Modul – 9 Antena dan Propagasi Gelombang Radio (2)

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 )


Band Frekuensi Radio (ITU)

• ELF • SLF • ULF• VLF• LF• MF• HF• VHF• UHF• SHF• EHF


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



Sistem Komunikasi Radio yang sederhana


Atmosfir dari Bumi

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


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.


Mekanisme perambatan


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).



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,

Propagasi Gelombang Tanah (Ground Wave / Surface Wave)


Space wave propagation


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.


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


There are numerous other synonyms, including:

intrinsic impedance of vacuum,intrinsic impedance of free space,the vacuum impedance,


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.


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


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



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


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


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

• 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.


Propagasi Gelombang Angkasa (Sky Wave)


Ionospheric wave :

A radio wave returned to the Earth by ionospheric reflection.


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)

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 .



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


Ringkasan Mode Propagasi

Modul – 9 Antena dan Propagasi Gelombang Radio (2)

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