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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
Chapter 2 - Antenna Parameters
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..
Chapter 2 - Antenna Parameters
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.
Chapter 2 - Antenna Parameters
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.
Chapter 2 - Antenna Parameters
Antenna Parameters
Radiation Pattern
Radiation Intensity
Field Regions
Directivity
Antenna Efficiency
Chapter 2 - Antenna Parameters
Antenna Parameters (2)
Antenna Gain
Beamwidths and Sidelobes
Impedance
Polarization
Chapter 2 - Antenna Parameters
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
Chapter 2 - Antenna Parameters
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.
Chapter 2 - Antenna Parameters
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.
Chapter 2 - Antenna Parameters
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)
Chapter 2 - Antenna Parameters
Polar Pattern
Chapter 2 - Antenna Parameters
Rectangular/Cartesian Pattern
Chapter 2 - Antenna Parameters
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).
Chapter 2 - Antenna Parameters
Radiation Properties
Main lobe
Half-power
Beamwidth
HPBW
Side Lobe
Back
lobe
Minor
lobes
First-nulls
Beamwidth
FNBW
Nulls
Chapter 2 - Antenna Parameters
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
Chapter 2 - Antenna Parameters
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
Chapter 2 - Antenna Parameters
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
Chapter 2 - Antenna Parameters
Dipole Radiation pattern
Chapter 2 - Antenna Parameters
Exam
ple
of
Rad
iati
on
Patt
ern
43
Chapter 2 - Antenna Parameters
Radiation Pattern
• Dipole Antenna with Views of the Corresponding Radiation Pattern
Chapter 2 - Antenna Parameters
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
Chapter 2 - Antenna Parameters
E-Plane and H-Plane
Dr. Mohammed Taha El [email protected]@gmail.com
10/2020