Basic Propagation Theory

Radio-Navigation

Navigation using ground, air, space equipments.

​Instructor: Sutharshan Ganesan
Institute: EAS Barcelona

RADIO PROPAGATION

​What it could be?

In basic propagation theory we are going to learn about ELECTROMAGNETIC WAVES, such as
How the wave travel through the atmosphere, frequency bands, types of propagation, Speeds, Amplitude, Wavelength, Modulation types etc...

​1.Basic Radio propagation theory

• Radio means the radiation of electromagnetic waves carrying information.

• Radio wave travel at the speed of light approximately 300 000km/s, also the wave can travel through a vacuum such as in space until it’s absorbed by a metallic absorber.

Electromagnetic radiation is a form of energy which contains a wide range of electromagnetic wavelength grouped into 7 categories.
Electromagnetic waves are characterized by frequency measured in Hertz (Hz) and the wavelength in meters (m).
As we can see on the following representation as WAVELENGTH increases FREQUENCY decreases and FREQUENCY increases WAVELENGTH decreases.

ELECTROMAGNETIC WAVE PROPAGATION

Electric (E) & Magnetic (H) Fields

An electromagnetic wave always consists of an oscillating electric (E) and an oscillating magnetic (H) field which propagates at the speed of light (300 000 000m/s).

The (E) and (H) fields are perpendicular to each other.
The oscillations are perpendicular to the propagation direction.

Difference between Electromagnetic waves
and Mechanical waves

​LET’S COMPARE THE DIFFERENCE BETWEEN ELECTROMAGNETIC WAVES AND MECHANICAL WAVES.

•For example, SPEED OF SOUND is mechanical, they transport their energy from one location to another via a medium, such as AIR.

•We vibrate the air in order to create a sound (the air is our medium)

•However Electromagnetic waves travel through the vacuum of outer space.

•We vibrate both ELECTRIC and MAGNETIC charges.

Electromagnetic wave's velocity

As we know electromagnetic waves transport their energy at a speed of light such as:

~300 000 000 m/s,

~300 000 Km/s

~300 000/ 1.852 = 162 000 NM/S ( exactly 161 987 NM/S)

To convert

1 NM (Nautical Miles) = 1.852 KM

Basic Terminology

Cycle: Is a complete series of values of a periodical process.

Amplitude: The maximum displacement of absolute value from the reference.

Frequency: The number of cycles occurring in 1 second expressed in Hertz (Hz).

Wavelength: The physical distance traveled by a radio wave during one cycle of transmission.

A CYCLE

The time needed to generate one cycle of a radio wave is called period.

Following this figure, if we consider that one cycle occurs during one second, we can conclude that the frequency of this wave is one Hertz.

Some common frequency units:

Hertz (Hz) = 1 cycle/s

Kilohertz (kHz) = 1 000 cycles/s

Megahertz (MHz) = 1 000 000 (one million) cycles/s

Gigahertz (GHz) = 1 000 000 000 (one billion) cycles/s

Phase differences

Phase angle: Fraction of one wavelength expressed in degrees from 000 to 360 degrees.

Phase difference / Shift: The angular difference between the corresponding points of 2 cycles of equal wavelength, which is measurable in degrees

OUT OF PHASE

ANTI-PHASE

Wavelength & Frequency relationship

As frequency increases, the wavelength decreases and vice versa.

This is expressed using the following formula:

Wavelength (λ) = Speed of light (c) / Frequency (f)

Or

Frequency (f) = Speed of light (c) / Wavelength (λ)

•

Multiple Choice

What is the velocity of an electromagnetic wave in KM/s?

• 300 000 000

• 162 000

• 3000 000 000

• 300 000

Multiple Choice

What is the formula to calculate FREQUENCY?

• Frequency = Wavelength / Velocity

• Frequency = Velocity / Wavelength

• Wavelength = Frequency / Velocity

• Wavelength = Velocity / Frquency