[Physics Class Notes] on Space Wave Propagation Pdf for Exam

Space wave propagation is the term used for radio signals travelling through space. The sun is an example of a natural transmitter sending out radio waves that can be detected on Earth. Of all the Electromagnetic Spectrum, Radio Waves are the most extensively used in our daily lives. They are commonly known as ‘Space Waves’. 

With almost every action that we do use a radio signal, be it our daily communications or even just listening to music. There are two types of space wave propagation that you should know about, namely Electromagnetic Waves and Microwaves. This article will explain both their differences as well as similarities. Electromagnetic waves are basically simple transverse electric and magnetic waves that propagate at the speed of light. They are generated by accelerating electric charge and can be transmitted through a vacuum. Microwaves, on the other hand, are a type of electromagnetic radiation with wavelengths ranging from 1 mm to 30 cm. They are used in microwave ovens and radar technology. 

The similarities between electromagnetic waves and microwaves are that they are both types of electromagnetic radiation. They also propagate at the speed of light and can be transmitted through a vacuum. The key difference between these two types of waves is their wavelength. Electromagnetic waves have a much larger wavelength than microwaves. This is because microwaves have a higher frequency than electromagnetic waves.

Uses of Microwave 

In the case of microwaves, these waves are used in a wide range of technological applications. Some examples would be TV and radio communication, cellular phone service, GPS navigation and satellite communication. Microwaves also have a very long wavelength which increases their ability to penetrate objects, including raindrops. This makes them very useful for communication as they can pass through the object. For example, radio waves from a tower are picked up by an antenna, even in a car with metal roofs and windshields.

Uses of Electromagnetic Wave

On the other hand, electromagnetic waves have a much shorter wavelength than microwaves. They cannot penetrate objects which is why they are limited to line of sight communication. However, they can carry more information than microwaves due to their increased frequency. This makes them useful in the fields of astronomy and meteorology for gathering data about distant objects or events that may be obscured by clouds or sunlight.

When Does Space Wave Propagation Happens?

Space wave propagation takes place when the radio waves from a transmitting antenna propagate through the space around the Earth to reach a receiving antenna. The radio waves here can propagate either directly or after reflection from the ground or in the troposphere. Hence, to understand the term space wave propagation, we first need to know a bit about radio wave propagation.

 

What is Radio Wave Propagation?

Radio wave propagation defines how radio waves propagate or travel from one point to another. Besides defining the behaviour of waves as they are transmitted from one point to another, radio wave propagation also showcases the way radio waves are affected by the medium along which they propagate, and in particular, how they travel in various parts of the atmosphere. The mode of radio wave propagation in free space and atmosphere can be classified into different categories, and space wave propagation is one which we often notice. 

 

What is Space Wave Propagation?

Space wave propagation is defined as a category of radio wave propagation for the radio waves that occur within 20km from the Earth’s surface, i.e., the troposphere. It comprises direct or reflected waves. It is also known by two other names: 

• Tropospheric propagation as the waves here can propagate directly from the Earth’s surface to its troposphere surface.  

• Line-of-sight propagation as the waves travel in a straight line and cover a minimum distance of sight. It means the waves propagate to a distance up to which one can see with the naked eye.

Space Wave Propagation Depends on Three Components:

1. Direct Waves: The radio waves that, when transmitted from the transmitting antenna, reach the receiving antenna directly.

2. Ground Reflected Waves: The radio waves that reach the receiving antenna after reflection from the ground. 

3. Tropospheric Wave: The radio waves that reach the receiving antenna after reflection from the troposphere. 

As the figure depicts, space wave propagation, i.e., line-of-sight propagation is not always smooth. It means this mode of propagation can face obstacles that result in attenuation or loss of signal strength. Therefore, to prevent these issues, there is a need to adjust the height of both the transmitting and receiving antennas and the distance between them. The below formula appears helpful in this:

DM = [ (2 times R times hT)^{frac {1}{2}} +  (2 times R times hR)^{frac {1}{2}} ]

Where,

DM: Distance between the two antennas

R: Radius of the Earth

hT: Height of transmitting antenna

hR: Height of receiving antenna 

 

Applications of Space Wave Propagation

Space wave mode of propagation has its application in various systems like:

Things to keep in Mind

Space waves are used for very high-frequency bands ranging from 30 MHz to 300 MHz, ultra-high frequency (UHF) bands, and microwaves. It is because, at such high frequencies, both the skywave propagation and ground wave propagation fail. 

The antennas at these frequencies are comparatively smaller and can be placed at heights of several wavelengths above the ground. Due to the line-of-sight nature of this propagation, the waves here get blocked by the curvature of the Earth. That’s why if one wants to receive the signal beyond the horizon, then he/she needs to ensure that the receiving antenna possesses a height enough to intercept the line-of-sight waves.

Hence, we can conclude that the space wave propagation is limited to the line of sight distance, which is defined as the distance amid the transmitting and receiving antenna at which both can view each other. It is also known as the range of communication, which can be increased by increasing the heights of both antennas. Besides, the curvature of the Earth is another aspect by which space wave propagation gets affected.  

Example: Calculate the maximum distance up to which the signal transmitted from a tower with a height of 80m can be received?

Space wave propagation is defined as the mode of propagation in which the radio waves transmitted from the transmitting antenna reach the receiving antenna after travelling or propagating through space. It is why the waves here are also known as space waves and propagation as line-of-sight communication. Space wave propagation is suitable for UHF (Ultra High Frequency) and VHF (Very High Frequency) regions. Hence, TV broadcast, microwave links, and satellite communication are some of its examples. 

Based on this definition, the maximum distance (d) up to which the signal transmitted from transmitting antenna having height 80m will be:

Given, h = 80 m, R = Radius of the earth = 6400 km

d = [ sqrt {2Rh} ]

 = [ sqrt {2 times 6400 times 1000 times 80 }]

 = 32000m = 32km

Hence, the required distance will be 32km.

Conclusion

Understanding different aspects of Space Wave Propagation and examples will really help with getting deep insight and learning for the long-term.