02 radio engineering - radio propagation

Rekayasa RadioTTG4B3SEMESTER GANJIL 2015 – 2016

Radio PropagationElectromagnetic (EM) Waves• EM wave is a wave produced by the interaction of time

varying electric and magnetic field• Electromagnetic fields are typically generated by

alternating current (AC) in electrical conductors• The EM field composes of two fields (vectors)

• Electric vector E• Magnetic vector H

• Electromagnetic waves can be• Reflected and scattered• Refracted • Diffracted • Absorbed (its energy)

Radio PropagationElectromagnetic (EM) Waves Properties• E and H vectors are orthogonal • In free space environment, the EM-wave propagates at the

speed of light (c)• The distance between the wave crests is called the

wavelength (λ)• The frequency ( f )is the number of times the wave

oscillates • The relation that combines the EM-wave frequency and

wavelength with the speed of light is: λ = c / f

Radio PropagationRadio Wave Propagation

Radio PropagationRadio Wave Propagation• Ground Wave

Radio PropagationRadio Wave Propagation• Ground Wave

• Keuntungan: tidak dipengaruhi kondisi atmosfer• Kerugian:

Memerlukan daya yang besar Memerlukan Dimensi antena yg besar

Radio PropagationRadio Wave Propagation• Sky Wave

Radio PropagationRadio Wave Propagation• Sky Wave

• Terjadi pada HF (3 – 30MHz)• Propagasi ini dipengaruhi kondisi atmosfer siang/malam• Contoh: Pemancar Radio Amatir

Radio PropagationRadio Wave Propagation• Line of Sight Propagation

Radio PropagationRadio Wave Propagation

Radio PropagationRadio Wave Propagation

Radio Propagation

The propagation of radio wave is affected by :Frequency EffectTerrain EffectAtmospheric EffectMultipath Effect

All the above mentioned effects cause a degradation in quality

Radio Wave Propagation

Radio PropagationFrequency Effect• Attenuation: Loss• Propagation of radio depends on frequency band

• At frequencies above 6 GHz radio wave is more affected by gas absorption and precipitation• At frequencies close to 10 GHz the effects of precipitation begins to

dominate• Gas absorption starts influencing at 22 GHz where the water

vapour shows characteristic peak

Radio PropagationTerrain Effect

• Reflection and scattering • The radio wave propagating near the surface of earth is influenced by:

• Electrical characteristics of earth• Topography of terrain including man-made structures

Radio PropagationAtmospheric Effect

• Loss and refraction• The gaseous constituents and temperature of the atmosphere

influence radio waves by:• Absorbing its energy• Variations in refractive index which cause the radio wave reflect,

refract and scatter

Radio PropagationAtmospheric Effect

Radio PropagationAtmospheric Effect

Radio PropagationMultipath Effect

• Multipath effect occurs when many signals with different amplitude and/or phase reach the receiver

• Multipath effect is caused by reflection and refraction

• Multipath propagation cause fading