ANTENNA AND WAVE PROPAGATION

1. EC6602 ANTENNA AND WAVE
PROPAGATION
M.KRISHNAMOORTHY
Asst.Professor/ECE
GOJAN SCHOOL OF BUSINESS AND
TECHNOLOGY

2. UNIT-I
Electromagnetic Radiation And
Antenna Fundamentals
2

3. Antenna: Linkage Between Circuits and Fields
• Steady-state time-varying signals (e.g., RF CW)
• Transient signals (e.g. Electromagnetic pulses)
• Knowledge of basic RF concepts needed.
3
Circuits Fields
V, I, Z, P E, H,h, S
Antenna

4. Electromagnetic Spectrum
4
• The Electromagnetic Spectrum covers a very wide range of frequency,
from almost DC to gamma rays.
• Radio frequency (RF) is a subset of the EM spectrum and is loosely
defined as:
“The frequency in the portion of the electromagnetic spectrum that is
between the audio-frequency portion and the infrared portion. The present
practical limits of radio frequency are roughly 10 kHz to 100 GHz.” [IEEE
Std 100-1988 Standard Dictionary of Electrical and Electronic Terms]
• EM (Electromagnetic) waves can propagate in vacuum but not acoustic
waves.

5. 5
Frequency – Wavelength Relationship
• The wavelength l of an electromagnetic wave is related to its frequency f
by:
• Conveniently in practice, we can quickly estimate the wavelength of a
frequency given in MHz or GHz by:
f
c
=l where c = 3x108 m/s (speed of light in vacuum)
)m(
fMHz
300
=l
)mm(
fGHz
300
=l
5
e.g., l of 100 MHz is 3 m.
e.g., l of 10 GHz is 30 mm.

6. what is an antenna ?
(everything can radiate)
- antenna is a filter in frequency
and spatial domain

7. Antenna as an Interface/Transducer
Antennas are conducting or dielectric structures that allow efficient launching or
radiating of electromagnetic waves into space. (Theoretically, any structure can
radiate EM waves but not all structures can do it efficiently.)
An antenna can be viewed as a transducer between a transmission line (or
directly from an electrical or electronic circuit) and the surrounding medium. It
can be used for either transmitting or receiving.
7
RF Generator
(including
Transmission Line)
EM wave
radiating
into space
Antenna
wave front of EM
wave

8. Hertzian Dipole
• A Hertzian Dipole is an infinitesimal current element Idl (i.e.,
current I flowing in a conductor dl long). The current I is
assumed to be constant along the whole length of dl.
• Such a current element does not exist in real life in isolation.
• It forms the basic building block of a practical antenna – e.g. a
dipole is made up of many of these current elements connected
together end to end, each with a different current I.
8
~
I
dl

10. Reciprocity

16. The principles of radiation of electromagnetic energy are
based on two laws:
1. A MOVING ELECTRIC FIELD CREATES A MAGNETIC (H)
FIELD.
2. A MOVING MAGNETIC FIELD CREATES AN ELECTRIC (E)
FIELD.
In space, these two fields will be in phase and perpendicular
to each other at any given point
Charge in Motion Gives Rise to a Magnetic Field the
magnitude of the resulting magnetic field depends
upon the velocity of the charge and the amount of
charge

21. Choosing Antennas
• Frequency – Dictates size
• Mounting location – Base or mobile
• Omni or directional – Coverage or gain
• Polarization – Horizontal, vertical, circular
• Resonant or non-resonant – Tuner required?
• Power available
• Feedline length and type
• Cost

22. Radiation Pattern

23. Radiation Pattern

24. Radiation Pattern

25. Radiation Pattern

26. Radiation Pattern

28. Radiation Pattern

29. Radiation Pattern

30. Radiation Pattern

31. Radiation Pattern

32. Radiation Intensity

33. Solid Angle and Steradian

34. Solid Angle and Steradian

35. Directive Gain and Directivity

36. Directive Gain and Directivity

37. Power Gain

38. E.I.R.P

39. Efficiency

40. Radiation Resistance

41. Effective Area

42. Bandwidth

43. Polarization

44. Plane wavefront
E
H
ˆn
nHE ˆ⊥⊥
E
Hˆn
Plane waves are TEM waves.
(Transverse ElectroMagnetic)
Plane Electromagnetic Waves

45. POLARIZATION

49. Polarization
Polarization is a description of how the direction of the electric field vector changes
with time at a fixed point in space. If the wave is propagating in the positive z-
direction, the electric field vector at a fixed point, say z=0, can be expressed in the
following general form:
Then, the polarization can be categorized using the two real
quantities A and .
( ) ( ) ( ) ++== tAEatEatzE yx cosˆcosˆ,0 00

50. Polarization
If the locus of the tip of the E-field is a straight line, linear polarization.
Circular locus → Circular polarization.
Elliptical locus → Elliptical polarization.
The polarization is called right-handed, if the fingers of the right hand follow the
direction of rotation of the E-vector while the thumb points in the direction of
propagation. Otherwise, left-handed.
Linear Circular Elliptical

51. Friis Transmission Equation

52. Radiation Theory

57. Infinitesimal Dipole

58. Radian Distance
and Radian Sphere

60. The E- and H-fields for the infinitesimal dipole, as
represented by equations derived and shown in previous
slide are valid everywhere (except on the source itself).
At a distance r = λ/2π (or kr = 1), which is referred to as the
radian distance, the magnitude of the first and second
terms within the brackets of
are same.

62. Also at the radian distance the
magnitude of all three terms within the
brackets of
is identical; the only term that
contributes to the total field is the
second, because the first and third
terms cancel each other. This is
illustrated in Figure in the following
slides

63. At distances less than the radian distance r < λ/2π (kr <1), the magnitude of the second
term within the brackets of
is greater than the first term and begins to dominate as r <λ/2π.
For
and r < λ/2π, the magnitude of the third term within the brackets is greater than the
magnitude of the first and second terms while the magnitude of the second term is
greater than that of the first one; each of these terms begins to dominate as r < λ/2π.

64. Magnitude variation, as a function of the radial distance, of the
field terms radiated by an infinitesimal dipole.
This is illustrated in this Figure .
The region r < λ/2π (kr <1) is
referred to as the near-field
region, and the energy in that
region is basicallyimaginary
(stored).

65. Magnitude variation, as a function of the radial distance, of the
field terms radiated by an infinitesimal dipole.
At distances greater than the radian distance r >
λ/2π (kr >1), the first term within the brackets
is greater than the magnitude of the second
term and begins to dominate as r> λ/2π (kr >
1). For
and r > λ/2π, the first term withinthe brackets
is greater than the magnitude of the second
and third terms while the magnitude of the
second term is greater than that of the third;
each of these terms begins to dominate as
r >> λ/ 2π. This is illustrated inFigure . The
region r > λ/2π (kr >1) is referred to as the
intermediate-field regionwhile that forr>> λ/2π
(kr >> 1) is referred to as the far-field region,
and the energy in that region is basically real
(radiated).

66. Magnitude variation, as a function of the radial distance, of the
field terms radiated by an infinitesimal dipole.
The sphere with radius equal to the radiandistan ce
(r = λ/2π) is referred as the radian sphere, and it
defines the region within which the reactive power
density is greater than the radiated power density .
For an antenna, the radian sphere represents the
volume occupied mainly by the stored energy of the
antenna’s electric and magnetic fields. Outside the
radian sphere the radiated power density is greater
than the reactive power density and begins to
dominate as r > λ/2π. Therefore the radian sphere
can be used as a reference, and it defines the
transition between stored energy pulsating
primarily in the ±θ direction and energy radiating in
the radial (r) direction [represented by the first term
the second term represents stored energy pulsating
inwardly and outwardly in the radial (r) direction].
Similar behavior, where the power density near the
antenna is primarily reactive and far away is
primarily real, is exhibited by all antennas, although
not exactly at the radiandistance.

67. Near-Field (kr << 1) Region

68. An inspection of
reveals that for kr << λ or r <<λ/2π they can be reduced in much simpler form and can
be approximated by
The E-field components, Er and Eθ , are intime-phase but they are intime-phase
quadrature with the H-field component Hφ; therefore there is no time-average
power flow associated with them. The condition of kr << 1 can be satisfied at moderate
distances away from the antenna provided that the frequency of operation is very low.

69. Intermediate-Field (kr > 1) Region

70. As the values of kr begin to increase and become greater than unity, the terms
that were dominant for kr << 1 become smaller and eventually vanish.
For moderate values of kr the E-field components lose their in-phase
condition and approach time-phase quadrature. Since their magnitude is not
the same, in general, they form a rotating vector whose extremity traces an
ellipse.
At intermediate values of kr, the Eθ and Hφ components approach time-phase,
which is an indication of the formation of time-average power flow in the
outward (radial) direction (radiation phenomenon).
As the values of kr become moderate (kr > 1), the field expressions can be
approximated againbut ina different form.

71. In con trast to the region where kr << 1, the first term within the brackets in
becomes more dominant and the second term can be neglected.

72. Far-Field (kr >>1) Region

73. The ratio of Eθ to Hφ is equal to
Where Zw = wave impedance
η = intrinsic impedance (377 120π ohms for free-space)
The E- an dH-field components are perpendicular to each
other, transverse to the radial direction of propagation, and
the r variations are separable from those of θ and φ. The
shape of the pattern is not a function of the radial distance
r, and the fields form a T ransverse ElectroMagnetic (TEM)
wave whose wave impedance is equal to the intrinsic
impedance of the medium

74. Directivity

75. The average power density radiated by the dipole is
Integrating the above equation over a closed sphere of radius r reduces it to .
Associated with the average power density is the radiation intensity U which
is given by
The maximum value occurs at θ = π/2 and it is equal to
So the the directivity is
the maximum effective aperture is

76. Radiation Resistance :Exercise to u

77. Dual Equations for Electric (J) and Magnetic (M) Current Sources

78. Dual Quantities for Electric (J) and Magnetic (M) Current Sources

79. Antennas for Mobile
Communication Systems

80. ➢The dipole and monopole are two of the most widely used
antennas for wireless mobile communication systems
➢An array of dipole elements is extensively used as an
antenna at the base station of a land mobile system
➢The monopole, because of its broadband characteristics
and simple construction, is perhaps to most common
antenna element for portable equipment, such as cellular
telephones, cordless telephones, automobiles, trains, etc.
➢An alternative to the monopole for the handheld unit is the
loop.Other elements include the inverted F, planar inverted F
antenna (PIFA), microstrip (patch), spiral, etc…

81. TYPICAL ANTENNA PROBLEMS
• Radio Interference to nearby devices.
• Transmission line radiation.
• The above are due to “common mode
currents” on the transmission line.
• Loss of power to antenna due to mismatch
between coax and antenna.
• BALUNS can address these problems.

82. BALUN – A Coined Word
• Balun formed from BALance – UNbalance.
• Name suggest device converts between
“Balance <> Unbalance”.
• BALUN is name of device that can be many
things like a common mode choke, unbalance
to balance transformer, and a step up or down
transformer.

83. A Typical BALUN

84. What is a balun?
• A Balun is special type of transformer that performs
two functions:
– Impedance transformation
– Balanced to unbalanced transformation
• The word balun is a contraction of “balanced to
unbalanced transformer”

85. Why do we need a balun?
• Baluns are important because many types of antennas
(dipoles, yagis, loops) are balanced loads, which are fed with
an unbalanced transmission line (coax).
• Baluns are required for proper connection of parallel line to a
transceiver with a 50 ohm unbalanced output
• The antenna’s radiation pattern changes if the currents in the
driven element of a balanced antenna are not equal and
opposite.
• Baluns prevent unwanted RF currents from flowing in the
“third” conductor of a coaxial cable.

86. Gain/Loss Calculations
• ERP (Effective Radiated Power) is the real
number to consider
• Gain uses a Log-10 scale
▪ 3dB = 2-fold improvement
▪ 6dB = 4-fold improvement
▪ 10dB = 10-fold improvement
▪ 20dB = 100-fold improvement
• ERP=Power x (Gain - Feedline Loss)

87. Antenna Design Considerations
• Gain, SWR, Bandwidth, Front/Back ratio are
related and optimum values are not achieved
simultaneously for each
• Does antenna have power going in desired
direction? Gain/Beamwidth

88. EIRP and ERP
• EIRP = effective isotropic radiated power
– Equal to the amount of power that would have to
be applied to an isotropic radiator to give the
same power density at a given point
• ERP = effective radiated power
– Equal to the amount of power that would have to
be applied to a half-wave dipole, oriented in
direction of maximum gain, to give the same
power density at a given point

89. EIRP/ERP Conversion
• EIRP = ERP + 2.14 dB
• EIRP is used in all our equations
• Sometimes government regulations specify
ERP for transmitting installations
• Conversion is easy (see above)