This presentation is about antennas and covers the following topics: -Antenna -Hertzian dipole -Half wave dipole -Dipole antenna -Quarter wave monopole antenna -Antenna characteristics This presentation is as per the course of DAE Electronics ELECT-212.

1. Antennas
Irfan Sultan
Instructor (Telecom)
Govt. College of Technology,
Pindi-Bhattian

2. Contents
 Understand The Term “Antenna”
 Discuss Hertzian Dipole
 Discuss Half Wave Dipole Antenna
 Describe Quarter Wave Monopole Antenna
 Discuss Antenna Characteristics

3. Introduction to Antennas
 An antenna is a metallic structure which is used to transmit or receive
Electromagnetic energy in the form of radio waves.
 These are normally used when using a transmission line or waveguide is:
 Uneconomical
 Impractical and
 Impossible
 Some example of usage of antennas in real life are:
 Aircraft Communication
 Communication between ships
 Broadcasting & satellites
 Antennas are not just used in communication applications but are also used in
Medical and Industrial applications

4. Antennas Examples
 Antennas are found in several shape, some of which are as under.

5. Dipole Antenna
 A dipole antenna is a straight electrical conductor (measuring 1/2 wavelength
from end to end for a half wave dipole antenna and) connected at the center to a
radio-frequency (RF) feed line.

6. Parabolic Dish Antenna

7. Loop Antenna

8. Helix Antenna

9. Horn Antenna

10. Hertzian Dipole
 A Hertzian Dipole is a very small i.e. Infinitesimal dipole, which is oscillating a very high
frequency. It is also called a Point Dipole.
 It is basically such an antenna whose size (length) is much smaller than the wavelength of the
signal applied to it.
 The Hertzian dipole or Elementary doublet refers to a theoretical construction, rather than a
physical antenna design. It may be defined as a finite oscillating current (in a specified direction)
over a tiny or infinitesimal length 𝛿ℓ at a specified position. The solution of the fields from a
Hertzian dipole can be used as the basis for analytical or numerical calculation of the radiation
from more complex antenna geometries (such as practical dipoles) by forming the
superposition of fields from a large number of Hertzian dipoles comprising the current pattern
of the actual antenna.
Hertzian dipole of tiny length δℓ,
with current I, and field sensed at a
distance r in the θ direction.

11. Hertzian Dipole
 A Hertzian dipole antenna is a very small dipole antenna with a uniform current
distribution. Then ends of this short antenna are capacitively loaded by small
metallic spheres or disks so as to create a current that is approximately uniform, as
shown in the figure.
 Without the capacitive loading the current would be approximately triangularly
shaped with a maximum value at the center of antenna and linearly decreasing to
zero at both ends.
Current
Distribution

12. Hertzian Dipole
Hertzian Dipole is normally used to find Electric or Magnetic field at some point.
For this purpose:
 First, find Vector Potential (A) at that point.
 Then find Magnetic Field Intensity (B)
 Finally, find Electric Field Intensity (E)

13. Vector Potential Due to Hertzian Dipole
 The magnetic vector potential (A) for a Hertzian dipole can be found using the
following formula:

14. Half-Wave (𝜆/2) Dipole Antenna
 It is such a structure which is made of two metallic conductors which are held 180o apart
in the opposite direction to each other. And the length of the conductor is 𝜆/2, i.e. half of
the wavelength of the operating frequency of the antenna.
 The length of each of the conductors is quarter (1/4) of the wavelength, i.e. 𝜆/4.
Note: "half-wave" term means that the length of
this dipole antenna is equal to a half-wavelength at the
frequency of operation

15. Half Wave Dipole: Working

16. Half Wave Dipole: Radiation Pattern
Radiation Pattern: is the directional variation in intensity of the radiation from an aerial or other
source.

17. Half Wave Dipole: Radiation Pattern

18. Antenna Characteristics

19. Antenna Characteristics