modul – 9 antena dan propagasi gelombang radio (2)
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Modul – 9Antena dan
Propagasi Gelombang Radio (2)TE-09-1313
2 sksTim Bidang Studi
Telekomunikasi Multimedia(Achmad Ansori, Devy Kuswidiastuti, Gatot Kusrahardjo, M Aries Purnomo)
1Anetenna & Radio-Wave Propogation
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 )
3Anetenna & Radio-Wave Propogation
Band Frekuensi Radio (ITU)
• ELF • SLF • ULF• VLF• LF• MF• HF• VHF• UHF• SHF• EHF
Anetenna & Radio-Wave Propogation 4
3-30 Hz Extremely Low Frequency 30-300 Hz Super Low Frequency 300 Hz-3 kHz Ultra Low Frequency 3-30 kHz Very Low Frequency 30-300 kHz Low Frequency 300 kHz-3 MHz Medium Frequency 3-30 MHz High Frequency 30-300 MHz Very High Frequency 300 MHz-3 GHz Ultra High Frequency 3-30 GHz Super High Frequency 30-300 GHz Extremely High
Frequency
Band Frekuensi Radio (IEEE)(Alternatif)
• P Band 0.23 - 1 GHz• L-Band 1 - 2 GHz• S-Band 2 - 4 GHz• C-Band 4-8 GHz• X-Band 8-12.5 GHz• Ku-Band 12.5-18 GHz• K Band 18-26.5 GHz• Ka Band 26.5-40 GHz• U Band 40-60 GHz
Anetenna & Radio-Wave Propogation 5
Anetenna & Radio-Wave Propogation 6
Sistem Komunikasi Radio yang sederhana
Anetenna & Radio-Wave Propogation 7
Atmosfir dari Bumi
Anetenna & Radio-Wave Propogation 8
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
9Anetenna & Radio-Wave Propogation
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.
10Anetenna & Radio-Wave Propogation
Anetenna & Radio-Wave Propogation 11
Mekanisme perambatan
Anetenna & Radio-Wave Propogation 12
Anetenna & Radio-Wave Propogation 13
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 waves-the 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 thereceiving antenna (direct wave or path), and the other reflected from the ground to the receiving antenna (ground-reflected wave or path).
14Anetenna & Radio-Wave Propogation
Anetenna & Radio-Wave Propogation 15
Propagasi Gelombang Tanah (Ground Wave/Surface wave)
Anetenna & Radio-Wave Propogation 16
Mengikuti contour bumi Dapat merambat pada jarak tertentu Frekuensi sampai 2 MHz Contoh :
Gelombang Radio AM, Komunikasi untuk navigasi,
Propagasi Gelombang Tanah (Ground Wave / Surface Wave)
Anetenna & Radio-Wave Propogation 17
Space wave propagation
Anetenna & Radio-Wave Propogation 18
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.
Anetenna & Radio-Wave Propogation 19
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
Anetenna & Radio-Wave Propogation 20
There are numerous other synonyms, including:
intrinsic impedance of vacuum,intrinsic impedance of free space,the vacuum impedance,
Anetenna & Radio-Wave Propogation 21
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.
Anetenna & Radio-Wave Propogation 22
Anetenna & Radio-Wave Propogation 23
Fn = The nth Fresnel Zone radius in metresd1 = The distance of P from one end in metres
d2 = The distance of P from the other end in metresλ = The wavelength of the transmitted signal in metres
Anetenna & Radio-Wave Propogation 24
Propagasi Line-of-Sight (diatas 30 MHz)
Propagasi Line-of-Sight
• Sinyal pada VHF dan range yang lebih tinggi tidak selamanya dapat dikembalikan ke bumi oleh ionosphere
• Kebanyakan komunikasi terrestrial menggunakan frekuensi-frekuensi yang diradiasikan langsung dari pemancar ke penerima
• Tipe propagasi ini disebut propagasi gelombang ruang (space-wave), garis pandang (line-of-sight), atau propagasi troposfer
Anetenna & Radio-Wave Propogation 25
Anetenna & Radio-Wave Propogation 26
Persamaan Line-of-Sight LOS, secara optik (Penerima harus bisa
melihat pemancar) :
LOS efektif, atau radio (Penerima bisa “melihat” sinyal yang dikirim) :
d = jarak antara antenna dan horizon (km) h = Tinggi antenna (m) K = faktor kelengkungan bumi, karena sifat
refraksi, misal : K = 4/3
hd 57.3
hd 57.3
Anetenna & Radio-Wave Propogation 27
Rugi Free Space Rugi Ruang bebas, antena isotropik
ideal
Pt = daya sinyal antena pemancar
Pr = daya sinyal antena penerima = panjang gelombang carrier d = jarak propagasi antar antena c = Kecepatan cahaya (3 10-8 m/s)
Dimana d dan sama satuannya (misal: meter)
2
2
2
2 44
c
fdd
P
P
r
t
Anetenna & Radio-Wave Propogation 28
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
Anetenna & Radio-Wave Propogation 29
• 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 (siang-malam) dan aktivitas matahari.
Anetenna & Radio-Wave Propogation 30
Propagasi Gelombang Angkasa (Sky Wave)
Anetenna & Radio-Wave Propogation 31
Ionospheric wave :
A radio wave returned to the Earth by ionospheric reflection.
Anetenna & Radio-Wave Propogation 32
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
Propagasi Gelombang Angkasa (Sky Wave, 2 – 30 MHz)
Anetenna & Radio-Wave Propogation 33
Anetenna & Radio-Wave Propogation 34
Anetenna & Radio-Wave Propogation 35
Anetenna & Radio-Wave Propogation 36
Mode Propagasi Lainnya
• Tropospheric Scatter – memungkinkan peng-gunaan penghamburan (scattering) gelombang radio di lapisan troposfer untuk merambatkan sinyal dalam range frekuensi 250 MHz –5 GHz .
Anetenna & Radio-Wave Propogation 37
Anetenna & Radio-Wave Propogation 38
Sistem Troposcatter di Indonesia
Surabaya – Banjarmasin Troposcatter System :
Surabaya – G Sandangan ( Madura ) : Line of SightG Sandangan – G Gerahan Lalang (Madura) : Line of SightG Gerahan Lalang – G Karamaian ( Kalimantan ) : TroposcatterG Karamaian – Banjarmasin : Line of Sight
Anetenna & Radio-Wave Propogation 39
Anetenna & Radio-Wave Propogation 40
Anetenna & Radio-Wave Propogation 41
Ringkasan Mode Propagasi
Anetenna & Radio-Wave Propogation 42
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