Modul – 9
Antena dan
Propagasi Gelombang Radio (2)
TE-09-1313
2 sks
Tim Bidang Studi
Telekomunikasi Multimedia
(Achmad Ansori, Devy Kuswidiastuti, Gatot Kusrahardjo, M Aries Purnomo)
Anetenna & Radio-Wave Propogation
1
Propagasi Gelombang Radio
Anetenna & Radio-Wave Propogation
2
radio waves, hertzian waves :
An electromagnetic wave propagated in space without artificial
guide and having by convention a frequency lower than 3 000
GHz.
Note :
The electromagnetic waves having frequencies around 3 000
GHz may be regarded either as radio waves or optical waves.
Propagasi adalah perambatan gelombang melalui suatu media
( udara, air, ruang hampa )
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Band Frekuensi Radio (ITU)
•
•
•
•
•
•
•
•
•
•
•
ELF
SLF
ULF
VLF
LF
MF
HF
VHF
UHF
SHF
EHF
3-30 Hz
30-300 Hz
300 Hz-3 kHz
3-30 kHz
30-300 kHz
300 kHz-3 MHz
3-30 MHz
30-300 MHz
300 MHz-3 GHz
3-30 GHz
30-300 GHz
Extremely Low Frequency
Super Low Frequency
Ultra Low Frequency
Very Low Frequency
Low Frequency
Medium Frequency
High Frequency
Very High Frequency
Ultra High Frequency
Super High Frequency
Extremely High Frequency
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Band Frekuensi Radio (IEEE)
(Alternatif)
•
•
•
•
•
•
•
•
•
P Band
L-Band
S-Band
C-Band
X-Band
Ku-Band
K Band
Ka Band
U Band
0.23 - 1 GHz
1 - 2 GHz
2 - 4 GHz
4-8 GHz
8-12.5 GHz
12.5-18 GHz
18-26.5 GHz
26.5-40 GHz
40-60 GHz
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Sistem Komunikasi Radio yang sederhana
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Atmosfir dari Bumi
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Anetenna & Radio-Wave Propogation
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Troposphere :
The lower part of the Earth’s atmosphere extending
Upwards from the Earth’s surface, in which temperature
decreases with height except in local layers of
temperature inversion.
This part of the atmosphere extends to an altitude of
about 9 km at the Earth’s poles and 17 km at the
equator.
Stratosphere : 20 – 50 km
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Ionosphere :
That part of the upper atmosphere characterized by the
presence of ions and free electrons mainly arising from
photo-ionization, the electron density being sufficient to
produce significant modification of the propagation of radio
waves in certain frequency bands.
Note :
The Earth’s ionosphere extends approximately from a height
of 50 km to a height of 2 000 km.
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Anetenna & Radio-Wave Propogation
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Mekanisme perambatan
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Ground wave :
A radio wave basically determined by the properties of the
ground which propagates in the troposphere and which is mainly
due to diffraction around the Earth.
A ground wave is composed of two separate component wavesthe surface wave and the space wave
The surface wave travels along the surface of the ground.
A surface wave flows the curvature of the Earth due to the
process of diffraction.
The space wave follows two distinct paths from transmitting
antenna to receiving antenna--one through the air directly to the
receiving antenna (direct wave or path), and the other reflected
from the ground to the receiving antenna (ground-reflected wave
or path).
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Propagasi Gelombang Tanah
(Ground Wave/Surface wave)
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Propagasi Gelombang Tanah
(Ground Wave / Surface Wave)




Mengikuti contour bumi
Dapat merambat pada jarak tertentu
Frekuensi sampai 2 MHz
Contoh :
 Gelombang Radio AM, Komunikasi untuk
navigasi,
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Space wave propagation
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line-of-sight propagation :
Propagation between two points for which the direct ray is
sufficiently clear of obstacles for diffraction to be of negligible
effect.
free-space propagation :
Propagation of an electromagnetic wave in a homogeneous
ideal dielectric medium which may be considered of infinite
extent in all directions.
Note :
For propagation in free space, the magnitude of each vector of the
electromagnetic field in any given direction from the source beyond a
suitable distance determined by the size of the source and the wavelength
is proportional to the reciprocal of the distance from the source.
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Impedance of free space :
The impedance of free space, Z0, is a physical constant relating
the magnitudes of the electric and magnetic fields of
electromagnetic radiation travelling through free space.
That is, Z0 = |E|/|H|, where |E| is the electric field strength and
|H| magnetic field strength.
The impedance of free space equals the product of the vacuum
permeability Ɛ0 or magnetic constant μ0 and the speed of light
in a vacuum c; its value is approximately 376.73031 ohms
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There are numerous other synonyms, including:
intrinsic impedance of vacuum,
intrinsic impedance of free space,
the vacuum impedance,
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Fresnel zones :
If unobstructed, radio waves will travel in a straight line from
the transmitter to the receiver.
But if there are obstacles near the path, the radio waves
reflecting off those objects may arrive out of phase with the
signals that travel directly and reduce the power of the received
signal.
On the other hand, the reflection can enhance the power of
the received signal if the reflection and the direct signals arrive
in phase.
Sometimes this results in the counterintuitive finding that
reducing the height of an antenna increases the signal-to-noise
ratio.
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Fn = The nth Fresnel Zone radius in metres
d1 = The distance of P from one end in metres
d2 = The distance of P from the other end in metres
λ = The wavelength of the transmitted signal in metres
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Propagasi Line-of-Sight
(diatas 30 MHz)
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Propagasi Line-of-Sight
• Sinyal pada VHF dan range yang lebih tinggi tidak
selamanya dapat dikembalikan ke bumi oleh ionosphere
• Kebanyakan komunikasi terrestrial menggunakan frekuensifrekuensi yang diradiasikan langsung dari pemancar ke
penerima
• Tipe propagasi ini disebut propagasi gelombang ruang
(space-wave), garis pandang (line-of-sight), atau propagasi
troposfer
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Persamaan Line-of-Sight

LOS, secara optik (Penerima harus bisa
melihat pemancar) :
d  3.57 h

LOS efektif, atau radio (Penerima bisa
“melihat” sinyal yang dikirim) :
d  3.57 h



d = jarak antara antenna dan horizon (km)
h = Tinggi antenna (m)
K = faktor kelengkungan bumi, karena sifat
refraksi, misal : K = 4/3
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Rugi Free Space

Rugi Ruang bebas, antena isotropik
ideal
2
2


Pt
4d 
4fd 


2
Pr

c2
Pt = daya sinyal antena pemancar
 Pr = daya sinyal antena penerima
  = panjang gelombang carrier
 d = jarak propagasi antar antena
-8 m/s)
 c = Kecepatan cahaya (3 10
Dimana d dan  sama satuannya (misal: meter)

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Propagasi Line-of-Sight


Pemancar dan Penerima harus dalam garis pandang
(line of sight)
 Komunikasi satelite – sinyal diatas 30 MHz tidak
dipantulkan oleh ionosfer
 Komunikasi di Bumi (Terrestrial) – antena harus berada
dalam garis effective karena adanya refraksi
Refraksi – pembelokan gelombang mikro oleh
atmosfer
 Kecepatan gelombang elektromagnetik merupakan
fungsi kerapatan medium
 Bila gelombang berubah medium, kecepatan akan
berubah.
 Gelombang akan dibelokkan pada bidang batas antar
medium
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Propagasi Gelombang Angkasa
(Sky Wave)
• Komunikasi jarak-jauh pada band frekuensi tinggi,
dimungkinkan karena adanya refraksi didaerah
atmosfer yang disebut ionosfer
• Ionosfer dibagi menjadi tiga daerah yang disebut
lapisan D, E, dan F
• Ionisasi berbeda untuk ketinggian diatas bumi
yang berbeda dan dipengaruhi oleh waktu (siangmalam) dan aktivitas matahari.
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Ionospheric wave :
A radio wave returned to the Earth by ionospheric reflection.
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Propagasi Gelombang Angkasa
(Sky Wave, 2 – 30 MHz)




Sinyal dipantulkan dari lapisan ionofer kembali ke
bumi
Sinyal dapat menjalar dalam beberapa lintasan,
bolak-balik antara ionosfer dan permukaan bumi
Efek pantulan disebabkan oleh refraksi
Contoh :
 Radio Amatir
 Radio CB
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Mode Propagasi Lainnya
• Tropospheric Scatter – memungkinkan penggunaan penghamburan (scattering) gelombang
radio di lapisan troposfer untuk merambatkan
sinyal dalam range frekuensi 250 MHz –5 GHz .
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Sistem Troposcatter di Indonesia
Surabaya – Banjarmasin Troposcatter System :
Surabaya – G Sandangan ( Madura ) : Line of Sight
G Sandangan – G Gerahan Lalang (Madura) : Line of Sight
G Gerahan Lalang – G Karamaian ( Kalimantan ) :
Troposcatter
G Karamaian – Banjarmasin : Line of Sight
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Ringkasan Mode Propagasi
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