

O* 0ernhard" U.!." Mayes" P.4." -chaubert" #." and Mailou," ?.U."SA

commemoration of #eschamps’ and -icha’s Microstrip Microwave Antennas’;

@D years of #evelopment" divergence" and new directions"S Proceedings of the

@B



2003 Antenna Applications Smposi!m " Moticello" IIIinois" -eptember *DD:" pp.

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OB #enlinger" 4.U." R?adiation from Microstrip ?adiators’" I444 !ransaction on

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OG I444 !ransaction n Antenna And Propagation" Uanuary 1KJ1.

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OK Microstrip patch Antenna Antenna7theory.com.

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Antennas and Propagation 9ibrary5.

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microstrip Antenna" SI444 !ransaction n Antenna And Propagation" March1KGK"

vol. AP7*G" pp. 1:G71>K.

O1@ ?ichards" /.." 9" E.!." and 8arrison" #.#." RAn improved theory formicrostrip antennas G* and applicationS I444 !ransactions on antenna and

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Microwave j ? -eptember *DD:" ol. >:" pp. @17B*.

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http;``transition.fcc.gov`0ureaus`4ngineeringk!echnology`&ewsk?eleases`*DD*`nr

etD*D:.html.

@G

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our 97-haped -lots and CP/7ed for /i MA^ ApplicationS *D1: :rd International

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O1K ishwaarma" ?.T. " erma" T.T." R4lectromagnetically Coupled -quare

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Electronics En!ineerin! (ELEC?, +*" )th nternational Conference ?n EEE +*".

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9etters " I444 11 3*D1*5 ; *K:7*KB.

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;+)= Mani %u9ral, 3ao Juan, Chen!#Wei ui, Le#Wei Li and Fen 3aei, G6andwidth

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BD

arun verma thesis

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