1. SECTION 3 - Antenna Fundamentals

2. Introduction
The antenna is the interface between the transmission line and space
Antennas are passive devices; the power radiated cannot be greater than the power entering from the transmitter
When speaking of gain in an antenna, gain refers to the idea that certain directions are radiated better than others
Antennas are reciprocal - the same design works for receiving systems as for transmitting systems

3. Decibels (dB)
Used for all mathematical calculations in the radio world.
dB is a logarithmic number
dB =10 log (linear number)
A gain of 2 = 10 log (2) = 3 dB
A gain of 4 = 10 log (4) = 6 dB
When a number doubles it goes up 3 dB
When a number reduces by 1/2, it goes down -3 dB
To multiply linear numbers you add logarithms
To divide linear numbers you subtract logarithms

4. Antenna Gain Antenna Gain measure in decibels (dB)
SECTION 3 - Antenna Fundamentals
Antenna Gain measure in decibels (dB)
Double every 3 dB
Effective Radiated Power (ERP) = Tx Power + Antenna Gain - Feedline Losses
Received Signal = Rx Power + Antenna Gain - Feedline losses
As Antenna Gain increases Antenna Pattern becomes more directional
Antenna gain is a logarithmic equation, gain doubles for every 3db increase, but is cut in half for every 3db decrease.
High Gain antennas become more directional. This slide give an example of a High Gain UHF antenna.
Erp is the rf power plus or minus the gain or loss of the antenna. The loss that is incurred at the transmit site can quite possibly be made up at the receive site, through the same practice.

5. Radiation Patterns Omni-Directional / Isotropic
Radiates RF energy in all directions from antenna
RF Energy
Antenna
Top View

6. RF Basics - Omni-Directional Antennas
Omni-Directional / Isotropic Antenna
Radiates RF energy in all directions from antenna
Usually used at the Master and Repeater Nodes
Omni-directional Antenna Vertical Polarized
360 degrees
Side View
Radiation Pattern Vertical Polarization
Top View
Radiation Pattern Vertical Polarization

7. RF Basics - Antenna Gain
As Antenna Gain increases the Antenna Pattern becomes more directional
Omni- Directional Antenna Shown Below
3 dB Points
360 degrees
Remains Unchanged
Vertical Beam Width (degrees)
Top View
Radiation Pattern Vertical Polarization
Side View
Radiation Pattern Vertical Polarization

8. Radiation Patterns Directional Compresses RF Energy in one direction
Antenna
Top View

9. RF Basics - Directional Antennas
Radiates RF energy in one direction
Usually used at Remote Nodes in a Point to Multi-point system or Point to Point Site
Side View Radiation Pattern Vertically Polarized
Vertical Beam Width (degrees)
Back Lobe
3 dB Points
Horizontal Beam Width (degrees)
Back Lobe
Top View Radiation Pattern Vertically Polarized
3 dB Points

10. RF Basics - Antenna Gain
SECTION 3 - Antenna Fundamentals
As Antenna Gain increases the Antenna Pattern becomes more directional
Directional Antenna Shown Below
3 dB Points
3 dB Points
Horizontal Beam Width (degrees)
Vertical Beam Width (degrees)
Antenna gain is a logarithmic equation, gain doubles for every 3db increase, but is cut in half for every 3db decrease.
High Gain antennas become more directional. This slide give an example of a High Gain UHF antenna.
Erp is the rf power plus or minus the gain or loss of the antenna. The loss that is incurred at the transmit site can quite possibly be made up at the receive site, through the same practice.
Back Lobe
Back Lobe
Top View
Radiation Pattern
Vertically Polarized
Side View
Radiation Pattern Vertically Polarized

11. Antenna Polarization Vertical Or Horizontal Polarization
SECTION 3 - Antenna Fundamentals
Vertical Or Horizontal Polarization
Polarization is the radiating element referenced to earth
All nodes must be the same polarization
Cancellation of signal if mismatched
Vertical Polarization for Most Radio Applications
Mixture of Omni and Directional Antennas
No Horizontal Polarization of Omni-Directional
Directional Antenna Horizontal Polarized
There are two types of polarization for antennas, they are vertical and horizontal. You must always place the antennas in the same polarization. If you do not theoretically they will never see each other. Thus they will effectively cancel each other out. Normally all antennas for SCADA applications the antennas are vertically polarized.
Directional Antenna Vertical Polarized
Omni-directional Antenna Vertical Polarized

12. Antenna Types 1/2 Wave Antenna Close to Isotropic Radiation
Approximately 3 dB gain
No ground planes needed

15. Antenna Gain Specifications
dBi means decibels with respect to an isotropic radiator
dBd means decibels with respect to an ideal half-wave dipole in its direction of maximum radiation
The gain of a dipole is 2.14 dBi

16. Beamwidth
The width of this bean is defined as the angle between its half-power points.
A half-wave dipole has a beamwidth of about 79º in one plane and 360º in the other

17. Antenna Theory Radiation from an Antenna
An antenna is a transducer designed to transmit or receive electromagnetic waves.
The official IEEE definition of an antenna is “That part of a transmitting or receiving system that is designed to radiate or receive electromagnetic waves”.
Radiation from an Antenna
Radiation of antenna can be explained by using capacitor concept.
During positive half cycle of current capacitor charges with upper plate positive and lower plate negative chargers . This creates electric line of forces and there direction is from top to bottom.
In anticlockwise direction of current, polarity reverses and electric lines of forces become bottom to top.

18. Radiation From an Antenna
When current flowing in one direction and is required to reverse their direction rapidly, those lines of forces at the extreme edge are unable to make this change with sufficient rapidly and are forced to out of the system.
In this way a certain amount of energy, stored in capacitor is radiated during each cycle. This affect increases with frequency, so that at radio frequencies, efficient radiations obtained from the conductor i.e. antenna.

19. Field Regions of Antenna
The fields surrounding an antenna are divided into 3 principle regions:
Reactive Near Field
Radiating Near Field or Fresnel Region
Far Field or Fraunhofer Region

20. Field Regions of Antenna
Reactive Near Field Region
In the immediate vicinity of the antenna, we have the reactive near field.
In this region, the fields are predominately reactive fields, which mean the E- and H- fields are out of phase by 90 degrees to each other.
In this region, energy is only stored and no energy is dissipated.
The boundary of this region is commonly given as:
Where R is the distance from the antenna surface,
D is the largest dimension of the antenna and
λ is the wavelength

21. Field Regions of Antenna
Radiating Near Field (Fresnel) Region
The radiating near field or Fresnel region is the region between the near and far fields.
Reactive fields are smaller in this field as compared to the reactive near-field region and the radiation fields dominate.
The outermost boundary for this region is given by:
Where R is the distance from the antenna surface,
D is the largest dimension of the antenna and
λ is the wavelength

22. Field Regions of Antenna
Far-field region (Fraunhofer region)
The region beyond is the far field region.
In this region, the reactive fields are absent and only the radiation fields exist; with the E- and H-fields orthogonal to each other and the direction of propagation as with plane waves.
The far field region is the most important, as this determines the antenna's radiation pattern.
Also, antennas are used to communicate wirelessly from long distances, so this is the region of operation for most antennas.

23. Antenna Performance Parameters
Radiation Pattern An antenna radiation pattern or antenna pattern is defined as “a mathematical function or a graphical representation of the radiation properties of the antenna as a function of space coordinates”. In most cases, the radiation pattern is determined in the far field region and is represented as a function of the directional coordinates. Directivity Directivity of an antenna defined as “the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions”. It may be regarded as the ability of the antenna to direct radiated power in a given direction.

24. Antenna Performance Parameters
Antenna Efficiency
The efficiency of an antenna relates the power delivered to the
antenna and the power radiated or dissipated within the antenna. The
antenna efficiency (or radiation efficiency) can be written as the ratio
of the radiated power to the input power of the antenna:
Antenna Gain
The term Antenna Gain describes how much power is transmitted in
the direction of peak radiation to that of an isotropic source. Antenna
Gain (G) can be related to directivity (D) by:
Thus, Antenna gain is defined as antenna directivity times a factor
representing the radiation efficiency.

25. Antenna Performance Parameters
Return Loss Return Loss is the measure of the amount of power which is reflected back to the source from an incorrectly terminated line. Return loss is expressed in dB as: Where Pi is the incident power and Pr is the reflected power. There are many types of antennas but for the study of Specific Absorption Rate, dipole antenna is best due to its simple structure and isotropic radiation pattern.

26. Dipole / Doublet H

27. The Dipole Antenna
Some of the basic parameters of a half wave dipole antenna are as described below: Radiation pattern Dipoles have a radiation pattern, shaped like a toroid (doughnut) symmetrical about the axis of the dipole. The radiation is maximum at right angles to the dipole, dropping off to zero on the antenna's axis.

28. The Dipole Antenna
Frequency versus length The length of a half-wave dipole l, for frequency f hertz is given by the formula: Where λd is the wavelength on the dipole elements, λ0 is the free-space wavelength, c is the speed of light in free space (299,792,458 meters per second) and k is an adjustment factor (typically from 0.95 to about 0.915) Current and voltage distribution

29. Phased Array Antennas
For some applications single element antennas are unable to meet the gain or radiation pattern requirements.
A proper combination of various types of antennas might yield the required pattern.
Thus there is control over the direction in which the power is transmitted.
An antenna array is a cluster of antennas arranged in a specific physical configuration .
Each individual antenna is called an element of the array.
The excitation (both amplitude and phase) applied to each individual element may differ.
Once an array has been designed to focus towards a particular direction, it becomes a simple matter to steer it towards some other direction by changing the relative phases of the array elements; a process called steering or scanning.

30. Zero Phase Shift Animation

31. Constant Phase Shift Animation

32. YAGI–UDA ANTENNA Most high gain antennas 3 elements: Driven element
Parasitic element
Spacing = to 0.25
Director
Reflectors
Dipole impedance = 73ohms

33. Yagi-Uda Antenna (Yagi)
One driven element and one or more parasitic elements
Operates over a small range of frequencies (not a wide-band antenna)

34. Yagi Antenna – 3 elements
A 3 element Yagi
Associated radiation pattern

35. Log-Periodic Antenna
Lengths of driven elements are related logarithmically
The longest element has a length of ½ the wavelength of the lowest frequency
The shortest element is ½ the wavelength of the highest frequency
Advantage is very wide bandwidth

36. Log-Periodic Antenna
Ratio of two adjacent elements is held constant, usually 36 36 36

38. Log periodic Antenna
Electrical properties must repeat periodically with the logarithm of frequency
Basic geometric structure that is repeated but with a changing size
Structure size changes with each repetition by a constant scale factor so that the structure expand or contract

39. Log Periodic Dipole Array
LPDA
All the dimensions increase in proportion to the distance from the origin

40. LPDA No. of dipoles of different lengths and spacings
Fed by a balanced two wire tXion line
Included angle  is constant
Length =L Spacing=R
Scale factor or design ratio  <1

41. LPDA
Properties at frequency f , the same properties will be repeated at freq nf or f/ n

44. Antenna Arrays
Simple antennas can be combined to achieve desired directional effects
Individual antennas are called elements and the combination is an array

45. Types of Arrays
Broadside: maximum radiation at right angles to main axis of antenna
End-fire: maximum radiation along the main axis of antenna
Phased: all elements connected to source
Parasitic: some elements not connected to source
They re-radiate power from other elements

46. Broadside Array Bidirectional Array
Uses Dipoles fed in phase and separated by 1/2 wavelength

48. End-Fire Array
Similar to broadside array except dipoles are fed 180 degrees out of phase
Radiation max. off the ends

50. Log-Periodic Dipole Array
Multiple driven elements (dipoles) of varying lengths
Phased array
Unidirectional end-fire
Noted for wide bandwidth
Often used for TV antennas

52. 4.6 Helical Antennas
Diameter of ground plane at least 3λ/4

53. Helical Antennas (Cont’d..)

55. The Helical Antenna
Several types of antennas are classified as helical
The antenna in the sketch has its maximum radiation along its long axis
A quarter-wave monopole can be shortened and wound into a helix— common in rubber ducky antenna used with many handheld transceivers

56. Loop Antennas
Sometimes, smaller antennas are required for certain applications, like AM radio receivers
These antennas are not very efficient but perform adequately
Two types of loop antennas are:
Air-wound loops
Ferrite-core loopsticks

58. Discone Antennas