Microwave Transmission

Microwave is a part of the electromagnetic Spectrum. Their frequency ranges from 300 MHz to 300 GHz, which corresponds to wavelengths of 1 mm to 30 cm. Sending and receiving information by microwaves is known as Microwave Transmission. Microwaves come under Unguided or wireless transmission media.

The repeaters form a network known as a microwave relay network. But these systems are used only in special roles as they are very expensive. These technologies such as wireless networks, and broadcast satellites broadcast television and radio directly into consumers’ houses. Microwaves can also be used for wireless power transmission.

What is Microwave Transmission?

Sending and receiving information using a microwave is known as microwave transmission. It is the Transmission of information (voice, data, television, telephony, radio signals)by microwave signals. Microwaves are widely used for point-to-point communications.

Properties of Microwaves

• It is the wave that radiates electromagnetic energy with a shorter wavelength.
• Microwave links consist of a Transmitting station (Tx), a Relay station or Repeaters (RPT), and a Receiving station (Rx).
• Microwaves travel in straight lines, so stations should be aligned to each other.
• Microwave links require clear LOS (line of sight ), so antennas are installed high up to avoid the interference of obstacles in their path.
• They do not pass through buildings, thus reducing the efficiency of inside receivers.
• They are unidirectional and allow multiple receivers.
• Receivers are added to boost the power of the signal so that it can travel a longer distance.
• They are also refracted by atmospheric layers thus refracted rays take more time to reach the destination than direct rays.

Characteristics of Microwave Transmission

• Microwaves are unidirectional.
• Microwave transmission Involves line-of-sight (LOS) communication technology.
• Affected greatly by environmental factors like rain fading.
• Microwaves cannot penetrate through obstacles such as hills, buildings, and trees due to their high frequency.
• Signals can be degraded during Solar proton events.
• Atmospheric disturbances such as rain and snow can scatter microwave signals.

General Properties of Microwave Transmission

The General properties of microwave transmission are as follows :

• Configuration : Arrangement and Setting of Transmission equipment such as antennas, towers, and whole network design is known as configuration.
• Bandwidth: It is a measure of the width of the frequency range. It determines the rate of data transfer.
• Error: Due to interference and obstacles disruptions occur in data transmission. These inaccuracies are known as errors.
• Performance : In Microwave transmission, the successful transmission of data in terms of speed, latency, and reliability is known as performance.
• Distance: The Maximum span over which microwaves can effectively transmit data without weakening of signals is known as distance.
• Security: Protection of data from unauthorized access or interception in microwave transmission is known as security.
• Cost : The Financial investment required for maintaining a microwave transmission system, including equipment, licensing, and operational expenses is known as cost.

These properties play an important role in Microwave Transmission.

Process of Microwave Transmission

• At first, the signal to be transmitted (baseband signal ) is processed or encoded at the transmitting station.
• Then it is used to modulate an intermediate carrier of 70 MHz or 140 MHz .
• Then the modulated signal is up-converted to microwave frequency.
• Then it is amplified before being fed to the antenna for radiation.
• Repeaters placed at several points are used to boost the power of the signal.
• Repeaters can be of two types i.e. Active and passive receivers.

• Passive repeater : They are beam diverters to make the beam pass the obstacle using several parabolic antennas connected by a section of the waveguide. They don’t have any amplifying devices.
• Active repeater : Active repeater includes an amplifier for boosting the signal strength. They also have Frequency translation circuits to change the frequency of the signal before retransmitting it.

• At the receiving stations, the signal is down-converted to 70 MHz or 140 MHz.
• Then it is demodulated to recover the baseband signal.

Microwave Transmission Link

Antennas Used for Microwave Transmission

Antennas can be defined as a transducer between guided and unguided media. It transforms energy between free space and a guided media such as cable or waveguide.

Antennas can be divided further as :

• Parabolic Dish Antenna : They are used at the receiving end of the transmission link. They are parabolic in shape. They permit the greatest focus of energy possible in a single beam. Parabolic Antennas are highly directional.

Parabolic Dish Antenna

• Horn Antenna : It is a radiating element in the shape of a horn with a stem. Its one end is flared out to improve the efficiency. Radiation is poor and non-directive.

Advantages of Microwave Transmission

• Cheaper as compared to Radio waves .
• Supports larger Bandwidth so more information is transmitted.
• They are used for point-to-point communication.
• More Antenna gain is possible.
• Antenna size gets reduced as the frequency is higher.
• Low power consumption as signals are of higher frequency.
• The effect of fading gets reduced by using LOS (line of sight ) propagation.
• Does not require any land for the installation of cables.
• Easy communication over rugged terrain.
• Communication over oceans is also possible.

Disadvantages of Microwave Transmission

• The cost of equipment or installation cost is high.
• Susceptible to weather conditions.
• Eavesdropping
• Limited Bandwidth (between 300MHz to 300GHz)

Applications of Microwaves

• Bluetooth: In Bluetooth, Communication is done through Ultra high frequency (UHF) radio waves .
• Wi-Fi: In Wi-fi , data is transferred using microwave.
• Direct broadcast satellites: Since microwaves are able to pass through the atmosphere layer so communication is done through satellites
• GPS: In order to locate the positions, microwaves are used.
• FM Radio: Microwave transmitter and receiver is used to transfer information through a line to other and so form radio connection.
• Satellite T.V: Since microwaves are able to pass through the atmosphere layer so the information passes from Tv to satellite and vice versa.

Types of Microwave Data Transmission System

Microwave Transmission can be of two types:

• Terrestrial Transmission
• Satellite Transmission

Types of Microwave Data Transmission System

Terrestrial Transmission

• They cannot pass through any obstacle.
• They Use directional Parabolic Antenna.
• Signals are highly focused.
• Line of Sight Transmission is needed i.e. their path should be free of any sort of obstacle.
• For long-distance transmission signal strength weakens.
• Repeaters are used for every 35-40 km as such.

Advantages

• They are used to carry thousands of voice channels at the same time.
• Data Transmission rate of 16 Gbps.

Disadvantages

• Installation cost is high.
• Maintaining a LOS or obstacle-free path for a long distance is a difficult task.
• EMI effect and jamming affect the signal strength.

Applications

• Cellular phone
• Television
• Telephone

Satellite Transmission

• Microwave Relay station is placed in outer space.
• A satellite is launched by a rocket or space shuttle.
• Satellite is precisely positioned 360000 km above.
• Orbit speed matches Earth’s rotation speed.
• A satellite is stationary relative to Earth.

Advantages

• Single microwave relay station visible from any point in a large area.
• Transmission and reception costs are independent of the distance between the 2 points.
• The transmitting station can receive back its transmission and check whether the satellite transmitted information correctly.

Disadvantages

• High cost of placing a satellite in orbit.
• The signal is sent to satellite broadcast to all receivers in satellite range.
• Security measures are required to prevent unauthorized tempering of Information.

Applications

• Used for Broadcasting and receiving signals.

Microwave Propagation and Path Losses

When the signal propagates even a slight directional LOS link’s beam can cause losses in Transmission. These losses are known as path losses.

Factors of Path Losses

• Free space path loss (FSL) is typically the greatest portion of path loss. It is the effect of the signal spreading out as it propagates from the transmitting antenna. These losses are directly proportional to the link’s distance and signal frequency. When these two increase the path loss increases.
• Atmospheric absorption: Both oxygen and water vapor present in the air attenuate the microwave signals. When the link length increases the loss increases.
• Diffraction:Diffraction is yet another cause of path losses.

Path Reliability in Microwave Transmission

Considering all the path loss factors, we can quantify path reliability, also known as path availability. Due to poor propagation conditions, the path fails to perform and data transmitted from one end is not successfully received at the other end. So Path availability is a measurement of the path’s ability to reliably communicate data over year.

Path’s performance can typically be improved by :

• Increasing overall system gain by increasing power.
• Reducing losses in transmission lines.
• Increasing the size of the Antenna itself.

Conclusion

Microwave signals require a clear LOS (Line of sight), so for long-distance Transmission using these signals, a series of repeaters are used. The repeaters form a network known as a microwave relay network. Microwave signals can be used for over-the-horizon communications using tropospheric scatter. There has been a rapid increase in the use of microwave spectrum by telecommunication technologies. Microwave Transmission has become one of the leading technologies in the recent years.

FAQs on Microwave Transmission

1. What is meant by LOS?

LOS stands for Line of sight. It means a clear path free of any obstacles, between Transmission and reception of Microwaves.

2. What is a Link?

Link is a connection of two fixed microwave sites by a LOS path.

3. Microwave Transmission is a wireless communication?

Microwave is a LOS wireless communication.

4. Is Microwave Transmission faster than Fiber Optic?

Fiber Optic cables transmit data at a speed of Light so they are much faster than a microwave.

5. Why Microwaves are used for long-distance transmission?

Microwaves have high-frequency signals, so they can transmit signals over a long distance without a loss of data.

6. Microwaves are faster than Radio waves?

Yes, Microwaves are faster than Radio waves.

7. What is Modulation?

Modulation is the practice of encoding large amounts signals of data into carrier signals to allow Transmission.

8. What makes Microwaves suitable for Transmitting signals to satellites?

Microwaves can easily be focused into narrower beams thus allowing frequency reuse suitable, so this makes Microwaves suitable for transmitting signals to satellites.

9. What are the components of Microwave Transmission?

1. Transmitter
2. Receiver
3. Transmission lines
4. Antennas