Chapter 2: Antenna & Fundamental Parameters of Radio Antennas...

EELE 5333

Antenna & Radio

Propagation

Part I:

Antenna Basics

Winter 2020

Re-Prepared by

Dr. Mohammed Taha El Astal

Chapter 2:

Fundamental Parameters of Antennas

Session 1

Chapter 2 - Antenna Parameters

Acknowledgment

This PPT is prepared based mainly on Dr.Talal Skaik’s PPT, Balanis

Antenna Book, and Dr. Nurul Noordin


Introduction• To design an antenna... “We need to know what is the desired frequency, gain,

bandwidth, impedance, and polarization?“

• Before we can design an antenna or discuss

antenna types, we must understand the basics of

antennas, which are the fundamental

parameters that characterize an antenna.

• So let us learn something. We'll start with frequency

and step through radiation patterns, directivity and

gain, and so on..

• Let’s get started..


Overview of what is antenna?

• In wireless communication systems, an RF signal generated by a transmitter is sent into free space and eventually picked up by a receiver.

• The interface between the transmitter and free space and between free space and the receiver is the antenna.

• Antenna is the device for radiating or receiving electromagnetic wave in free space.

• The antenna is the interface between transmission lines and free space.


Radio Waves

• A radio signal is called an electromagnetic wave because it is made up of both electric and magnetic fields.

• Whenever voltage is applied to the antenna, an electric field is set up. At the same time, this voltage causes current to flow in the antenna, producing a magnetic field.

• The electric and magnetic fields are at right angles to each other.

• These electric and magnetic fields are emitted from the antenna and propagate through space over very long distances at the speed oflight.


Antenna Parameters

Radiation Pattern

Radiation Intensity

Field Regions

Directivity

Antenna Efficiency


Antenna Parameters (2)

Antenna Gain

Beamwidths and Sidelobes

Impedance

Polarization


Monopole vs Dipole Antennas

• Dipole Figure 2

The monopole and dipole antennas are used for cellular phones, broadcasting and wireless communications due to their omnidirectional property.

• Monopole Figure 1


Monopole

• Figure 1 depicts monopole antenna with its radiation pattern. It also depicts foldedmonopole antenna. The monopole antenna has image through a metal or groundplane.

• There are variations to monopole antenna which will provide antennas of inverted-Land inverted-F types. These type of monopole antennas are used for hand heldportable telephones.


Dipole

• Figure 2 depicts dipole antenna with its radiation pattern. It also depictsfolded dipole antenna.

• The most common dipole antenna is a half-wave dipole which is a piece ofwire or rod which is one half wavelength in length.

• The antenna is cut into two quarter wavelength sections. The transmissionline is connected at center point as shown. The dipole antenna has animpedance of about 73 Ohm.

• The radiation pattern of half wave dipole antenna has shape of doughnut.

• For multiple of λ radiation pattern changes as shown in the figure2.

• The max gain of a typical half-wavelength dipole antenna is 2.15dB.


Half-wave Dipole Antenna

• The half-wave dipole antenna is just a special case of the dipoleantenna.

• Half-wave term means that the length of this dipole antenna isequal to a half-wavelength at the frequency of operation.

• The dipole antenna, is the basis for most antenna designs, is abalanced component, with equal but opposite voltages andcurrents applied at its two terminals through a balancedtransmission line.

Radiation Patterns, types, representations, lobes, Beamwidth

Radiation Patterns, & it lobes“a mathematical function or a graphical representation (2D and 3D) of theradiation properties of the antenna as a function of space coordinates.

Various parts of a radiation pattern

are referred to as lobes, which may

be sub classified into major or

main, minor, side, and back lobes.

A major lobe (also called main

beam) is defined as “the radiation

lobe containing the direction of

maximum radiation.”

A minor lobe is any lobe except a

major lobe

3d-field pattern of a directional antenna with maximum radiation in z-direction at θ = 0◦.

Most of the radiation is contained in a main beam (or lobe) accompanied by radiation also

in minor lobes (side and back). Between the lobes are nulls where the field goes to zero.

Radiation Patterns Types

(a) Field pattern (in linear scale)

typically represents a plot of the

magnitude of the electric or magnetic

field as a function of the angular space.

(b) Power pattern (in linear scale)

typically represents a plot of the

square of the magnitude of the

electric or magnetic field as a

function of the angular space.(c) Power pattern (in dB) represents the magnitude of

the electric or magnetic field, in decibels, as a function

of the angular space.

Normalized Patterns

The half-power level occurs at those angles θ and φ for which

Eθ (θ, φ)n = 1

2= 0.707.

Patterns in 2D

In practice, 3d- pattern is

measured and recorded in a

series of 2d- patterns.

for most practical

applications, a few plots of the

pattern as a function of 𝜃 for

some particular values of 𝜙,

plus..

a few plots as a function of 𝜙for some particular values of 𝜃,

give most of the useful and

needed information.

Two-dimensional

(a)field,

(b) power

(c) and decibel plots of the 3-D

antenna pattern shown before.

Rectangular and polar 2d-pattern representation (linear & dB scale)


Polar Pattern


Rectangular/Cartesian Pattern

Dr. Mohammed Taha El [email protected]@gmail.com

10/2020

EELE 5333

Antenna & Radio

Propagation

Part I:

Antenna Basics

Winter 2020

Re-Prepared by

Dr. Mohammed Taha El Astal

Chapter 2:

Fundamental Parameters of Antennas

Session 2

24

Lobes & BeamWidth

a) Radiation lobes and beamwidths of an antenna pattern. (b) Linear plot of powerpattern and its associated lobes and beamwidths.

• The angular beamwidth at the half-

power level or half-power beamwidth

(HPBW) (or −3-dB beamwidth)

and

• nulls the beamwidth between first

(FNBW) are important pattern

parameters.

The half-power beam width

(HPBW)=40◦ is measured at the

E = 0.707 level.

or at Pn=0.5 (-3dB in dB scale).


Radiation Properties

Main lobe

Half-power

Beamwidth

HPBW

Side Lobe

Back

lobe

Minor

lobes

First-nulls

Beamwidth

FNBW

Nulls


Beamwidth and Sidelobes

• A major lobe (also called main beam) is defined as “the radiationlobe containing the direction of maximum radiation.”– the major lobe is pointing in the θ = 0 direction. In some

antennas, such as split-beam antennas, there may exist morethan one major lobe.

• A minor lobe is any lobe except a major lobe and all the lobes withthe exception of the major can be classified as minor lobes.– Minor lobes usually represent radiation in undesired directions,

and they should be minimized.• A side lobe is “a radiation lobe in any direction other than the

intended lobe.”– Usually a side lobe is adjacent to the main lobe and occupies the

hemisphere in the direction of the main beam.– Side lobes are normally the largest of the minor lobes.

• A back lobe is “a radiation lobe whose axis makes an angle ofapproximately 180◦ with respect to the beam of an antenna.”– Usually it refers to a minor lobe that occupies the hemisphere in

a direction opposite to that of the major (main) lobe.

Half-Power Beamwidth

An antenna has a field pattern given by E(θ) = cos2 θ for 0◦ ≤ θ ≤ 90◦

Find the half-power beamwidth (HPBW).

E(θ) at half power = 0.707.

Thus 0.707 = cos2 θ

so cos θ =√0.707 and θ = 33◦

HPBW = 2θ = 66◦

Example

Half-Power Beamwidth and First Null Beamwidth

An antenna has a field pattern given by E(θ) = cos θ cos 2θ for 0◦ ≤ θ

≤ 90◦. Find (a) the half-power beamwidth (HPBW) and (b) the

beamwidth between first nulls (FNBW).

Example


Front-to-Back Ratio

• The direction of maximum radiation is in the horizontal plane is considered to be thefront of the antenna, and the back is the direction 180º from the front

• For a dipole, the front and back have the same radiation, but this is not always the case


Rectangular/Cartesian Pattern

Beam Efficiency (BE):

>90% for radiometry,

astronomy, radar, etc. total _ power _ tx _ or _ rxBE

tx _ or _ rx _ power _ within _

FNBW

Lobes, nulls, and beamwidths (HPBW and FNBW)

Patterns in term of Isotropic, directional & Omnidirectional property

An isotropic radiator:is defined as “a hypothetical lossless antenna having equal radiation

in all directions.” Although it is ideal and not physically realizable, it

is often taken as a reference for expressing the directive properties of

actual antennas.

An Isotropic radiator

• Power Density: (W/m2)PT

4r 2S

A directional antenna is one “having the property of radiating or

receiving electromagnetic waves more effectively in some directions than

in others.

Example:

Directional Antenna

N.B: The radiation patterns areplotted in E-plane and H-plane ofthe antenna.

37

Directional Antenna

An omnidirectional Antenna is defined as

one “having an essentially non-directional

pattern in a given plane and a directional

pattern in any orthogonal plane.”

An omnidirectional pattern is then a special

type of a directional pattern.

An omnidirectional antenna

What do u think?

Antenna with the following radiation, decide ? Isotropic, directive, and omnidirectional?

A plot of the radiated field/power as a function of angle.

Radiation Patterns - Example: Half-wave Dipole

Radiation Patterns - Example: Half-wave Dipole


Dipole Radiation pattern


Exam

ple

of

Rad

iati

on

Patt

ern

43


Radiation Pattern

• Dipole Antenna with Views of the Corresponding Radiation Pattern


E-Plane and H-Plane

E-plane H-plane

x

E plane (elevation)

• Electromagnetic field is in vertical plane

• θ= 90°

• 0°<Φ<90°, 270°<Φ<360°z

H plane (azimuth)

• Electromagnetic field is in horizontal plane

• 0° < θ < 180°

• Φ = 0°y

x


E-Plane and H-Plane

Dr. Mohammed Taha El [email protected]@gmail.com

10/2020

Chapter 2: Antenna & Fundamental Parameters of Radio Antennas...

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