nurhidayahmoktar.weebly.comnurhidayahmoktar.weebly.com/uploads/6/4/8/7/6487407/05... · web viewthe...

TOPIC 5: MICROWAVE ANTENNA MICROWAVE DEVICES (EP603)

DEFINATION:A conductor or group of conductors used either for radiating electromagnetic energy

into space or for collecting it from space.

or

Is a structure which may be described as a metallic object, often a wire or a collection

of wires through specific design capable of converting high frequency current into em

wave and transmit it into free space at light velocity with high power (kW) besides

receiving em wave from free space and convert it into high frequency current at much

lower power (mW).

Also known as transducer because it acts as a coupling devices between microwave

circuits and free space and vice versa.

Electrical energy from the transmitter is converted into electromagnetic energy by the

antenna and radiated into space. On the receiving end, electromagnetic energy is

converted into electrical energy by the antenna and fed into the receiver.

Basic operation of transmit and receive antennas.

Transmission - radiates electromagnetic energy into space

Reception - collects electromagnetic energy from space

In two-way communication, the same antenna can be used for transmission and

reception.

PREPARED BY : ROHANA BT. IBRAHIMPOLIMASDECEMBER 2012 SESSION

1/47


Short wavelength produced by high frequency microwave, allows the usage of highly

directive antenna. For long distant signal transmission, the usage of antenna at

microwave frequency is more economical. Usage of waveguide is suitable for short

distant signal transmission.

FUNCTIONS OF ANTENNA Transmit energy with high efficiency (beberpa kW).

Receive energy as low as mW.

Provide matching between transmitter and free space and between free space

and receiver, thus maximum power transfer is achieve besides preventing the

occurence of reflection.

Directs radiation toward and suppresses radiation Mengarahkan penyinaran ke

arah yang dikehendaki atau merekamkan (suppressed) penyinaran dalam arah-

arah yang tidak dikehendaki.

2 similar characteristic exist 2 between ciri yang sama wujud pada bahagian antena

Tx dan antena Rx adalah corak sinaran dan impedan, cuma ia berbeza dari segi

kuasa pemancaran dan kuasa penerimaan.

Figure 1 below, shows the energy transmitted into free space via an open ended λ /

4 transmission line. The proportion of wave escaping the system is very small due

to :


2/47


λ/4

Mismatch exist that is surrounding space as load.

Since the two wires are closed together and in opposite direction (180°), therefore

it is apparent that the radiation from one tip will cancelled that from the other.

TYPES OF MICROWAVE ANTENNA

Horn / aperture antenna

Paraboloid / dish antenna

Dipole antenna

Slotted (leaky-wave) antenna

Dielectric lens antenna

Printed (patch or microstrip) antenna

Phase Array antenna

A) HORN / APERTURE ANTENNA

Like parabolic reflectors, you can use HORN RADIATORS to obtain directive radiation

at microwave frequencies. Because they do not use resonant elements, horns have the

advantage of being useful over a wide frequency band.

The operation of a horn as an rf radiating device is similar to that of an automobile horn

radiating sound waves. However, the throat of an automobile horn usually is sized much

smaller than the sound wavelengths for which it is used. The throat of the rf radiating

horn is sized to be comparable to the wavelength being used.


3/47

FIGURE 1

radiation (small portion of em wave energy escapes from


Horn radiators are used with waveguides because they serve both as an impedance-

matching device and as a directional radiator. Horn radiators may be fed by coaxial and

other types of lines.

Horn radiators are constructed in a variety of shapes, as illustrated in figure 3-9. The

shape of the horn determines the shape of the field pattern. The ratio of the horn length

to the size of its mouth determines the beam angle and directivity. In general, the larger

the mouth of the horn, the more directive is the field pattern.

Is produced from an open ended waveguide. Horn antenna is used to provide a

gradual flare at the end of the waveguide, thus producing maximum radiation into

space with minimum reflection back to the source

Because of impedance mismatch, the horn is tapered in one dimension to a

rectangular shape as shown in Figure 4 (a) and (b), thus produce an impedance

matching between the waveguide and that of the impedance of free space. Horn

tapered / flared in the E or H planes are called sectoral horn. If flared in E and H

plane (2 dimensions) it is called a pyramidal horn. A circular waveguide can be

matched to free space with conical taper as shown in Figure 4 (d) and is called

conical horn antenna.

Higher gain and directivity – for longer horn dimension.

Enhance performance when use together with parabolic reflector.

Its narrow beam angle caused increase in antenna gain.


4/47


WAVEGUIDE AS A

TRANSMITTER Rf energy reaching the open end of

a waveguide will be partly radiated

into space and partly reflected back

into the waveguide because the end

is not well matched to free space so

VSWR will result.

Produce a weak and tidak berarah

radiation pattern due to refraction

around the open ends.

BASIC HORN ANTENNA

Used to overcome the problem facing

by an open ended waveguide. (i.e to

avoid mismatch).

Directivity improved and diffraction

reduced.

Difference type of Antena horn can be produced based on open ended flaring of the

horn (FIGURE 4).


5/47


E – PLANE HORN SECTORAL ANTENNA

H – PLANE HORN SECTORAL ANTENNA

PYRAMIDAL HORN ANTENNA (E & H PLANE)

CONICAL HORN ANTENNA

FIGURE 4

3 TYPES OF HORN ANTENNA :-i) Horn antenna tapered / flared in one dimension only i.e in E-plane or H-plane

(known as sectoral horn).

ii) Horn antenna tapered / flared in two dimensioni.e in E-plane and H-plane

(known as pyramidal horn).

iii) Conical taper / flares uniformly in all direction i.e in circular form.


6/47


E–plane, H–plane Horn sectoral antenna and the pyramidal antenna is used to provide

matching between rectangular waveguide and free space. Whereas matching between

circular waveguide and free space can be achieved by using conical horn.

THE DIFFERENCES BETWEEN THE E-, H- PLANE & PYRAMIDAL HORN SECTORAL ANTENNA E- PLANE HORN SECTORAL ANTENNA Radiation pattern exhibits side lobe

H- PLANE HORN SECTORAL ANTENNA Radiation pattern exhibits no side lobe,

thus more popular.

PYRAMIDAL HORN ANTENNA Radiation pattern flares in 2 direction i.e in

E-plane and H-plane. Therefore improves

directivity.

FACTORS AFFECTING THE GAIN AND DIRECTIVITY OF HORN ANTENNA

Selection of horn frequency depend s on aperture area, beam angle and length

Better impedance and small losses - the longer the horn and its open ended.

Higher gain and directivity – bigger flare-out shape (though it is not as good as

parabola antenna).

Easy to construct and robust..


7/47


DIMENSION OF HORN ANTENNA

SIDE VIEW

APEX

BEAM / FLARING ANGLE

END / FRONT VIEW

H

W

Whereby ;

A = H x W , m2 A - area (m2 ); H – height (m); W – width (m)

Horn length : between 2 – 15 from the wavelength of operational the frequency.

Beam angle range for antenna directivity : between 10° - 60° and gain range

between :10 - 20 dB.

BEAM WIDTH ; α = 80_ α = beam width ( °) ;

W / λ W = horn width (m)

λ = wavelength of the operational

frequency (m)

GAIN ; G = 4 π k A__ G = gain;

λ2 A = area (m2)

k = uniform phase distribution & e.m field


8/47

l

WAVEGUIDE APERTURE


amplitude across the aperture (0.5 -0.6)

Small Beam width produce wavefront , shallow horn, and flared radiation pattern. Thus

not suitable for long distance transmission.

RADIATION PATTERN OF SECTORAL HORN

The used of horn pyramid helps to improve directivity due to dual flaring (Kegunaan

horn piramid dapat memperbaiki pengarahan disebabkan oleh kembangannya

adalah dalam 2 arah.)’

Pyramid and conical horm produce pencil beam radiation pattern, hence better

directivity as compared to sectoral horn.

Horn antenna is a non resonant (wide band) device which operate at a very high

frequency range (usually at 10 % of the operational frequency).

Example; At operanting frequency of 10 GHz, the bandwidth is 1 GHz.

b) PARABOLIC (REFLECTOR / DISH) ANTENNA

Is a big dish like structure made from metal or wire mesh / grid.

Mesh hole ≤ λ / 12.

Widely used in microwave propagation via free space.

Also known as secondary antenna since it depends on primary antenna which acts

as a feeder at the focal point (horn antenna or dipole antenna) to enhance the

performance quality of the transmitter and the receiver.

A point source, such as an omnidirectional antenna produces a spherical radiation

pattern, or spherical wavefront. As the sphere expands, the energy contained in a given

surface area decreases rapidly. At a relatively short distance from the antenna, the

energy level is so small that its reflection from a target would be useless in a radar

system.


9/47


A solution to this problem is to form the energy into a PLANE wavefront, In a plane

wavefront, all of the energy travels in the same direction, thus providing more energy to

reflect off of a target. To concentrate the energy even further, a parabolic reflector is

used to shape the plane wavefront’s energy into a beam of energy. This concentration

of energy provides a maximum amount of energy to be reflected off of a target, making

detection of the target much more probable.

The basic paraboloid reflector used to produce different beam shapes required by

special applications. The basic characteristics of the most commonly used paraboloids

are presented as below:

Basic paraboloid reflector Truncated Paraboloid Pillbox

TRUNCATED PARABOLOIDSince the reflector is parabolic in the horizontal plane, the energy is focused into a

narrow beam. With the reflector TRUNCATED (cut) so that it is shortened vertically, the

beam spreads out vertically instead of being focused. This fan-shaped beam is used in

radar detection applications for the accurate determination of bearing. Since the beam

is spread vertically, it will detect aircraft at different altitudes without changing the tilt of

the antenna. The truncated paraboloid also works well for surface search radar

applications to compensate for the pitch and roll of the ship.

Truncated paraboloid may be used in target height-finding systems if the reflector is

rotated 90 degrees, as shown in figure 3-5B. Since the reflector is now parabolic in the


10/47


vertical plane, the energy is focused vertically into a narrow beam. If the reflector is

truncated, or cut, so that it is shortened horizontally, the beam will spread out

horizontally instead of being focused. Such a fan-shaped beam is used to accurately

determine elevation.

ORANGE-PEEL PARABOLOID

A section of a complete circular paraboloid, often called an ORANGE-PEEL

REFLECTOR because of its orange-peel shape. Since the reflector is narrow in the

horizontal plane and wide in the vertical plane, it produces a beam that is wide in the

horizontal plane and narrow in the vertical plane. In shape, the beam resembles a huge

beaver tail. The microwave energy is sent into the parabolic reflector by a horn radiator

(not shown) which is fed by a waveguide. The horn radiation pattern covers nearly the

entire shape of the reflector, so almost all of the microwave energy strikes the reflector

and very little escapes at the sides. Antenna systems which use orange-peel

paraboloids are often used in height-finding equipment.

Orange-peel paraboloid Cylindrical paraboloid Corner reflector

CYLINDRICAL PARABOLOID


11/47


When a beam of radiated energy that is noticeably wider in one cross-sectional

dimension than in another is desired, a cylindrical paraboloidal section which

approximates a rectangle can be used. A PARABOLIC CYLINDER has a parabolic

cross section in just one dimension which causes the reflector to be directive in one

plane only. The cylindrical paraboloid reflector is fed either by a linear array of dipoles, a

slit in the side of a waveguide, or by a thin waveguide radiator. It also has a series of

focal points forming a straight line rather than a single focal point. Placing the radiator,

or radiators, along this focal line produces a directed beam of energy. As the width of

the parabolic section is changed, different beam shapes are obtained. You may see this

type of antenna system used in search radar systems and in ground control approach

(gca) radar systems.

CORNER REFLECTOR

The CORNER-REFLECTOR ANTENNA consists of two flat conducting sheets that

meet at an angle to form a corner, as shown in figure 3-8. The corner reflector is

normally driven by a HALF-WAVE RADIATOR located on a line which bisects the angle

formed by the sheet reflectors.

A microwave source is placed at focal point F. The field leaves this antenna as a

spherical wavefront. As each part of the wavefront reaches the reflecting surface, it is

phase-shifted 180 degrees. Each part is then sent outward at an angle that results in all

parts of the field traveling in parallel paths. Because of the special shape of a parabolic

surface, all paths from F to the reflector and back to line XY are the same length.

Therefore, when the parts of the field are reflected from the parabolic surface, they

travel to line XY in the same amount of time.


12/47


Parabolic reflector radiation.

X

A A`

B B`

C FOCAL POINT C`

D D‘

E E`

Y

PLANE WAVE

A point-radiation source is placed at the focal point F. The field leaves this antema with

a spherical wavefront. As each part of the wavefront moving toward the reflector

reaches the reflecting surface, it is shifted 180 degrees in phase and sent outward at

angles that cause all parts of the field to travel in parallel paths. Because of the shape of

a parabolic surface, all paths from F to the reflector and back to line XY are the same

length. Therefore, all parts of the field arrive at line XY at the same time after reflection.

A parasitic array to direct the radiated field back to the reflector, or a feed horn pointed

at the paraboloid is used to make the beam sharper and to concentrates the majority of

the power in the beam.


13/47

WAVE FRONT

FIGURE 5

TO FREE SPACE

FROM FREE SPACE


The radiation pattern of the paraboloid contains a major lobe, which is directed along

the axis of the paraboloid and several minor lobes. Very narrow beams are possible

with this type of reflector.

PARABOLIC RADIATION PATTERN

AS TRANSMITTER


14/47


The wave at the focus point will be directed to the main reflector and will be reflected

parallel to the parabola axis. Thus the wave will travell at the same the and phase at

A`E` (XY) line and the plane wave produce will be transmitted to the free space.

. Gelombang dari titik fokus akan dipancar ke dinding dan dipantul semula

secara selari dengan paksi parabola dan akan sampai pada waktu dan fasa yang

sama pada garisan dan akan membentuk gelombang satah seterusnya

dipancarkan ke ruang bebas.

AS RECEIVER The plane wave received which is parallel to the parabola axis will be reflected by

the main reflector to the focus point.

Semua gelombang yang diterima yang selari dengan paksi parabola akan dipantul

oleh dinding ke titik penumpuan .

This charistic makes the parabola antenna to possess high gain and a confined

beam width.

Ciri-ciri ini menyebabkan parabola mempunyai gandaan yang tinggi dan lebar alur

yang terfokus.

C) SLOTTED (LEAKY-WAVE) ANTENNACan be fabricated from a length of a waeguide. They are simple to fabricate, have

low-loss (high efficiency) and radiate linear polarization with low cross-polarization.

Slotted antenna arrays used with waveguides are a popular antenna in navigation,

radar and other high-frequency systems. These antennas are often used in aircraft

applications because they can be made to conform to the surface on which they are

mounted. The slots are typically thin (< 0.1 ʎ) and 0.5 ʎ (at the center frequency of

operation).

The slots on the waveguide will assumed to have a narrow width. Increasing the

width increases the bandwidth (recall that a fatter antenna often has an increased


15/47

http://www.antenna-theory.com/basics/bandwidth.php

http://www.antenna-theory.com/definitions/crosspolarization.php

http://www.antenna-theory.com/basics/polarization.php

http://www.antenna-theory.com/basics/gain.php


bandwidth); the expense of a larger width is a higher degree of cross-polarization.

The Fractional Bandwidth for thin slots can be as low as 3-5%; wide slots can have a

FBW on the order of 75%.

An example of a slotted waveguide array is shown in Figure 1 (dimensions given by

length a and width b)

Figure 1. Basic geometry of a slotted waveguide antenna.

As in the cavity-backed slot antenna, each slot could be independently fed with a

voltage source across the slot. This would be very difficult to construct especially for

large arrays. The waveguide is used as the transmission line to feed the elements.

The position, shape and orientation of the slots will determine how (or if) they radiate. In

addition, the shape of the waveguide and frequency of operation will play a major role.

EXAMPLE;

The dominant TE10 mode will be assumed to exist within the waveguide. Radiation

occurs when the currents must "go around" the slots in order to continue on their

desired direction. As an example, consider a narrow slot in the center of the waveguide,

as shown in Figure 2.


16/47

http://www.antenna-theory.com/antennas/aperture/slot2.php

http://www.antenna-theory.com/definitions/fractionalBW.php


Figure 2. Waveguide with a thin slot centered about its width.

In this case, the z-component of the current will not be disturbed, because the slot is

thin and the z-current would not need to travel around the slot.

Hence, the x-component of the current will be responsible for the radiation. However, at

this location (x=a/2), the x-component of the current density is zero - i.e. no current and

therefore no radiation. As a result, slots can not be placed in the center of the

waveguide as shown in Figure 2.

If the slots are displaced from the centerline as shown in Figure 1, the x-directed current

will not be zero and will need to travel around the slot. Hence, radiation will occur.

Note: the distance from the edge will determine the magnitude of the current. As a

result, the power that the slot radiates can be altered by moving the slots closer or

farther from the edge. In this manner, a phased array can be designed with varying

excitation to each element.

If the slot is oriented as shown in Figure 3, the slot will disturb the z-component of the

current density. This slot will then radiate. If this slot is displaced away from the center

line, the amount of power that it radiates can be adjusted.


17/47

http://www.antenna-theory.com/arrays/basics.php


Figure 3. Horizontal slot in a waveguide.

If the slot is rotated at an angle about the centerline as shown in Figure 4, it will radiate.

The power it radiates will be a function of the angle (phi) that it is rotated - specifically

given by . Note that the z-component of the current is still responsible for

radiation in this case. The x-component is disturbed; however the currents will have

opposite magnitudes on either side of the centerline and will thus tend to cancel out the

radiation.

Figure 4. Rotated slot antenna in a waveguide.

The most common slotted waveguide resembles that shown in Figure 5:


18/47


Figure 5. Geometry of the most common slotted waveguide antenna.

The front end (the open face at the y=0 in the x-z plane) is where the antenna is fed.

The far end is usually shorted (enclosed in metal). The waveguide may be excited by a

short dipole (as seen on the cavity-backed slot antenna) page, or by another

waveguide.

The waveguide itself acts as a transmission line, and the slots in the waveguide can be

viewed as parallel (shunt) admittances.

Figure 4. Slotted waveguide antenna fed by a coaxial feed.


19/47

http://www.antenna-theory.com/antennas/aperture/slot2.php



20/47

FIGURE 9


Shunt load Longitudinal slot in broad face

Series load Center inclined slot in broad face

Series load Transverse slot in broad face

Shunt load Inclined slot in narrow face

The end of the waveguide is terminated in a pyramid terminator to avoid line reflections.

The radiating field pattern depends on the spacing of the slots (phase relationship) and

their orientation with reference to the waveguide.


21/47

FIGURE 12

FIGURE 10

FIGURE 11


A slot cut in the wall of the waveguide, transverse to the direction of the interior

boundary currents ( due to the interior em wave) will couple the em energy from inside

the wave guide to a radiant free-space wave.

The length of slot is cut to be a resonant one-half (ʎ/2) wavelength.

D) DIPOLE ANTENNAS

TWO TYPES OF DIPOLE ANTENNAS:

Half-wave (ʎ/2) dipole antenna (or Hertz antenna)

Quarter-wave (ʎ /4) vertical antenna (or Marconi antenna)

Is the simplest practicle antenna. It is very short wavelength of wire over which the current distribution can be assumed to be uniform.With the aid of Maxwell equations, the strength of the radiated field is ;

This result for a free space short-dipole and the radiation pattern (polar diagram) in the

vertical plane is a ‘figure of 8’ and a circular in a horizontal plane. The electric field,

Є is directional in the vertical plane but is omnidirectional on the horizontal plane.


22/47

Є = 60 π dl I cosӨ cos w ( t – r/Vc) λr

Є3

Є1

Є4

Є2

dl

Ө

Vertical plane

Єmax

Horizontal plane


The dipole antenna is the simplest antenna, despite of not being used practically in

applications, it is used to test antenna labs (so it is considered the reference antenna), a

dipole antenna consists of 2 wires (ʎ/4 for its length) , the two wires are separated by a

gap and their terminals are connected to the transmitter or the receiver.

This type of dipoles is called half wave length

dipole as the total length is ʎ / 2

Dipole geometry Dipole configuration


23/47

ʎ/4

ʎ/4

+-


RADIATION PATTERN

The dipole is an electric field antenna, means that the magnetic field is zero at the near

field. The radiation pattern is like a donut cake with the maximum perpendicular to the

dipole, and a null along it. The polarization is along the dipole.

The 3D plot of the radiation pattern of a dipole antenna.

The radiation pattern for the Electric field for a folded dipole antenna


24/47


The radiation pattern of the dipole , The radiation pattern of the all the field is electric as shown dipole, the magnetic field equals zero

When the length of the dipole exceeds lambda the radiation pattern takes a new shape due to the appearance of the grating lobes where the major lobes divides into multiple lobes .

E) DIELECTRIC (LENS) ANTENNAS

Lenses play a similar role to that of reflectors in reflector antennas: they collimate

divergent energy. Used at the higher microwave frequencies (often preferred to

reflectors at frequencies > 100 GHz) and are useful in mm microwave region.


25/47

No radiationNo radiation pattern forpattern for thethe magnetic fieldmagnetic field. ThisThis means thatmeans that a dipole is ana dipole is anelectric field antenna. electric field antenna.


LENS ANTENNA converts spherically radiated microwave energy into a plane wave (in

a given direction) by using a point source (open end of the waveguide) with a

COLLIMATING LENS.

A collimating lens forces all radial segments of the spherical wavefront into parallel

paths .

The point source can be regarded as a gun which shoots the microwave energy toward

the lens. The point source is often a horn radiator or a simple dipole antenna.

(Lens – refraction, parabolic reflector – reflection)

BASIC PRINCIPLE

LENS

COLLIMATEDRAY

PLANE WAVE

LENS A A`

POINT O B B`

SOURCE C C`

Spherical wavefront changed to plane wavefront through dielectric lens.


26/47


DIELECTRIC LENS ANTENNA LENS ANTENNA AS WAVE COLLIMATOR

The velocity of em wave through a dielectric materal is less than that in free space.

The section of spherical em wave that travels through the center (the greatest

thickness) of the dielectric material will travel most slowly compared to both end.

The velocities of the spherical wave entering the lens will be controlled and the curved

wavefront will become a plane wavefront with constant phase in front of the dielectric

antenna (refraction based on Snell’s law).

Are contructed from polistyrene, teflon or any denser dielectric material to produce

large diffraction (belauan) although its size and weight is small. The material use will

cause the wave to attenuate greatly (losses and absortion of signal - greatest

attenuation at center – thickest lens).

To avoid this situation, zoned and stepped dielectric antennas are used so that the

optical path can be divided into paths differing by integral multiples of a wavelength from

one zone to another.

BASIC DIELECTRIC LENS STEPPED DIELECTRIC LENS


27/47

ZONED DIELECTRIC LENS


Basic dielectric lens requires a specific wavelength due to its thicness. Hence its usage

is not practical as compared to the stepped or zoned dielectric lens antenna which has

different path for different wavelength.

The stepped or zoned dielectric lens antenna is used to reduced the lens thickness and

to decrese the curveture of the spherical wave.

F) PRINTED (MICROSTRIP OR PATCH) ANTENNA

A patch antenna is a narrowband, wide-beam antenna.

Fabricated by etching the antenna 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 and elliptical, but

any continuous shape is possible.

Some patch antennas do not use a dielectric substrate and instead made of a metal

patch mounted above a ground plane using dielectric spacers; the resulting structure is

less rugged but has a wider bandwidth.

Because such antennas have a very low profile, are mechanically rugged and can be

shaped to conform to the curving skin of a vehicle, they are often mounted on the

exterior of aircraft and spacecraft, or are incorporated into mobile radio communications

devices.

A microstrip antenna consists of :


28/47

http://en.wikipedia.org/wiki/Mobile_radio

http://en.wikipedia.org/wiki/Bandwidth_(signal_processing)

http://en.wikipedia.org/wiki/Ground_plane

http://en.wikipedia.org/wiki/Printed_circuit_board

http://en.wikipedia.org/wiki/Dielectric

http://en.wikipedia.org/wiki/Light_beam


The patch ( radiating element ) may be circular, rectangular or any other shape.

TYPES OF MICROSTRIP ANTENNAS:

Open Circuit Microstrip Short Circuit Microstrip

The patch is totally isolated from the

ground plane.

Higher efficiency than short circuit

microstrip antennas.

Side length of the patch is ʎg / 2.

The patch is connected to the ground

Have only one radiating edge.

Side length is ʎg / 4

ADVANTAGES

High accuracy in manufacturing , the design is executed by Photo etching.

Easy to integrate with other devices.

An array of microstrip antennas can be used to form a pattern that is difficult to

synthesize using a single element.

We can obtain high directivity using microstrip arrays.

Have a main radiating edge , this makes it useful for mobile Phones to avoid

radiation inside the device .

Small sized applicable for handheld portable communication.


29/47


Smart antennas when combined with phase shifters .

DISADVANTAGES

Narrow band width ( 1% ) , while mobiles need ( 8% ).

Low efficiency , especially for short circuited microstrip antenna.

Some feeding techniques like aperture and proximity coupling are difficult to

fabricate.

An array suffers presence of feed network decreasing efficiency , also microstrip

antennas are relatively expensive.

MICROSTRIP VS. REFLECTORS Microstrip Antennas Reflector Antennas Preferred for low directivity

applications.

Lower efficiency.

Suffers low efficiency caused by feed

network for arrays.

Smart antennas, uses electronic

scanning when combined with phase

shifters.

More accurate manufacturing by photo

etching.

Feeding is by coupling or coax feed

lines.

Performed for high directivity

applications as the effect of blockage is

less.

Higher efficiency.

Suffers blockage caused by fixation

Struts.

Uses mechanical scanning .

Less accuracy , sometimes parabolic

surfaces are rough.

Uses other antenna (dipole , monopole,

apertures , etc) as a feed.

G) PHASED ARRAY ANTENNA


30/47


Is an array of antennas in which the relative phases of the respective signals feeding

the antennas are varied in such a way that the effective radiation pattern of the array is

reinforced in a desired direction and suppressed in undesired directions.

Phased array transmission is use to enhance transmission of radio waves in one

direction.

A phased array antenna is composed of lots of radiating elements each with a phase

shifter. Beams are formed by shifting the phase of the signal emitted from each

radiating element, to provide constructive/destructive interference so as to steer the

beams in the desired direction.

Areas of the antenna matrix can act as separate antennas. This allows many antenna

beam patterns to be individually controlled at the same time. A large,phase-steered

antenna system could be used to control the positions of many aircraft as at larger

airport.

In the figure 1 (left) both radiating elements are fed with the same phase. The signal is

amplified by constructive interference in the main direction. The beam sharpness is

improved by the destructive interference

Figure 1: left : two antenna elements, fed with the same phase,

Right : two antenna elements, fed with different phase shift


31/47

Phased patch array

http://www.radartutorial.eu/18.explanations/ex31.en.html

http://www.radartutorial.eu/06.antennas/an16.en.html


http://en.wikipedia.org/wiki/Radio

http://en.wikipedia.org/wiki/Radiation_pattern

http://en.wikipedia.org/wiki/Signaling_(telecommunication)

http://en.wikipedia.org/wiki/Phase_(waves)

http://en.wikipedia.org/wiki/Antenna_array_(electromagnetic)


In the figure 1 (right), the signal is emitted by the lower radiating element with a phase

shift of 22 degrees earlier than of the upper radiating element. Because of this the main

direction of the emitted sum-signal is moved upwards.

(Note: Radiating elements have been used without reflector in the figure. Therefore the

back lobe of the shown antenna diagrams is just as large as the main lobe.)

The main beam always points in the direction of the increasing phase shift.

If the signal to be radiated is delivered through an electronic phase shifter giving a

continuous phase shift, the beam direction will be electronically adjustable. However,

this cannot be extended unlimitedly.

The highest value, which can be achieved for the Field of View (FOV) of a phased array

antenna is 120° (60° left and 60° right). With the sine theorem the necessary phase

moving can be calculated.

Advantages Disadvantages

high gain width los side lobes

Ability to permit the beam to jump from one

target to the next in a few microseconds

Ability to provide an agile beam under

computer control

arbitrarily modes of surveillance and

tracking

free eligible Dwell Time

multifunction operation by emitting several

the coverage is limited to a

120 degree sector in

azimuth and elevation

deformation of the beam

while the deflection

low frequency agility

very complex structure

(processor, phase shifters)


32/47

http://www.radartutorial.eu/17.bauteile/bt36.en.html

http://www.radartutorial.eu/01.basics/rb21.en.html


http://www.radartutorial.eu/06.antennas/an14.en.html#calc

http://www.radartutorial.eu/06.antennas/an14.en.html#calc

http://www.radartutorial.eu/17.bauteile/bt36.en.html



beams simultaneously

Fault of single components reduces the

capability and beam sharpness, but the

system remains operational

still high costs

CONCLUSION:Beamforming antenna systems improve wireless network performance

increase system capacity

improve signal quality

suppress interference and noise

save power

Beamforming antennas improve infrastructure networks performance. They may

improve ad hoc networks performance. New MAC protocol standards are needed.

Vector antennas may replace spatial arrays to further improve beamforming

performance

.

The relative amplitudes of — and constructive and destructive interference effects

among — the signals radiated by the individual antennas determine the effective

radiation pattern of the array. A phased array may be used to point a fixed radiation

pattern, or to scan rapidly in azimuth or elevation.


33/47

http://en.wikipedia.org/wiki/Azimuth

http://en.wiktionary.org/wiki/scan

http://en.wikipedia.org/wiki/Radiation_pattern

http://en.wikipedia.org/wiki/Interference_(wave_propagation)

http://en.wikipedia.org/wiki/Amplitude


DIFFERENT TYPES OF PHASED ARRAYS

There are two main types of beamformers:

time domain beamformers

frequency domain beamformers

A graduated attenuation window is sometimes applied across the face of the array to

improve side-lobe suppression performance, in addition to the phase shift.

TIME DOMAIN BEAMFORMER

works by introducing time delays.

The basic operation is called "delay and sum". It delays the incoming signal from

each array element by a certain amount of time, and then adds them together.

The most common kind of time domain beam former is serpentine waveguide.

Active phase array uses individual delay lines that are switched on and off. Yttrium

iron garnet phase shifters vary the phase delay using the strength of a magnetic

field.

FREQUENCY DOMAIN BEAMFORMERS

TWO DIFFERENT TYPES OF FREQUENCY DOMAIN BEAMFORMERS:1) separates the different frequency components that are present in the received signal

into multiple frequency bins (using either an DFT or a filterbank). When different

delay and sum beamformers are applied to each frequency bin, the result is that the

main lobe simultaneously points in multiple different directions at each of the

different frequencies. This can be an advantage for communication links, and is

used with the SPS-48 radar.

2) makes use of Spatial Frequency. Discrete samples are taken from each of the

individual array elements. The samples are processes using a Discrete Fourier

Transform (DFT). The DFT introduces multiple different discrete phase shifts during


34/47

http://en.wikipedia.org/wiki/Discrete_Fourier_Transform

http://en.wikipedia.org/wiki/Discrete_Fourier_Transform

http://en.wikipedia.org/wiki/SPS-48

http://en.wikipedia.org/wiki/Filterbank

http://en.wikipedia.org/wiki/DFT

http://en.wikipedia.org/wiki/Yttrium_iron_garnet


http://en.wikipedia.org/wiki/Frequency_domain

http://en.wikipedia.org/wiki/Time_domain


processing. The outputs of the DFT are individual channels that correspond with

evenly spaced beams formed simultaneously. A 1 dimensional DFT produces a fan

of different beams. A 2 dimensional DFT produces beams with a pineapple

configuration.

These techniques are used to create two kinds of phase array.

Dynamic - an array of variable phase shifters are used to move the beam

Fixed - the beam position is stationary with respect to the array face and

the whole antenna is moved

There are two further sub-categories that modify the kind of dynamic array or fixed

array.

Active - amplifiers or processors in each phase shifter element

Passive - large central amplifier with attenuating phase shifters

Dynamic Phased ArrayEach array element incorporates an adjustable phase shifter that are collectively used

to move the beam with respect to the array face.

Dynamic phase array require no physical movement to aim the beam. The beam is

moved electronically. This can produce antenna motion fast enough to use a small

pencil-beam to simultaneously track multiple targets while searching for new targets

using just one radar set (track while search).

As an example, an antenna with a 2 degree beam with a pulse rate of 1 kHz will require

approximately 16 seconds to cover an entire a hemisphere consisting of 16,000 pointing

positions. This configuration provides 6 opportunities to detect a Mach 3 vehicle over a

range of 100 km (62 mi), which is suitable for military applications.

The position of mechanically steered antennas can be predicted, which can be used to

create electronic countermeasures that interfere with radar operation. The flexibility

resulting from phase array operation allows beams to be aimed at random locations,

which eliminates this vulnerability. This is also desirable for military applications.

Fixed Phase ArrayPREPARED BY : ROHANA BT. IBRAHIMPOLIMASDECEMBER 2012 SESSION

35/47

http://en.wikipedia.org/wiki/Electronic_countermeasures

http://en.wikipedia.org/wiki/Pineapple


Fixed phase array antennas are typically used to create an antenna with a more

desirable form factor than the conventional parabolic reflector or cassegrain reflector.

Fixed phased array radar incorporate fixed phase shifters. This kind of phase array is

physically moved during the track and scan process. There are two configurations.

Multiple frequencies with a delay-line

Multiple adjacent beams

The SPS-48 radar uses multiple transmit frequencies with a serpentine delay line along

the left side of the array to produce vertical fan of stacked beams. Each frequency

experiences a different phase shift as it propagates down the serpentine delay line,

which forms different beams. A filter bank is used to split apart the individual receive

beams. The antenna is mechanically rotated.

Semi-active radar homing uses monopulse radar that relies on a fixed phase array to

produce multiple adjacent beams that measure angle errors. This form factor is suitable

for gimbal mounting in missile seekers.

Active Phase ArrayActive phase arrays elements incorporate transmit amplification with phase shift in each

antenna element (or group of elements). Each element also includes receive pre-

amplification. The phase shifter setting is the same for transmit and receive.

Active phase array do not require phase reset after the end of the transmit pulse, which

is compatible with Doppler radar and Pulse-Doppler radar.

Passive Phase ArrayPassive phase arrays typically use large amplifiers that produce all of the microwave

transmit signal for the antenna. Phase shifters typically consist of waveguide elements

that contain phase shifters controlled by magnetic field, voltage gradient, or equivalent

technology.

The phase shift process used with passive phase array typically puts the receive beam

and transmit beam into caddy-corner quadrants. The sign of the phase shift must be

inverted after the transmit pulse is finished and before the receive period begins to

place the receive beam into the same location as the transmit beam. That requires a


36/47

http://en.wikipedia.org/wiki/Pulse-Doppler_radar

http://en.wikipedia.org/wiki/Doppler_radar

http://en.wikipedia.org/wiki/Gimbal

http://en.wikipedia.org/wiki/Monopulse_radar

http://en.wikipedia.org/wiki/Semi-active_radar_homing

http://en.wikipedia.org/wiki/SPS-48

http://en.wikipedia.org/wiki/Cassegrain_reflector

http://en.wikipedia.org/wiki/Parabolic_reflector


phase impulse that degrades sub-clutter visibility performance on Doppler radar and

Pulse-Doppler radar. As an example, Yttrium iron garnet phase shifters must be

changed after transmit pulse quench and before receiver processing starts to align

transmit and receive beams. That impulse introduces FM noise that degrades clutter

performance.

MICROWAVE FEEDER SYSTEM (DRIVER ELEMENT)TPYES OF FEEDER

a) Omnidirectional b) Cassegrain c) Gregorian d) Horn feed Parabolic antennas are also classified by the type of feed, that is, how the radio waves

are supplied to the antenna.

The primary antena is place at the parabola focus point. primer diletakkan pada titik fokus parabola.

Reason: produce better tramsmission and reception. (enhance directivity and gain)

The primary antenna has to be used together with the reflector to avoid the flaring of

the radiation pattern and thus reduced the directivity. The microwave feeder is used

to overcome this problem.


37/47

http://www.tutorgigpedia.com/ed/Antenna_feed


http://en.wikipedia.org/wiki/Pulse-Doppler_radar

http://en.wikipedia.org/wiki/Doppler_radar


Antena primer ini mesti digunakan bersama-sama dengan pemantul, jika tidak sinaran yang dihasilkan akan diserak dalam semua arah dan ini akan menyebabkan pengarahannya menurun.

DIPOLE FEEDER

AXIAL OR FRONT FEED


38/47

SPHERICAL REFLECTOR TO DIRECT WAVE TO THE MAIN REFLECTOR

MAIN REFLECTOR

PRIMARY FEED DIPOLE AT FOCUS


This is the most common type of feed, with the feed antenna located in front of the dish

at the focus, on the beam axis. A disadvantage of this type is that the feed and its

supports block some of the beam, which limits the aperture efficiency to only 55 - 60%.

OFF-AXIS OR OFFSET FEED

The reflector is an asymmetrical segment of a paraboloid, so the focus, and the feed

antenna, are located to one side of the dish. The purpose of this design is to move the

feed structure out of the beam path, so it doesn't block the beam. It is widely used in

home satellite television dishes, which are small enough that the feed structure would

otherwise block a significant percentage of the signal. Offset feed is also used in

multiple reflector designs such as the Cassegrain and Gregorian.

CASSEGRAIN FEEDThe feed is located on or behind the dish, and radiates forward, illuminating a convex

hyperboloidal secondary reflector at the focus of the dish.


39/47

http://en.wikipedia.org/wiki/Hyperboloid

http://www.tutorgigpedia.com/ed/Satellite_television

http://www.tutorgigpedia.com/ed/Antenna_feed

http://en.wikipedia.org/wiki/File:Parabolic_antenna_types2.svg


The radio waves from the feed reflect back off the secondary reflector to the dish, which

forms the outgoing beam.

An advantage of this configuration is that the feed, with its waveguides and " front end"

electronics does not have to be suspended in front of the dish, so it is used for antennas

with complicated or bulky feeds, such as large satellite communication antennas and

radio telescopes. Aperture efficiency is on the order of 65 - 70%.

GREGORIAN FEED


40/47

http://en.wikipedia.org/wiki/Radio_telescope

http://en.wikipedia.org/wiki/Satellite_communication

http://en.wikipedia.org/wiki/RF_front_end

http://en.wikipedia.org/wiki/File:Parabolic_antenna_types2.svg


Similar to the Cassegrain design except that the secondary reflector is concave,

(ellipsoidal) in shape.

Aperture efficiency over 70% can be achieved.

HORN FEED

CASSEGRAIN FEEDER

Titik fokus pemantul

sekunder dan titik fokus

pemantul primer bertemu

pada titik yang sama.

Sinaran daripada antena

horn akan dipantul oleh

pemantul sekunder &

seterusnya dipancarkan

kepada pemantul utama

untuk mengkolimatkan


41/47

PENYUAP HORN PRIMER

PEMANTUL UTAMA

PANDUGELOMBANG

SUBREFLECTOR

MAIN REFLECTORPRIMARY FEED HORN

WAVEGUIDE/TRANSMISSION LINE

http://www.tutorgigpedia.com/ed/Ellipsoid


sinaran.

HORN FEEDER Sering digunakan

sebagai penyuap primer,

disebabkan oleh corak

pengarahannya yang

menyuar keluar, jadi

dapat mengelakkan

serakan.

5.2 performance characteristic of Horn and Parabolic Antenna. 5.2.1 Determine the characteristics of the radiation pattern. 5.2.2 Relate the aperture efficiency and effective area. 5.2.3 Explain the antenna gain and efficiency. 5.2.4 Apply the formula to calculate the antenna gain.

FACTORS AFFECTING THE ANTENNA :-

RADIATION PATTERN Refers to the performance ot the antenna itself i.e when it is mounted well away

from any object such as building or the earth by which reflecting signal might

effect the shape of the pattern.


42/47

PEMANTUL UTAMAANTENA HORN

PANDUGELOMBANG


Is a 3-dimensional model (polar graf/diagram) of field strength or power density

measurements made at a fixed distance from an antenna in a given plane.

(Figure 2)

Maximum radiation ialah dalam arah 90°

daripada titik rujukan corak sinaran mutlak

(corak sinaran diplot dalam bentuk Є

RELATIVE RADIATION PATTERN. Є or

P is plotted wrt reference point.


43/47


atau P.

RELATIVE RADIATION PATTERN in dB. Dalam arah ± 45° daripada rujukan.

Ketumpatan kuasa ialah -3 dB relatif

kepada ketumpatan kuasa dalam arah

sinaran maksima.

RELATIVE RADIATION PATTERN FOR OMNIDIRECTIONAL ANTENNA. (Transmits power equally in all direction.

Thus produce a circular or spherical

radiation pattern.)

BEAMWIDTH (BEAM / FLARED ANGLE)

It is the angle substended by the points at which the radiation power fall to half its

maximum power or the field strength has fallen to 1/√2 (70.7 % ) of its max voltage or

the angle measured between the -3dB down (half power) points on the major lobe of an

antenna’s radiation pattern. ( Figure 3)


44/47

FIGURE 3


ANTENNA GAIN

Defined as the ratio of power per unit area received from the antenna at some point

in space to the power received from an isotropic antenna at the same point in space.

Capability of a directive antenna to concentrate power in a given direction i.e the

capability to direct rf energy into a given region and not in all direction.

For transmitting antenna, it refers to how far is the concentration of transmission

power in a given direction.

For receiving antenna, it refers to how far its receive the best signal in a given

direction rather than in all direction.

CHARACTERISTIC OF PARABOLOID ANTENNAMenukarkan mukagelombang sfera yang terhasil pada titik fokus kepada gelombang

satah.

Semua tenaga yang diterima daripada ruang bebas yang sama dengan paksi parabola (Rx) akan dipantul ke titik penumpuan.

ADVANTAGES DISADVANTAGESGandaan boleh ditingkatkan mengikut keperluan.

Boleh beroperasi pada sebarang frekuansi di dalam zon gelombang mikro.

Pemasangan yang ringkas.

Susah untuk dibina dengan ketepatan yang tinggi

Frekuansi kendalian terhad kepada piring yang digunakan.


45/47


GAIN

GAIN ; G = 4 π A λ2

Where;

G = gain; A = area of parabolic dish (m2); λ = wavelength of operational frequency (m)

If the area of the dish, A A = π d 2 4

Where;

A = area of parabolic dish (m2); d = diameter of dish opening (m)

Beamwidth α = 115 λ ° d

α = antenna beamwidth or angle between half power points ( °)λ = wavelength (m) d = diameter of dish opening (m)

EXAMPLE

1. Calculate the gain and the half-wave (λ/2) antenna angle of a parabolic antenna operating at a frequency of 1 GHz. The dish diameter is 2.5 m.

λ = Vc / f GdB = 10 log G


46/47


= 3 x 108 / 1 x 109

= 0.3 m. = 10 log 685

= 28.4 dB.

GAIN; G = 4 π A λ 2

= 4 π (π d 2 ) λ2 4

= 4 x 3.14 ( 3.14 x 2.5 2 ) 0.32 4

= 685 .

Antenna beam widh, α = 115 λ °

d

= 115 x 0.3 2.5

= 13.8 °.


47/47

nurhidayahmoktar.weebly.comnurhidayahmoktar.weebly.com/uploads/6/4/8/7/6487407/05... · web viewthe...

Documents