Radio communication

Research 01 (P2.1, M1, D1)
1.1 Introduction to Electromagnetic
First I would like explain what a wave is. Wave is a disturbance or oscillation that
travels through space time, accompanied by a transfer of energy. Wave motion
transfers energy from one point to another, often with no permanent displacement of
the particles of the medium. Basically waves can be divided into two categories.
Longitudinal and transverse categories behave in two different ways in moving and
oscillating. Longitudinal waves oscillating parallel way with its energy travel; slinky
is an example for longitudinal waves. But transverse waves are oscillated
perpendicular to its energy flowing direction; water ripples is an example for this
type. Mechanical and Electromagnetic are two main types of waves. Mechanical
Wave needs a medium to be travelled and Electromagnetic Waves do not want any
medium to travel. Mechanical wave may be longitudinal or transverse while
Electromagnetic wave is just transverse.
Electromagnetic wave is a creation of mixing, binding electrical field and a magnetic
field together. In 1873, Scottish scientist James Clerk Maxwell unified the theories of
electricity and magnetism, and eloquently represented their relations through a set of
profound equations best known as “Maxwell’s equations”. Maxwell said, if electricity
flows through a conductor, magnetic field is generated around that conductor
perpendicular to direction of electricity flows. To find the direction of magnetic field
Fleming’s right hand law can be utilized. So, Electrical field and magnetic field is
always perpendicular each other in electromagnetic waves to the direction of flowing.
Electromagnetic wave has some properties such as polarity and electromagnetic
energy. Polarization is a measurement of the electromagnetic field alignment. There
are three main properties of electromagnetic waves as frequency, wavelength and
velocity.

Current direction
(Towards the paper)
Magnetic field (clockwise direction)
Figure 01: Fleming’s right hand law indicating.
This diagram shows that electrical field is always perpendicular to magnetic field.
Electromagnetic waves have different wave lengths.
Figure 02 : electromagnetic wave directions [1]

Figure 03: wave length of a wave.
Wave length is 360 degree (one cycle) change of wave (in phase). Wave length is one
parameter to measure a considered wave. Another parameter was found by Heinrich
Hertz, a German physicist as cycles per one second. Electromagnetic waves have
different wave lengths and frequencies. Because of that, Electromagnetic spectrum
was introduced.
Figure 04: Electromagnetic spectrum with its sizes.[2]

Electromagnetic spectrum consist different waves with different wave lengths and
frequencies. Radio, micro, infrared (I.R), Visible light, U.V, X rays and Gamma are
represent areas of this spectrum. These entire wave has speed of light (3
in free space approximately and that means no need of media to flow. Additionally,
power level (amplitude) of electromagnetic wave is also considered. It needs high
amplitude to transmit far distance. Furthermore considering, phase angle, gain,
attenuation can be taken as properties of an electromagnetic wave. According to
properties, different kind of electromagnetic waves are included in electromagnetic
spectrum.
Radio Waves
According to definition of Radio frequency in a Wireless LAN, High Frequencies
(300 kHz – 300 GHz) electromagnetic waveforms that are passed along a copper
conductor and then radiated into the air via an antenna Radio wave is the first area of
electromagnetic spectrum. Radio waves have lowest frequency and highest
wavelength. Radio wave area can be divided again into certain frequency levels.
Below chart indicates those different areas frequencies, wavelengths and their
applications. According to graph of
Frequency Band Wave length Applications
3- 30 KHz VLF 100 – 10 Km Sonar, fax, Navigation
30 – 300 KHz LF 10 – 1 Km Navigation
0.3 – 3 MHz MF 1 – 0.1 Km AM Broadcasting
3 – 30 MHz HF 100 – 10 m T. phones, fax, CB
30 – 300 MHz VHF 10 -1 m TV, FM Broadcasting
0.3 – 3 GHz UHF 1 – 0.1 m TV, mobile , radar
3 – 30 GHz SHF 100 – 10 mm Radar, satellite, microwave links
30 – 300 GHz EHF 10 – 1 mm Radar, wireless communication
0.3 – 3 THz THF 1 – 0.1 mm THZ imaging
Figure 5: EM spectrum and applications

Microwave
Microwave is the next class of electromagnetic spectrum. This class has higher
frequencies and lower bandwidths compared to radio waves. There is an interference
region in both radio and microwave classes. Above mentioned SHF (Super High
Frequency) and EHF (Extremely High Frequency) in that region. Because of higher
frequency, attenuation is higher there. So can’t travel over large distances without
broadcasting/ distributing centers in near distances compared to radio broadcasting
centers (mobile phone towers). Microwave waves carry higher energy (eV) compared
to radio waves. Microwaves are utilized for mobile communication, Radar
communication. In mobile communication, microwaves are very important. Because
of low wavelength very small antennas are needed. As well as this wave is used at
microwave ovens because of higher energy of these waves.
Infrared
Infrared class has better frequency than microwaves. IR is the abbreviation for
Infrared. Terahertz region is between microwave and infrared classes. Most times,
Infrared waves transfer energy as Heat. Infrared is divided into three parts.
 Far infrared: 300GHz – 30 THz (1mm – 10um).
 Mid infrared: 30THz – 120 THz (10um – 2.5um).
 Near infrared: 120THz – 400THz (10um - 750 nm).
Infrared is used at remote controllers, night vision cameras, weather forecasting.
Night vision cameras are mostly used in military operations, because it indicates
temperature differences by different colors even in dark. Night mode options of usual
cameras are operated by Infrared technology. Usually Infrared is considered as it is
flowing heat. In night vision cameras, infrared is indicating live things from others,
because temperature of blood is identified by infrared.

Figure 08 : Photo of a IR camera
http://www.x20.org/thermal/
Light
This is the most important class, which associated with human eyes. Some other
animal can see other classes such as IR, UV also. Although, Human been only can see
in this light region. Electromagnetic radiation with a wavelength between 380 nm and
760 nm (790–400 terahertz) is detected by the human eye and perceived as visible
light. Our main Light source, sun sends various kinds of waves although visible light
can see us. Visible light can be produced by using Laser, which is used in compact
disks, DVD,CD players and some printers. Visible light is a mixture of some wave
frequencies. Different colors have different frequencies and wavelengths.
Ultraviolet
Ultraviolet is the next class of electromagnetic spectrum. UV is the abbreviation for
ultraviolet. Upper region of UV is more close to light properties. Sun provide UV
rays. UV use to destroy microbes. UV used to clean surgery devices also. UV lamp is
a one made of UV, which do two duties. Provide purple color and attract insects are
them. UV rays are not good for our skin specially, eyes.

X – Rays
X rays have giant energy. Stars emit X rays. upper ranges of UV are also ionized.
Because of very short wavelength and higher energy X rays can go through many
particles. Because of that X rays mainly utilized at medical science to view inside
body. Detecting to X rays long time cause cancers. As well as X rays are used in
security also. Airport bag and passenger checker is one example.
Gamma Rays
Gamma rays discovered by Paul Villard in 1900. These conduct protons with giant
energy. Gamma rays have very small wavelength and can go through many items.
Gamma rays given off by stars and radioactive substances. Gamma rays are utilized to
destroy unwanted cancer cells, which called as radiotherapy. Gamma rays are also
used for the irradiation of food and seed for sterilization.
1.2 Definition for Antenna
An antenna is a device, which is involved in signal broadcasting. According to
Webster’s dictionary, Antenna is defined as “a usually metallic device (as a rod or
wire) for radiating or receiving radio waves.” According to the IEEE standard the
antenna or Arial as” a means for radiating or receiving radio waves.” In other words,
the antenna is a transitional structure between free space and a guiding device.
Usually, Antenna is an isolated device. It associates with Source/ receiver,
Transmission line also. According to Yi Huang, Kevin Boyle (2008), Antenna is a
device which can radiate and receive electromagnetic energy in an efficient and
desired manner. If antenna is transmitting antenna, it consist a source (voltage).
Receiver is replaced source if that is a receiving antenna. Antenna use voltage and

current and produce electromagnetic wave in transmission antenna. In receiving side
opposite tsk is happened. [3]
History of antenna
According to historical reviews, first incident associates with antennas is belongs to
Michel Faraday. He had sent a key to sky by using a kite working as an antenna.
However, the history of antennas dates back to James Clerk Maxwell who unified the
theories of electricity and magnetism and their relationships. In 1873, he proved that
light is electromagnetic and both light and electromagnetic waves travel by wave
disturbances of the same speed. In 1886, Professor Heinrich Rudolph Hertz
demonstrated the first wireless electromagnetic system. He utilized a variable voltage
source, two conducting balls and a dipole ( piece if wire) to check sparks occurring at
both transmitter side and receiver side.He was able to produce in his laboratory at a
wavelength of 4m a spark in the gap of transmitting half of wavelength ( dipole
which, was then detected as a spark in the gap of a nearby loop. That was the first
practical implementation of broadcasting. In 1901, Guglielmo Marconi was able to
send signal over long area from Poldhu in Cornwall to St. John’s Newfoundland in
Canada. That transmitting antenna consisted of fifty vertical wires in the form of a fan
connected to ground through a spark transmitter. By 1940, radio frequency
transmission was further developed UHF (Ultra high frequency). A contributing
factor to this new era was the invention of microwave sources with 1 GHz and above
frequencies. In this time most of antenna elements were wire made such as long wires,
dipoles, rhombuses, fans, helices etc.. And they were used either as single elements or
in arrays. Later, some new concepts were invented to develop and increase radiation
of antenna as whole antennas (open ended wave guides, slots, horns, lenses,
reflectors) .These antennas were used in advanced utilizations like radar, deep space
projects, and remote sensing projects by using microwaves region. Infinite bandwidth

antennas did a great revolution in antenna history. These were called as “frequency
independent”. These antennas were primarily used in the 10- 10,000 MHz region in a
variety of applications including television, point to point communication, lenses
etc….
1.3 Basics of an Antenna
Antennas basically can be divided into two main categories. Those are Transmitting
antenna and Receiving antenna. As I mentioned before antenna is not an isolated
device.
Figure 06: Antenna as a transition node. [4]

If consider about architecture of antenna it’s easy to demonstrate that using thevenin
equivalent circuit as below.
Figure 07: Thevenin equivalent for an antenna system
Here voltage source is replaced by an ideal generator and the transmission line is
represented by a line with characteristic impedance ( while antenna is represented
by a load when, ( . The load resistance is representing the
conduction and dielectric losses associated with the antenna system. is called as
radiation resistance which, is used to demonstrate radiation occur by antenna. Is
the reactance part which, is utilized to represent the imaginary part of the impedance
associated with the radiation by antenna. If antenna is ideal, magnitude of must be
zero. That means the energy generated by source should be totally converted to
(for radiation). Consist with both real and imaginary parts such as a complex
number. This reveals us that electromagnetic waves behave in two planes.
The losses due to the line, antenna and the standing waves are badly affect on
transmission process. These losses can be reduced by low loss lines (by minimize
). The standing waves can be reduced and the energy storage of the line could be
minimized by matching load impedance of the antenna to the characteristic
impedance of the line.

Radiation mechanism of an antenna
If consider about radiation mechanism, antenna responsible for distributing waves or
collecting waves. Let us consider how this is happening. In transmitting antennas, for
pull the wave from antenna, high frequency with high power is needed. For this
purpose, higher frequencies with high power supply to the transmitting antenna. In
transmitting antenna, current is converted into Electromagnetic field. This is discussed
above with Maxwell’s law. When current is travelling through conductor, magnetic
field is induced around that conductor. Magnetic field is varying according to rate of
change of charge (electrons) flowing. For obtain higher frequency, modulation
concept is utilized. Voltage is obtained by electrical field and current is obtained by
magnetic field. When magnetic field is varying current is induced in that circuit
according to Faraday’s law Process of transmitting antenna system is shown in figure
06. In simply saying, Transmitting antenna convert current and voltage into radio
waves (electromagnetic), while receiving antennas gather electromagnetic waves.
Transmission Line
As mentioned above, antenna is not an isolated node. Transmission line is also there
to connect signal generator or receiver with the antenna. In an antenna
communication, transmission line must be suitable. If not phase distortions, energy
losses, fading waves might be occurred. Even by transmission line type, purpose of
antenna is varied. There are some types of transmission lines as,
 Double wire (two wires).
 Microstrip.
 Coaxial.
 Stripline.
 Coplanar Waveguide.
These types of antennas varied with their bandwidth, loss characteristic, characteristic
impedance, radiation, etc.

Two wire
Below you can see a cross sectional view of two wire transmission line. Current are
flowing opposite directions in these two wires.
Figure no: 08 cross sectional view of two wire transmission line
[5]http://www.rfcafe.com/references/electrical/transmission-lines.htm
This is the most common transmission line type usually. Here, two separate wires are
covered with another medium(electrical insulator). According to above diagram, each
wire has diameter if d and length between two wires is D. If that cover has
permittivity of Inductance (L) and capacitance(C) for unity length is given by,
√
√
Usually the characteristic impedance ( Value is being varied in 270 to 310 Ωs.
Main application is television antennas ( rabbit ear antennas).When current flowing in
two directions in these two wires dielectric field is occurred around this transmission
line and Radiation is occurred here at higher frequencies. Because of that these
transmission lines have less efficiency when frequency is greater than 300MHz.

The characteristic impedance of this transmission line is given by,
√
√
Microstrip
Figure no 09 : named cross sectional of Microstrip transmission line.[6]

http://www.photond.com/products/fimmwave/fimmwave_applications_09.htm
Microstip transmission line procedure is very familiar with two – wire system. Instead
of two wires, there are two plates called as microstrip and ground plates are separated
by dielectric (electrical insulator) plate (substrate according to above figure). By that
radiation resistance can be reduced as well. Mainly, utilized in microwave
components. If consider about electromagnetic distribution, majority of both electrical
and magnetic field are flowing in the transverse plane. This might be hazardous
sometimes if there is big current. Characteristic impedance of microstrip line is given
by,
√
When,
√
d= thickness of substrate.
W = width of strip.
Conductor loss and dielectric substance loss are common errors / losses occurs in
microstrip transmission lines.
Coaxial

Figure no 10: named cross sectional of coaxial cable.[7]
http://www.phy.davidson.edu/stuhome/phstewart/IL/speed/cableinfo.html
Coaxial cable is the most common transmission line in domain and household. This
consist of tubal conductor is covered by another tubal conductor. These two
conductors are separated by electrical insulator. This entire package is covered by
another dielectric cover. Data is transmitted through the center wire, while the outer
braided layer serves as a line to ground. Both of these conductors are parallel and
share the same axis. As all electrical components, coaxial cables have characteristic
impedance. This impedance depends on the dielectric material also. That is given by,
√
√ ⁄
When,
R = Diameter of outer conductor.
r = Diameter of inner conductor (main conductor).
Data transmission velocity of main conductor (v) is
√
⁄ when; c is the speed of
light.

Stripline
Figure no 11 : cross sectional of stipline with dimensions.[8]
This configuration is usually called as single stripline. Dual stripline configuration is
the other configuration available. Stripline has bit differences compared to microstrip
configuration. In microstrip, there are one conductor and one ground plate separated
by dielectric plate. Here, there are two ground plates and one conductor separated
each other with dielectric medium. Stripline filters and couplers always offer better
bandwidth than their counterparts in a microstrip. Another advantage of the stripline
is that fantastic isolation between adjacent traces can be achieved. Because of extra
ground plate, stripline is harder and expensive than microstrip. As well Because of the
second ground plane, the strip width is much narrower for given impedance and the
board is thicker than that for a microstrip. Usually, characteristic impedance of
stripline transmission line is being varied 50 to 75 ohms. That is given by,
√
W = width of the conductor.
t = thick of the conductor.
d = length between two ground plates.
A = [2 ( ( (
B =
√⁄

Coplanar waveguide
Figure 11(a) : coplanar waveguide without ground cross sectional.[9]
Figure 11(b) : coplanar waveguide with ground cross sectional. [9]
Coplanar waveguide is very efficiency transmission line, which uses a ground
conductor that is coplanar with the signal conductor. This structure is very similar to
stripline configuration. In here conductor is always separated. So, it can keep constant
impedance. This configuration can be used for high frequencies and has higher
bandwidth also. There are two basic configurations as with ground and without
ground.

1.4 Types of antennas
By today, antennas are used in various fields in various ways. At there, different types
of antennas are being used for different purposes. There are many types of antennas.
Some of them are,
Wire antennas
These type antennas are the most common antennas in everywhere such as
automobiles, buildings, ships, aircrafts, spacecraft and many other places. There are
various shapes of wire antennas such as dipole, loop, and helix.
Dipole
Dipole is an antenna which is made of two conductors connected together. Half wave
dipole, quarter wave dipole and folded dipoles are categories of dipole antennas.
According to Yi Huang and Kevin Boyle (2008), Dipoles are one of the simplest but
most widely used types of antenna. This is also called as Hertz’s antenna, because
hertz used dipole for his inventions. In half wave dipole consist of two conductors
which have quarter of wavelength in each conductor. Total length of antenna is half of
wave length. Current is flowing in these conductors with association of voltage to
radiate electromagnetic wave. Let us consider how that radiation happens.
⁄ ⁄
Current
Voltage

Figure 12: half wave dipole basic moment
Here in this basic moment, current is maximum and voltage is minimum at the
middle point. Because of low voltage and higher current, a low impedance point is
created in middle point and gets the ability to detect electromagnetic waves as well
because other two corners hard to detect electromagnetic waves. In odd harmonics
can see same incident. Because of that these dipoles can detect even two or three
harmonics of based frequency as well.
Yagi- Uda antenna
This is another famous wire type antenna, which used in VHF and UHF
communication. This is same as dipole, but there are more elements to change
directivity, radiation pattern and phase angle. These elements are called as reflector,
director. According to Ian Poole (2003), “The basic antenna consists of a central
boom with the elements mounted to it at right angles as shown. The antenna consists
of the main driven element to which the feeder is connected, and parasitic elements
either side. These parasitic elements are not directly connected to the feeder but
operate by picking up and re-radiating power in such a phase that the directional
properties of the antenna are altered. This is achieved having the phase of the current
in the parasitic element or elements in such a phase that it reinforces the signal in a
particular direction, or cancels it out. There are two main types of parasitic element:
reflectors that reflect power back towards the driven element, and directors that
increase the power levels in the direction of the directors. The properties of a parasitic
element are determined by their spacing and their electrical length.”

http://en.wikibooks.org/wiki/Communication_Systems/Antennas
Aperture Antennas
Aperture antenna is mainly used for projects at higher frequencies. There are some
antennas, such as pyramid, conical or rectangular shape. According to Yi Huang and
Kevin Boyle (2008) is another group of antennas that are not made of metal wires but
plates to form certain.
Configurations that radiate/receive EM energy in an efficient and desired manner,.
These antennas are very useful in the aeronautics and space applications, because they
can be very easily built on the skin of the object. In addition, these antennas are
coated with a dielectric material to protect them from the harmful effects on the
environment. Horn antenna is usually used as an antenna to the opening. Horn
antenna is the easiest to work with microwave transmission. This is widely used as a
feeding element for large parabolic antenna radio astronomy and communication are
installed worldwide. Besides its usefulness as a feed reflectors and lenses, is a
common element of the phased array and serve as a universal standard for measuring
the calibration and other high-gain.Usually there are four types of electromagnetic

horns in E plane and H-plane pyramid cornial.
Figure 13 : E plane, H plane and pyramid configuration horn antenna.[10]
Figure 14 : Conical horn configuration antenna [11]

Microstrip Antennas
Microstrip antennas consist of a metallic patch or patches on grounded substratum.
The metallic patch may have one of several configurations. Among them circular and
rectangular configurations are widely used, because of ease of analysis and fabrication
and good radiation characteristics such as low cross polarization radiation and also
very versatile in terms of resonant frequency, pattern, impedance and polarization.
These antennas can be placed in many applications and places such as airplanes,
satellites, vehicles, mobile phones, missiles and many other applications because of
inexpensive, high performance, easy to handle, easy to place.
Array antennas
Array antennas depend on arrays. Specific radiation pattern requirements cannot be
obtained or fulfilled by single antenna element, because single elements usually have
relativity wide radiation patterns and low values of directivity. These reasons occur
low efficiency of an antenna and have to use numbers of antennas to achieve
considered results. To design antennas with large directivity electrical dimensions of
the antenna must be higher. But, that’s not practically success, because, high cost,
high power, mechanical problems, disabilities and space problems. An alternative
way to achieve large directivities, without increasing the size of the individual
elements, is to use multiple single elements to form an array. Array is a sampled
version of a very large single element. In an array, the mechanical problems are
overcome.
Arrays are most versatile antenna type because of higher efficiency. These antennas
are being used in many applications such as aerospace, earthbound and many others.
Yagi- Uda array, aperture array, Microstrip arry and slotted-waveguide array are some
array configurations available.

Figure 15 : A Phased Array Antenna with Microstrip Radiating Elements.[12]
Figure 16 : Basic geometry of a slotted waveguide antenna.[13]

Lens Antennas
Main reason of using lens antennas in focus divergent energy/ waves to appropriate
direction to reduce spreading in undesirable directions. By properly shaping the
geometrical configuration and choosing the appropriate material of the lenses and can
transform various forms of divergent energy into plane waves. These antennas can be
used in most of the applications related to higher frequencies. In telecommunication,
Television broadcasting and even in satellite communication these kind of antennas
are utilized.
Figure 17 : Schematic representation of a phased antenna array beam shaping
system[14]

Reflector Antennas
Reflector antennas are mainly used in long way transmission tasks. Sometimes, called
as “Dish” antennas because of its shape. That distance might be outer space to earth or
large geographical area. These antennas are made for spread EM waves to large area
in considered target. Parabolic reflector and corner reflector are two types of reflector
antennas. Dipole or Horn antenna is used as the feed or radiating element. Very large
gain can be achieved by reflector antennas. But placement of the antenna must be
correct, because these antennas beam width is compared low. According to Ian Poole
(2003), Initially these antennas were only used for professional applications,
especially radio astronomy or satellite communications. However, with the advent of
satellite television these antennas are often seen on the sides of houses for reception of
these broadcasts. The gain mainly depend on dimensions of the reflector.
Feed
Figure 18(a) : Parabolic reflector with front feed

Figure 18(b) : parabolic reflector with cassegrain feed.
Figure 18(c) : A corner reflector.

1.5 Antenna parameters
Above we discussed various kinds of antennas. Performances of those antennas
depend on some of parameters. These parameters need to specify for complete
description of the antenna performance. Some of those Antenna parameters are,
 Antenna Gain.
 Radiation pattern.
 Beam-width.
 Bandwidth.
 Polarization.
 Directivity.
 Efficiency.
Radiation Pattern
Radiation pattern is also called as antenna pattern. Radiation pattern is variation of
power, which radiated by the antenna as a functional representation. According to
C.A. Balanis (2005), This is defined as “ a mathematical function or a graphical
representation of the radiation properties of the antenna as a function of space
coordinates”. This is represented as a function of the directional coordinates.
Radiation properties include power flux density, radiation density, field strength,
directivity, polarization or phase. The radiation property of most concern is the two or
three dimensional spatial distribution of radiated energy as a function of observer’s
position along a path or surface of constant radius. In an antenna radiation pattern is
shown by three dimensions (3D) . Those are,
 Field pattern (in linear scale) represent a plot of the magnitude of the electric
or magnetic field as a function of the angular space.
 Power Pattern (in linear scale) represents a plot of the square of the magnitude
of electric or magnetic field as a function of angular space.
 Power Pattern (in decibels) represents the magnitude of the electric or
magnetic field in decibels as a function of angular space.

Figure 19 : coordinate system for antenna analysis [15]
Radiation power density
The quantity used to describe the power associated with an electromagnetic wave is
the instantaneous poynting vector defined by
(
(
(

Radiation Intensity
Radiation intensity in a given direction is defined as “the power radiated from an
antenna per unit solid angle.” The radiation intensity is a far field parameter and it can
be obtained by simply multiplying the radiation density by the square of the distance.
This is given as,
U : Radiation intensity.
r : Radius.
: Radiation density.
The radiation intensity always related to the far zone electric field of an antenna.
BeamWidth
The beamwidth of pattern is defined as the angular separation between two identical
points on opposite side of the pattern maximum. In an antenna pattern, there are
number of beamwidths. Half power beamwidth (HPBW) is the most common
beamwidth type. That is defined as “In a plane containing the direction of the
maximum of a beam, the angle between two directions in which the radiation intensity
of one half value of the beam.” The beamwidth of an antenna is a very important
factor of merit and often is used as a tradeoff between it and the side lobe level; that
is, as the beamwidth decreases, the side lobe increases and vice versa. In addition, the
beamwidth of the antenna is also used to describe the resolution capabilities of an
antenna to distinguish between two adjacent radiating sources or radar targets.

Directivity
Directivity is defined as “the ratio of the radiation intensity in a given direction from
the antenna to the radiation intensity averaged over all directions. This shows how
much efficiency has in a considered direction. The average radiation intensity is equal
to the total power radiated by the antenna divided by 4 If the direction is not
specified, the direction of maximum radiation intensity is implied.” It can be stated as
follows.
When, the direction is mentioned, it implies the direction of maximum radiation
intensity is expressed as,
When,
D = directivity
D max = Maximum directivity
U = Radiation intensity.
U max = Maximum radiation intensity.
U0 = Radiation intensity of isotropic source.
P rad = Total radiated power.

Antenna Efficiency
The total antenna efficiency is used to take into account losses at the input terminal
and within the structure of antennas. Such losses may be occur due to below reasons.
 Mismatching of impedances in transmission line and Antenna. Reflections and
side waves occur due to this incident.
 Conduction and dielectric losses ( ). This r is radiation impedance, which
discussed in Basics in antennas.
This total antenna efficiency can be formed as,
( ( | |
.
Voltage standing wave ratio =
| |
| |

Antenna Gain
Antenna gain is always related to directivity and it’s a measure that takes with
efficiency of the antenna as well as its directional capabilities. Antenna gain is defined
as “the ratio of the intensity, in a given direction, to the radiation intensity, that would
be obtained if the power accepted by the antenna were radiated isotropic. The
radiation intensity corresponding to the isotropic radiated power is equal to the power
input by the antenna divided by 4 Gain is expressed as,
Bandwidth
The bandwidth of an antenna is defined as “the range of frequencies within which the
performance of the antenna, with respect to some characteristic, conforms to an
specified standard.” If consider a dipole, bandwidth is the range which can be
detected by corner to corner of dipole. We know, electromagnetic wave has speed of
light according to invention of Scottish scientist James Clerk Maxwell. So, we can
assume detecting frequency by calculating length of entire dipole. For broadband
antennas, the bandwidth is usually express as the ratio of the upper to lower
frequencies of acceptable operation. Bandwidth ratio reveals the upper and lower
frequencies of an antenna. As an example, 10: 1 bandwidth indicates that, the upper
frequency is 10 times greater than lower frequency. This technique is differing at
narrowband antennas. For narrowband antennas, the bandwidth is expressed as a
percentage of the frequency difference over the center frequency of the bandwidth.
Bandwidth of an antenna is depending on other parameters (gain, input impedance,
pattern, polarization) as well. Bandwidth is controlled at center of many antennas. By
today bandwidth of antennas have been increased giant. 40: 1 is an example for that
type antenna.

Polarization
Antenna is designed sometimes to transmit or receive signals to or from only one or
two considered directions. Because of that even polarization is differ from direction to
direction. Polarization of an antenna in a given direction is defined as “the
polarization of the wave radiated by the antenna.” When the direction is not stated, the
polarization is taken to be the polarization in the direction, which has maximum gain.
The polarization of a wave is defined using wave radiated by the antenna in
considered direction. Polarization is categorized as linear, circular or elliptical. If the
vector that describes the electrical field at a point in space as a function of time
always directed along the line, that is linear polarized field. According to shape of
electric field traces can identify category of polarization. The figure of the electric
field is traced in a clockwise or counterclockwise sense. Clockwise rotation of the
electric field vector is also designated as right hand polarization. while,
counterclockwise is left hand polarization.
In practical world, the axis of antenna’s main beam must be directed along the polar
axis of the radiation sphere. The polarization of the wave radiated by the antenna can
also be represented on Poincare sphere. [16]

References/ Bibliography
[1] http://www.geo.mtu.edu/rs/back/spectrum/.
[2]
[3] IEEE transactions on antennas and propagation, vols. AP-17, No.3, May 1969;
AP-22, No. 1, January 1974 and AP-31, No.6, Part ii, November 1983.
[4] http://www.google.lk/imgres?imgurl=http://denmasbroto.com/files/antenna-as-a-
transition-device.PNG&imgrefurl=http://denmasbroto.com/cetak-13-antenna-basic-
theory.html&usg=__XzFWWQi-
SXiFbe5FwVEHB64muJw=&h=529&w=454&sz=62&hl=en&start=1&zoom=1&tbn
id=lU3TLvs5v8QDnM:&tbnh=132&tbnw=113&ei=l7EBUJmrKIa2hQe_xpDyBw&p
rev=/search%3Fq%3Dantenna%2Bas%2Ba%2Btransitional%2Bdevice%26um%3D1
%26hl%3Den%26safe%3Doff%26sa%3DN%26biw%3D1360%26bih%3D667%26tb
m%3Disch&um=1&itbs=1
[10] http://www.radio-electronics.com/info/antennas/waveguide/waveguide-
impedance-matching-iris-post.php
[11]http://www.google.lk/imgres?imgurl=http://img.directindustry.com/images_di/ph
oto-g/high-gain-feed-horn-antenna-
764325.jpg&imgrefurl=http://www.directindustry.com/prod/ets-lindgren/high-gain-
feed-horn-antennas-35072-764325.html&usg=__LjnhuZIyvjGv8DcGeFt3O-
udeT0=&h=572&w=647&sz=29&hl=en&start=58&zoom=1&tbnid=Od8u-
6USyYJ6tM:&tbnh=121&tbnw=137&ei=808CUPSYCMenhAfyvYH4Bw&prev=/se
arch%3Fq%3Dconical%2Bhorn%2Bantenna%26start%3D40%26hl%3Den%26safe%
3Doff%26sa%3DN%26biw%3D1360%26bih%3D667%26tbm%3Disch&itbs=1
[12] http://www.google.lk/imgres?imgurl=http://www.radio-
electronics.com/info/antennas/waveguide/waveguide-e-h-horn-
antenna.gif&imgrefurl=http://www.radio-
electronics.com/info/antennas/waveguide/waveguide-impedance-matching-iris-
post.php&usg=__mstNd_jliVd41R0B-
uclNfluvI0=&h=307&w=250&sz=3&hl=en&start=2&zoom=1&tbnid=-OqdybTwTc-
dHM:&tbnh=117&tbnw=95&ei=5k4CUNP5H4i3hAfknvSXCA&prev=/search%3Fq
%3De%2Bplane%2Bhorn%2Bantenna%26hl%3Den%26safe%3Doff%26biw%3D13
60%26bih%3D667%26tbm%3Disch&itbs=1

[13]http://www.google.lk/imgres?imgurl=http://www.wtec.org/loyola/satcom/fh2_26.
gif&imgrefurl=http://www.wtec.org/loyola/satcom/c2_s1b.htm&usg=__3uif0JppUpa
2j_09nUsL99YwK0k=&h=550&w=733&sz=29&hl=en&start=20&zoom=1&tbnid=k
Lt_wt5W5a3VgM:&tbnh=106&tbnw=141&ei=YFICUPOEEai80QXU0421Bw&prev
=/search%3Fq%3Darray%2Bantenna%26hl%3Den%26safe%3Doff%26biw%3D136
0%26bih%3D667%26tbm%3Disch&itbs=1
[14] http://www.antenna-theory.com/antennas/aperture/slottedWaveguide.php
[15]http://www.google.lk/imgres?imgurl=http://www.aanda.org/articles/aa/full/2004/
46/aa1435/img60.gif&imgrefurl=http://www.aanda.org/articles/aa/full/2004/46/aa143
5/aa1435.fig.html&usg=__E-PzQOeZTM0zmNR65xCf_-
Q_1ss=&h=425&w=461&sz=18&hl=en&start=12&zoom=1&tbnid=KkEh8L7zQuH2
oM:&tbnh=118&tbnw=128&ei=zocCUNLvK4yBhQfmyaH-
Bw&prev=/search%3Fq%3Dcoordinate%2Bsystem%2Bfor%2Bantenna%2Bplotting
%26hl%3Den%26safe%3Doff%26biw%3D1360%26bih%3D667%26tbm%3Disch&i
tbs=1
[16] C.A Balanis (1989), Advanced Engineering Electromagnetics, John Wiley &
sons, New York.

Research 02 (P2.2, M3)
Electromagnetic wave is a combination of Electrical field and Magnetic field
according to Maxwell’s law. Electromagnetic wave is a transverse wave. In transverse
waves, Energy transmitting direction is perpendicular to wave oscillating direction.
One characteristic of transverse wave is no need of medium to transmit. Even in
vacuum it can be transmitted. Any Electromagnetic wave has same transmitting speed
of speed of light (3 . There are Electromagnetic wave having different
Wave lengths and frequencies.
At the beginning Light was the only one thing, which found in electromagnetic
spectrum. 1n 1800, William Herschel found infrared light. He could find out the
temperature of different colors by moving a thermometer through light split by a
prism. In 1801 Johann Ritter invented that there are chemical rays as visible violet
rays. This is called as Ultra violet rays. Light was named as an electromagnetic wave
after 1845. In 1845, Michel Faraday invented that, light is a one type of
electromagnetic. In 1895, Wilhelm Rontgen invented X rays, which can go through
even human body.
V = Velocity of transmitting wave.
.
= Wave length (2 .

Figure 01 : Electromagnetic spectrum
http://www.colourtherapyhealing.com/colour/electromagnetic_spectrum.php

In electromagnetic waves as mentioned above, velocity is a constant value. So,
frequency is inversely proportional to wave length. By considering above
characteristics Electromagnetic wave spectrum has been created.
Electromagnetic spectrum is classified into classes as,
 Radio wave.
 Microwave.
 Infared.
 Visible light.
 Ultraviolet.
 X – Ray.
 Gamma.

Figure 02 : Electromagnetic waves classes and wave lengths of them
http://lasp.colorado.edu/cassini/education/Electromagnetic%20Spectrum.htm

Radio Frequency
Radio frequency defined as frequencies between 3kHz and 300GHz. This class has
the lowest frequency in electromagnetic spectrum. This is the most useful class in
communication field. Radio waves are divided into many classes according to their
frequency and wave length.
Frequency Band Wave length Applications
3- 30 KHz VLF 100 – 10 Km Sonar, fax, Navigation
30 – 300 KHz LF 10 – 1 Km Navigation
0.3 – 3 MHz MF 1 – 0.1 Km AM Broadcasting
3 – 30 MHz HF 100 – 10 m T. phones, fax, CB
30 – 300 MHz VHF 10 -1 m TV, FM Broadcasting
0.3 – 3 GHz UHF 1 – 0.1 m TV, mobile , radar
3 – 30 GHz SHF 100 – 10 mm Radar, satellite, microwave links
30 – 300 GHz EHF 10 – 1 mm Radar, wireless communication
Figure 03: EM spectrum (Radio waves) and applications.
Let’s consider about these frequency ranges separately.

Very Low Frequency (VLF)
Very low frequencies range is called for radio frequencies in 3 – 30 kHz which has
wave length of 10 – 100 km. High bit range data cannot be transmitted such as voice
because of low bandwidth. These waves can go through salt water till 40 meters.
Because of high wave length these waves cannot be blocked easily. Because of above
reasons this range is used in military operations often.
If consider about antennas for VLF, it’s hard, impossible to establish dipoles or
quarter poles because of high wave length of VLF. Antennas, which used for VLF,
relatively giant and be placed in vertically. Because of inability to establish giant
antennas, efficiency of radiating is laying 10% to 20% like very low.
Low frequency (LF)
Low frequency refers to radio frequencies in the range of 30 300 kHz. This is used
for AM broadcasting in long waves. Additionally, navigation systems, air balloons,
military tasks are some other applications of LF. Ground wave can cover an area with
a radius of 2000 km about the transmitting antenna. By using these ground waves
Radio clock concept has been introduced.
In the frequency range 40 kHz–80 kHz, there are several standard time and frequency
stations, such as
 JJY in Japan (40 kHz and 60 kHz)
 MSF in Anthorn, England (60 kHz)
 WWVB in Fort Collins, Colorado, US (60 kHz)
 DCF77 in Mainflingen near Frankfurt am Main, Germany (77.5 kHz)

Medium Frequency (MF)
Electromagnetic waves from 300 kHz to 3MHz series belong to medium frequency
series. This frequency range is mainly utilized for AM broadcasting. Propagation
occurs as ground waves. Ground wave propagation at these frequencies follows the
curvature of the Earth over conductive surfaces such as the sea and damp earth. At
sea, MF communications can typically be heard over several hundred miles.
Furthermore, Maritime, codeless phones are some applications in medium
frequencies.
Figure 04: Medium frequency generator for plasma operation
http://www.redline-technologies.de/index.php?File=E0ProductsHvGenerator

High frequency (HF)
Electromagnetic waves from 3MHz to 30MHz series belong to high frequency band.
Wave length is between 100 to 10 meters. Not like previous bands, this band wave
propagation way is different. Previous waves transmitted as ground waves. These
waves propagate as sky waves. Sky wave is propagation of radio waves bent back to
earth surface by ionosphere. Ionosphere is upper part of atmosphere from about 85 km
to 600 km altitude. Ionosphere is divided into 4 layers. Because of ion molecules,
dust, water and other particles waves are reflected back to earth. This wave band is
utilized at codeless phones, land phones, fax machines, CB radios and some aviation
activities.
Very High Frequency (VHF)
VHF band is valid from 30MHz to 300MHz frequency and wavelength of 10 meter to
1 meter. This is ideal for short distance communication. Some VHF waves are
reflected by ionosphere, where some frequencies are not reflected. FM broadcasting,
Television broadcasting, air navigation systems are some applications of VHFs.
Usually line of sight transmission is used at VHF. This is also less affected by
atmospheric noise and interference from electrical equipment than lower frequencies.

Ultra High Frequency (UHF)
UHF band is laid frequency range from 300MHz to3GHz. Wave length is between 1m
to 10cm. Sky wave propagation method is used for UHF also. UHF TV signals are not
carried along the ionosphere but can be reflected off of the charged particles down at
another point on Earth in order to reach farther than the typical line of
sight transmission distances. UHF produces short waves with higher frequencies.
Because of that, no need to use bigger antennas to transmitting and receiving. Because
of short waves line of sight is occurred at here. TV broadcasting, FM broadcasting,
mobile communication and Radar communication are some applications of UHF.
Figure 05 : A UHF antenna (MX – 075)
http://www.cabletech.com.hk/index.php?product=UHF_Antenna&c=12&pp=1&p=11
64968&ph=l

Super High Frequency (SHF)
Radio frequencies in between 3GHz and 30GHz are called as SHF. Wave length of
this band is between 10cm to 1cm. This is not ideal for AM or FM broadcasting
because it hasn’t enough wave length for propagation. This band is referred to
microwave band. By today, mobile communication uses this band for Wireless local
area network, wireless USB and military tasks. Main utilizations of SHF are radar
communication and microwave devices.
Figure 06 : A Radar Antenna
http://www.fas.org/spp/military/program/com/an-gsc-52.htm

Extremely High Frequency (EHF)
Radio frequencies in between 30GHz and 300GHz are called as SHF. Wave length of
this band is between 10mm to 1mm.This cannot be used for radio broadcasting
because of very short wavelength. Because of short wave length atmospheric
attenuation percentage is a higher value at here. Only used in short distance
communication. Usually this Band used in radio astronomy and remote sensing.
Compared to other bands, small antennas are required for this band waves. Medical
treatments, military tasks, security screening, weapon systems, telecommunication,
scientific researchers are some typical applications of EHF.
Figure 07 : Hand EHF therapy and ear EHF therapy.

Conclusion
Radio wave is one region of electromagnetic spectrum, which has lowest frequency
and highest wavelength. In communication, this is the most utilized region. Radio
waves again categorized according to wave properties. Very low frequencies (VLF),
low frequency (LF), medium frequency (MF) are used in long way communications
such as sonar, navigation and inter-continental AM broadcasting. Efficiency is very
less there, because these waves are propagated as ground waves due their higher wave
length and absorption by troposphere. High frequency wave (HF) is utilized at fax,
land phones. Since high frequency band waves ape propagated as sky waves. Then,
very high frequency (VHF) and Ultra high frequency (UHF) bands are the most
familiar bands with civilians in day today life utilizations such as radio, TV
broadcasting and mobile communication. Super high frequency (SHF) is also use for
wireless communication and Extreme High frequency (EHF) bands are belong to
smooth low distance tasks in medical, military, scientific fields. When frequency get
higher its compulsory to implement in short distance applications or need to establish
communication towers to make a network. With the utilization of various bands is
used for different tasks in day today life and new inventions.

Research 03 (P2.3, M2)
As we know, Radio waves are one part of Electromagnetic waves. These waves are
transmitted through atmosphere. On the way these waves are facing to different
phenomena such as reflection, refraction, diffraction. Because of above phenomena
the way of radio wave and light also is changed. This could be advantage or
disadvantage or both. In Radio wave propagation both advantages and disadvantages
are occurred. Let us consider these phenomena separately.
Reflection
Reflection can be defined as the angle of incidence is the angle of incidence is equal
to the angle of reflection for a conducting surface. According to reflection surface
reflection is going to be differing. If that surface is pure flat above incident is
happened. If not wave is scattered due to unbalance of surface.
Figure 09 : A Pure reflection without refraction.

Refraction
But in real life we can’t expect this kind of incident. While reflection, portion of wave
is refracted also. refractive index is different according to mediums. According to
Snell’s law,
Figure 10 : refraction and reflection.
According to above graph and Snell’s law,

Diffraction
Diffraction is a phenomenon, which reduce the strength of the signal. This is differing
from reflection bit. This is occurs due to objectives in surround.
In communication, radio waves and other waves are transmitted with above
phenomena. Usually waves are transmitted in atmosphere above earth. Usually
atmosphere is divided into four parts
Figure 11 : Four layers of Atmosphere with dimensions.

Troposphere
The closest region is called as troposphere. This is overspread about 11 km in middle
latitudes, 12 km in tropical regions, and 7km at the poles.
. All mountains, Buildings and all particles we can see are in this region. Additionally,
water and dust molecules are in this region also. Waves less than 30MHz frequency
such as LF, MF, and VLF can be partly reflected of refracted in this region.
Troposphere is compared warm other regions. This phenomenon is occurred because
of heat reflection of Earth. 75% to 80% of mass of atmosphere is consisted in this
region and Majority of water molecules dust molecules also in this region. In the
troposphere air temperature on average decreases with height at an overall
positive lapse rate of about 6.5°C per kilometer, until the tropopause, the boundary
between the troposphere and stratosphere is reached.
Ionosphere
This is the most important region with related to wave propagation. Ionization is
occurred in between thermosphere and mesosphere. This ionization area is called as
Ionosphere. This consists of about 0.1% of total mass of Earth atmosphere.
Ionosphere is a shell of electrons and electrically charged atoms and molecules’
stretching from about 50km to 1000km. Ionosphere is created because of ionized
particles. Because of Sun (ultraviolet rays mainly) particles in this region are ionized
as both (+) and (-). So, free electrons and holes are in this region and because of that
radio waves are attenuated of reflected of refracted.
X rays, UV rays and some other short length waves are ionized in this region.
Basically all these radiations, ionizations depend on behavior of the Sun. Because of
that at day time and night times behavior of ionosphere is different.
Ionosphere consists of three basic layers called, D layer, E layer and F layer.

D layer
D layer is the closest layer in ionosphere towards the Earth. This is above 50km to
90kms from Earth surface. In D layer, Recombination is higher and radiation and free
electron density is lower. High frequency and other waves below 10MHz are blocked
by the D layer. The effect of D layer is maximum at day time and lowest at night time.
The layer is chiefly generated by the action of a form of radiation known as Lyman
radiation which has a wavelength of 1215 Angstroms and ionises nitric oxide gas
present in the atmosphere.
E layer
This is the second and middle layer of ionosphere. About 90 km to 120 km above the
surface of the Earth. Also called as, Kennelly – Heaviside layer. E layer is ionized
because of X rays and UV rays both. Waves from 10MHz to 50MHz frequencies are
reflected by this layer. The vertical structure of the E layer is primarily determined by
the competing effects of ionization and recombination. The effect of E layer is
maximum at daytime and minimum at night. Broadly the radiation that produces
ionisation in this region has wavelengths between about 10 and 100 Angstroms.
F layer
F layer is outer layer of ionosphere. This is called as Appleton layer also. Extends
from about 110km to 500km from earth surface. Extreme UV radiation is absorbed in
this layer. This is acting as two layers at day time and one layer at night time as F1 and
F2. They are found at altitudes of around 300 and 400 km in summer, and then during
the winter they may fall to around 200 and 300 km. At night the two layers generally
combine to form a single layer and this is generally around an altitude of 250 to 300

km.. This is the most important layer HF wave propagation. The F layer acts as a
"reflector" of signals in the HF portion of the radio spectrum enabling worldwide
radio communications to be established. It is the main region associated with HF
signal propagation.
Radio wave is reflected by ionosphere
The behavior of Ionosphere is varying with the heat/ temperature of surround.
Because of that wave propagation is always depends on effect of Sun as the main
Light and heat source of Earth. Atoms and molecules to split into free electrons and
positive ions. When a negative electron meets a positive ion, the fact that dissimilar
charges attract means that they will be pulled towards one another and they may
combine. This means that two opposite effects of splitting and recombination are
taking place. This is known as a state of dynamic equilibrium. Accordingly the level
of ionization is dependent upon the rate of ionization and recombination. This has a
significant effect on radio communications. As same as ionosphere protect Earth from
hazardous rays such as X rays and high radiated UV rays.
As I mentioned above, performances of layers is highest at day time. Below image
gives a clear idea how these layers behave.

Figure 12 : Behavior of ionosphere layers in day time and night time.
http://www.radio-electronics.com/info/propagation/ionospheric/sun-hf-radio-
propagation.php
According to above graph D layer is active in daytime and it’s disappeared in night
time. If consider about E layer, as same as D layer in day time. In nighttime it
becomes very weak. That can be neglected the effect of E layer at night time. F layer
is departed into two different layers as F1 and F2 in day time. Although, Those two
layers recombine as one layer at night time. Because of this behavior of ionosphere,
(low absorption of waves) we can hear many sounds clearly than day time in
practically.
Sky wave propagation can be varied according to season also. There are four seasons
on Earth affected on some countries. As an example, in summer, effect of sun is
higher and radiation and ionization is higher of ionosphere. So, even low frequencies
are absorbed of reflected back to Earth. As an example there is less absorption and
wide area communication in winter compared to summer. Behavior of sun is changed
in every 27 days, because of rotation and every 11 years, because of sun spots. The
overall effect on HF communications is that there will be higher critical frequencies
occur for every 11 years.

Conclusion
A wave can be described as a disturbance that travels through a medium from one
location to another location under effect of wave phenomena. Radio waves in
electromagnetic spectrum mainly transmitted through the atmosphere as ground wave
propagation, line of sight propagation or sky wave propagation. Ionosphere of Earth is
divided into four layers as troposphere, Stratosphere, Mesosphere and Thermosphere.
Ionosphere is made because of ionized particles in between Stratosphere and
Mesosphere regions. In particular the ionosphere is widely known for affecting
signals on the short wave radio bands where it "reflects" signals enabling these radio
communications signals to be heard over vast distances. This is again divided into
three layers as D, E & F. radio frequency phenomena occur due to these layers in HF,
VHF bands mainly. The behavior of these layers mainly depend on Sun. Radiation of
sun, atoms are ionized as electrons or holes and make barriers. Because of that
behavior of those layers are changed according to daily, seasonal, long term variations
and that affects on radio wave communication as broadcasting efficiency, power level
(quality), transmitting distance and magnitude coverage area.

Research 04 (P2.4, D3)
In above researches we considered about different wave types of radio waves and
those waves are differ according to their properties such as frequency, wave length,
etc. Usually radio waves are travelling through atmosphere from transmitter to
receiver. According to properties of radio waves, method of propagation is varied.
There are few main methods of propagation such as ground wave, sky wave, space
wave and line of sight propagation.
Ground Wave Propagation
Long and medium bands of radio waves such as VLF, LF, and MF have higher
wavelength and frequency below 2MHz. Ground wave radio propagation is used to
provide relatively long radio communications coverage and used in long way
communication such as AM Radio broadcasting and military operations. According to
Steve Winder and Joe Carr (2002), “Waves in the bands from very low frequencies
(VLF, 3–30 kHz), low frequencies (LF, 30–300 kHz) and medium frequencies (MF,
300–3000 kHz) travel close to the earth’s surface: the ground wave Transmissions
using the ground wave must be vertically polarized to avoid the conductivity of the
earth short-circuiting the electric field.” As mentioned in Ian Poole (2003), “The
ground wave is only signals below about 2MHz. it is found that as a frequency
increases the attenuation of the whole signal increases and the coverage is
considerably reduced. Obviously the exact range will be depending on many factors.
Typically a high power medium wave station may be heard over distances 150km and
more. There are also many low power stations running 100W or so. These might have
a coverage area extending to 15 or 20 miles.” Ground waves are useful at day time,
because medium frequencies can be absorbed by the D region of ionosphere. Ground
waves travel very close to earth. These waves propagate from transmitter to receiver.
Usually these waves’ propagating is affected on troposphere objects such as natural
and syntactic objects and even surface properties of the Earth. There is another type of

ground wave, which follow the curvature of Earth. These waves called as surface
wave. Antennas, which use for ground wave transmit and receive are relatively
bigger. Even in other way broadcasting, ground wave propagation might be occurred
as a side effect. Polarization of antenna is also affect on propagating efficiency.
Vertical polarized antenna has better efficiency than horizontal polarized antenna,
because horizontally polarized ground wave would be shorted out by the conductivity
of the ground.
Surface wave propagation. http://www.ustudy.in/node/5139
Sky Wave Propagation
Sky wave propagation can be defined as, the propagation of radio waves refracted to
towards the Earth by the ionosphere. High frequency (3MHz to 30MHz) broadcasting
is occurred due to sky wave propagation. According to Steve Winder and Joe Carr
(2002), “Radio signals travelling away from the earth’s surface are called as sky
waves and they reach the layers of ionosphere.” Especially, High frequency waves are
reflected by ionization of atmosphere. Sky wave propagation can be vary according to
time of the day or season.

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