Sky Wave Propagation

For the various applications like wireless communication, satellite, mobile communications, etc. we need transmission of the signal. The signal travels in different frequencies and also in different layer of our earth’s atmosphere.

RADIO WAVE SIGNALS

There are many types of signal propagating in our earth’s atmosphere, radio wave signal is one of them. Radio wave signal is an electromagnetic type of signal that has very long frequency range up to 300 GHz. There can be three types of radio wave propagation:

1.GROUND WAVE PROPAGATION

It is also known as Surface wave propagation as it travels though the lower and medium level of earths surface. This kind of radio wave propagation generally covers area between the earth surface and ionosphere. It finds its application in television broadcasting, amplitude and frequency modulation techniques.

2.SPACE WAVE PROPAGATION

This wave propagation is also known as Tropospheric wave propagation as it propagates in the troposphere region of the atmosphere having a frequency range of 3 MHz to 30 MHz The waves here are either directly transmitted through the antenna from earth surface to troposphere or are reflected back to the ground. This type of propagation is useful for line-of-sight communication, cellular communications, navigation, etc.

3.SKY WAVE PROPAGATION

Sky wave propagation is a type of propagation in which the ionosphere portion of the atmosphere. Due to this, it is also known as Ionospheric wave propagation. The ionosphere which ranges 60 to 400 Km of height from earth surface consist of four different layers namely D, E, F1 and F2 layers.

The ionosphere is denser at the lower layers as compared to the outer layers i.e., the density of the neutral atoms is higher at middle and lower region of ionosphere. The rays coming from the outer space therefore gets ionized mostly at E layer consisting highest number of atoms resulting ionization.

There is various terminology, related to sky wave propagation that must be understand. Let’s learn about them:

SKIP DISTANCE:

It is the minimum distance between the two points, from earth and point of radio signal that is transmitted back. The wave refracted back travels through different layers in the ionosphere, including a hop in the ionosphere.

The size of the skip distance depends on the critical angle, also the formulae for the skip distance is given by:

where,

D= Skip Distance

f= frequency of the wave i.e., electromagnetic wave that is been transmitted

fc= critical frequency of the ionosphere layer

h= earth surface to layer height

Now, let us understand what is a Critical Angle.

CRITICAL FREQUENCY:

It is the maximum frequency value of the radio wave which gets reflected back to the earths surface. The value that exceeds the critical frequency, goes into the ionosphere and is not returned to the earth back.

The value for critical frequency is given by:

where,

fcr = critical frequency of the layer

Nmax = Density of electrons (Maximum value) in the ionosphere

3.1 ADVANTAGES & DISADVANTAGES OF SKY WAVE PROPAGATION

ADVANTAGES

It is useful for long distance propagation of the wave.

The chances of the wave attenuation in very less.

It can support high frequency range of the waves that can be transmitted.

The reflective nature or the property of the propagation gives continuous communication.

DISADVANTAGES

There may occur variation in signal due to day and night, as far and near ionosphere occur respectively.

The strength of the signal might get affected due to large distances between transmitter and receiver.

The antenna used for this kind of communication requires to be highly ionized.

Also, the ionosphere layer is not a stable medium as ions keeps variating in density that may affect communication.

3.2 APPLICATION OF SKY WAVE PROPAGATION

· Sky wave propagation is used in satellite communication

· It is also useful in television and cellular mode of communication

· It finds its use in line-of-sight communication

· Various communication sectors are also linked by it

· Useful in RADAR and other navigation communication

Hope, this article helped you understanding Sky Wave Propagation concept and the relevant topics related to it.