Factors Affecting the Behavior of Radio Waves- Complete Guide - Technopediasite

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Wednesday, December 12, 2018

Factors Affecting the Behavior of Radio Waves- Complete Guide

Factors Affecting the Behavior of Radio Waves: There are so many factors affect the behavior of radio wave. Affect means loss of radio waves or some changes in the actual nature of the radio wave. Loss decrease in signal amplitude. Radio wave propagates through any medium even through air its energy is lost.
If excessive losses of radio wave occur between transmitter and receiver the problem can be corrected by removing objects causing loss,increasing transmission power,increasing the sensitivity of the receiver. Now I will discuss about the main factors which affect the behavior of radio waves.


Behavior of  Radio Waves complete guide
Behavior of Radio wave

Reflection Affecting the Behavior of Radio Waves

Reflection occurs when a propagating electromagnetic wave strikes an object that has very large dimension as compared to the wavelength of the propagating waves. Reflection occur from the surface of earth, buildings, wall,trees etc. The surface it strikes determine the shape of the reflected signal. Multipath reflection of the radio wave can cause serious problem for microwave such degradation, or causing holes in the coverage area.

Reflected signal has 180 degree phase offset with the direct los signal. Reflection can be defined as the abrupt change in direction of a wave front as it strikes a dissimilar media, which has a smooth surface and is much larger than the wave itself.

Depending on the item reflecting the wave, the reflected wave may be inverted or shifted in phase. This inverted, or phase-shifted, wave can cause interference at a receiver that can see both reflected and direct waves. 

Because the direct wave can be reflected off many objects, the signals arriving at the receiver can be at different times and phases, partially canceling each other, which is known as multipath fading.
reflection of radio waves
Reflection of radio wave

Refraction Affecting the Behavior of Radio Waves

Refraction is bending of waves as they pass through medium of different density. While passing through such medium some waves are reflected away and some will be bent through the medium in other direction. Refraction can be serious problem for the long distance communication. In other words we can say that Refraction is the abrupt change in direction as well as the absorption of a wave front as it strikes a dissimilar media of different densities.
Refraction of radio waves
Refraction of Radio Waves

Scattering Affecting the Behavior of Radio Waves

Scattering is the phenomenon in which the direction, frequency, or polarization of the wave is changed when the wave encounters rough surfaces or objects smaller than the wave itself. Scattering also can be a result of the wave’s interaction with materials at the atomic or molecular level. With the help of below figure it will be very clear.


Scattered radio wave from surface
Scattered Radio waves
Scattering results in many reflected and disordered waves, which can weaken or even cancel the main wave front.Scattering also can be the result of atmospheric changes due to heavy rain or dust.

Its occur when the medium through which the wave travels consists of object dimensions that  are small as compared to wave length. Scattering wave are also produce by rough surfaces. Scattering can take place in two different ways-
1. Can occur when the wave strikes an uneven surface and reflected in many directions.
2. Can occur as the wave travels through small particles such as dust.   

Diffraction Affecting the Behavior of Radio Waves

Diffraction is the deviation of an electromagnetic wave front from the predicted path when it strikes a surface with sharp corners or an object with a rough surface. The waves are bent around the object, thus changing the wave front’s path.

It occur when radio path between the transmitter and receiver is obstructed by a surface that has sharp irregularities. At high frequency diffraction depends on the geometry of the obstructing object. Diffraction is slowing of the wave front from the point where the wave front strikes the obstacle while rest of the wave front maintain same speed of propagation.
 
Diffraction of radio wave
Diffraction of Radio waves



Absorption Affecting the Behavior of Radio Waves

It occurs when the RF signal strikes the objects and is absorbed in to the material.It does not pass through or reflect or bend. It constitute to the attenuation of the signal. Absorption is the dissipation of an electromagnetic wave when it strikes a medium that does not allow the wave to be reflected, refracted, or diffracted.
Absorption of radio wave
Absorption of radio wave


technopediasite.com explaining about the "Factors Affecting the Behavior of  Radio Waves". Here it is also very important to explain about the DUCTING and K-Factor. Without this post will be incomplete. So I can not ignore about the Ducting and K-Factor.

Ducting
On rare occasions, usually when temperature inversions occur, the atmosphere may become stratified with a few layers of varying index of refraction. A microwave signal can become trapped between these layers, causing it to be carried away from its intended destination (the remote receiver). Ducting is usually quite deep and can last many hours. It typically occurs on hot, humid summer nights when there is no wind to stir the atmosphere.

K-Factor
For a normal atmosphere K value equals 4/3. K-factor is a common used value to indicate ray bending with respect to the physical radius of the earth.

The k-factor is a calculation used in both tropospheric and ionospheric propagation:
In tropospheric radio propagation, the ratio of the effective Earth radius to the actual Earth radius. The k-factor is approximately 4/3. 
➽ In ionospheric radio propagation, a correction factor that is applied in calculations related to curved layers and is a function of distance and the real height of ionospheric reflection.
K Factor details on Earth
K Factor Details
Earth bulge is the curvature of the Earth over a given distance. For LOS radio operations, it must be considered for those radio shots exceeding 11.3 km (7 mi). Antenna height calculations need to be considered for the Earth’s bulge for shots more than 11.3 km (7 mi), as the Earth’s bulge can affect the Fresnel zone.

Fresnel Zones Affecting the Behavior of Radio Waves

The first Fresnel zone is the surface containing every point for which the sum of the distances from that point to the two ends of the path is exactly one-half wavelength longer than the direct end-to-end path.


Each of the other Fresnel zones (“nth” Fresnel zone) is defined in the same way as the first zone, except the difference is “n-half” (n/2) wavelengths.

The first Fresnel zone is a nominal unit used to measure certain distances (e.g., path clearances) in terms of their effect on the frequency involved, rather than in terms of meters (feet). The other zones also are important under certain conditions (e.g., highly reflective paths).

Clearance requirements expressed in Fresnel zones apply to the sides and top of the path as well as to the bottom. A cross section of the zones at any point along the path shows a series of concentric circles completely surrounding the path.
Fresnel Zones details image
Fresnel Zones details


Summary
Loss or factors affecting the behavior of radio wave can be caused due to several reasons e.g.resistance of cable, connectors, loss because of heat, impedance mismatch. Fading is also a important topic may be i will write separate post  about Fading. How's my post please comment in box or you can drop a mail technopedia1979@gmail.com. 

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