ANTENNA
Definition of Antenna
An antenna is an electrical device which
converts electric power into radio waves. It
is usually used with a radio transmitter or radio receiver.
Antenna is one of the important elements that should be present on a radio
telescope, TV, radar, and all other wireless communication devices. An antenna is a vital part of a transmitter or receiver that used to transmit radio signals into the air. The shape is various kinds according to the design, the pattern of the spread, frequency,
and gain. The length of the antenna effectively is the wavelength of the
emitted radio frequency. The
half-wave dipole antenna is very popular because it’s easy to make and being able to transmit radio waves effectively.
Antenna Characters
There are a few important characters an
antenna that needs to be considered in selecting the type
of antenna for an application (including for use
on a radio telescope), the radiation pattern, directivity,
gain, and polarization. This characters are generally the
same on an antenna, either
when the antenna into radiate or into the
receiver, for a given frequency, polarization, and areas
of particular slices.
a.
Radiation pattern
Radiation pattern of an antenna is the
plot 13-dimensional distribution of signals emitted by an antenna,
or 3-dimensional plots levels of signal
reception received byan antenna. The antenna radiation pattern is formed by
two pieces of sliced field based radiation pattern, radiation pattern
applies in the field direction elevation slices (elesi pattern). 3-dimensional
radiation pattern this is generally referred to as a dipole antenna radiation
pattern. An antenna signal that as great
as in any direction is referred to as isotropic antenna. Antenna like
this will have a ball-shaped radiation pattern. However,
if an antenna has a certain direction,
where the distribution of the signal in the direction
of greater than in the other direction, then this will
have directivity antenna. The more
specific direction distribution of a signal by an
antenna, the antenna directivity.
Dipole antenna including
non-directive antenna. With characters like these, many of
the dipole antenna used for communication systems with a broad coverage
area. On radio astronomy, the dipole antenna is used on a radio telescope for
observing High Frequency range (HF). A form of data that can be
obtained is the variability of the intensity of the
signal emitted by an astronomical object. However, due
to dipole antenna directivity on does not have a
specific direction, radio telescope antenna using
a single element of this type cannot be used to do
the Imaging.
There are a few things to note in the
pattern of radiation, the first is the Half-power Beamwidth
(HPBW), or commonly known as an antenna
beamwidth. In radio astronomy, beamwidth is the spatial resolution of a radio
telescope, is a minimum of
twoAngular diameter fruit capable point separated by a
radio telescope. In theory, the beamwidth for a parabolic antenna can be
determined.
b.
Gain
Gain (directive gain) antenna is a
character that is associated with the ability of the
antenna radiation signal, directing or receiving the
signal from a certain direction. The gain is not
the quantity that can be measured
in physical units in general such as Watts, ohms, or
another, but rather a form
of comparison. Therefore, the units used for gain
is decibels.
The gain of an antenna is fixed, the two notions are
different between the gain of the antenna, transmit power and radiated power EIRP or, by
lowering the transmit power will not change the
gain of the antenna and radiation pattern, just lower
the EIRP or the power is radiated into the air.
Antennas with low gain have different radiation
pattern with a type that had big gains antenna. Radiation patterns of
antennas with low gain are widened so that the emitted energy is
distributed widely in sectoral (angle). While the antenna with
gainhave a pattern of narrow, measured radiant energy
is emitted not widens, but at the direction of the
main glow, this energy can reach out to more
distant places.
The big gain of
an antenna to determine the ability of the antenna to focus the energy of the emitted to a direction. Example: antenna with 20 dB gain
is more focus than an antenna with a gain of 10 dB.
c.
Polarization
The polarization is defined as the direction
of the orientation of the electric
field. Dipole antenna has linear polarization (vertical or
horizontal). Recognize the polarization of the antenna is very useful in communications
systems, in particular for obtaining maxium efficiency in the transmission of
the signal. On the application of the radio, WLAN and cellular radio,
the polarization is vertical linear polarization. The antenna of the
transmitter and receiver must be oriented vertically. While, in application of
the TV broadcast, the polarization is horizontal linear polarization. And, in
the application of RFID (Radio Frequency Identification), polarization use
circular polarization. On radio astronomy, the goal of recognizing
the polarization of the signal emitted
by an astronomical object was to study the magnetic
field of the object.
Antenna Types
a.
Based on the functions
Based on its functions, antenna divided into transmitter antenna, receiver antenna, and the
transmitter at the same time the receiver antenna. In Indonesia,
the
transmitter antennas used on radio stations and television. Then, the receiver antenna is usually used
in devices such as radio, tv and other communication devices.
b.
Based on the gain
Based on the gain,
antenna divided into VHF antenna and UHF
antenna that usually used on TV. Let everyone know that the magnitude of the emissive
power, will affect the magnitude of the signal reception of television broadcasts in a
certain place at a certain distance from the
television transmitter station. The higher of the emissive power, then the greater level of strength field of broadcast television. But the
magnitude of the reception broadcast television is not only affected by the magnitude of the emissive
power.
To increase the emissive power on the
TV station and the power receive on the TV then you need to use an
antenna.
The magnitude of the gain of an antenna is affected by the number, antenna composition and the frequencies are used. UHF transmitter
antenna will not be used for VHF TV transmitters
because it will cause high VSWR. While VHF receiver antenna can receive the signal UHF, but the gain antenna will be smaller than it should be. The quality of the beam of a VHF transmitter with the quality of UHF transmitter is the same as long as its meet the requirements and specifications that have been determined.
c.
Based on the polarization
Based on polarization,
antenna is divided into 2, dipole and monopole.
Dipole antenna has a linier polarization vertical, meanwhile monopole antenna has a polarization only in one direction. With the characters like these, many of the dipole antenna used for communication systems with a
broad coverage area.
-
Directional Antenna and
Omnidirectional Antenna
Directional antenna is emissive radiation pattern antenna was so that the effectiveness of the radio beam or only to one direction only, while the
omnidirectional antenna can radiate wave to all directions. That includes the antenna directional antenna Yagi model is like
most antenna used as a recipient
of the TV broadcast. The example
is omnidirectional antenna is an
antenna model groundplane.
d.
Based on shape
Antennas based on its shape, among others: mikrostrip, vee, parabola, horn, helix,
and loops. Although very often encountered using a radio
telescope parabolic antenna, there are some other type of anenna
which is also often used in a telescope or radio interferometer. For
example, the Mauritius Radio Telescope (MRT) which uses fruit-shaped antenna 1084 helix. Another
example is a radio telescope antenna usingshaped horn,
used by Arno Penzias and Robert Woodrow Wilson when it discovered the
Cosmic Microwave Background (CMB). Example antenna based
on its shape, the parabolic antenna is a parabolic antenna is a parabolic antennas radiate signalswill
be concentrated at the midpoint of the antenna. Usually parabolic
antenna is designed for the Ultra High Frequency (UHF), receiver satellite
TV broadcast, and microwave transmission.
Function
The function
of the antenna is to convert electrical signals into
electromagnetic signals, and then radiate (release of electromagnetic
energy into the air/free space). And the antenna can
also serve to receive electromagnetic signals (receiver of electromagnetic
energy of free space) and convert it into electrical signals. On
the radar or satellite communication systems, often
encountered an antenna that performs both functions (radiation
and receiver) at once. But, on radio telescope, antenna just run the function
of the receiver.
The Use of The Antenna
a.
The use of an
antenna on the radio
The antenna is one of the important
elements that must be present on a radio telescope. Its
function is to convert electrical
signals into electromagnetic signals, and
then meradiasikannya. And vice versa, the antenna can
also serve to receive electromagnetic signals and
convert it into electrical signals. So the radio
signal emitted by the radio station can be captured by
radio.
b.
The use
of antennas on television
Based
on international regulations relating to the use
of the frequency setting (Radio Regulations)
for television broadcasting in the
VHF and UHF frequency bands. History of
television in Indonesia beginning in
1962 by TVRI in Jakarta by using VHF television transmitter. The
construction of the transmitter TVRI walking quickly,
especially after the launch of palapa satellite in
1975. In 1987, that is, the birth of the first
private television broadcasting station in Indonesia,
station TVRI transmitters has reached the number
of approximately 200 stations transmitter using
frequency VHF entirely, and the first
private TV transmitters are given frequency
allocation in the UHF bands. The wisdom of the use of the
VHF frequency bands to TVRI and private for UHF. So to catch the broadcast TV UHF VHF antenna and used.
c.
The use of an antenna on
the radar
Radar or Radio Detection and Ranging, is
a system tool that emits electromagnetic waves in the
form of radio waves and microwaves. The
reflection of waves emitted last used to detect
objects. Radar uses electromagnetic wave spectrum in the frequency range 300
MHz to 30 GHz or a wavelength of 1 cm to 1 meter. Radar system components :
1.
Transmitter to
generate radio signals from oscillators.
2.
Waveguide is a
liaison between the Transmitter and the antenna.
3.
Receiver is the recipient
of the reflected radio signals
4.
Signal processor is
a piece of equipment that converts analog
signals into digital signals.
5.
Radar Controller is a
connector that will deliver information to the user
The Impat of
Antenna
This antenna
has a positive and negative impact. Positive impact of accelerating the flow of
information, easy access to the latest information, to help individuals in
finding information, and share the files. The negative impact is there are
radiation for used, if the antenna are struck by lightning then it can damage electronic
devices.
Conclusion
From
above discussion, it can be inferred that the antenna has a
strong emissivity for broadcast
television, radio and other communication devices, but the antenna would also have a negative impact, namely the affected radiation.
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