Antennas and PropagationReview/Recap

Lecture 17

Overview

2

Antenna Functions Isotropic Antenna Radiation Pattern Parabolic Reflective Antenna Antenna Gain Signal Loss in Satellite Communication Noise Types Refraction Fading Diffraction and Scattering Fast and Slow Fading Flat and Selective Fading Diversity Techniques ……

Review Question: Antenna Functionality

Q:- What two functions are performed by an antenna?

3

Antenna Definition An antenna is defined as

usually a metallic device (as a rod or wire) for radiating or receiving radio waves.

The IEEE Standard Definitions of Antenna defines the antenna or aerial as “a means for radiating or receiving radio waves.” In other words the antenna is the transitional structure between free-space and a guiding device, as shown in Figure 4

Why Antennas of Different Shapes

In addition to receiving or transmitting energy, an antenna in an advanced wireless system is usually required to optimize or accentuate the radiation energy in some directions and suppress it in others.

Thus the antenna must also serve as a directional device in addition to a probing device.

It must then take various forms to meet the particular need at hand, and it may be a piece of conducting wire, an aperture, a patch, an assembly of elements (array), a reflector, a lens, and so forth.

For wireless communication systems, the antenna is one of the most critical components. A good design of the antenna can relax system requirements and improve overall system performance.

The antenna serves to a communication system the same purpose that eyes and eyeglasses serve to a human 5

Basic Antenna Functions As Antenna resides between cable/waveguide and the

medium air, the main function of antenna is to match impedance of the medium with the cable/waveguide impedance. Hence antenna is impedance transforming device.

The second and most important function of antenna is to radiate the energy in the desired direction and suppress in the unwanted direction. This basically is the radiation pattern of the antenna. This radiation pattern is different for different types of antennas.

6

7

The Role of Antennas Antennas serve four primary functions Spatial filter

directionally-dependent sensitivity Polarization filter

polarization-dependent sensitivity Impedance transformer

transition between free space and transmission line Propagation mode adapter

from free-space fields to guided waves (e.g., transmission line, waveguide)

8

Spatial filter Antennas have the property of being more sensitive in one

direction than in another which provides the ability to spatially filter signals from its environment.

Directive antenna.Radiation pattern of directive antenna.

9

Polarization filter

Dipole antenna

Incident E-field vector

z

xy

0EzE V = h E0

+_

EhV

hzh

Incident E-field vector

0EyE

z

xy

V = 0+_

Dipole antenna

EhV

hzh

Antennas have the property of being more sensitive to one polarization than another which provides the ability to filter signals based on its polarization.

In this example, h is the antenna’s effective height whose units are expressed in meters. 10

Impedance transformer Intrinsic impedance of

free-space, E/H

Characteristic impedance of transmission line, V/I

A typical value for Z0 is 50 .

Clearly there is an impedance mismatch that must be addressed by the antenna.

7.376

120000

11

Propagation Mode Adapter

In free space the waves spherically expand following Huygens principle: each point of an advancing wave front is in fact the center of a fresh disturbance and the source of a new train of waves.

Within the sensor, the waves are guided within a transmission line or waveguide that restricts propagation to one axis.

12

Propagation Mode Adapter During both transmission and receive operations the

antenna must provide the transition between these two propagation modes.

13

14

Antenna purpose Transformation of a guided EM

wave in transmission line (waveguide) into a freely propagating EM wave in space (or vice versa) with specified directional characteristics

Transformation from time-function in one-dimensional space into time-function in three dimensional space

The specific form of the radiated wave is defined by the antenna structure and the environment

Space wave

Guided wave

15

Antenna functions Transmission line

Power transport medium - must avoid power reflections, otherwise use matching devices

Radiator Must radiate efficiently – must be of a size

comparable with the half-wavelength Resonator

Unavoidable - for broadband applications resonances must be attenuated

Ans:- Two functions of an antenna are: For transmission of a signal, radio frequency electrical energy from the transmitter is converted into electromagnetic energy by the antenna and radiated into the surrounding environment (atmosphere, space, water); For reception of a signal, electromagnetic energy impinging on the antenna is converted into radio-frequency electrical energy and fed into the receiver. 16

Q:- What two functions are performed by an antenna?

Review Question: Antenna Functionality

17

Isotropic AntennaQ:- What is an isotropic antenna?

18

Isotropic Antenna Isotropic antenna or isotropic

radiator is a hypothetical (not physically realizable) concept, used as a useful reference to describe real antennas.

Isotropic antenna radiates equally in all directions.

Its radiation pattern is represented by a sphere whose center coincides with the location of the isotropic radiator.

19

Reference Antenna for Gain Gain is Measured Specific to a Reference Antenna isotropic antenna often used - gain over isotropic

Isotropic antenna – radiates power ideally in all directions Gain measured in dBi Test antenna’s field strength relative to reference isotropic

antenna at same power, distance, and angle -Isotropic antenna cannot be practically realized

e.g. A lamp is similar to an isotropic antenna

20

Isotropic

21

22

An Isotropic Source: Gain Every real antenna radiates more

energy in some directions than in others (i.e. has directional properties)

Idealized example of directional antenna: the radiated energy is concentrated in the yellow region (cone).

Directive antenna gain: the power flux density is increased by (roughly) the inverse ratio of the yellow area and the total surface of the isotropic sphere

Gain in the field intensity may also be considered - it is equal to the square root of the power gain.

Isotropic sphere

23

Antenna Gain Measurement

Antenna Gain = (P/Po) S=S0

Actual antenna

P = Power delivered to the actual antenna

S = Power received

(the same in both steps)

Measuring equipment

Step 2: substitution

Reference antenna

Po = Power delivered to

the reference antenna

S0 = Power received

(the same in both steps)

Measuring equipment

Step 1: reference

Isotropic AntennaQ:- What is an isotropic antenna?

Ans:- An isotropic antenna is a point in space that radiates power in all directions equally. 24

Isotropic sphere

25

Review: Radiation PatternQ:- What information is available from a radiation pattern?

26

Radiation Pattern In the field of antenna design the term radiation pattern (or antenna

pattern or far-field pattern) refers to the directional (angular) dependence of the strength of the radio waves from the antenna or other source.

Particularly in the fields of fiber optics, lasers, and integrated optics, the term radiation pattern may also be used as a synonym for the near-field pattern or Fresnel pattern. This refers to the positional dependence of the electromagnetic field in the near-field, or Fresnel region of the source. The near-field pattern is most commonly defined over a plane placed in front of the source, or over a cylindrical or spherical surface enclosing it.

The far-field pattern of an antenna may be determined experimentally at an antenna range, or alternatively, the near-field pattern may be found using a near-field scanner, and the radiation pattern deduced from it by computation. The far-field radiation pattern can also be calculated from the antenna shape by computer programs such as NEC. Other software, like HFSS can also compute the near field.

27

Antenna Radiation Pattern Radiation pattern

Graphical representation of radiation properties of an antenna Depicted as two-dimensional cross section

The radiation pattern of an antenna is a plot of the far-field radiation from the antenna. More specifically, it is a plot of the power radiated from an antenna per unit solid angle, or its radiation intensity U [watts per unit solid angle]. This is arrived at by simply multiplying the power density at a given distance by the square of the distance r, where the power density S [watts per square metre] is given by the magnitude of the time-averaged Poynting vector:

U=r²S28

29

Radiation pattern The radiation pattern of antenna is a representation (pictorial or

mathematical) of the distribution of the power out-flowing (radiated) from the antenna (in the case of transmitting antenna), or inflowing (received) to the antenna (in the case of receiving antenna) as a function of direction angles from the antenna

Antenna radiation pattern (antenna pattern): is defined for large distances from the antenna, where the spatial (angular) distribution

of the radiated power does not depend on the distance from the radiation source is independent on the power flow direction: it is the same when the antenna is used to

transmit and when it is used to receive radio waves is usually different for different frequencies and different polarizations of radio wave

radiated/ received

30

Power Pattern Vs. Field pattern

The power pattern is the measured (calculated) and plotted received power: |P(θ, ϕ)| at a constant (large) distance from the antenna

The amplitude field pattern is the measured (calculated) and plotted electric (magnetic) field intensity, |E(θ, ϕ)| or |H(θ, ϕ)| at a constant (large) distance from the antenna

Power or field-strength meter

Antenna under test

Turntable

Generator

Auxiliaryantenna

Large distance

• The power pattern and the field patterns are inter-related:P(θ, ϕ) = (1/)*|E(θ, ϕ)|2 = *|H(θ, ϕ)|2

P = powerE = electrical field component vectorH = magnetic field component vector = 377 ohm (free-space, plane wave

impedance)

31

Normalized pattern Usually, the pattern describes the normalized field

(power) values with respect to the maximum value. Note: The power pattern and the amplitude field pattern are

the same when computed and when plotted in dB.

32

3-D pattern Antenna radiation

pattern is 3-dimensional

The 3-D plot of antenna pattern assumes both angles θ and ϕ varying, which is difficult to produce and to interpret

3-D pattern

33

2-D pattern

Two 2-D patterns

Usually the antenna pattern is presented as a 2-D plot, with only one of the direction angles, θ or ϕ varies

It is an intersection of the 3-D one with a given plane

usually it is a θ = const plane or a ϕ= const plane that contains the pattern’s maximum

34

Example: a short dipole on z-axis

35

Principal Patterns Principal patterns are the 2-D patterns of

linearly polarized antennas, measured in 2 planes

1. the E-plane: a plane parallel to the E vector and containing the direction of maximum radiation, and

2. the H-plane: a plane parallel to the H vector, orthogonal to the E-plane, and containing the direction of maximum radiation

36

Example

37

Antenna Mask (Example 1)Typical relative directivity- mask of receiving antenna (Yagi ant., TV dcm waves)

-20

-15

-10

-5

0

-180

-120 -6

0 0

60

120

180

Azimith angle, degrees

Rel

ativ

e g

ain

, dB

38

Antenna Mask (Example 2)

-50

-40

-30

-20

-10

0

0.1 1 10 100

Phi/Phi0

Re

lati

ve g

ain

(d

B)

RR/1998 APS30 Fig.9

COPOLAR

CROSSPOLAR

Reference pattern for co-polar and cross-polar components for satellite transmitting antennas in Regions 1 and 3 (Broadcasting ~12 GHz)

0dB

-3dBPhi

Review: Radiation PatternQ:- What information is available from a radiation pattern?

Radiation Patterns in Polar and Cartesian Coordinates Showing Various Types of Lobes

Ans:- A radiation pattern is a graphical representation of the radiation properties of an antenna as a function of space coordinates. 39

40

Parabolic Reflective AntennaQ:- What is the advantage of a parabolic reflective antenna?

41

Two Main Purposes of Antenna

Impedance matching: matches impedance of transmission line to the intrinsic impedance of free space to prevent wanted reflection back to source.

Antenna must be designed to direct the radiation in the desired direction.

So a parabolic antenna is a high gain reflector antenna. It is used for television,

radio and data communications. It may also be used for radar on the UHF and SHF sections of the electromagnetic spectrum.

42

Reflector Antenna Reflector antenna such as parabolic antenna are

composed of primary radiator and a reflective mirror.

43

Parabolic Reflector Antenna

Any electromagnetic wave incident upon the paraboloid surface will be directed to the focal point.

Primary antenna is used at the focal point of the parabolic reflector antenna instead of isotropic antenna. The isotropic antenna would radiate and receive radiation from all directions resulting in spillover.

Primary antenna should be designed to “illuminate” just the reflector uniformly.

44

Loss

45

Characteristics Aperture: r= radius of the diameter Larger dish has more gain than smaller Clear line of sight is important

2^rA

46

Calculations Physical area:

D= Diameter Effective area:

= illumination efficiency Wavelength:

Gain:

3db beamwidth:

4

2^DAp

ApiAe *

f

c

2^

4

Ae

Gi

DegreesD

dB 703

47

Half Power BeamwidthThe half power graph showing the angle between the half power point on either side of maximum

48

Radiation Pattern for Parabolic Antenna

49

Advantage of a Parabolic Antenna

The advantage of a parabolic antenna is that it can be used as primary mirror for all the frequencies in the project, provided the surface is within the tolerance limit; only the feed antenna and the receiver need to be changed when the observing frequency is changed.

An advantage of such a design is the small irradiation loss, which allows for an optimum antenna gain.

It is an advantage of such an arrangement that the exciter system and/or the exciter 3 are/is protectively located within the parabola or the parabolic reflector.

Parabolic antenna is the most efficient type of a directional antenna - large front/back ratio, sharp radiation angle and small side lobes. It fits well for noisy locations where other antennas factually do not work.

The antenna's Gain is adequate to the area of the reflector. The reflector can be central-focused(the focus is in the center of the dish) or offset (the focus is off the axis of the dish).

In general, they serve for connection of end users (so-called last mile) to a wireless network. However, in areas with lower intensity of Wi-Fi networks, they can be successfully used also for back-bone links. In fact, this frequency is used for connections up to maximum 10 km

50

Parabolic Reflective AntennaQ:- What is the advantage of a parabolic reflective antenna?

A parabolic antenna creates, in theory, a parallel beam without dispersion. In practice, there will be some beam spread. Nevertheless, it produces a highly focused, directional beam. 51

52

Antenna GainQ:- What factors determine antenna gain?

53

Antenna Gain

Antenna Gain (Directivity) Power output, in a particular direction, compared to that produced in any

direction by a perfect omnidirectional antenna [usual reference is an isotropic antenna (dBi) but sometimes a simple ½ antenna is a more practical reference; good sales trick to use an isotropic reference when a dipole is inferred resulting in a 1.64 power gain]

Antenna gain doesn’t increase power; only concentrates effective radiation pattern

Effective area (related to antenna aperture) Expressed in terms of effective area Related to physical size and shape of antenna related to the operational

wavelength of the antenna

Change in coverage by focusing the area of RF propagation

54

Passive Gain Focusing isotropic energy in a specific pattern Created by the design of the antenna

Uses the magnify glass concept

55

Passive Gain… Antennas use passive gain

Total amount of energy emitted by antenna doesn’t increase – only the distribution of energy around the antenna

Antenna is designed to focus more energy in a specific direction Passive gain is always a function of the antenna (i.e.

independent of the components leading up to the antenna

56

Passive Gain… Advantage…

Does not require external power Disadvantage…

As the gain increases, its coverage becomes more focused Highest-gain antennas can’t be used for mobile users because

of their tight beam

57

Active Gain Providing an external power source

Amplifier High gain transmitters

Active gain involves an amplifier

58

Antenna Gain Relationship between antenna gain and effective area

G = antenna gain Ae = effective area f = carrier frequency c = speed of light (≈ 3 x 108 m/s) = carrier wavelength

59

Antenna gain Antenna gain is increased by focusing the antenna

The antenna does not create energy, so a higher gain in one direction must mean a lower gain in another.

Note: antenna gain is based on the maximum gain, not the average over a region. This maximum may only be achieved only if the antenna is carefully aimed.

This antenna is narrower and results in 3dB higher gain than the dipole, hence, 3dBD or 5.14dBi

This antenna is narrower and results in 9dB higher gain than the dipole, hence, 9dBD or 11.14dBi

60

Antenna gainInstead of the energy going in all horizontal directions, a reflector can be placed so it only goes in one direction => another 3dB of gain, 3dBD or 5.14dBi

Further focusing on a sector results in more gain.A uniform 3 sector antenna system would give 4.77 dB more.A 10 degree “range” 15dB more.The actual gain is a bit higher since the peak is higher than the average over the “range.”

Mobile phone base stations claim a gain of 18dBi with three sector antenna system. • 4.77dB from 3 sectors – 13.33 dBi• An 11dBi antenna has a very narrow range.

61

Antenna GainThe power gain G, or simply the gain, of an antenna is the ratio of its radiation intensity to that of an isotropic antenna radiating the same total power as accepted by the real antenna. When antenna manufacturers specify simply the gain of an antenna they are usually referring to the maximum value of G.

62

Antenna gain and effective areas

Type of antenna Effective area Power gain

Isotropic 2/4ג 1

Infinitesimal dipole or loop

1.52/4 1.5

Half-wave dipole 1.642/4 1.64

Horn, mouth area A 0.81A 10A/ 2

Parabolic, face area A 0.56A 7A/ 2

turnstile 1.152/4 1.1563

Antenna GainQ:- What factors determine antenna gain?

Ans:- Effective area and wavelength

64

65

Satellite CommunicationQ:- What is the primary cause of signal loss in satellite communications?

66

Basics: How do Satellites Work

Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means.

The two stations can use a satellite as a relay station for their communication

One Earth Station sends a transmission to the satellite. This is called a Uplink.

The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink.

67

Basics: Advantages of Satellites

The advantages of satellite communication over terrestrial communication are:

The coverage area of a satellite greatly exceeds that of a terrestrial system.

Transmission cost of a satellite is independent of the distance from the center of the coverage area.

Satellite to Satellite communication is very precise. Higher Bandwidths are available for use.

68

Basics: Disadvantages of Satellites

The disadvantages of satellite communication: Launching satellites into orbit is costly. Satellite bandwidth is gradually becoming used up. There is a larger propagation delay in satellite communication

than in terrestrial communication.

69

Basics: Factors in Satellite Communication

Elevation Angle: The angle of the horizontal of the earth surface to the center line of the satellite transmission beam.

This effects the satellites coverage area. Ideally, you want a elevation angle of 0 degrees, so the transmission beam reaches the horizon visible to the satellite in all directions.

However, because of environmental factors like objects blocking the transmission, atmospheric attenuation, and the earth electrical background noise, there is a minimum elevation angle of earth stations.

70

Basics: Factors in satellite communication ….

Coverage Angle: A measure of the portion of the earth surface visible to a satellite taking the minimum elevation angle into account.

R/(R+h) = sin(π/2 - β - θ)/sin(θ + π/2) = cos(β + θ)/cos(θ) R = 6370 km (earth’s radius) h = satellite orbit height β = coverage angle θ = minimum elevation angle

71

Basics: Factors in satellite communication….

Other impairments to satellite communication: The distance between an earth station and a satellite (free

space loss). Satellite Footprint: The satellite transmission’s strength is

strongest in the center of the transmission, and decreases farther from the center as free space loss increases.

Atmospheric Attenuation caused by air and water can impair the transmission. It is particularly bad during rain and fog.

72

Atmospheric Losses Different types of atmospheric losses can disturb radio

wave transmission in satellite systems: Atmospheric absorption Atmospheric attenuation Traveling ionospheric disturbances

73

Atmospheric Absorption Energy absorption by atmospheric

gases, which varies with the frequency of the radio waves.

Two absorption peaks are observed (for 90º elevation angle):

22.3 GHz from resonance absorption in water vapour (H2O)

60 GHz from resonance absorption in oxygen (O2)

For other elevation angles: [AA] = [AA]90 cosec

Source: Satellite Communications, Dennis Roddy, McGraw-Hill 74

Atmospheric Attenuation Rain is the main cause of atmospheric attenuation (hail,

ice and snow have little effect on attenuation because of their low water content).

Total attenuation from rain can be determined by: A = L [dB] where [dB/km] is called the specific attenuation, and can be

calculated from specific attenuation coefficients in tabular form that can be found in a number of publications

where L [km] is the effective path length of the signal through the rain; note that this differs from the geometric path length due to fluctuations in the rain density.

75

Traveling Ionospheric Disturbances

Traveling ionospheric disturbances are clouds of electrons in the ionosphere that provoke radio signal fluctuations which can only be determined on a statistical basis.

The disturbances of major concern are: Scintillation; Polarisation rotation.

Scintillations are variations in the amplitude, phase, polarisation, or angle of arrival of radio waves, caused by irregularities in the ionosphere which change over time.

The main effect of scintillations is fading of the signal. 76

Satellite CommunicationQ:- What is the primary cause of signal loss in satellite communications?

Ans:- Free space loss. 77

78

ImpairmentsQ:- Name and briefly define four types of noise.

79

Transmission Impairments Signal received may differ from signal transmitted

causing: Analog - degradation of signal quality Digital - bit errors

Most significant impairments are Attenuation and attenuation distortion Delay distortion Noise

80

Noise Signal strength falls off with distance over any transmission

medium Varies with frequency

81

Categories of Noise

82

Categories of Noise

Crosstalk: a signal from one line is

picked up by another can occur by electrical

coupling between nearby twisted pairs or when microwave antennas pick up unwanted signals

Impulse Noise: caused by external

electromagnetic interferences

noncontinuous, consisting of irregular pulses or spikes

short duration and high amplitude

minor annoyance for analog signals but a major source of error in digital data

83

Noise Thermal noise due to thermal agitation of electrons. Present in all electronic devices and transmission

media. As a function of temperature. Uniformly distributed across the frequency spectrum,

hence often referred as white noise. Cannot be eliminated – places an upper bound on the

communication system performance. Can cause erroneous to the transmitted digital data

bits.

84

Noise: Noise on Digital Data

Error in bits 85

Thermal Noise The noise power density (amount of thermal noise to be

found in a bandwidth of 1Hz in any device or conductor) is:

W/Hz k0 TN N0 = noise power density in watts per 1 Hz of bandwidthk = Boltzmann's constant = 1.3803 10-23 J/KT = temperature, in kelvins (absolute temperature)

0oC = 273 Kelvin86

Thermal Noise Noise is assumed to be independent of frequency Thermal noise present in a bandwidth of B Hertz (in

watts):

or, in decibel-watts (dBW),

BTN log10 log 10k log10 BT log10 log 10dBW 6.228

TBN k

87

Noise Terminology Intermodulation noise – occurs if signals with different

frequencies share the same medium Interference caused by a signal produced at a frequency that is

the sum or difference of original frequencies Crosstalk – unwanted coupling between signal paths Impulse noise – irregular pulses or noise spikes

Short duration and of relatively high amplitude Caused by external electromagnetic disturbances, or faults and

flaws in the communications system

88

89

ImpairmentsQ:- Name and briefly define four types of noise.

Ans:- Thermal noise is due to thermal agitation of electrons. Intermodulation noise produces signals at a frequency that is the sum or difference of the two original frequencies or multiples of those frequencies. Crosstalk is the unwanted coupling between signal paths. Impulse noise is noncontinuous, consisting of irregular pulses or noise spikes of short duration and of relatively high amplitude. 90

91

Refraction?Q:- What is refraction?

92

Law of refraction

A refracted ray lies in the plane of incidence and has an angle θ2 of refraction that is related to the angle of incidence θ1 by:

the symbols n1   and n2    are dimensionless constant, called the index of refraction

ii

cn

v

93

Refraction

94

Refraction occurs when an RF signal changes speed and is bent while moving between media of different densities.

Refraction

95

Refraction?Q:- What is refraction?

Ans:- Refraction is the bending of a radio beam caused by changes in the speed of propagation at a point of change in the medium 96

FadingQ:- What is fading?

97

Fading in a Mobile Environment The term fading refers to the time variation of received

signal power caused by changes in the transmission medium or paths.

Atmospheric condition, such as rainfall The relative location of various obstacles changes over

time

98

Types of Fading Fast fading Slow fading Flat fading Selective fading Rayleigh fading Rician fading

99

Fading in the Mobile Environment

Fading: time variation of received signal power due to changes in the transmission medium or path(s)

Kinds of fading: Fast fading Slow fading Flat fading independent from frequency Selective fading frequency-dependent Rayleigh fading no dominant path Rician fading Line Of Sight (LOS) is dominating +

presence of indirect multipath signals

100

FadingQ:- What is fading?

Ans:- The term fading refers to the time variation of received signal power caused by changes in the transmission medium or path(s). 101

102

Q:- What is the difference between diffraction and scattering?

103

Diffraction

104

Diffraction is a change in the direction and/or intensity of a wave as it passes by the edge of an obstacle.

Diffraction occurs because the RF signal slows down as it encounters the obstacle and causes the wave front to change directions

Diffraction is often caused by buildings, small hills, and other larger objects in the path of the propagating RF signal.

Diffraction Diffraction - occurs at the edge of an impenetrable body

that is large compared to wavelength of radio wave

105

Scattering

106

Scattering happens when an RF signal strikes an uneven surface causing the signal to be scattered. The resulting signals are less significant than the original signal.Scattering = Multiple Reflections

Scattering Scattering – occurs when incoming signal hits an object

whose size in the order of the wavelength of the signal or less.

Irregular objects such as walls with rough surfaces,furniture and vehicles and foliage and the like scatter rays in all the direction in the form of spherical waves.

107

Multipath Propagation

108

Diffraction and ScatteringQ:- What is the difference between diffraction and scattering?

Ans:- Diffraction occurs at the edge of an impenetrable body that is large compared to the wavelength of the radio wave. The edge in effect become a source and waves radiate in different directions from the edge, allowing a beam to bend around an obstacle. If the size of an obstacle is on the order of the wavelength of the signal or less, scattering occurs. An incoming signal is scattered into several weaker outgoing signals in unpredictable directions

109

Summary

110

Antenna Functions Isotropic Antenna Radiation Pattern Parabolic Reflective Antenna Antenna Gain Signal Loss in Satellite Communication Noise Types Refraction Fading Diffraction and Scattering

111

Complimentary Session for Antennas and Propagation (Lecture 17)

112

Antenna Gain (Q)

113

Where

Sol

114

Q

Q:- For each of the antenna types listed in Table above , what is the effective area and gain at a wavelength of 30 mm? Repeat for a wavelength of 3 mm. Assume that the actual area for the horn and parabolic antennas is m2 .

115

Antenna Gain

116

Where

Ans

117

Q:- For each of the antenna types listed in Table above , what is the effective area and gain at a wavelength of 30 mm? Repeat for a wavelength of 3 mm. Assume that the actual area for the horn and parabolic antennas is m2 .

118

Q

119

Question:-

Solution

120

Q

121

Question

122

Thermal Noise

123

Where

Question:-

124

The Expression Eb /N0

in decibel notation,

125

Question:-

126

Q:- It is often more convenient to express distance in km rather than m and frequency in MHz rather than Hz. Rewrite Equation using these dimensions.Solution:- The equations from Text Book are

Solution:-

127

128

QQ:- Suppose a transmitter produces 50 W of power.a.Express the transmit power in units of dBm and dBW.b.If the transmitter's power is applied to a unity gain antenna with a 900-MHz carrier frequency, what is the received power in dBm at a free space distance of 100 m?c.Repeat (b) for a distance of 10 km.d.Repeat (c) but assume a receiver antenna gain of 2.

129

Q/A

a) .

b)

Therefore, received power in dBm = 47 – 71.52 = –24.52 dBm

130

Q:- Suppose a transmitter produces 50 W of power.a.Express the transmit power in units of dBm and dBW.b.If the transmitter's power is applied to a unity gain antenna with a 900-MHz carrier frequency, what is the received power in dBm at a free space distance of 100 m?c.Repeat (b) for a distance of 10 km.d.Repeat (c) but assume a receiver antenna gain of 2.

Q/A

c)

d)

131

Q:- Suppose a transmitter produces 50 W of power.a.Express the transmit power in units of dBm and dBW.b.If the transmitter's power is applied to a unity gain antenna with a 900-MHz carrier frequency, what is the received power in dBm at a free space distance of 100 m?c.Repeat (b) for a distance of 10 km.d.Repeat (c) but assume a receiver antenna gain of 2.

132

Free Space Loss

133

Free Space Loss

134

135

136