This document discusses different methods of electromagnetic wave propagation through space. There are three basic paths: ground waves which follow the Earth's curvature for lower frequencies; space waves which travel line-of-sight; and sky waves which are reflected by ionized layers in the atmosphere, allowing higher frequency signals to travel farther than line-of-sight. The ionosphere, located 30-240 miles above the Earth, plays a key role in sky wave propagation by reflecting radio signals back to Earth, enabling long-distance HF radio communications.

1. Wave Propagation

2. A vibration
Or
Disturbance in space

3.  This diagram shows typical combination
system in which signal is transmitted in the
form Electromagnetic waves and received.

4.  The electromagnetic transmission in space
must be in high frequencies because in low
frequency there are two problems.
 Size of antenna
 Low radiation power.

5.  It is a wave which occurs in directions
perpendicular to the direction of the
propagation.
 Transverse wave is also called travelling
wave.

7.  There areThree basic paths that an EM signal
can take through space
 Ground wave or Surface wave
 Space wave
 Sky wave

8.  A frequency up to about 2MHz, the most
important method of propagation is by
ground wave which are vertically polarized.
 They follow the curvature of earth to
propagate.
 Relatively high power is required.

9.  Surface wave is very dependent upon the
nature of the ground of which the signal
travels. Such as :
 Ground conductivity
 Roughness

11.  The radio waves having high frequencies are
called as space wave.
 The other name of space wave is Line of
sight propagation

12.  Those waves have the ability to propagate
through atmosphere, from transmitting
antenna to receiving antenna. It can travel
directly or can travel after reflecting from
earth’s surface to the *troposphere surface of
earth.
*the lowest region of the atmosphere(15km)

14.  It is useful for FM,T.V and RADAR application.
 It is also used inVHF, UHF and microwave
signals.

15.  Some waves travel upwards into the space
towards the sky and get reflected back to the
receiver
 Signal reflected ionized layer of atmosphere
and back down to the earth.
 These wave are called Sky wave.

16.  Signal that is radiated by the antenna into
upper atmosphere where it is bent or
reflected back to earth.
 This bending of signal caused by a region in
the upper atmosphere known as ionosphere

17.  High energy radiation(Ultraviolet) from
our sun(Solar Radiation) strikes atoms
of various gasses and vapors in the
earth’s upper atmosphere.
 Electrons are knocked off the outer
orbits of the atoms creating an ion. The
process is called ionization.
 Because this event takes place in the
upper atmosphere, we call the layer
ionosphere

18.  Ranges from about 30 to 55 miles
 Primarily exist only during daylight
hours.

19.  Ranges from about 55 to 90 miles
 It exist only during daylight and almost
gone by midnight.
 Also called Kennelly-Heaviside Layer.

20. Exists from about 90 to 240 miles
The most highly ionized.
In daytime, this layer split into two
parts: F1 and F2. After sunset, this
layer combines into one.

22.  These waves can have medium as well
as high frequencies. So, due to this
reason these waves can be used for long
distance transmission.
 This mode is used in HF band
International Broadcasting