miniaturized antenna 2008

8/12/2019 Miniaturized Antenna 2008

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Miniaturised Multi-FrequencyPrinted Circuit Antenna

By

BINAY K. SARKAR.

ISRO CHAIR PROFESSOR

( Lecture prepared for delivering at the Summer School on Recent Trend in Antenna

Technology to be held at KIIT , Bhubaneswar on Aug.05,2008 )

Department of Electrical and Electronic Communication Engineering

Indian Institute of Technology, KharagpurKharagpur-721302


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Printed Circuit Antenna: A review In telecommunication, there are several types of microstrip

antennas, the most common of which is the microstrip patchantennaor patch antenna. Common microstrip antenna shapes are square,

rectangular, circular and elliptical, but any continuous shape is

possible.

Microstrip antennas are also inexpensive to manufacture and design

because of easy physical geometry.

The dielectric loading of a microstrip antenna affects both its

radiation pattern and impedance bandwidth.

As the dielectric constant of the substrate increases, the antenna

bandwidth decreases which increases the Q factorof the antenna and

therefore decreases the impedance bandwidth.

The basic half-wavelength (/2) center-fed dipole and quarter-

wavelength (/4) monopole with ground plane are still widely used.

The most popular types of antenna are the loop, patch, inverted-F, and

meander line.
http://en.wikipedia.org/wiki/Telecommunicationhttp://en.wikipedia.org/wiki/Patch_antennahttp://en.wikipedia.org/wiki/Q_factorhttp://en.wikipedia.org/wiki/Q_factorhttp://en.wikipedia.org/wiki/Q_factorhttp://en.wikipedia.org/wiki/Q_factorhttp://en.wikipedia.org/wiki/Patch_antennahttp://en.wikipedia.org/wiki/Patch_antennahttp://en.wikipedia.org/wiki/Patch_antennahttp://en.wikipedia.org/wiki/Telecommunication


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Miniaturisation Techniques

The Aim for miniaturisation is that for a given configuration, the

design of the antenna should be to use the maximum volume available. This

maximum volume will theoretically give the upper bound for both gain and

bandwidth.

Where a is the radius of the sphere enclosing the antenna

2

max

2

max 2

2 22 ;

11

1 3

a aG

a aB

a


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The art of antenna miniaturization is to find the best trade offbetween bandwidth and gain for the antenna volume allotted for a given

application.

Miniaturizing an antenna will affect its radiation characteristics.

Antenna miniaturization affects gain, bandwidth, and efficiency, but

can, in many cases, also affect polarization purity.

Indeed, there are efficient way to make antennas smaller is to bend their

geometry, in order to force the current to meander, so that the antennas

seem electrically larger than it really is.


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A limitation in antenna miniaturization is the difficulty of correctly feeding

small antennas. The correct feeding of a very small antenna is often neither

balanced nor unbalanced, but somewhere in between.

The microstrip antenna is a simple example that illustrates this effect: A

microstrip patch (a typical case of an unbalanced antenna) can be made

electrically small by using a substrate with a high permittivity.

However, the overall size of the microstrip antenna will also depend on the

size of its ground plane.


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The different Miniaturizing techniques are:

Loading the antenna with lumped elements,

High-dielectric materials;

Using ground planes and short circuits;

Optimizing the geometry;

Using the antenna environment (such as the Casing) to reinforce the

radiation.


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Introduction

The Objective of choosing ring was a size of the resonant ring is

substantially smaller than that of the corresponding patch and

depends on the width of the microstrip used.

The mean circumference of ring equals the guide wavelength of the

microstrip used. Input impedance of a ring operated in the TM11mode is considerably higher, whereas its impedance bandwidth is

smaller, in comparison with the patch.

As the strip width is increased, the characteristics of a ring approach

that of the patch.

In order to reduce the antenna size and provide a suitable input impedance match,

two techniques are employed; the insertion of strips into the annular ring and

placing a cross-slot into the ground plane.


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The proposed design annular-ring patch antennas with a cross-slotted

ground plane yield a much smaller size for a given frequency and areeasily matched to 50 ohms.

The antenna can be designed for single band circular-polarization, dual-

band circular polarization, triple band, or further modification for

wideband operation, depending on parameter selection.

Some significant advantages are evident for these structures, such as the

centre-frequency exhibiting weak dependence on the position of the

feedpoint as well as compact size.

Nearly Good circularly polarized properties and obtained for these compact

antennas. The multi-frequency versions can provide small frequency ratios.


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Design of Circular patch antenna

i. The most Popular configuration is the circular patch or disk

ii. The mode supported by the circular patch antenna can be found by

treating the patch, ground plane, and the material between the two as a

circular cavity.

iii. The modes that are supported primarily by a circular microstrip

antenna whose substrate height is small (h


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Design of Circular patch antennai. Resonant frequencyf11:

The resonant frequencies of the cavity, and thus of the microstripantenna, where the substrate height h is very small, the fields are

along z are constant. Therefore the resonant frequencies for the

TMzmn0modes are as

The dominant mode is the TMz110whose resonant frequency is

(fr)110 = (1.8412/2a) = (1.8412v0/2ar)

where vo

is the speed of light


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ii. Radius of Circular Disk: A first order approximation to the solution

of below equation for ais to find ae

To find ae

& substituting for ae

1 2

21 ln 1.7726

2r

Fa

h F

F h

0

110

1.8412

2r e r

vf

a

1 2

21 ln 1.77262

e

r

h aa aa h

98.791 10

r r

Ff


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Design Equations for Annular ring

i. Resonant Frequency :Approximate value of resonant frequency can be

obtained by the following approaches used for the other patch

antennas. To the zeroth-order approximation, the resonant frequency is

obtained by setting

Or

nm

a

2

nmnm

r

cfa


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ii. Inner & Outer radius :Approximate value of resonant frequency can

be obtained by the following approaches used for the other patch

antennas. To the zeroth-order approximation, the resonant frequency is

obtained by setting

Where u = W/h

The modified values of the inner & outer radius are as

ae= a (We- W)/2

be= b + (We- W)/2

34 2

4

0.053

521 11 ln ln 1

49 0.432 18.7 18.1

0.90.564

0.3

r

r

u u ua

u

b


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Weis the effective width of the ring conductor

Where 0= 120

The modified radii equation is as

ae = a 3h/4

be = b + 3h/4

0

0

ere

hZW


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iii. Radiation fields:The radiation fields of a circular ring antenna can be

obtained either from the magnetic current approach or the electric

current distribution on the surface of the ring. The equations are

Where

Where the ratio b/a increases, the directivity of the antenna increases

and the side lobes level also increases. This is because for higher b/a

ratio the two apertures are electrically far apart, giving rise to higher

side lobe levels.

0

0

0 0 0

'2' sin ' sin cos

'

n jk rnmn

n nnm nmn

J k aE eE j k h J k a J k b n

k r J k b

0 0 000

0 0

sin ' sin2sin cossin ' sin

jk rn nm nn

n

nm n nm

k a J k a J k bE eE nj k h J nk r k a J k b k b

nm nmk a


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Design for Single Band application

The geometry of a single band compact circularly polarized antenna is

shown below. A circular patch is centered in the narrow annular-ring, of

outer radius Ro and inner radius Ri. These patches are printed on FR4

substrate, of r = 4.3, a thickness of 1.58mm, and a loss tangent of 0.022.. The

crossed slot in the ground plane has unequal lateral lengths, Lh and Lv, with

a slot width w. This structure excites two degenerate orthogonal modes with

equal amplitude and 90 degree phase difference by tuning various

parameters (Ri, Rp, Lh, and Lv) right-hand circular polarization (RHCP)

radiation is obtained.


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Calculated Parameters for SB

Parameter Value

(Ground plane ) a 60

(Ground plane ) b 60

(Slot horizontal) c 48

(Slot width) d 2

(Slot vertical) e 50

f 48

(feed point) fx 1.54

(feed point) fy 5

g 2

h 50

ri_gdisk 0

ri_icable 0

ri_ocable 1.83

ri_pdisk 0

ri_ring1 22

ri_subcable 0

ro_g1disk 4

ro_gdisk 4

ro_icable 0.325

ro_ocable 2.08

ro_pdisk 9

ro_ring1 24.5

ro_subcable 1.83


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Simulated Structures


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Fabricated Structures

Lh

Lv

RpRi

Ro


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Simulation Time Signals


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S11for the Single band antenna


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Measurement Results


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Radiation pattern (E-field)


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Directivity


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Axial Ratio


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VSWR

f l d l


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Design for Dual Band application

Dual band operation is achieved by employing an extra annular-ring, in addition

to the first one which surrounds the small circular patch as shown in below Figure. The

circularly-polarized frequency ratio of the two resonant modes is tunable to a small

value, suitable for wireless communications systems. The resonant frequency of the

lower mode is mainly determined by the larger outer ring radius while the resonant

frequency of the higher mode is dependent on both the inner ring radius and the

separation between the inner annular-ring and the inner circular patch.

By adjusting the lengths of the cross-slot arms, the upper and lower resonances

can be split into two orthogonal modes with nearly equal amplitude and 90 degree

phase difference.

Hence, a dual-frequency circularly-polarized antenna is achieved.

lateral slot length Lh>Lv, then right-hand circular polarization

lateral slot length Lh


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Top containingpatch & 2 Ring

Bottom containingcross Slot


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Calculated Parameters for DBParameter Value

(Ground plane ) a 60

(Ground plane ) b 60


(Slot width) d 2

(Slot vertical) e 42.4

(feed) fx 4

(feed) fy 5

ri_ocable 1.83

ri_ring1 14

ri_ring2 19.7

ro_gdisk 4

ro_icable 0.325

ro_ocable 2.08

ro_osubcable 1.83

ro_patch 6.5

ro_ring1 18.9

ro_ring2 24


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S11for the Dual band antenna

M t R lt


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Measurement Results


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Gain (fr=1.1 GHz)


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Design for Triple Band application

To provide triple band operation, the addition of rings on the inner

circular patch is used. This is shown in below Figure. The crossed slot in the

ground plane remains, in order for miniaturisation. The additional ring can

also broaden the lower band by adding them to the outer ring.

This structure excites three resonant frequencies by using the outer

annular-ring, inner annular-rings, and the circular patch, which decreases

the Q-factor and increases surface current path lengths, hence a compact

triple-frequency antenna is realised. A very small frequency ratio of the

order of 1.25 is realizable.


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Top containingpatch & 3 Ring

Bottom containingcross Slot specifiedfeed loaction


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Calculated Parameters for TB

Parameter Value(Ground plane) a 60

(Ground plane) b 60


(Slot width) d 2(Slot vertical) e 42

(feed) fx -3

(feed) fy -3

ri_icable 0

ri_ocable 1.83

ri_patch 0

ri_ring1 14

ri_ring2 19.7ri_ring33 7.3

ri_subcable 0

ro_gdisk 4

ro_icable 0.325

ro_ocable 2.08

ro_patch 6.5

ro_ring1 18.9

ro_ring2 24

ro_ring33 12.51

ro_subcable 1.83

w 1.58


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Fabricated Structures


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S11for the Triple band antenna

f1= 1.082GHz (-19.57), f2= 1.8259GHz (-22.27),f3= 4.9642GHz (-19.43)


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VSWR(f1)


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VSWR(f2)


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VSWR(f3)


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Di ti it


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Directivity


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Directivity

l


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Detail specifications for the Design ofMulti-frequency antenna

Sr.No.

Antenna Types Single Band Dual Band Triple Band

Ground Plane 60mm x 60mm 60mm x 60mm 50mm x 50mm

Frequency working 1.8 GHz 1.1GHz, 1.8 GHz 1.1GHz, 1.8 GHz, 5.0 GHz

Frequency ratios achieved Approx order of 1.6

Size Reduction achieved Approx. 50 %

1. Radius circular Patch 9.0 mm 6.5 mm 6.9 mm

2. Inner Radius Ring 1 22 mm 19.7 mm 14 mm

3. Outer Radius Ring 1 24.8 mm 24 mm 18.9 mm

4. Inner Radius Ring 2 --- 16.5 mm 19.7 mm

5. Outer Radius Ring 2 --- 14 mm 24 mm

6. Inner Radius Ring 3 --- --- 7.3 mm

7. Outer Radius Ring 3 --- --- 12.5 mm

M t R lt f P d


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Measurement Results for Proposedantenna

Antenna f1, BW (MHz, %) f2, BW (MHz, %) f3, BW (MHz, %) f2/f1

ARL_ring1 1.8

203, 11.27

-------- --------

ARL_ring2 1.1036

45, 4.07

1.8698

139, 7.46

------- 1.69

ARl_ring3 1.125

180, 16

1.8

180, 10

** 1.6


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THANK YOU

miniaturized antenna 2008

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